Particulate Matter Air Pollution and Health Risks
What is Particulate Matter? Particulate matter (PM) describes a wide variety of airborne material. PM pollution consists of materials (including dust, smoke, and soot), that are directly emitted into the air or result from the transformation of gaseous pollutants. Particles come from natural sources (e.g., volcanic eruptions) and human activities such as burning fossilImage from http://www.epa.gov/eogapti1/ fuels, incinerating wastes, andmodule3/distribu/distribu.htm smelting metals.
How is PM Regulated?PM is one of the six EPA “criteria pollutants” that have beendetermined to be harmful to public health and the environment.(The other five are ozone, sulfur dioxide, nitrogen dioxide,carbon monoxide, and lead.)EPA is required under the Clean Air Act to set nationalambient air quality standards (NAAQS) to protect publichealth from exposure to these pollutants. Areas that exceed theNAAQS are designated as nonattainment, and must instituteair pollution control programs to reduce air pollution to levelsthat meet the NAAQS.
Where Does PM Originate?Sources may emit PM directly into the environment or emit precursorssuch as sulfur dioxide (SO2), nitrogen dioxide (NO2), and volatileorganic compounds (VOCs), which are transformed throughatmospheric chemistry to form PM. VOCs NO2 Ammonia (NH3) PM Ammonia (NH3) SO2
Sources of PM and PM Precursors Mobile Sources Stationary Sources (vehicles) (power plants, factories) VOCs, NO2, PM NO2, SO2, PM Area Sources Natural Sources(drycleaners, gas stations) (forest fires, volcanoes) VOCs PM
Determinants of PM Concentration • Weather patterns • Wind • Stability (vertical movement of air) • Turbulence • Precipitation • Topography • Smokestack height and temperature of gasesNearby natural and built structures may lead to downward movingcurrents causing aerodynamic or building downwash ofsmokestack emissions.
The Role of Inversions An inversion is an extremely stable layer of the atmosphere that forms over areas. Temperature inversions trap pollutants close to the ground. These inversions involve layers of hot air sitting above cooler air near ground level. When particles accumulate in the air layer, they are unable to rise into the atmosphere where winds will disperse them.Source: http://www.epa.gov/apti/ course422/ce1.html
Major Episodes of Severe Air Pollution due to Inversions1930: Meuse River Valley, Belgium • An inversion led to a high concentration of pollutants during a period of cold, damp weather • Main sources: zinc smelter, sulfuric acid factory, glass manufacturers • 60 deaths recorded1948: Donora, Pennsylvania • Similar inversion to Meuse River Valley • Main sources: iron and steel factories, zinc smelting, and an acid plant • 20 deaths observed1952: London • Killer fog (right) • Primary source: domestic coal burning • 4,500 excess deaths recorded during week- The Great London Smog long period in December (1952)
Particulate Matter: Aerodynamic DiameterEstablishing a particle sizedefinition for irregularly shapedparticles necessitates the use of astandardized measure referred toas the aerodynamic diameter,measured in microns ormicrometers (μm), a unit equal toone millionth of a meter. The graphat the right shows the distribution ofthe 4 main particle size categories,with the categories historically andcurrently regulated by EPAindicated below. By comparison, ahuman hair is approximately 70microns in diameter. Top: Modified from Online Reference Module by JR Richards et al. http://registrar.ies. ncsu.edu/ol_2000. Bottom: U.S. EPA. Office of Research and Development.
Particulate Matter: Size MattersSize is important to the behaviorof PM in the atmosphere andhuman body and determines theentry and absorption potentialfor particles in the lungs.Particles larger than 10 µm aretrapped in the nose and throatand never reach the lungs.Therefore, particles 10 µm indiameter or less are of mostconcern for their effects onhuman health. Particlesbetween 5 and 10 µm areremoved by physical processesin the throat. Particles smallerthan 5 µm reach the bronchialtubes, while particles 2.5 µm in Image: PM2.5. By D. Hershey. From New York State Department of Environmental Conservation.diameter or smaller are http://www.dec.state.ny.us/website/dar/baqs/microbreathed into the deepest /two.htmlportions of the lungs.
