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On the final day of April 2010, unbeknownst to most locals, a small fleet of specialists and equipment from the U.S. government descended on the seas and skies around Los Angeles.

A “Hurricane Hunter” Lockheed P-3 flew in from Denver. The U.S. Navy vessel Atlantis loitered off the coast of Santa Monica. Orbiting satellites took special measurements. And dozens of scientists set up temporary labs across the basin, in empty Pasadena parking lots and at the peak of Mount Wilson.

This was all part of a massive U.S. government study with an ambitious goal: Measure every type of gas or chemical that wafted by in the California air.

Jessica Gilman, a research chemist at the National Oceanic and Atmospheric Administration, was one member of the invading horde. For six weeks, she monitored one piece of equipment—a kind of “souped-up, ruggedized” instrument—as it sat outside in Pasadena, churning through day and night, measuring the amount of chemicals in the air. It was designed to detect one type of air pollutant in particular: volatile organic compounds, or VOCs. VOCs are best known for their presence in car exhaust, but they are also found in gases released by common household products, like cleaners, house paints, and nail polish.

It found them. As she recently told me, there were far more VOCs in the air than she expected—and many more, specifically, than could be explained just through car exhaust. What was releasing them?

In a new study, published this month in the journal Science, a team of researchers including Gilman propose an answer. They find that a wide range of household goods—such as paints, printing inks, cleaning products, fragrances, nail polishes, and hair sprays—now emit about as many VOCs as cars do in U.S. cities.

That has potential implications for public health—and for how the government protects it. As air pollutants go, VOCs are kind of the ack of all trades. While some of them are toxic, causing irritation and headaches and nausea by themselves, even nontoxic VOCs can be unhealthy. When exposed to another type of air pollution, VOCs produce ozone, which can trigger asthma attacks. And when VOCs are exposed to sunlight, they produce particulate matter, which is linked to heart attacks and premature death.

The list of products that produce VOCs is staggeringly long. “The type of products are pretty much everything you would think of if you look under the kitchen sink, on the shelf in your garage, or in your bathroom,” says Gilman. “They’re soaps, shampoos, lotions, cleaning products, as well as degreasers, adhesives, ink, house paints.”

One common word found in many ingredients lists is a likely indication of VOC-emitting chemicals. “You see a single word, fragrances—with that one label, there’s up to 2,000 different VOCs that could be listed as a fragrance,” she says.

Two popular fragrances are limonene and beta-Pinene, which smell like lemons and pine trees, respectively. Though both occur in nature, they also produce VOCs when used at high concentrations, like in cleaning solution or a car air freshener.

“Traditionally, we think of the transportation sector as the main source of urban air pollution. But as the transportation sector has gotten cleaner in response to things like the Clean Air Act, other sources of emissions are becoming more important in a relative way,” says Brian McDonald, the lead author of the study and another research chemist at NOAA.

“You don’t have to use a lot of consumer products to emit a significant fraction of these VOCs,” he adds.“What this means is that the person in the car—and all the products they use in the morning—is now as big a source of VOCs as what comes out of the tailpipe as they drive to work.”

To be clear, the idea that household products could trigger air pollution isn’t new. Many household products contain ingredients produced by refining crude oil, and researchers have known that these ingredients could off-gas VOCs for decades.

They just thought these ingredients caused fairly little pollution—and much less, certainly, than cars did. They cited data showing that 95 percent of crude oil is refined into fossil fuel, while only about 5 percent of it becomes an ingredient in some kind of household product.

But much has changed in the ensuing decades. Government regulation—and the advances in pollution-controlling technology that followed—slashed into the amount of VOC pollution from cars. Meanwhile, VOCs from household products fell less rapidly. While the government can regulate VOCs, it’s considered a trickier problem, and regulators have spent less time on it. After all, there are many more toiletry and hardware companies than there are carmakers, and they use a much wider variety of chemicals.

Also, these products’ existence often depends on VOCs. Crude-oil-derived ingredients allow liquid products like nail polish to change states after application—either evaporating into the air, or drying as a solid. Any such process is probably emitting VOCs.“Anything that you’re kind of waiting to dry is emitting these VOCs while you’re waiting,” says Gilman.

McDonald’s team used the 2010 California data, as well as computer models and tests of indoor and outdoor air, to demonstrate that VOCs are a much larger segment of air pollution than previously thought. The U.S. government’s previous estimate of VOC pollution from household products was two to three times smaller than the reality.

More worryingly, the finding suggests that the quality of U.S. indoor air may be poor. “Typically, VOCs, in particular, are higher in indoor air, by a factor of 7, than they are in outdoor air,” says Suzanne Paulson, the director of the Center for Clean Air at UCLA, who was not connected to the study. “They are probably not that good for you, but we just don’t study them that much.”

Because the Clean Air Act doesn’t give the government the power to regulate indoor air, fewer scientists study it. (Indoor air also isn’t a public good in the same way as outdoor air.) But the new study suggests that indoor VOC pollution is making it outside in large enough quantities to affect people’s health, whatever the air quality inside their houses.

Jesse Kroll, a professor of chemical engineering at MIT, lauded the study. “The research team, who come from multiple institutions in both government and academia, bring together an impressive set of modeling and measurement tools to really zero in on contributors to air pollution in our cities,” he told me in an email.

Scientists know much more about vehicular air pollution than they do about household-product air pollution, he added. For instance, they don’t know much about how VOCs from household products turn into particulate matter. “This is something that’s pretty well studied for vehicular emissions, but not so much for [household products],” he said.

It’s also worth noting that the study only looked at VOCs and not at any other air pollutant. Gas-burning cars still emit plenty of carbon dioxide and greenhouse gases, which cause climate change. And despite years of regulation, cars still emit more traditional air pollutants, too: tiny particles of soot and metal, nitrogen oxides, carbon monoxide, and other toxic gases.

But Kroll said that the study suggested some good news: Regulation works.

“In North America and Europe, VOC emissions from gasoline and diesel vehicles are rapidly decreasing, thanks to emissions regulations. This really speaks to the effectiveness of agencies such as the EPA at improving our air quality and health,” he said. “But it also means that cleaning up our air still further requires considering other anthropogenic sources of VOCs as well.”

Perhaps scientists can start by looking under the kitchen sink.