Hei ccs london_airquality


Published on

Published in: Technology
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Hei ccs london_airquality

  1. 1. R e s e a R c h R e p o Rt HEA LTH The Impact of the Congestion Charging EF F E CTS Scheme on Air Quality in London IN STITUTE Part 1. Emissions Modeling and Analysis of Air Pollution Measurements Number 155 April 2011 Part 2. Analysis of the Oxidative Potential of Particulate Matter (To Be Released in May 2011) Frank Kelly, H. Ross Anderson, Ben Armstrong, Richard Atkinson, Ben Barratt, Sean Beevers, Dick Derwent, David Green, Ian Mudway, and Paul WilkinsonIncludes a Commentary by the Institute’s Health Review Committee
  2. 2. The Impact of the Congestion Charging Scheme on Air Quality in London Part 1.Emissions Modeling and Analysis of Air Pollution Measurements Part 2. Analysis of the Oxidative Potential of Particulate Matter (To Be Released in May 2011) Frank Kelly, H. Ross Anderson, Ben Armstrong, Richard Atkinson, Ben Barratt, Sean Beevers, Dick Derwent, David Green, Ian Mudway, and Paul Wilkinsonwith a Commentary by the HEI Health Review Committee Research Report 155 Health Effects Institute Boston, Massachusetts Trusted Science · Cleaner Air · Better Health
  3. 3. Publishing history: The Web version of this document was posted at www.healtheffects.org in April andMay 2011.Citation for Research Report 155 in its entirety Kelly F, Anderson HR, Armstrong B, Atkinson R, Barratt B, Beevers S, Derwent D, Green D, Mudway I, Wilkinson P. 2011. The Impact of the Congestion Charging Scheme on Air Quality in London. Research Report 155. Health Effects Institute, Boston, MA.Citation for Part 1 only Kelly F, Anderson HR, Armstrong B, Atkinson R, Barratt B, Beevers S, Derwent D, Green D, Mudway I, Wilkinson P. 2011. Part 1. Emissions modeling and analysis of air pollution measurements. In: The Impact of the Congestion Charging Scheme on Air Quality in London. Research Report 155. Health Effects Institute, Boston, MA.Citation for Part 2 only Kelly F, Anderson HR, Armstrong B, Atkinson R, Barratt B, Beevers S, Derwent D, Green D, Mudway I, Wilkinson P. 2011. Part 2. Analysis of the Oxidative Potential of Particulate Matter. In: The Impact of the Congestion Charging Scheme on Air Quality in London. Research Report 155. Health Effects Institute, Boston, MA.© 2011 Health Effects Institute, Boston, Mass., U.S.A. Cameographics, Belfast, Me., Compositor. Printed byRecycled Paper Printing, Boston, Mass. Library of Congress Catalog Number for the HEI Report Series:WA 754 R432. Cover paper: made with at least 55% recycled content, of which at least 30% is post-consumer waste; freeof acid and elemental chlorine. Text paper: made with 100% post-consumer waste recycled content; acid free;no chlorine used in processing. The book is printed with soy-based inks and is of permanent archival quality.
  4. 4. CONTENTSAbout HEI viiAbout This Report ixPreface xiHEI STATEMENT 1INVESTIGATORS’ REPORT Part 1 by Kelly et al. 5ABSTRACT 5INTRODUCTION 7 Historical Background of London’s Air Quality 7 Air Pollution in London Today 8 London’s Air Quality Strategy 9 The CCS in London 9 The CCS and Air Quality in London 10SPECIFIC AIMS 11MODELING THE AIR POLLUTION IMPACTS OF THE CCS IN LONDON 12 Introduction 12 Methods 12 The King’s College LET for Road Traffic 12 The King’s College LAPT 12 Results 13 LAPT Model Predictions of Air Pollutant Concentrations for 2001 Through 2004 13 LET Model Predictions of Vehicle Emission Concentrations for 2001 Through 2004 13 Emission Assumptions for the Air Pollution Model 14 Air Pollution Predictions for 2001 Through 2004 15 Comparison of Projected Air Pollutant Concentrations Before and After CCS Introduction for Within and Outside the Zone 16 Model Sensitivity Tests 21 NOx Concentrations 27 Discussion 28 The Physical Properties of the CCS Area 28 The Representation of Road Traffic As a Proportion of All Emissions in London and Predicted Trends 28 The Ability of Small Numbers of Measurement Sites to Reflect Complex Urban Traffic Management Changes 29 Model Impact Assessment: Before Versus After CCS Introduction 31 Model Impact Assessment: Impact of Each Vehicle Type 32
  5. 5. Research Report 155ESTABLISHING A CCS STUDY DATABASE OF AIR QUALITY MEASUREMENTS 32 Introduction 32 Selection of Monitoring Sites 32 Site Classification Definitions 34 Monitored Pollutants 34 Quality Assurance and Quality Control of Measurements 35 CCS Study Database Structure and Analysis 35 Summary Statistics 35 Time-Series Charts 40ANALYSIS OF TEMPORAL CHANGES IN MEAN MEASURED POLLUTANT CONCENTRATIONS ACROSS LONDON 42 Introduction 42 Methods 43 Data Compilation 43 Selection of Monitoring Sites 43 Statistical Methods 43 Results 45 Analysis of Weekday Data 45 Analysis of Weekend Data 51 Descriptive Analysis of Changes in Pollutant Concentrations over Time for All Monitoring Sites Within the CCZ, in the Area Surrounding It, and in the Control Area 52 Discussion 52 Summary of Findings from the Weekday Analysis 52 Summary of Findings from the Weekend Analysis 54 Effects of the CCS on Areas Outside the Zone 54 Data Availability 54 Potential Confounding 54 Choice of Time Period 54 Serial Correlation in Pollutant Measurements 55 Conclusions 55SUMMARY OF INVESTIGATIVE ANALYSES 55 Use of Ethane as a Dispersion Indicator 56 Background and Methods 56 Findings 56 Strengths and Weaknesses 56 Application of the CUSUM Technique to Air Pollution Data 56 Background and Methods 56 Initial Findings and Subsequent Action 56 Ultimate Findings 56 Strengths and Weaknesses 57 Use of Bivariate Polar Plots to Characterize Local Emissions 58 Introduction and Methods 58 Findings 58 Strengths and Weaknesses 59
  6. 6. Research Report 155INTEGRATED DISCUSSION 59 Modeling Studies of the Likely Air Quality Impacts of the CCS 60 Statistical Analysis of Measurement Data 60 Data Availability 61 Background Versus Roadside 61 Potential Confounding 61 Choice of Time Period 61 Serial Correlation in Pollutant Measurements 62 Weekend Analysis 62 Effects of the CCS on Areas in Greater London Outside the Zone 62 Synthesis of Findings 62IMPLICATIONS FOR OTHERS INTRODUCING TRAFFIC MANAGEMENT SCHEMES TO IMPROVE AIR QUALITY 63ACKNOWLEDGMENTS 64REFERENCES 64APPENDIX A. HEI Quality Assurance Statement 66APPENDIX B. Background and Roadside Monitoring Sites in Greater London Used in the Temporal Analyses of Changes in Mean Measured Pollutant Concentrations 67APPENDICES AVAILABLE ON THE WEB 70ABOUT THE AUTHORS 70OTHER PUBLICATIONS RESULTING FROM THIS RESEARCH 71ABBREVIATIONS AND OTHER TERMS 71INVESTIGATORS’ REPORT Part 2 by Kelly et al. 73COMMENTARY by the Health Review Committee 75INTRODUCTION 75SCIENTIFIC BACKGROUND 75 London Congestion Charging Scheme 76 Outcomes Evaluation Cycle 77SUMMARY OF THE STUDY’S SPECIFIC AIMS 77PART 1. EMISSIONS MODELING AND ANALYSIS OF AIR POLLUTION MEASUREMENTS (SPECIFIC AIMS 1–3) 78 Methods 78 Modeling the Impact of the CCS on Air Pollution (Specific Aim 1) 78 Establishment of the CCS Study Database of Air Quality Measurements (Specific Aim 2) 79 Analysis of Changes in Geometric Mean Pollutant Concentrations Measured Across London (Specific Aim 3) 79 Additional Exploratory Analyses 80
  7. 7. Research Report 155 Summary of Main Results for Part 1 80 Modeling Studies 80 Analysis of CCS-Related Changes in Geometric Mean Pollutant Concentrations Measured Across London 81 Investigators’ Conclusions for Part 1 83PART 2. ANALYSIS OF THE OXIDATIVE POTENTIAL OF PM10 (SPECIFIC AIM 4) 83 Methods 83 Filter Archive 83 Filter Extraction and Analysis 84 Derivation of Metrics for Oxidative Potential 85 Characterization of Contributors to Oxidative Potential 85 Data Analysis 85 Summary of Main Results for Part 2 86 Characterization of Oxidative Potential and the Metal Composition of PM10 Extracts 86 Effect of the CCS on the Oxidative Potential and Metal Content of PM10 86 Characterization of Within-City Spatial Variation in the Oxidative Potential of PM10 88 Modeling Vehicle Contributions to Primary PM10 89 Investigators’ Conclusions for Part 2 89HEALTH REVIEW COMMITTEE’S EVALUATION OF THE STUDY 89 Modeling the Impact of the CCS on Air Quality in London (Specific Aim 1) 90 Evidence from Monitoring Data on the Impact of the CCS (Specific Aims 2 and 3) 91 Additional Exploratory Analyses 92 Oxidative Potential of London’s PM (Specific Aim 4) 92CONCLUSIONS AND IMPLICATIONS FOR RESEARCH ON THE EFFECTIVENESS OF AIR QUALITY INTERVENTIONS 94ACKNOWLEDGMENTS 95REFERENCES 95Related HEI Publications 99HEI Board, Committees, and Staff 101
  8. 8. ABOUT HEI The Health Effects Institute is a nonprofit corporation chartered in 1980 as an independentresearch organization to provide high-quality, impartial, and relevant science on the effects of airpollution on health. To accomplish its mission, the institute • Identifies the highest-priority areas for health effects research; • Competitively funds and oversees research projects; • Provides intensive independent review of HEI-supported studies and related research; • Integrates HEI’s research results with those of other institutions into broader evaluations; and • Communicates the results of HEI’s research and analyses to public and private decision makers. HEI receives half of its core funds from the U.S. Environmental Protection Agency and halffrom the worldwide motor vehicle industry. Frequently, other public and private organizations inthe United States and around the world also support major projects or certain researchprograms. HEI has funded more than 280 research projects in North America, Europe, Asia, andLatin America, the results of which have informed decisions regarding carbon monoxide, airtoxics, nitrogen oxides, diesel exhaust, ozone, particulate matter, and other pollutants. Theseresults have appeared in the peer-reviewed literature and in more than 200 comprehensivereports published by HEI. HEI’s independent Board of Directors consists of leaders in science and policy who arecommitted to fostering the public–private partnership that is central to the organization. TheHealth Research Committee solicits input from HEI sponsors and other stakeholders and workswith scientific staff to develop a Five-Year Strategic Plan, select research projects for funding, andoversee their conduct. The Health Review Committee, which has no role in selecting oroverseeing studies, works with staff to evaluate and interpret the results of funded studies andrelated research. All project results and accompanying comments by the Health Review Committee are widelydisseminated through HEI’s Web site (www.healtheffects.org), printed reports, newsletters andother publications, annual conferences, and presentations to legislative bodies and public agencies. vii
