Consumer and industrial products – not vehicles – now dominate urban air pollution

smog in LA

A smoggy view of Los Angeles in 2010. Scientists captured this image from a research aircraft that was part of the CALNEX mission to study the region’s air quality. Findings now emerge that emissions from common household and industrial products rival motor vehicle emissions as the top source of the city’s air pollution. Photo credit: Raul Alvarez/NOAA.

Chemical products that contain compounds refined from petroleum, like household cleaners, pesticides, paints and perfumes, now rival motor vehicle emissions as top sources of urban air pollution, according to a NOAA-led study that includes key contributions from Colorado State University.

People use a lot more fuel than they do petroleum-based compounds in chemical products – about 15 times more by weight, according to the new assessment. Even so, lotions, paints and other products contribute about as much to air pollution as the transportation sector does, said lead author Brian McDonald, a scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) who works in NOAA’s Chemical Sciences Division. CIRES is a partnership of NOAA and the University of Colorado Boulder. “As transportation gets cleaner, those other sources become more and more important,” McDonald said. “The stuff we use in our everyday lives can impact air pollution.”

In the case of one type of pollution – tiny particles that can damage people’s lungs – particle-forming emissions from chemical products are about twice as high as those from the transportation sector, the team found. McDonald and colleagues from NOAA, CSU and several other institutions reported their results Feb. 15 in the journal Science. They shared the results during a media briefing at the American Association for the Advancement of Science annual meeting.

Modeling urban pollutants

CSU co-authors Shantanu Jathar, Energy Institute researcher and assistant professor of mechanical engineering; and graduate student Ali Akherati, provided model-based estimates for determining how important consumer products could be for fine particle pollution in urban areas. Secondary organic aerosols produced from motor vehicles are well understood through laboratory experiments, but the same isn’t true for volatile chemical products, Jathar said. Thus the CSU team used models trained on previous laboratory data to extrapolate how volatiles from consumer products could form secondary organic aerosols in the atmosphere.

“Our contribution was significant in that there were few experimental data for compounds found in volatile chemical products,” said Jathar, who studies a wide array of organic aerosol pollutants, from vehicle emissions to wildfire smoke.

For the new assessment, the scientists focused on volatile organic compounds or VOCs. VOCs can waft into the atmosphere and react to produce either ozone or particulate matter –both of which are regulated in the United States and many other countries because of health impacts, including lung damage.

Those who live in cities and suburbs assume that much of the pollution they breathe comes from car and truck emissions or leaky gas pumps. That’s for good reason: it was clearly true in past decades. But regulators and car manufacturers made pollution-limiting changes to engines, fuels and pollution control systems.

So the scientists reassessed air pollution sources by sorting through recent chemical production statistics compiled by industries and regulatory agencies, by making detailed atmospheric chemistry measurements in Los Angeles air, and by evaluating indoor air quality measurements made by others.

Inventories underestimate volatile compounds

The scientists concluded that in the United States, the amount of VOCs emitted by consumer and industrial products is actually two or three times greater than estimated by current air pollution inventories, which also overestimate vehicular sources. For example, the Environmental Protection Agency estimates that about 75 percent of VOC emissions (by weight) come from vehicular sources, and about 25 percent from chemical products. The new study, with its detailed assessment of up-to-date chemical use statistics and previously unavailable atmospheric data, puts the split closer to 50-50.

The disproportionate air quality impact of chemical product emissions is partly because of a fundamental difference between those products and fuels, said NOAA atmospheric scientist Jessica Gilman, a co-author of the new paper. “Gasoline is stored in closed, hopefully airtight, containers and the VOCs in gasoline are burned for energy,” she said. “But volatile chemical products used in common solvents and personal care products are literally designed to evaporate. You wear perfume or use scented products so that you or your neighbor can enjoy the aroma. You don’t do this with gasoline,” Gilman said.

The team was particularly interested in how those VOCs end up contributing to particulate pollution. A comprehensive assessment published in the British medical journal Lancet last year put air pollution in a top-five list of global mortality threats, with “ambient particulate matter pollution” as the largest air pollution risk.

The new study finds that as cars have gotten cleaner, the VOCs forming those pollution particles are coming increasingly from consumer products.

“We’ve reached that transition point already in Los Angeles,” McDonald said.

He and his colleagues found that they simply could not reproduce the levels of particles or ozone measured in the atmosphere unless they included emissions from volatile chemical products. In the course of that work, they also determined that people are exposed to very high concentrations of volatile compounds indoors, which are more concentrated inside than out, said co-author Allen Goldstein, from the University of California Berkeley.

“Indoor concentrations are often 10 times higher indoors than outdoors, and that’s consistent with a scenario in which petroleum-based products used indoors provide a significant source to outdoor air in urban environments.”

Car regulations have been effective

The new assessment does find that the U.S. regulatory focus on car emissions has been very effective, said co-author Joost de Gouw, a CIRES chemist. “It’s worked so well that to make further progress on air quality, regulatory efforts would need to become more diverse,” de Gouw said. “It’s not just vehicles anymore.”

This research was supported by NOAA, the CIRES Visiting Fellowship Program, Aerodyne Research, Inc, the National Science Foundation and the Sloan Foundation.

An animation explains how consumer and industrial products have surpassed vehicles as sources of air pollution. Credit: AAAS