Scientists pick up smell of new form of pollution

Volatile organic compounds can even be found in personal care products. Photo / 123RF

In a major study released yesterday, a team of US government and university scientists say that the nature of air pollution is changing dramatically as cars become cleaner - leaving personal-care products, paints, indoor cleaners and other chemical-containing agents as an increasingly dominant source of key emissions.

"Over time, the transportation sector has been getting cleaner when it comes to emissions of air pollutants," said Brian McDonald, lead author of the study in Science, who works for the University of Colorado at Boulder and the National Oceanic and Atmospheric Administration.

"And as those emissions come down, the sources of air pollution are becoming more diverse."

The study focused on a class of chemical products that give off "volatile organic compounds", or VOCs - petroleum-based odorous substances that, in outdoor air, can contribute to the formation of ozone or even dangerous small particulate pollution. The research found that the contribution of these chemicals to the overall burden of VOCs has been significantly underestimated and is under-represented in current inventories used to judge the sources of pollution.

The volatile compounds in question take many diverse forms and have complicated origins, emerging from trees and grass as well as from human-made sources such as cars. They are also found in many kinds of consumer and industrial products. The new research in particular cites "pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products" as key sources of VOCs.

In some cases - pesticides, for instance - these chemical products give off VOCs outdoors. In other cases, the emissions occur indoors and then migrate outside.

One giveaway in terms of what products are relevant, the authors said, is simply if they have a smell.

"Say somebody is inside using perfume, cologne," explains Chris Cappa, another of the study's authors and a researcher at the University of California at Davis. "That smell eventually dissipates. And the question is, where did it go. And there's air exchange with the outside. Those odours dissipate because it's basically getting moved outside. It's just taking that indoor air and exchanging it with the outdoor air. It's not that hard to get things from the indoor environment outside."

McDonald and Cappa completed the research with a team of 19 others from NOAA, the National Centre for Atmospheric Research, and multiple universities in the United States and Canada.

The findings do not automatically mean that the substances are dangerous to breathe indoors - the study simply does not analyse that question - but rather that outdoors, they are interacting with sunlight and other substances, and undergoing other chemical reactions that contribute to outdoor air pollution.