  9. 9. ABOUT THIS REPORT Research Report 155, The Impact of the Congestion Charging Scheme on Air Quality in London:Part 1. Emissions Modeling and Analysis of Air Pollution Measurements, and Part 2. Analysis of theOxidative Potential of Particulate Matter, presents a research project funded by the Health EffectsInstitute and conducted by Professor Frank Kelly, of the School of Biomedical Sciences, King’sCollege London, London, U.K., and his colleagues. This report contains three main sections. The HEI Statement, prepared by staff at HEI, is a brief, nontechnical summary of the study and its findings; it also briefly describes the Health Review Committee’s comments on the study. The Investigators’ Report, Parts 1 and 2, prepared by Kelly and colleagues, describes the scientific background, aims, methods, results, and conclusions of the study. The Commentary is prepared by members of the Health Review Committee with the assistance of HEI staff; it places the study in a broader scientific context, points out its strengths and limitations, and discusses remaining uncertainties and implications of the study’s findings for public health and future research. This report has gone through HEI’s rigorous review process. When an HEI-funded study iscompleted, the investigators submit a draft final report presenting the background and results ofthe study. This draft report is first examined by outside technical reviewers and a biostatistician.The report and the reviewers’ comments are then evaluated by members of the Health ReviewCommittee, an independent panel of distinguished scientists who have no involvement inselecting or overseeing HEI studies. During the review process, the investigators have anopportunity to exchange comments with the Review Committee and, as necessary, to revise theirreport. The Commentary reflects the information provided in the final version of the report. ix
  10. 10. P R E FAC EHEI’s Outcomes Research Program The goal of most air quality regulations is to protect research and identified the types of evidence requiredthe public’s health by implementing regulatory actions and the methods by which the evidence should beor providing economic incentives that help reduce the obtained. It has also guided the development of the HEIpublic’s exposure to air pollutants. If this goal is met, air Health Outcomes Research program, which is dis-pollution should be reduced, and indicators of public cussed below.health should improve or at least not deteriorate. Evalu- Between 2002 and 2004, HEI issued four requests forating the extent to which air quality regulations succeed applications (RFAs) for studies to evaluate the effects ofin protecting public health is part of a broader effort — actions taken to improve air quality. The study by Pro-variously termed outcomes research, accountability re- fessor Frank Kelly and colleagues described in thissearch, or research on regulatory effectiveness — de- Research Report (Kelly et al. 2011a,b) was funded undersigned to assess the performance of environmental RFA 04-1, “Measuring the Health Impacts of Actionsregulatory policies in general. In recent decades, air That Improve Air Quality.” HEI funded eight additionalquality in the United States and Western Europe has outcomes studies resulting from other RFAs.improved substantially, and this improvement is attrib- This preface describes both the framework of out-utable to a number of factors, including increasingly comes research as it relates to air quality regulationsstringent air quality regulations. However, the cost of and HEI’s Outcomes Research program.the pollution-control technologies and mechanismsneeded to implement and enforce these regulations isoften high. It is therefore prudent to ask whether the BACKGROUNDregulations have in fact yielded demonstrable improve-ments in public health and provided information to in- The first step in assessing the effectiveness of airform future efforts to do so. quality regulations is to measure emissions of the tar- Several U.S. government agencies have concluded geted pollutants to see whether they have in factthat direct evidence about the extent to which air quality decreased as intended. A series of intermediate assess-regulations have improved health (measured as a ments, described in detail below, are needed in orderdecrease in premature mortality and excess morbidity) to accurately measure the adverse health effects asso-is lacking. This finding is well documented by the National ciated with air pollution to see whether they, too,Research Council (NRC) in its report Estimating the decreased in incidence or severity relative to emissions.Public Health Benefits of Proposed Air Pollution Regu- Some outcomes studies to date have used hypotheticallations (NRC 2002), as well as by the California Air scenarios (comparing estimated outcomes under exist-Resources Board, the U.S. Environmental Protection ing and more stringent regulations) and risk estimatesAgency (EPA), the U.S. Centers for Disease Control obtained from epidemiologic studies in an attempt toand Prevention (CDC), and other agencies. quantify past effects on health and to predict future In 2003, the Health Effects Institute published a effects (U.S. EPA 1999). However, more extensive vali-monograph on outcomes research, Communication dation of these estimates with data on actual outcomes11, Assessing Health Impact of Air Quality Regulations: would be helpful.Concepts and Methods for Accountability Research The long-term improvements in U.S. air quality have(HEI 2003). This monograph was written by the mem- been associated with improved health in retrospectivebers of HEI’s multidisciplinary Accountability Working epidemiologic studies (Chay and Greenstone 2003;Group after a 2001 workshop on the topic. Communi- Laden et al. 2006; Pope et al. 2009). Considerable chal-cation 11 set out a conceptual framework for outcomes lenges, however, are inherent in the assessment of theHealth Effects Institute Research Report 155 © 2011 xi
  11. 11. Preface health effects of air quality regulations. Different regula- Ireland by Clancy and colleagues (2002) and in Hong tions go into effect at different times, for example, and Kong by Hedley and colleagues (2002) are examples of may be implemented at different levels of government such scenarios. (e.g., national, regional, or local). Their effectiveness These inherent challenges are well documented in therefore needs to be assessed in ways that take into Communication 11 (HEI 2003), which was intended to account the varying times of implementation and levels advance the concept of outcomes research and to foster of regulation. In addition, other changes at the same time the development of methods and studies throughout the and place might confound an apparent association relevant scientific and policy communities. In addition, between pollution reduction and improved health, such recent advances in data collection and analytic tech- as economic trends (e.g., changes in employment), niques provide an unprecedented oppor tunity to improvements in health care, and behavioral changes improve our assessments of the effects of air quality (e.g., staying indoors when government warnings indi- interventions. cate pollution concentrations are high). Moreover, adverse health effects that might be caused by exposure to air pollution can also be caused by other environ- THE OUTCOMES EVALUATION CYCLE mental risk factors (some of which may have changed over the same time periods as the air pollution con- The NRC’s Committee on Research Priorities for centrations). These challenges become more pro- Airborne Par ticulate Matter set out a conceptual nounced when regulations are implemented over long framework for linking air pollution sources to adverse periods and when changes in air quality and health out- health effects (NRC 1998). This framework can be comes are not seen immediately, thus increasing the used to identify factors along an Outcomes Evaluation chance for confounding by other factors. For these Cycle (see Preface Figure), each stage of which affords reasons, scenarios in which regulations are expected its own opportunities for making quantitative measure- to have resulted in rapid changes in air quality tend to ments of the intended improvements. be among the first, and most likely, targets for investiga- At the first stage (regulatory action), one can assess tion, rather than evaluations of complex regulatory whether controls on source emissions have in fact been programs implemented over multiple years. Studies in put into place. At the second stage (emissions), one can Outcomes Evaluation Cycle. Each box represents a stage in the process between regulatory action and human health responses to air pollution. Arrows con- necting the stages indicate possible directions of influence. The text below the arrows identifies factors affecting the effectiveness of regulatory actions at each stage. At several of the stages, knowledge gained from studies on outcomes can provide valuable feedback for improving regulatory or other actions.xii
