Air Pollution as a Climate Forcing: A Workshop

Day 4 Presentations

Global Impact of Outdoor Particulate Air Pollution

H. Ross Anderson
Dept. Public Health Sciences, St George's Hospital Medical School, Univ. London

On behalf of the Outdoor Air Pollution Working Group of the WHO Global Burden of Disease Comparative Risk Assessment Project: H. Ross Anderson (Chair), Aaron Cohen (Co-Chair), Kersten Gutschmidt, Michal Krzyzanowski, Nino Kunzli, Bart Ostro, Kiran Pandey, Arden Pope, Isabelle Romieu, Jonathan Samet, Kirk Smith

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The serious consequences of exposure to high levels of ambient air pollution were made clear in the mid-20th century when cities in Europe and the United States experienced air pollution episodes, such as the infamous 1952 London fog, that resulted in a sharp increase in acute health problems including many deaths. Subsequent clean air legislation and other actions reduced ambient air pollution in many regions. However, recent epidemiological studies, using sensitive designs and analyses, have identified important health effects of combustion-derived air pollution even at the low ambient concentrations typical of Western European and North American cities(1-6). At the same time, the populations of the rapidly expanding mega-cities of Asia, Africa and Latin America are increasingly exposed to levels of ambient air pollution that rival and often exceed those experienced in developed countries in the first half of the 20th century (7).

Urban air pollution is largely and increasingly the result of the combustion of fossil fuels for transport, power generation and other human activities. All combustion processes produce particles that are small enough to be inhaled into the lung, either as primary emissions, such as from diesel engines, or via subsequent atmospheric transformation, such as when sulphur dioxide, produced by the oxidation of sulphur in fuel combines with ammonia to form sulphate particles.

Air pollution from combustion sources is associated with a broad spectrum of acute and chronic health effects (3,4), the nature of which may vary with the pollutant constituents. Particulate air pollution is nevertheless consistently and independently related to the most serious effects, including lung cancer and other cardio-pulmonary mortality (1,5,6). The aim of the present project was to estimate attributable deaths and estimated life-years lost due to particulate outdoor air pollution in all major cities of the world.

The availability of measurements of ambient concentrations of particulate matter (PM) varies widely across the globe, making estimation of annual average concentrations in all cities a considerable challenge. We collected as much available PM measurement data as possible, but in order to provide estimates all 14 WHO regions, we relied on models developed by the World Bank to estimate PM10 (particulate matter with aerodynamic diameter <10 micrometres) using econometric data and the available PM10 measurements (available for several hundred cities) for 3226 cities with populations greater than 100,000 plus capital cities. These PM10 estimates were converted to PM2.5 (fine particles that tend to penetrate more deeply into the lung) using available information on geographic variation in the ratio of PM2.5 to PM10. Data on the percentage of urban dwellers was used to derive population-weighted annual averages for each PM metric.

We calculated four estimates of impact: mortality from cardio-pulmonary causes in adults, mortality from lung cancer, mortality from all-natural causes in adults and in children 0-5, and mortality from acute respiratory infections in children 0-5. Risk coefficients from a large United States cohort study of adults (1) were used to calculate attributable numbers of deaths and years-of-life lost for adults and children (<5 yr.).="yr.)." impact="Impact" estimates="estimates" were="were" calculated="calculated" over="over" a="a" range="range" of="of" annual="annual" average="average" concentrations="concentrations" of="of" pm2.5="PM2.5" between="between" 7.5="7.5" and="and" 50="50" micrograms="micrograms" per="per" cubic="cubic" meter.="meter." the="The" uncertainty="uncertainty" of="of" the="the" estimates="estimates" was="was" quantified="quantified" by="by" propagating="propagating" the="the" errors="errors" in="in" the="the" estimates="estimates" of="of" annual="annual" average="average" concentration="concentration" and="and" the="the" relative="relative" risks.="risks." additional="Additional" uncertainty="uncertainty" due="due" to="to" assumptions="assumptions" about="about" the="the" shape="shape" of="of" the="the" concentration-="concentration-" response="response" function="function" and="and" the="the" ratio="ratio" of="of" pm2.5="PM2.5" to="to" pm10="PM10" was="was" assessed="assessed" in="in" sensitivity="sensitivity" analyses.="analyses." an="An" additional="additional" estimate="estimate" of="of" attributable="attributable" deaths="deaths" was="was" calculated="calculated" from="from" time-series="time-series" studies="studies" of="of" daily="daily" mortality,="mortality," based="based" on="on" results="results" of="of" a="a" meta-analysis="meta-analysis" of="of" the="the" world="world" literature.="literature."

The preliminary and provisional analyses on which this presentation was based estimate that ambient air pollution causes about 1% of cardiorespiratory disease and about 3% of trachea, bronchus and lung cancer globally. This amounts to about 0.6 million (1.2%) premature deaths and 7.4 million (0.5%) years of life lost. This burden predominently falls on cities in developing countries.


  • 1. Pope CA, Burnett RT, Thun MJ, Calle EE, Krewski D, Ito K, Thurston G. Lung Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. JAMA 2002; 287(9):1132-1141
  • 2. Health Effects Institute. Airborne Particles and Health: HEI Epidemiologic Evidence. HEI Perspectives June 2001. Charlestown, MA USA
  • 3. Committee Of The Environmental And Occupational Health Assembly Of The American Thoracic Society (ATS). Health effects of outdoor air pollution, Part 1. Am J Resp Crit Care Med, 153: 3-50 (1996)
  • 4. Committee of the Environmental and Occupational Health Assembly of the American Thoracic Society (ATS). Health effects of outdoor air pollution, Part 2. Am J Resp Crit Care Med, 153: 477-498 (1996)
  • 5. Pope CA III, Dockery DW. 1999. Epidemiology of particle effects. In: Air Pollution and Health (Holgate ST, Samet JM, Koren HS, Maynard RL, eds). Academic Press, San Diego CA.
  • 6. Samet JM, Cohen AJ. Air Pollution and Lung Cancer. In: Air Pollution and Health (Holgate ST, Samet JM, Koren HS, Maynard RL, eds). Academic Press, San Diego CA
  • 7. Krzyzanowski M, Schwela D. Patterns of Air Pollution in Developing Countries. In: Air Pollution and Health (Holgate ST, Samet JM, Koren HS, Maynard RL, eds). Academic Press, San Diego CA.

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Summaries: Overview, Gases, Aerosols, Tech., Health, Agri./Eco.
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