27 July 2021
adapted from the story by CIRES Communications
Air pollution triggered by use of common chemicals, fuels may kill 10 times more people than previously recognized.
Hundreds of thousands of people around the world die too soon every year because of exposure to air pollution caused by our daily use of chemical products and fuels, including paints, pesticides, charcoal and gases from vehicle tailpipes, according to a new study.
The new work, led by former CIRES postdoctoral researcher Benjamin Nault and CIRES Fellow Jose-Luis Jimenez, calculated that air pollution caused by "anthropogenic secondary organic aerosol" causes 340,000-900,000 premature deaths. Those are tiny particles in the atmosphere that form from chemicals emitted by human activities.
And "that's more than 10 times as many deaths as previously estimated," said Nault, who is now a scientist at Aerodyne Research, Inc. His work, published in Atmospheric Chemistry and Physics, builds on findings by CU Boulder, NOAA, NASA, and others that emissions from everyday products are increasingly important in forming pollutants in urban air.
"The older idea was that to reduce premature mortality, you should target coal-fired power plants or the transportation sector," Nault said. "Yes, these are important, but we're showing that if you're not getting at the cleaning and painting products and other everyday chemicals, then you're not getting at a major source."
Atmospheric researchers have long understood that particles in the atmosphere small enough to be inhaled can damage people's lungs and increase mortality. Studies have estimated that fine particle pollution, often called PM2.5, leads to 3-4 million premature deaths globally per year, possibly more.
Many countries, including the United States, therefore have laws limiting how many of those particles get into the atmosphere. We regulate soot from power plants and diesel exhaust, for example, which are "direct" sources of particulate matter. And regulations also target fossil fuel emissions of sulfur and nitrogen oxides, which can react in the atmosphere to form fine particles – an indirect, "secondary inorganic" source of particles.
The new work suggests that a third broad category of chemicals – anthropogenic secondary organic pollutants – is a significant indirect source of deadly fine particles.
To determine the mortality impact of several sources of fine particles, the team dug into data from 11 comprehensive air quality studies carried out in cities around the world in the last two decades. They drew on detailed databases of chemical emissions from cities including Beijing, London, and New York City, and they ran those numbers through sophisticated air quality models that also incorporate satellite data.
They found that the production of secondary organic aerosol in those 11 cities was strongly correlated with specific organic compounds emitted by people's activities. The chemicals at issue – called aromatics and intermediate- and semi-volatile organic compounds – are emitted from tailpipes and cooking fuels like wood and charcoal, and increasingly also from industrial solvents, house paints, cleaning products, and other chemicals.
In previous work in Los Angeles, CIRES, NOAA and other scientists have reported that such volatile chemical products contribute as much as vehicles do to the formation of particle pollution. "What's new here," said NOAA CSL scientist and co-author Brian McDonald, "is that we are showing this is an issue in cities on three continents, North America, Europe, and east Asia."
Air quality regulations have tended to focus on volatile chemicals that produce ozone, another hazardous pollutant, said Jimenez, who is also a professor of chemistry at CU Boulder. But it is increasingly clear, most recently from the new work, that chemicals which contribute little to ozone formation may still contribute seriously to particle formation.
"Because this effect has been thought to be small, it hasn't been targeted for control," Jimenez said. "But when you take the atmospheric chemistry into account and put it into a model, you find that this particular source is killing a lot of people."
Nault and Jimenez said they hope to expand their work to include more urban areas of the world, where there haven't been enough measurements yet to confirm that volatile chemical products contribute substantially to fine particles. But the trend is holding so far in all places where there are enough measurements.
"If you care about air pollution impacts on health and mortality, you have to take this problem seriously," Jimenez concluded.
Nault, B.A., D.S. Jo, B.C. McDonald, P. Campuzano-Jost, D.A. Day, W. Hu, J.C. Schroder, J. Allan, D.R. Blake, M.R. Canagaratna, H. Coe, M.M. Coggon, P.F. DeCarlo, G.S. Diskin, R. Dunmore, F. Flocke, A. Fried, J.B. Gilman, G. Gkatzelis, J.F. Hamilton, T.F. Hanisco, P.L. Hayes, D.K. Henze, A. Hodzic, J. Hopkins, M. Hu, L.G. Huey, B.T. Jobson, W.C. Kuster, A. Lewis, M. Li, J. Liao, M.O. Nawaz, I.B. Pollack, J. Peischl, B. Rappenglück, C.E. Reeves, D. Richter, J.M. Roberts, T.B. Ryerson, M. Shao, J.M. Sommers, J. Walega, C. Warneke, P. Weibring, G.M. Wolfe, D.E. Young, B. Yuan, Q. Zhang, J.A. de Gouw, and J.L. Jimenez, Anthropogenic secondary organic aerosols contribute substantially to air pollution mortality, Atmospheric Chemistry and Physics, doi:10.5194/acp-21-11201-2021, 2021.
Anthropogenic secondary organic aerosol (ASOA), formed from anthropogenic emissions of organic compounds, constitutes a substantial fraction of the mass of submicron aerosol in populated areas around the world and contributes to poor air quality and premature mortality. However, the precursor sources of ASOA are poorly understood, and there are large uncertainties in the health benefits that might accrue from reducing anthropogenic organic emissions. We show that the production of ASOA in 11 urban areas on three continents is strongly correlated with the reactivity of specific anthropogenic volatile organic compounds. The differences in ASOA production across different cities can be explained by differences in the emissions of aromatics and intermediate- and semi-volatile organic compounds, indicating the importance of controlling these ASOA precursors. With an improved model representation of ASOA driven by the observations, we attribute 340 000 PM2.5-related premature deaths per year to ASOA, which is over an order of magnitude higher than prior studies. A sensitivity case with a more recently proposed model for attributing mortality to PM2.5 (the Global Exposure Mortality Model) results in up to 900 000 deaths. A limitation of this study is the extrapolation from cities with detailed studies and regions where detailed emission inventories are available to other regions where uncertainties in emissions are larger. In addition to further development of institutional air quality management infrastructure, comprehensive air quality campaigns in the countries in South and Central America, Africa, South Asia, and the Middle East are needed for further progress in this area.