  12. 12. Prefacedetermine whether controls on sources have indeed These studies involve the measurement of indicatorsreduced emissions, whether emitters have changed along the entire outcomes evaluation cycle, from regu-their practices, and whether there have been unin- lator y or other inter ventions to human health out-tended consequences. At the third stage (ambient air comes. Some of the studies focused on interventionsquality), one can assess whether controls on sources that are implemented over relatively short periods ofand reductions in emissions have resulted in improved time, such as a ban on the sale of coal, the replacementair quality. At the fourth stage (personal or population of old wood stoves with more efficient, cleaner ones,exposure), one can assess whether the improvement in reductions in the sulfur content of fuels, and measuresair quality has reduced people’s actual exposure and to reduce traffic. Other groups focused on longer-term,whether susceptible subpopulations (those most likely wider-ranging interventions or events; for instance, oneto experience adverse health effects) have benefited. study assessed complex changes associated with the re-At this stage, it is impor tant to take into account unification of the former East and West Germany, in-changes in time–activity patterns that could either cluding a switch from brown coal to natural gas forincrease or reduce exposure. The actual dose that an fueling power plants and home-heating systems and anindividual’s organs may be exposed to should also be increase in the numbers of modern diesel-powered ve-considered (i.e., whether reductions in exposure have hicles in eastern Germany. HEI is also supporting re-led to reductions in concentrations in body tissues such search, including the development of methods, in anas the lung). Finally, at the fifth stage (human health especially challenging area — the effects of regulationsresponse), one can assess whether risks to health have that are implemented incrementally over extended peri-declined, given the evidence about changes in health ods of time, such as those resulting from Title IV of theoutcomes such as morbidity and mor tality that have 1990 Clean Air Act Amendments (U.S. EPA 1990),resulted from changes in exposure. The challenge at which aimed at reducing sulfur dioxide emissions fromthis stage is to investigate the health outcomes that are power plants by requiring compliance with prescribedmost directly related to exposure to air pollution. emission limitations. Studies on health outcomes funded At each stage in the outcomes evaluation cycle, the by HEI to date are summarized in the Preface Table andopportunity exists to collect evidence that either vali- described in more detail in an interim evaluation of thedates the assumptions that motivated the intervention HEI Outcomes Research program (van Erp and Cohenor points to ways in which the assumptions were incor- 2009).rect. The collection of such evidence can thus ensurethat future interventions are maximally effective. Ultimately, the framework for outcomes research FUTURE DIRECTIONSwill need to encompass investigations of the broader As a part of its new Strategic Plan for 2010 throughconsequences of regulations, not just the intended con- 2015 (HEI 2010a), HEI has looked closely at opportuni-sequences. Unintended consequences should also be ties for unique new contributions to health outcomesinvestigated, along with the possibility that risks to pub- research. Key recommendations for future researchlic health in fact increased, as discussed by Wiener were made at a December 2009 planning workshop(1998) and others who have advanced the concept of a (HEI 2010b), which led to HEI issuing a new Request forportfolio of effects of a regulation. Applications in January 2011 for a second wave of out- comes research. RFA 11-1, “Health Outcomes Research — Assessing the Health Outcomes of Air QualityHEI’S OUTCOMES RESEARCH PROGRAM Actions,” solicits applications for studies designed to HEI’s Outcomes Research program currently includes assess the health effects of actions to improve air qualitynine studies. The study by Professor Frank Kelly and col- and to develop methods required for, and specificallyleagues presented in this report is the third of the nine suited to, conducting such research. Preference will beto be published; four additional studies are in press and given to (1) studies that evaluate regulatory and otherare expected to be published in 2011. The remaining actions at the national or regional level implementedtwo studies are in review and are expected to be pub- over multiple years; (2) studies that evaluate complexlished in 2012. sets of actions targeted at improving air quality in large xiii
  13. 13. Preface HEI’s Outcomes Research Programa RFA / Investigator (Institution) Study or Report Title Intervention RFA 02-1 Douglas Dockery “Effects of Air Pollution Control on Coal ban in Irish cities (Harvard School of Public Health, Mortality and Hospital Admissions in Boston, Mass.) Ireland” (in review) Annette Peters The Influence of Improved Air Quality Switch from brown coal to natural gas (GSF–National Research Center for on Mortality Risks in Erfurt, Germany for home heating and power plants, Environment and Health, (published as HEI Research Report changes in motor vehicle fleet after Neuherberg, Germanyb) 137, 2009) reunification of Germany RFA 04-1 Frank Kelly The Impact of the Congestion Measures to reduce traffic (King’s College London, Charging Scheme on Air Quality in congestion in the center of London London, U.K.) London: Part 1. Emissions Modeling and Analysis of Air Pollution Measurements. Part 2. Analysis of the Oxidative Potential of Particulate Matter (published as HEI Research Report 155, 2011) RFA 04-4 Frank Kelly “The London Low Emission Zone Measures to exclude most polluting (King’s College London, Baseline Study” (in press) vehicles from entering Greater London, U.K.) London Richard Morgenstern “Accountability Assessment of Title IV Measures to reduce sulfur (Resources for the Future, of the Clean Air Act Amendments of emissions from power plants east of Washington, D.C.) 1990” (in press) the Mississippi River Curtis Noonan “Assessing the Impact on Air Quality Woodstove change-out program (University of Montana, and Children’s Health of Actions Missoula, Mont.) Taken to Reduce PM2.5 Levels from Woodstoves” (in press) Jennifer Peel Impact of Improved Air Quality During Measures to reduce traffic (Colorado State University, the 1996 Summer Olympic Games in congestion during the Atlanta Fort Collins, Colo.) Atlanta on Multiple Cardiovascular Olympics and Respiratory Outcomes (published as HEI Research Report 148, 2010) Chit-Ming Wong “Impact of the 1990 Hong Kong Measures to reduce sulfur content in (University of Hong Kong, Legislation for Restriction on Sulfur fuel for motor vehicles and power Hong Kong) Content in Fuel” (in press) plants RFPA 05-3 Junfeng (Jim) Zhang “Molecular and Physiological Measures to improve air quality during (University of Medicine and Responses to Drastic Changes in PM the Beijing Olympics Dentistry of New Jersey, Concentration and Composition” (in Piscataway, N.J.) review) a Abbreviations: RFA, Request for Applications; RFPA, Request for Preliminary Applications. b As of 2008, this institution is called the Helmholtz Zentrum München–German Research Center for Environmental Health.xiv
  14. 14. Prefaceurban areas and major ports with well-documented air The workshop built on the work of the CDC’s Envi-quality problems and programs to address them; and ronmental Public Health Tracking Program (see the(3) studies that develop methods to suppor t such CDC Web site www.cdc.gov/nceh/tracking/) in the devel-health outcomes research (see www.healtheffects.org/ opment of standardized measures of air pollution–funding.htm). HEI hopes to fund 3 or 4 studies to evalu- related effects on health at the state and local levels inate the effectiveness of longer-term regulatory actions the United States. It brought together representativesthat are expected to start in 2012. of state and federal agencies and academic researchers In addition, HEI has also funded the development of to discuss methodologic issues in developing standard-two Web sites intended to enhance transparency and ized measures and made recommendations for theirprovide other researchers with access to extensive data further development and application in assessing theand software from HEI-funded studies: health impacts of air pollution, including the impacts of actions taken to improve air quality. The recommenda-1. Data and software from the National Morbidity, tions were provided in a September 2008 report to the Mortality, and Air Pollution Study (NMMAPS), as CDC, and the proceedings were published in the jour- described by Zeger and colleagues (2006) (data nal Air Quality, Atmosphere & Health in December 2009 available at the Johns Hopkins Bloomberg School of (e.g., Matte et al. 2009). The CDC has subsequently Public Health Web site www.ihapss.jhsph.edu); and funded a pilot project under the Environmental Public2. Data from the National Particle Components Tox- Health Tracking Program