What Adverse Health Effects Have Been Linked to PM?• Premature death• Lung cancer• Exacerbation of COPD• Development of chronic lung disease• Heart attacks• Hospital admissions and ER visits for heart and lung disease• Respiratory symptoms and medication use in people with chronic lung disease and asthma• Decreased lung function• Pre-term birth• Low birth weight
Increasing Evidence of Cardiovascular EffectsUntil the mid 1990s, mostresearch focused on theassociation of PM exposure withrespiratory disease. Since then,there has been growing evidenceof cardiovascular health effectsfrom PM. Source: Pope and Dockery, JAWMA, 2006
Integrating Toxicology, Epidemiology and Clinical StudiesToxicological, clinical andepidemiological studies haveincreased understanding of themechanism of action by whichPM leads to mortality and lung andheart disease.For example, at right are stainedphotomicrographs of abdominalarteries from mice exposed tofiltered air and air polluted with fineparticulate matter, with theincreased arterial blockage in thePM-exposed mice providingscientific support for the linkbetween PM and atherosclerosisfound in a study of human subjects(Kunzli et al., 2005). Sun et al. JAMA, 2005
How Does PM Cause Health Effects? Several theories have been advanced as to the mechanism of action. It is likely that more than one mechanism is involved in causing PM-related health effects. Theories include the following:– PM leads to lung irritation – PM causes inflammation which leads to increase of lung tissue, resulting in permeability in lung tissue; the release of chemicals that impact heart function;– PM increases susceptibility to viral and bacterial pathogens – PM causes changes in leading to pneumonia in blood chemistry that vulnerable persons who are results in clots that can unable to clear these cause heart attacks. infections;– PM aggravates the severity of chronic lung diseases causing rapid loss of airway function;
Types of Air Pollution and Health Studies• Ecologic study – Examines the association between exposure rates and disease rates in a group over time. In ecologic studies, the exposure and disease status of individuals in the group are unknown. Therefore, one limitation of this study design is that those exposed and those with the disease may not be the same individuals.• Time-series study – Analyzes a series of data points that results from repeated measurements over time. Adjustments are made for cyclical or seasonal trends such as daily peaks in PM levels or annual influenza trends in order to identify larger trends that demonstrate the association between exposure and disease.• Cohort study – The health status of individuals in a cohort (i.e., group of study participants) whose exposure status is known at the start of the study is monitored over time to see if there is an association between their exposure and particular health outcomes.
The Evolution of Air Pollution Research Methods - Early StudiesEarly studies of air pollutionconcentrated on the severeepisodes described earlier.These episodes demonstrated aclear link between increasedlevels of ambient pollution andadverse health outcomes.Methods used to describe theseevents included populationsurveys, ecological studies,and, later, time-series analyses. Donora, PA at noon on Oct. 29, 1948. Photo source: Pittsburgh Post-Gazette
The Evolution of Air Pollution Research Methods - The London FogThe London Fog event of1952 provides a clearexample of an early time-series analysis. The figureto the right shows theestimates of weeklymortality and average sulfurdioxide concentrations forLondon during the winter of1952-53. Deaths inDecember increasedapproximately 2.5 timesover comparable periods in1947 to 1951, and remainedelevated through February1953. Source: http://www.portfolio.mvm.ed.ac.uk/ studentwebs/session4/27/greatsmog52.htm
The Evolution of Air Pollution Research Methods - Modern StudiesThe modern era of air pollutionresearch involved using laboratorysampling equipment andepidemiologic methods todetermine personal exposures andto monitor health effects. Theseefforts were used in the HarvardSix Cities Study, a prospectivestudy pioneered in 1973, in whichmortality data from a cohort ofadults in six cities with differentlevels of air pollution wereanalyzed, controlling for P=Portage, WI H=Harriman, TNbehavioral risk factors such as T=Topeka, KS L=St. Louis, MOsmoking. This study led to more W=Watertown, MAcomplex techniques for both S=Steubenville, OHmeasuring exposure and modelingthe exposure-response Source: Dockery D, et al. An Association betweenrelationship between PM and Air Pollution and Mortality in Six U.S. Cities,health endpoints. NEJM 1993; 329 (24):1753-1759.
The Evolution of Air Pollution Research Methods - Multiple SitesMore recent studies haveintroduced sophisticated statisticalapproaches to the time-seriesrelationship. The NationalMorbidity, Mortality, and AirPollution Study (NMMAPS) hasmade substantial contributionstowards understanding theassociation of PM with mortality byapplying a consistent approach todata collected at 90 different sitesacross the nation.The graph at the right shows the Source: Samet JM, Zeger SL, Dominici FD et al. 2000. The National Morbidity, Mortality, and Air Pollution Study. Partrelative rates of mortality per 10 μg II: Morbidity and Mortality from Air Pollution in the Unitedincrease in PM10 levels for the 90 States. Cambridge, MA: Health Effects Institute.individual study sites.
Air Pollution Research: Setting the Future AgendaThe Committee on Research Priorities for Airborne ParticulateMatter was established by the National Research Council inJanuary 1998 in response to a request from Congress and the EPA.The Committee produced 4 reports over the period 1998 – 2004.I. Immediate Priorities II. Evaluating Research III. Early Research IV. Continuing Research and a Long-Range Progress and Updating Progress Progress Research Portfolio the Portfolio
Research PrioritiesThe Committee identified ten research areas of priority inestablishing the relation between PM exposure and public health:1. Outdoor measures vs. actual 1. Dosimetry: Deposition and human exposure fate of particles in the2. Exposures of susceptible respiratory tract subpopulations to toxic PM 2. Combined effects of PM and components gaseous co-pollutants3. Characterization of emission 3. Susceptible subpopulations sources 4. Mechanisms of injury4. Air-Quality-Model development 5. Analysis and measurement and testing5. Assessment of hazardous particulate matter components
For More Information Further information on particulate matter air pollution is available at:http://www.healtheffects.org/http://www.epa.gov/oar/particlepollution/http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.htmlhttp://www.epa.gov/air/oaqps/greenbk/pindex.html