This document provides an introduction to ultrafine particles (UFPs), which are particles smaller than 100nm. UFPs make up over 90% of particle numbers but only a small portion of total particle mass. Primary sources include traffic, industry, agriculture, and cooking. Secondary sources are formed from chemical reactions in the atmosphere. UFPs can deposit deep in the lungs and may be more toxic than larger particles due to their small size and large surface area. While no regulatory standards currently exist for UFPs, they are measured using devices like condensation particle counters and scanning mobility particle sizers. Levels typically follow traffic patterns and decline with distance from roads. Health effects are still being researched.

1. Introduction to ultrafine particles
Tiffany Cheung
Consultant
Tiffany.Cheung@arup.com
November 2020

2. 2
Context
https://www.theguardian.com/environment/2019/dec/
05/pollutionwatch-exposing-threat-ultrafine-
particles#comments
https://www.theguardian.com/environment/2019/nov/13/air-
pollution-particles-linked-to-brain-cancer-in-new-research
https://airqualitynews.com/2020/02/17/exposure-to-ultra-fine-particles-is-
linked-to-nonfatal-heart-attacks/
https://airqualitynews.com/2020/01/06/heathrow-airport-pollution-
detected-in-central-london/
https://www.bbc.com/future/article/20191113-the-toxic-killers-in-
our-air-too-small-to-see

3. 3
• What are ultrafine particles (UFPs)?
• What are the sources of UFPs?
• What are the health effects of UFPs?
• How are UFPs measured?
• UFP trends
• What are the relevant legislation for UFPs?
Contents

4. 4
• Ultrafine particles (UFPs) defined as
particles with aerodynamic diameter
<100nm (PM0.1µm)
• Contribution to particle mass is small
but >90% of particles in air is in UFP
size range
• Particle number concentration (PNC)
per unit volume air (particles/cm3)
- PM10 and PM2.5 are measured in
terms of mass concentration
(µg/m3)
What are ultrafine particles?
Kwon et al., 2020

5. 5
• Reveals formation, history of particles
• Highly dynamic atmospheric
processes
Particle number size distribution
 High temperature
processes
 New particle
formation (NPF)
 Minutes
 Growth of nucleation
mode particles
 Incomplete
combustion
 Primary and
secondary particles
 Days
 Break up of
bulk materials,
re-suspension
 Minutes to
hours
What are ultrafine particles?

6. 6
Primary sources
https://uk-air.defra.gov.uk/assets/documents/reports/cat09/1807261113_180703_UFP_Report_FINAL_for_publication.pdf
Natural
• Marine aerosol
• Volcanic particles
• Forest fires
Secondary source
Anthropogenic
• Transport
• Industry and power
plants
• Agricultural processes
• Cooking
• New particle formation –
photochemical reactions and
condensation of semi-
volatile vapours
What are the sources?
© The Standard, ©The Independent, © Telegraph, ©European Commission, © NBC news

7. 7
• Greater toxicity hypothesised
due to vast numbers, small
diameters, high surface area
• Deposition in bronchioles and
alveoli, greater potential to
diffuse into bloodstream
• Retention in lungs, increased
accumulation and potential for
interaction with cells and tissue
Why are we interested?
Kreyling et al. 2006

8. 8
• Condensation Particle Counter (CPC) to measure
particle number concentration (PNC)
(particles/cm3)
• Scanning Mobility Particle Sizer (SMPS) to
understand size distribution
• Others:
- Simpler portable instruments (PNC, mean size) –
accuracy ±30%
- Other metrics (surface area, mass)
How are ultrafine particles measured?
CPC
SMPS

9. 9
How are ultrafine particles measured?
London Honor Oak Park
Urban background
London Marylebone Road
Roadside (street canyon)
Chilbolton Observatory
Rural background
• European Committee
for Standardisation
(CEN) to publish
Technical Specification
for UFP measurements
• Environment
Agency’s MCERTS
performance
standard
Monitoring in the UK