to implement the recommen- icity Initiative (NPACT) on concentrations of com- dations of the workshop in selected states and metro- ponents of particulate matter with an aerodynamic politan areas. diameter 2.5 µm (PM2.5) collected at or near HEI will continue to seek opportunities to work with the 54 sites in the EPA’s PM2.5 Chemical Speciation the CDC and the EPA to apply methods newly devel- Trends Network (STN) (data available at the oped for tracking public health to the assessment of the Atmospheric and Environmental Research, Inc., effectiveness of environmental regulations. Web site http://hei.aer.com). Investigators who have identified a distinctive oppor- The data on pollution and health from a large num- tunity to evaluate the effects of environmental regula-ber of U.S. cities, as documented by the NMMAPS tions on air pollution and human health are encouragedteam and made available on the Internet-Based Health to contact HEI.and Air Pollution Surveillance System (iHAPSS) Website, constitute a valuable resource that allows other REFERENCESresearchers to undertake additional analyses, possiblyincluding further outcomes studies. The STN Web site Atmospheric and Environmental Research, Inc. (Sanprovides scientists an opportunity to investigate specific Ramon, CA). HEI Air Quality Database. http://hei.aerquestions about concentrations of PM2.5 components .com. Accessed 3/22/12.and their association with adverse health effects inregions covered by the STN network and to address Chay KY, Greenstone M. 2003. The impact of air pollu-questions related to outcomes research when inter- tion on infant mortality: Evidence from geographic vari-ventions in these regions are being planned. ation in pollution shocks induced by a recession. Q J Economics 118:1121–1167. In January 2008, HEI co-organized and cosponsored,with the CDC’s Environmental Public Health Tracking Clancy L, Goodman P, Sinclair H, Dockery DW. 2002.Program and the EPA, a workshop entitled “Method- Effect of air-pollution control on death rates in Dublin,ologic Issues in Environmental Public Health Tracking of Ireland: An intervention study. Lancet 360:1210–1214.Air Pollution Effects.” The workshop was par t of aneffort to implement the initiative outlined in HEI’s Stra- Health Effects Institute. 2003. Assessing Health Impacttegic Plan for 2005 through 2010 (HEI 2005) to “build of Air Quality Regulations: Concepts and Methods fornetworks with the U.S. Centers for Disease Control Accountability Research. HEI Communication 11.and Prevention and state public health tracking pro- Health Effects Institute, Boston, MA.grams to facilitate accountability research.” xv
  15. 15. Preface Health Effects Institute. 2005. HEI Strategic Plan for Priorities and a Long-Range Research Portfolio. Nation- Understanding Health Effects of Air Pollution. Health al Academy Press, Washington, D.C. Effects Institute, Boston, MA. National Research Council (U.S.). 2002. Estimating the Health Effects Institute. 2010a. HEI Strategic Plan for Public Health Benefits of Proposed Air Pollution Regu- Understanding the Health Effects of Air Pollution lations. National Academy Press, Washington, D.C. 2010–2015. Health Effects Institute, Boston, MA. Peel JL, Klein M, Flanders WD, Mulholland JA, Tolbert Health Effects Institute. 2010b. Proceedings of an HEI PE. 2010. Impact of Improved Air Quality During the Workshop on Further Research to Assess the Health 1996 Summer Olympic Games in Atlanta on Multiple Impacts of Actions Taken to Improve Air Quality. Com- Cardiovascular and Respiratory Outcomes. Research munication 15. Health Effects Institute, Boston, MA. Report 148. Health Effects Institute, Boston, MA. Hedley AJ, Wong CM, Thach TQ, Ma S, Lam TH, Peters A, Breitner S, Cyrys J, Stölzel M, Pitz M, Wölke Anderson HR. 2002. Cardiorespiratory and all-cause G, Heinrich J, Kreyling W, Küchenhoff H, Wichmann H- mortality after restrictions on sulphur content of fuel in E. 2009. The Influence of Improved Air Quality on Mor- Hong Kong: An intervention study. Lancet 360:1646– tality Risks in Erfurt, Germany. Research Report 137. 1652. Health Effects Institute, Boston, MA. Johns Hopkins Bloomberg School of Public Health (Bal- Pope CA III, Ezzati M, Dockery DW. 2009. Fine-partic- timore, MD). Internet-Based Health and Air Pollution ulate air pollution and life expectancy in the United Surveillance System (last updated 3/19/05). www.ihapss. States. N Engl J Med 360:376–386. jhsph.edu. Accessed 3/22/11. U.S. Centers for Disease Control and Prevention. Envi- Kelly F, Anderson HR, Armstrong B, Atkinson R, Barratt B, ronmental Public Health Tracking Program. www.cdc Beevers S, Derwent D, Green D, Mudway I, Wilkinson P. .gov/nceh/tracking/. Accessed 3/26/10. 2011a. Part 1. Emissions modeling and analysis of air pol- lution measurements. In: The Impact of the Congestion U.S. Environmental Protection Agency. 1990. A Bill to Charging Scheme on Air Quality in London. Research Amend the Clean Air Act to Provide for Attainment Report 155. Health Effects Institute, Boston, MA. and Maintenance of Health Protective National Ambient Air Quality Standards, and for Other Purposes. Kelly F, Anderson HR, Armstrong B, Atkinson R, Barratt B, S 1630, 101st Cong, 2nd Sess. Beevers S, Derwent D, Green D, Mudway I, Wilkinson P. 2011b. Part 2. Analysis of the oxidative potential of par- U.S. Environmental Protection Agency. 1999. Benefits ticulate matter. In: The Impact of the Congestion and Costs of the Clean Air Act 1990 to 2010: Report Charging Scheme on Air Quality in London. Research to Congress. EPA/410/R-99-001. Office of Air and Report 155. Health Effects Institute, Boston, MA. Radiation, Washington, D.C. Laden F, Schwartz J, Speizer FE, Dockery DW. 2006. van Erp AM, Cohen AJ. 2009. HEI’s Research Program Reduction in the particulate air pollution and mortality: on the Impact of Actions to Improve Air Quality: Extended follow-up of the Harvard Six Cities study. Am Interim Evaluation and Future Directions. Communica- J Respir Crit Care Med 173:667–672. tion 14. Health Effects Institute, Boston, MA. Matte TD, Cohen A, Dimmick F, Samet J, Sarnat J, Yip F, Wiener J. 1998. Managing the iatrogenic risks of risk Jones N. 2009. Summary of the workshop on method- management. Risk Health Safety Environ 9:39–82. ologies for environmental public health tracking of air Zeger SL, McDermott A, Dominici F, Peng R, Samet J. pollution effects. Air Qual Atmos Health 2:177–184. 2006. Internet-Based Health and Air Pollution Surveil- National Research Council (U.S.). 1998. Research Pri- lance System. Communication 12. Health Effects Insti- orities for Airborne Particulate Matter : I. Immediate tute, Boston, MA.xvi
  16. 16. H E I S TAT E M E N TSynopsis of Research Repor t 155The Congestion Charging Scheme and Air Qualityin LondonINTRODUCTION STUDY METHODS The study of the London Congestion Charging Kelly and his colleagues undertook a stepwiseScheme (CCS), conducted by Professor Frank Kelly approach to evaluating the impact of the CCS on airand colleagues, was funded under HEI’s research quality. In the first part of their study, they updatedprogram aimed at measuring the possible health emission estimates that had originally been devel-impacts associated with actions taken to improve air oped for the London transportation agency, Trans-quality. With this research program, HEI has sought port for London. Using the King’s College Londonto (1) fund studies to assess the health outcomes Emissions Toolkit (a set of statistical models andassociated with regulatory and incentive-based data), they developed detailed estimates of NO x,actions to improve air quality at local or national nitrogen dioxide (NO2), and PM10 emissions fromlevels, and (2) develop methods required for, and vehicular and non-vehicular sources throughout thespecifically suited to, conducting such research. London area for the 4-year period encompassing 2 The CCS offered an unusual opportunity to inves- years before (pre-CCS) and 2 years after (post-CCS)tigate the potential impact on air quality of a discrete the introduction of the scheme on February 17,and well-defined intervention to reduce traffic con- 2003. Vehicular PM 10 emissions were predictedgestion in the middle of a major city. The CCS was from two primary sources — tire and brake wear andimplemented in London in February 2003 with the exhaust. These emission estimates were then inputprimary aim of reducing traffic congestion by charg- to a modeling system (the King’s College London Airing vehicles to enter the central part of London, Pollution Toolkit), which the investigators used todefined as the congestion charging zone (CCZ). In an predict annual mean ambient concentrations of NOx,earlier study based on data from the first year of the NO2, and PM10 throughout London for each year ofscheme, members of the investigative team had the study. They explored how various assumptionsreported early findings of modest reductions in the about the mix of vehicles, speed, and congestionnumber of vehicles entering the zone and had pro- over the study period might affect the predicted spa-jected declines of about 12% in emissions of both tial patterns of changes in air quality associated withPM10 (particulate matter with an aerodynamic diam- the implementation of the CCS.eter of 10 µm) and nitrogen oxides (NOx) within The results of the modeling exercise were alsothe CCZ. Recognizing that these projected reduc-tions, coupled with the small area represented by the used to help select the fixed, continuous air moni-CCZ within Greater London, could lead to relatively toring sites from the London Air Quality Networksmall changes in air quality, the HEI Health Research (LAQN) with which to evaluate measured changes inCommittee recommended that the investigators first air quality. The investigators created a CCS Studyassess the actual changes in air quality and postpone Database consisting of validated (or ratified) mea-their proposal to study health impacts until the air surements of carbon monoxide (CO), nitric oxidequality studies were completed. The investigators (NO), NO2, NOx, and PM10 from monitors sited toproposed a multifaceted approach to exploring the record roadside or urban or suburban background airimpact of the CCS on air quality, which involved a pollutants across London. The investigators calcu-variety of modeling techniques, analysis of air moni- lated and compared geometric mean concentra-toring data, and a newly developed assay for the oxi- tions of these pollutants for the 2 years before (2001–dative potential of PM. 2002) and 2 years after (2003–2004) the scheme wasThis Statement, prepared by the Health Effects Institute, summarizes a research project funded by HEI and conducted by Professor Frank J.Kelly at the School of Biomedical Sciences, King’s College London, U.K., and colleagues. Research Report 155 contains both the detailedInvestigators’ Report and a Commentary on the study prepared by the Institute’s Health Review Committee. 1
