VOCs are naturally produced by plants, but about 30 percent of the emissions come from industrial processes, says Atul Jain, a professor of atmospheric sciences at the University of Illinois at Urbana Champaign. “They are short-lived but highly reactive gases that impact ozone and methane,” he says. VOCs actually act as a sink for methane, one of the most potent greenhouse gases—as VOCs cycle through different chemical reactions, they form hydroxyl radicals (OH−) that take methane out of the atmosphere. While reducing greenhouse gases is probably a good thing, there are some negative side effects. When VOCs react with sunlight and gases in the atmosphere, Jain explains, the compounds form tropospheric ozone (commonly known as smog) and particulate matter that makes its way into respiratory tracts.