Chemical products that contain compounds refined from petroleum, like household cleaners, pesticides, paints and perfumes, now rival motor vehicle emissions as the top source of urban air pollution, according to a surprising NOAA-led study.

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 CIRES scientist working in NOAA's Chemical Sciences Division. 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, his team found. McDonald and colleagues from NOAA and several other institutions reported their results today in the journal Science.

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 of us living in cities and suburbs assume that much of the pollution we 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 McDonald and his colleagues 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.

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.