  17. 17. Research Report 155 introduced. The changes over time at monitors by other investigators. Additional experiments were within the zone were compared with changes during done to understand the relative contribution of dif- the same period at similar classes of monitoring sites ferent metal and non-metal components of PM to in a control area more than 8 km from the center of the oxidative potential measured in the assays. the zone. In addition, the investigators also explored three other analytic techniques for characterizing and RESULTS AND INTERPRETATION evaluating both projected and measured changes in The modeling studies predicted small changes in pollutant concentrations over the period of the study: both emissions and ambient concentrations of NOx, ethane as an indicator of pollutant dispersion due to NO2, and PM10 across London that could be related regional atmospheric conditions; the cumulative sum to the implementation of the CCS, although the statistical technique to identify step changes in air effects within the CCZ were projected to be more pro- pollution data; and specialized graphical techniques nounced than elsewhere. They projected somewhat to improve the siting of pollutant monitors by charac- larger average reductions (about 20%) in NOx and terizing the dependence of pollutant concentrations at PM10 emissions than the 12% reductions that had potential monitoring sites on local emission sources. been predicted in the initial feasibility studies that In the second part of the study, the investigators preceded the CCS. However, the difference in these set out to explore whether implementation of the projections may partly be explained by the fact that CCS led to detectable changes in either the compo- the modeling in this study compared the 2 years sition of the PM10 mixture or in its oxidative poten- before and 2 years after the introduction of the CCS, tial — an indicator of toxicity. As part of this whereas the earlier estimates had been based on an analysis, they sought to establish a more compre- analysis of only the first year of the scheme (2003). hensive baseline of monitoring data to use in future The investigators reported that unusual meteorologic studies of the CCS by collecting data from addition- conditions had led to periods of elevated pollution al monitoring sites located within and outside a levels in London during that year. proposed expansion of the CCZ known as the West- Despite the somewhat larger projected reductions ern Extension. in emissions, the projected changes in concentra- For these purposes, the investigators created an tions of NO x , NO 2 , and PM10 related to the CCS archive of about 730 filters from tapered element were small. Within the CCZ, the investigators pro- oscillating microbalances, a type of PM10 monitor jected a net decline of 1.7 ppb in the annual average used at 16 sites within and surrounding the CCZ, mean NOx concentration and a decline of 0.8 µg/m3 including the Western Extension; the filter archive in PM10. The modeling also suggested that a major covered the 3 years before and 3 years after the CCS proportion of PM 10 might be accounted for by was introduced. After extracting the PM from the regional background levels, but that contributions filters, they measured the oxidative potential of the from tire and brake wear might also be important. extracts using an in vitro assay that measures the NO2 was projected to increase slightly, by 0.3 ppb ability of the extracts to deplete antioxidants in a on average; the investigators attributed this increase synthetic respiratory tract lining fluid. The investi- to higher NO2 emissions associated with the intro- gators’ focus on oxidative potential, a measure of duction of particle traps on diesel buses as part of the capacity to generate oxidation reactions, arises Transport for London’s improvements in the public from a leading theory about the causal role that oxi- transport system. dative stress may play in the health effects associ- From their comparison of actual air pollutant ated with exposure to air pollution. Their goal, in measurements within the CCZ with those at control essence, was to use oxidative potential as an indi- sites in Outer London, the investigators reported cator of the potential toxicity of PM and to evaluate little evidence of CCS-related changes in pollutant how it varied across London and in response to the levels at roadside monitoring sites, where their introduction of the CCS. modeling had suggested the most pronounced To study the composition of PM, each filter effects would be seen. The effects of the CCS were extract was also analyzed using inductively coupled more evident at urban background sites within the plasma mass spectrometry for a panel of metals that CCZ when compared with concentrations at sites in have been associated with traffic sources in studies the control area: PM10 concentrations declined by2
  18. 18. Research Report 15512% at the one background site in the CCZ where it meteorologic conditions the year the scheme waswas measured, and NO declined by between 10% introduced, and the influence of strong localand 25% at the three background sites where it was sources on particular monitors, would precludemeasured. However, levels of NO 2 increased by them from attributing these changes to the CCSbetween 2% and 20% at the three background sites alone. They also acknowledged that the area cov-compared with levels at the control sites; these ered by the CCS — approximately 1.4% of Greaterincreases were consistent with the predictions from London — was likely too small to influence air pol-the modeling studies and with the likely effects of lutant levels substantially either within or outsidethe parallel intervention that introduced more filter- the zone.equipped diesel buses. The investigators concludedthat the small net changes in NOx detected at both CONCLUSIONS AND IMPLICATIONSroadside and background monitoring sites — likely In its independent evaluation of the study, the HEIresulting from reductions in NO offset by increases Health Review Committee thought that Kelly and hisin NO 2 — did not provide strong evidence of an colleagues made a laudable effort to evaluate theimpact of the CCS. scheme’s impact. The team undertook a creative, In the study of the oxidative potential of PM10, stepwise, multidisciplinary approach beginningthe investigators were unable to identify a temporal, with updated modeling of potential changes in emis-CCS-related change during the 6-year period that sions and air pollutant concentrations, followed byencompassed the implementation of the scheme. multiple approaches to the analysis of actual airHowever, the city-wide spatial analysis of oxidative monitoring data. They demonstrated the value of apotential revealed that PM10 sampled from roadside careful modeling approach before decisions arelocations showed greater oxidative activity than made about whether and how to undertake studies ofPM10 sampled at urban background sites. the actual impacts of air quality interventions, When they coupled these spatial analyses of oxi- including insights as to where monitoring networksdative potential with analyses of the metal content might best be positioned to capture the impact of aof PM10 from the same filters, the investigators con- traffic-reduction scheme.cluded that their results provided suggestive evi- However, the investigators encountered a set ofdence that PM10 derived from tire and brake wear issues that have come to exemplify the general chal-(indicated by the presence of the metals arsenic, lenges posed by studies of this kind. One is simplybarium, copper, iron, manganese, nickel, and vana- the difficulty of detecting significant air qualitydium) might contribute to the oxidative potential of improvements related to an intervention against thePM seen in filters from roadside monitoring sites. backdrop of broader regional and meteorologicHowever, the investigators noted that correlations changes in the background concentrations of pollut-among the concentrations of PM 10 attributed to ants. A second is that other changes occurring at theexhaust and to tire and brake wear made it difficult same time (e.g., the introduction of more filter-to isolate how much these individual sources might equipped diesel buses in response to a separate