In Cities, Emissions from Everyday Products Rival Car Emissions

During a press briefing at the 2018 AAAS Annual Meeting, researchers shared their discovery that emissions from everyday products like cosmetics and soaps can contribute to poor air quality. | Carla Schaffer/AAAS

Petroleum-based chemicals in consumer products like soaps and paints drift into the air and contribute as much as car emissions do to air pollution, a new study in the journal Science reports.

Emissions from everyday chemical products, say the authors, are likely two or three times greater than currently estimated by government air pollution data in the United States.

The study reveals a previously underrecognized contributor to poor air quality, one that has come into plainer sight as emission control technologies have put tailpipe emissions on the decline. The findings are somewhat of a surprise since only about 5% of raw oil, which underlies the problematic emissions, is refined into chemicals for consumer products; 95% ends up in fuels.

"As the transportation sector gets cleaner, the other sources of emissions we identified become more and more important," said lead author Brian McDonald, a research chemist at the University of Colorado, Boulder, working at the National Oceanic and Atmospheric Administration. "A lot of chemicals we use in our everyday lives can impact air pollution."

"Our work indicates that new challenges await in achieving further declines in problematic emissions to urban air," said co-author Christopher Kappa, a professor of civil and environmental engineering at the University of California, Davis.

"While we focus on Los Angeles in our study," added Kappa, "we can confidently say that emissions from these non-traditional chemical products will negatively impact urban air quality anywhere they are used in large amounts — in pretty much any major city in the U.S., Europe and beyond."

The most recent Global Burden of Disease Study, which describes risk factors to health at national and regional levels, ranks air pollution as the fifth largest human health risk factor around the world.

Breathing in "fine particles" in the air is particularly concerning. Fine particles can be emitted into the atmosphere directly, from a dirty truck tailpipe, for example, or they can be formed through a cascade of reactions involving chemicals called volatile organic compounds (VOCs), which are found in both vehicle fuel and consumer products like shampoos, deodorant, cleaning agents, paints, adhesives and pesticides.

To improve human health related to air pollution, scientists need to better understand the most important sources of VOCs. While cars have long been thought to be the dominant culprits, regulations of tailpipe emissions in recent decades in the U.S. and Europe have led to cleaner cars. Getting a handle on VOC emissions from consumer products, meanwhile, has been challenging.

"Many of these chemical species, meant to evaporate fast, are still difficult to measure in the air," said co-author Jessica Gilman, a NOAA research chemist. "We converted multiple aircraft, portable trailers, and even a large ocean-going research vessel into highly instrumented laboratories all designed to investigate different components of the air that we breathe."

McDonald and colleagues were motivated to study the contributions of these non-traditional sources to air pollution in part after observing a gap in an extensive air quality assessment of Los Angeles conducted in 2010 — one that suggested sources other than fuels were contributing to smog.

" ... We can confidently say that emissions from these non-traditional chemical products will negatively impact urban air quality anywhere they are used in large amounts — in pretty much any major city in the U.S., Europe and beyond."

Christopher Kappa

"To reach consensus on the idea that chemical products were significant sources of air pollution required strong scientific evidence from multiple perspectives," said McDonald. "You can think of our research group as detectives in search of clues, questioning the conventional wisdom that cars are the primary source of VOCs in the urban atmosphere."

"Studies such as ours highlight the power of collaborative research, of bringing together people with unique skills and, importantly, state-of-the-science instrumentation to answer questions we didn't even know to ask," added Kappa.

The researchers undertook a comprehensive reassessment of air pollution sources in the United States through multiple efforts. First, to quantify the amount of chemical products manufactured and sold to consumers, they sorted through chemical production statistics compiled by industries and regulatory agencies. Next, using laboratory testing data, they discovered that about 40% of chemicals in these products emit to the atmosphere.

They then looked for the chemical fingerprints of these products in a series of air sampling missions, with a focus on Los Angeles. Both outdoor and indoor environments in Los Angeles featured these chemicals in significant quantities, they said.

Through further analyses involving atmospheric models, the team concluded that in the United States, nearly 50% of VOCs emitted are from the use of everyday chemical products. The Environmental Protection Agency, by contrast, estimates that about 75% of VOC emissions in the country are from vehicular sources, with about 25% coming from consumer products.

Providing a window into why fuel and everyday chemical products emit to the air differently, Gilman explained that fuel systems are designed to minimize the loss of gasoline to evaporation, in order to maximize energy generated by combustion. But common products like paints and perfumes, she said, are literally engineered to evaporate. "Perfume and other scented products are designed so that you or your neighbor can enjoy the aroma. You don't do this with gasoline."

While transportation remains an important source of air pollution in U.S. cities, the results of this study highlight that sources of poor urban air quality are far more diverse. The shift in scientists' understanding of urban air pollution that this work represents will "challenge the existing policy framework for emissions control," said Alastair C. Lewis, in a related Perspective.

Models are one of the major tools that can be used to develop targeted regulations that lead to improvements in urban air quality. "Our work provides a starting point for including emissions of non-traditional sources in models of air pollution," said Kappa, who notes such sources have been underrepresented before.

"One thing that I hope the public takes away from this study," said Gilman, "is that the collective choices we make as a society, from our energy sources to which chemical products we use in our daily lives, are continually changing the composition of our atmosphere — Earth's atmosphere — the one atmosphere that contains all the air we will ever breathe."

The study, published 16 February, was the focus of a press briefing at the 2018 AAAS Annual Meeting in Austin.

[Associated image: Diliff/Wikimedia Commons (CC BY-SA 3.0)]