10. 10
Ultrafine particle trends
Historical
• Limits to fuel sulphur as a key reason
for decline in past two decades
Temporal
• Generally follows road traffic diurnal
profile
AQEG, 2018 Historical PNC measurements at London Marylebone Road
AQEG, 2018 Diurnal profile of pollutants at London Marylebone
Road

11. 11
Ultrafine particle trends
Spatial
• Peak concentrations close to emission sources
• Background concentrations around 200m from
source
• Heterogeneous distribution
Relationship with other pollutants
• Association with road traffic
pollutants
• Slight difference compared to
PM10 and PM2.5 trends
Karner et al., 2010

12. 12
Existing
• No ambient air quality standards for UFP
• EU legislation – particle number emission
standards for new vehicles
- Not relevant for public UFP exposure
Relevant guidelines and legislation
Future
• WHO recommendation on UFP in next
update of air quality guidelines?
- 2005 update stated that epidemiological
evidence for UFPs was insufficient to
develop a guideline value
WHO, 2006

13. 13
• Health effects
• No regulatory or guideline values
• Monitoring currently not widespread
• Control of PM10 and PM2.5 would
not necessarily also control UFP
Conclusions
• How will UFP affect our
work in the future?
© Visual Capitalist
UFP /

14. 14
Air Quality Expert Group (2018) Ultrafine Particles (UFP) in the UK. Available at: https://uk-air.defra.gov.uk/assets/documents/reports/cat09/1807261113_180703_UFP_
Report_FINAL_for_publication.pdf [Accessed April 2020]
Carslaw, D.C., Taylor, P.J., Analysis of air pollution data at a mixed source location using boosted regression trees. Atmospheric Environment 43, 3563-3570
Chen, K. Schneider, A., Cyrys, J., Wolf, K. Meisinger, C., Heier, M., von Scheidt, W., Kuch, B., Pitz, M., Peters, A., Breitner, S. (2020) Hourly Exposure to Ultrafine
Particle Metrics and the Onset of Myocardial Infarction in Augsburg, Germany. Available at: https://ehp.niehs.nih.gov/doi/pdf/10.1289/EHP5478 [Accessed April 2020]
Defra, UK Air Information Resource Automatic Urban and Rural Network (AURN) Available at: https://uk-air.defra.gov.uk/networks/network-info?view=aurn
[Accessed April 2020]
Health Effects Institute (2013) Understanding the Health Effects of Ambient Ultrafine Particles. Available at: https://www.healtheffects.org/system/files/Perspectives3.pdf
[Accessed April 2020]
Karner AA, Eisinger DS, Niemeier DA. 2010. Near roadway air quality: Synthesizing the findings from real world data. Environ Sci Technology 44:5334–5344.
Kwon, H-S, Ryu, M.H., Carlsten, C. (2020) Ultrafine particles: unique physicochemical properties relevant to health and disease, Experimental & Molecular
Medicine 52: 318-328
Morawska, L. & Wierzbicka, A. & Buonanno, G. & Cyrys, J. & Schnelle-Kreis, J. & Kowalski, M. & Riediker, M. & Birmili, W. & Querol, X. & Cassee, F. & Yildirim, A.
& Elder, A. & Yu, I.J. & Ovrevik, J. & Hougaard, K. & Loft, S. & Schmid, O. & Stöger, T. & Peters, A. and Lucht, S. (2019) Ambient ultrafine particles: evidence for
policy makers. Available at: https://efca.net/files/WHITE%20PAPER-UFP%20evidence%20for%20policy%20makers %20(25%20OCT).pdf [Accessed April 2020]
Ohlwein, S., Kappeler, R., Kutlar Joss, M., Kunzli, N., Hoffmann, B. (2019) Health effects of ultrafine particles: a systematic literature review update of epidemiological
evidence. International Journal of Public Health 64(4): 547-559. Available at: https://www.ncbi.nlm.nih.gov/pubmed/30790006 [Accessed April 2020]
World Health Organization (2006) WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide global update 2005 summary
of risk assessment
References

15. Thank you!
Any Questions?