rule)contribute to the oxidative potential of PM10. Their may also affect air quality and obscure effects of theother experimental findings suggested that the non- intervention being studied. A third is that institu-metal components of PM10 did not contribute sub- tional or behavioral changes in response to an inter-stantially to oxidative potential in this assay, but the vention, not all of which may be fully anticipated,investigators could not rule out a role for all other can also partly offset the possible gains expected.non-metal components of ambient air pollution. Finally, their experience highlights the challenges Overall, the investigators concluded that their pri- of using existing monitoring networks, even one asmary and exploratory analyses collectively suggested well-established as the LAQN, for the purposes ofthat the introduction of the CCS in 2003 was associ- measuring small changes in air quality.ated with small temporal changes in air pollutant Their investigation into oxidative potential as aconcentrations within the CCZ compared with those possible toxicologically relevant measure of expo-in control areas thought to be beyond the influence of sure to the aggregate PM mixture was intriguing.the scheme. In addition, they observed that a number However, their findings on the temporal and spatialof limitations, including concurrent changes in trans- changes in oxidative potential or in PM componentsportation and emission control policies, unusual related to the CCS were likely constrained by the 3
  19. 19. Research Report 155 same limitations that affected the first part of the This study of the CCS in London adds to the study. The use of the oxidative potential assay in growing body of evidence that confirms the need to this study was largely exploratory, particularly with establish the extent to which interventions have respect to its ability to discern the contributions of improved, or are likely to improve, ambient air individual elements or classes of compounds in PM quality before health studies are contemplated. on archived filters. The HEI Health Review Com- These investigators, in essence, covered the first mittee thought the most interesting result was the three steps in the “Outcomes Evaluation Cycle”: they modest suggestion that metals that have been associ- (1) provided evidence that the intervention or con- ated with tire and brake wear might contribute to the trols had in fact been put in place, (2) modeled the oxidative activity levels observed. However, further potential impact of the intervention on emissions, work is necessary to solidify the role of oxidative and (3) assessed whether the intervention had potential in this assay, and in other assays of this resulted in improved air quality. By choosing not to nature, as an indicator of potential human toxicity. fund the evaluation of health outcomes that was orig- Ultimately, the Review Committee concluded inally proposed as part of the study, despite the pro- that the investigators, despite their considerable jected reductions in emissions, HEI had emphasized effort to study the impact of the London CCS, were the importance of meeting these initial requirements. unable to demonstrate a clear effect of the CCS The study’s subsequent challenges in identifying an either on individual air pollutant concentrations or improvement in air quality reinforce that decision. on the oxidative potential of PM10. The investiga- Ultimately, although several factors affect the statis- tors’ conclusion that the primary and exploratory tical power of studies to detect changes in health analyses collectively indicate a weak effect of the related to an intervention like the CCS, a docu- CCS on air quality should be viewed cautiously. mented expectation of a sufficient change in air The results were not always consistent and the quality is and will continue to be an important crite- uncertainties surrounding them were not always rion for deciding whether to engage in a health out- clearly presented, making it difficult to reach defin- comes study. itive conclusions.4
  20. 20. INVESTIGATORS’ REPORTThe Impact of the Congestion Charging Scheme on Air Quality in London:Part 1. Emissions Modeling and Analysis of Air Pollution MeasurementsFrank Kelly, H. Ross Anderson, Ben Armstrong, Richard Atkinson, Ben Barratt, Sean Beevers,Dick Derwent, David Green, Ian Mudway, and Paul WilkinsonKing’s College London, U.K. (F.K., B.B., S.B., D.G., I.M.); St George’s, University of London, U.K. (H.R.A., R.A.);London School of Hygiene & Tropical Medicine, London, U.K. (B.A., P.W.); rdscientific, U.K. (D.D.) a net 0.8-µg/m 3 decrease in the mean concentration ofABSTRACT PM10 and a net 1.7-ppb decrease in the mean concentra- On February 17, 2003, a congestion charging scheme tion of NO x within the CCZ. In contrast, a net 0.3-ppb(CCS*) was introduced in central London along with a pro- increase in the mean concentration of NO2 was predictedgram of traffic management measures. The scheme operated within the zone; this was partly explained by an expectedMonday through Friday, 7 AM to 6 PM. This program resulted increase in primary NO2 emissions due to the introductionin an 18% reduction in traffic volume and a 30% reduction of particle traps on diesel buses (one part of the improve-in traffic congestion in the first year (2003). We developed ments in public transport associated with the CCS).methods to evaluate the possible effects of the scheme on air In the second part of the project, we established a CCSquality: We used a temporal–spatial design in which mod- Study Database from measurements obtained from theeled and measured air quality data from roadside and back- London Air Quality Network (LAQN) for air pollutionground monitoring stations were used to compare time monitors sited to measure roadside and urban backgroundperiods before (2001–2002) and after (2003–2004) the CCS concentrations. Fully ratified (validated) 15-minute meanwas introduced and to compare the spatial area of the con- carbon monoxide (CO), nitric oxide (NO), NO 2 , NO x ,gestion charging zone (CCZ) with the rest of London. PM10, and PM2.5 data from each chosen monitoring site for In the first part of this project, we modeled changes in the period from February 17, 2001, to February 16, 2005,concentrations of oxides of nitrogen (NO x ), nitrogen were transferred from the LAQN database.dioxide (NO 2), and PM10 (particles with a mass median In the third part of our project, these data were used toaerodynamic diameter 10 µm) across the CCZ and in compare geometric means for the 2 years before and the 2Greater London under different traffic and emission sce- years after the CCS was introduced. Temporal changesnarios for the periods before and after CCS introduction. within the CCZ were compared with changes, over theComparing model results within and outside the zone sug- same period, at similarly sited (roadside or background)gested that introducing the CCS would be associated with monitors in a control area 8 km distant from the center of the CCZ. The analysis was confined to measurementsThis Investigators’ Report is Part 1 of Health Effects Institute Research obtained during the hours and days on which the schemeReport 155, which also includes Part 2. Analysis of the Oxidative Potential was in operation and focused on pollutants derived fromof Particulate Matter, a Commentary by the HEI Health Review Committee,and an HEI Statement about the research project. Correspondence concern- vehicles (NO, NO2, NOx, PM10, and CO).ing the Investigators’ Report may be addressed to Professor Frank Kelly, Pro-fessor of Environmental Health, Environmental Research Group, MRC-HPA This set of analyses was based on the limited data avail-Centre for Environment & Health, School of Biomedical Sciences, King’sCollege London, 150 Stamford Street, London SE1 9NH, U.K. Tel ++44 20 able from within the CCZ. When compared with data from7848 4004; Fax ++44 20 7848 3891; frank.kelly@kcl.ac.uk. outside the zone, we did not find evidence of temporalAlthough this document was produced with partial funding by the United changes in roadside measurements of NOx, NO, and NO2,States Environmental Protection Agency under Assistance Award CR–83234701 to the Health Effects Institute, it has not been subjected to the nor in urban background concentrations of NO x . (TheAgency’s peer and administrative review and therefore may not necessarilyreflect the views of the Agency, and no official endorsement by it should be latter result, however, concealed divergent trends in NO,inferred. The contents of this document also have not been reviewed by pri- which fell, and NO2, which rose.) Although based uponvate party institutions, including those that support the Health Effects Insti-tute; therefore, it may not reflect the views or policies of these parties, and fewer stations, there was evidence that background con-no endorsement by them should be inferred. centrations of PM10 and CO fell within the CCZ compared* A list of abbreviations and other terms appears at the end of the Investiga-tors’ Report. with outside the zone.Health Effects Institute Research Report 155 © 2011 5
