Household chemicals rival vehicles as smog source

Everyday items such as soaps, perfume, paint and pesticides now contribute as heavily to certain sorts of air pollution in US cities as cars and trucks — a finding that surprised even the researchers who made it.

Volatile organic compounds contribute to the formation of ozone and the fine airborne particulates that make up smog, which is linked to health problems from asthma to heart disease. Cars and trucks have historically pumped out most of these compounds, along with other pollutants such as nitrogen oxides. But significant levels of volatile organic compounds also escape from household and commercial products, according to a study published on 15 February in Science¹.

“The things I use in the morning to get ready for work are comparable to emissions that come out of the tailpipe of my car,” says Brian McDonald, an air-pollution researcher at the US National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, who led the work. “I think that’s what surprises a lot of people.”

Regulations to make vehicles cleaner have markedly reduced their emissions over the past 50 years. Yet notoriously smoggy cities such as Los Angeles, California, still struggle to comply with federal air standards. An extensive NOAA air-sampling effort in the city in 2010 found surprisingly high levels of certain volatile organic compounds that couldn’t be linked to vehicles. So McDonald and his team set out to track down other sources of the pollution.

Sniffing out the source

They used regulatory data, experimental results and indoor and outdoor air samples to test their hypothesis that chemical products contributed to smog. “We had to collect an overwhelming amount of evidence to say that these sources are important,” says McDonald.

The team drew on information compiled by the California Air Resources Board on the chemical composition of everyday items such as household cleaners, dry-cleaning fluids, nail-varnish removers and printing inks. They then analysed their air samples for a wide range of compounds that probably originated in these products. The researchers also estimated the proportion of volatile organic compounds from products such as soaps and cleaners that ends up in the air, as opposed to being washed down the drain.

The offending chemical products differ from vehicle emissions in an important way, says study co-author Jessica Gilman, a chemist at NOAA in Boulder. “They’re designed to evaporate,” she says. Once in the air, the compounds can escape outdoors, where a series of reactions transforms them into ozone and fine particles, she says.

The study focuses attention on an emerging target for air regulators, says Frank Gilliland, a public-health researcher at the University of Southern California in Los Angeles and the principal investigator of a long-term epidemiological study of the impact of air pollution on children’s health. But fossil-fuel combustion remains a major source of pollution, he says. “There are still health effects occurring” even with modern diesel trucks, says Gilliland. “We have a lot more that could be done on traditional control strategies for fossil-fuel combustion.”