  21. 21. The London CCS: Part 1. Emissions Modeling and Pollutant Measurements We also analyzed the trends in background concentra- dispersion. The technique had the potential to ascertaintions for all London monitoring stations; as distance from more accurately the likely impacts of the CCS on London’sthe center of the CCZ increased, we found some evidence air quality. Although this novel method appeared prom-of an increasing gradation in NO and PM10 concentrations ising over short time periods, a number of concerns arosebefore versus after the intervention. This suggests a pos- about whether the spatial and temporal variability ofsible intermediate effect on air quality in the area immedi- ethane over longer time periods would be representative ofately surrounding the CCZ. meteorologic conditions alone. Although London is relatively well served with air The major strength of CUSUM, the second method, isquality monitoring stations, our study was restricted by that it can be used to identify the approximate timing ofthe availability of only a few monitoring sites within the changes that may have been caused by the CCS. ThisCCZ, and only one of those was at a roadside location. The ability is weakened, however, by the effects of serial corre-results derived from this single roadside site are not likely lation (the correlation of data among measurements in suc-to be an adequate basis for evaluating this complex urban cessive time intervals) within air pollution data that istraffic management scheme. caused by seasonality and long-term meteorologic trends. Our primary approach to assessing the impact of the The secure interpretation of CUSUM requires that theCCS was to analyze the changes in geometric mean pol- technique be adapted to take proper account of the under-lutant concentrations in the 2 years before and 2 years after lying correlation between measurements without the usethe CCS was introduced and to compare changes at moni- of smoothing functions that would obscure a steppedtoring stations within the CCZ with those in a distant con- change in concentrations. Although CUSUM was not abletrol area (8 km from the CCZ center) unlikely to be to provide a quantitative estimation of changes in pollu-influenced by the CCS. We saw this as the most robust ana- tion levels arising from the introduction of the CCS, thelytical approach with which to examine the CCS Study strong signals that were identified were considered in theDatabase, but in the fourth part of the project we did con- context of other results from the study.sider three other approaches: ethane as an indicator of pol- The third method, bivariate polar plots, proved useful.lution dispersion; the cumulative sum (CUSUM) statistical The plots revealed important characteristics of the datatechnique; and bivariate polar plots for local emissions. from the only roadside monitoring site within the CCZ andAll three were subsequently judged as requiring further highlighted the importance of considering prevailingdevelopment outside of the scope of this study. However, weather conditions when positioning a roadside monitor.despite their investigative nature, each technique pro- The technique would benefit from further development,vided useful information supporting the main analyses. however, in transforming the qualitative assessment of The first method used ethane as a dispersion indicator to change into a quantitative assessment and including anremove the inherent variability in air pollutant concentra- estimate of uncertainty. Research is ongoing to developtions caused by changes in meteorology and atmospheric this method in air-quality time-series studies. Overall, using a range of measurement and modeling Air Monitoring Site Classifications in the approaches, we found evidence of small changes in air London Air Quality Network quality after introduction of the CCS. These include small decreases in PM10, NO, and CO. The possibility that some Rural. An open countryside location in an area of low of these effects might reflect more general changes in population density distanced as far as possible from roads London’s air quality is suggested by the findings of some- and populated and industrial areas. what similar changes in geometric means for weekends, Suburban. A location in a residential area on the outskirts of when the CCS was not operating. However, since some evi- a town or city with no major sources of pollution within 50 m. dence suggests that the CCS also had an impact on traffic Urban Background (also referred to as background). An urban volume on weekends, the CCS remains as one possible location with no major sources of pollution within 50 m and explanation for the observed pattern of changes in pol- broadly representative of city-wide background conditions; lutant concentrations. In addition, the CCS was just one of for example, urban residential areas. a number of traffic and emission reduction schemes intro- Roadside. A site sampling between 1 m from the curbside of duced in London over the 4-year study period; if the other a busy road and the back of the pavement (sidewalk). Typi- measures had an impact in central London, they might cally this is within 5 m of the road, but could be up to 15 m. partly explain our findings. Curbside. A site sampling within 1 m of the curb of a Although not the aim of this study, it is important to busy road. consider how the trends we observed might be translated6
  22. 22. F. Kelly et al.into health effects. For example, given that London alreadyhas NO2 concentrations in excess of the permitted limit INTRODUCTIONvalue, we do not know what the effects of an increase inNO2 created by diesel-exhaust after-treatment for particles HISTORICAL BACKGROUND OF LONDON’Smight mean for health. Further, although it is not likely AIR QUALITYthat NO affects health, the decrease in NO concentrations Air pollution has been a serious problem in Londonis likely associated with an increase in ozone concentra- since the 16th century owing to the city’s importance as ations (a pollutant associated with health effects), as has commercial and industrial center and because of the highbeen seen in recent years in London. These and other sim- concentration of domestic coal burning. As a consequence,ilar issues require further investigation. the city has long been referred to as “the big smoke” and Although the CCS is a relatively simple traffic manage- has given its name to the combination of urban smoke andment scheme in the middle of a major urban environment, natural fog, namely “London smog.” Concern over theanalyzing its possible impact on air quality was found to be health effects of London’s poor air quality also dates backfar from straightforward. Using a range of modeling and many centuries. In 1661 the diarist John Evelyn presentedmonitoring approaches to address the impact of the scheme Charles II with a treatise on the problem, in which he sug-revealed that each technique has its own advantages and gested that smoke pollution would shorten the lives oflimitations. The placement of monitoring sites and the Londoners (Evelyn 1661). Nearly 200 years later, an articleavailably of traffic count data were also identified as key in The Lancet (1856) stated that “The air of this great cityissues. The most compelling lesson we take away from this is, as all know too well, polluted by a variety of noxiousstudy is that such work is impossible to undertake without a gases and vapors diffused or held in solution.” The articlecoherent multi-disciplinary team of skilled researchers. went on to quote the Registrar-General at that time as In conclusion, our study suggests that the introduction saying “There can be no doubt that the dirty dust sus-of the CCS in 2003 was associated with small temporal pended in the air that the people of London breathe, oftenchanges in air pollutant concentrations in central London excites diseases of the respiratory organs. The dirt of thecompared with outer areas. However, attributing the cause streets is produced and ground down by innumerableof these changes to the CCS alone is not appropriate horses, omnibuses and carriages, and then beat up intobecause the scheme was introduced at a time when other fine dust, which fills the mouth, and inevitably enters thetraffic and emissions interventions, which might have had air passages in large quantities.”a more concentrated effect in central London, were also London’s dominance as an industrial city and majorbeing implemented. port steadily declined during the 20th century, giving way to commerce and public administration as its major activi- ties. Consequently, emissions of smoke and sulfur dioxide (SO 2 ) from industrial activities declined. Indeed, the annual mean black smoke concentrations fell by more than a factor of 80 over the period from 1922 to 1997 (Figure 1). In 1952, the infamous wintertime smog episode, whichFigure 1. Historical black smoke concentrations in London. Left panel: data from the Kew Observatory from 1922 to 1969; right panel: data from theLambeth air monitoring station from 1961 to 1998. Note that the units on the two x axes differ. Source: AQEG 2005. 7
  23. 23. The London CCS: Part 1. Emissions Modeling and Pollutant Measurementsclaimed an estimated 4,000 to 12,000 premature deaths, had and the equipment base of existing sites was extended. Con-a major impact on public health policies and led to the 1956 tinuous monitoring of PM10 began to replace the originalClean Air Act, the major focus of which was the curtailing of black smoke measurements. In order to coordinate the airdomestic coal burning in London and other major popula- quality monitoring established by the 33 London Boroughstion centers in the United Kingdom. As Figure 1 shows, and to ensure spatial and temporal comparability, in 1993however, the 1956 Act reinforced the declining black smoke the Environmental Research Group (ERG) at King’s Collegetrends that were already well in hand due to structural London created the LAQN. The LAQN has generated achanges in London’s economy. Over the last 50 years coal much clearer picture of London’s air quality and the stepsburning has continued to decline, being replaced by cen- required to ensure its improvement. For example, analysistrally generated electricity and the use of natural gas in com- of the LAQN data shows that, during the 1990s and earlymercial premises and homes. 2000s, airborne particulate and lead concentrations have declined steadily after lead was phased out of gasoline, and levels of CO, benzene, and 1,3-butadiene have fallenAIR POLLUTION IN LONDON TODAY dramatically (with annual reductions of 10% to 20%). In December of 1991, a severe wintertime air pollution Much of this improvement was brought about by the man-episode occurred in London. It was characterized by datory implementation of three-way catalysts and evapora-unprecedented levels of benzene, CO, NOx, and in partic- tive canisters in gasoline engines. In turn, the reduction inular, NO2 — all components of exhaust from gasoline- and emissions of volatile organic compounds (VOCs) has pro-diesel-powered motor vehicles. In response, new air quality duced a decline in the peak intensity of photochemicalmonitoring sites were established in and around London smog episodes.Figure 2. Relationship of the CCZ to Greater London. (Map includes the Western Extension, which was introduced in 2007.) Adapted with permissionfrom Transport for London 2006.8
  24. 24. F. Kelly et al. In contrast, the annual percentage of reductions in NOx health. The primary focus of the strategy was the reductionlevels (also achieved through use of three-way catalysts) of of pollution from road traffic in the city since this is theapproximately 3% to 5% are substantially lower than those main source of the pollutants of concern. In 2003, emissionsachieved for CO and VOCs. This is because of the substan- from road transport contributed approximately 40% of NOxtial and growing contributions to NO x emissions from emissions and 66% of PM10 emissions in Inner London. Adiesel-powered motor vehicles which, until recently, had reduction in London’s road traffic emissions is beingnot been the target of emission controls. The increasing use achieved through two goals: decrease the number of vehi-of diesel-powered vehicles also means that PM is still of cles on the road, and reduce emissions from individualmajor concern despite the enormous reduction in black vehicles (i.e., modernize the vehicle stock). To help achievesmoke levels. In fact, although concentrations of PM 10 the first goal, the Mayor introduced a CCS in centraldeclined during the 1990s, the trend has slowed down and, London on February 17, 2003. One approach to tackle theduring the early 2000s, levels have remained constant. So second goal is a London-wide Low Emission Zone, whichdespite the air quality gains achieved in previous decades, was introduced on February 4, 2008 (see Kelly et al. 2011).like many other large cities around the world, London con-tinues to have high levels of air pollution owing to a combi- THE CCS IN LONDONnation of mobile and regional background sources. The CCS is a scheme to charge vehicles that enter a spe- cific zone. It initially covered approximately 22 km2 orLONDON’S AIR QUALITY STRATEGY 1.4% of the Greater London area (enclosed approximately In view of widespread public concern about the health by the M25 London Orbital Motorway [Figure 2]) and con-effects of air pollution, in 2002 the Mayor of London tained some of the most congested traffic conditions inlaunched his Air Quality Strategy, entitled Cleaning London. On February 19, 2007, the CCZ was extendedLondon’s Air (Greater London Authority 2002). It set out westward to cover approximately 41.5 km2 or 2.6% of thepolicies and proposals to move toward the point where Greater London area (Figure 3). The designated zone ispollution no longer poses a significant risk to human clearly defined by signs or road markings at entrance andFigure 3. The CCZ with the 2007 Western Extension (in gray). The middle road that separates the original zone and the Western Extension is uncharged.Adapted with permission from Transport for London 2006. 9
  25. 25. The London CCS: Part 1. Emissions Modeling and Pollutant Measurementsexit points. Vehicles that cross a cordon line on weekdays [delivery vehicles], and lorries [trucks]) entering the CCZbetween 7:00 AM and 6:00 PM, referred to as the congestion during charging hours was lower; at the same time, thecharging hours (CCH), pay a daily charge that was origi- number of non-chargeable vehicles such as licensed taxis,nally 5 Great Britain pounds (then about 8 U.S. dollars) but buses, and two-wheelers all increased (Tfl 2007). In com-was increased to 8 GBP (then about 14 USD) in July 2005. paring values for 2006 against those for 2003, we saw fur-The charge does not apply on national holidays or the first ther declines across most vehicle types.3 charging days that follow December 26 each year. Vehi- Evaluating the overall impact of the CCS on congestioncles that are exempt from the charge include those for indi- is more complex. (Congestion is defined as excess delayviduals with disabilities and institutions that assist them [minutes/km] over and above uncongested conditions,throughout the European Union (which are identified by which are the early hours of the morning [1–5 AM].) Duringblue badges), roadside recovery vehicles (towing trucks), 2003 and 2004, levels of congestion in the CCZ were typi-accredited roadside breakdown organizations, electrically cally around 30% lower than those in 2002; but in 2005propelled vehicles, vehicles with nine or more seats and the average congestion reduction was only 22%. Moreover,registered as buses, licensed taxis, and motor tricycles 1 m during 2006, despite a continued reduction in vehicleor less in width and 2 m or less in length. In addition to count, congestion increased to higher than the 2002 levels.these exemptions, discounts are available to residents living This change correlated with an increase in road work andwithin the CCZ (90% reduction in fee) and drivers of vehi-cles powered by alternative fuels (up to 100% reduction). with a gradual longer-term trend of increased congestionAssisted by revenue from the CCS, concurrent improve- across London.ments in traffic management and in the fleet of public trans- In line with the decrease in vehicle counts, the introduc-port vehicles have been implemented to accommodate the tion of the CCS substantially increased traffic speeds duringshift in travel patterns after the introduction of the CCS as charging hours from 14 km/hour in 2002 to approximatelywell as continued growth in passenger numbers. 17 km/hour in 2003 (a level last seen in the early 1980s). The main objective of the CCS was to achieve a 15% Since 2003 however, average speeds observed duringreduction in traffic in the CCZ and 0% growth in traffic in charging hours have progressively fallen back to about 16Inner London surrounding the CCZ; each year, the prin- km/hour in 2005 and 15 km/hour in 2006 (TfL 2007).cipal traffic and transport objectives have been met. This Similar road pricing schemes are being considered forsuccess mirrors the effectiveness of similar schemes in other U.K. cities and it is likely that traffic zone paymentSingapore, Stockholm, and Norway (Chin 1996; Tuan Seik schemes will become more common elsewhere in the2000; Victoria Policy Transport Institute 2007). Changes to world. For example, Milan tested such a scheme at thetravel patterns (e.g., traffic entering the CCZ, congestion, beginning of 2007 to address the city’s severe air pollutionand speeds) that have arisen from the scheme occurred and traffic problems; and New York City is the first majorvery quickly in 2003; however, changes in the period since American city to seriously consider implementing a traffichave tended to reflect wider traffic trends and possibly congestion charge. The CCS in London can thus be consid-effects that have developed more slowly from the CCS and ered a forerunner in what is likely to become a powerfulother transport changes. These immediate and longer-term and widely adopted approach to traffic management.effects are discussed below. At the end of the first year of CCS operation, the number THE CCS AND AIR QUALITY IN LONDONof vehicles with four or more wheels that entered the zoneduring charging hours had dropped by 18% from 2002 In the current HEI study, we assessed whether the reduc-numbers; the most recent results reported from Transport tion in congestion and traffic achieved after a regulatoryfor London (TfL; the local government body responsible intervention has had an impact on the air quality infor managing the London transport system) illustrate that London. In principle, by reducing the number of vehiclessuch a reduction continues: traffic entering the CCZ during entering the zone, the CCS should reduce emissions and2006 was 21% lower than the pre-CCS conditions in 2002 improve air quality in the center of London. However, this(TfL 2007). In contrast to findings within the CCZ, traffic is an unrealistically simple assumption. We did not expecton the Inner Ring Road (IRR; the boundary of the CCZ the CCS to have more than a small effect on air qualityalong which no charge is applied) has remained similar to within the CCZ considering that it brought about a rela-levels before charging was introduced. As one would tively moderate reduction in traffic (approximately 20%expect, the immediate effect 1 year after the start of the fewer vehicles) in a small area (1.4%) of Greater London.CCS was that the number of chargeable vehicles (i.e., cars, A number of other factors made it likely that the effectminicabs [privately hired vehicles, limousines], vans elicited would be small. First, changes brought about by10