Volatile chemicals from everyday consumer items such as cleaning products, aerosols and even perfumes now rival vehicle emissions as a cause of air pollution.
A research team led by the National Oceanic and Atmospheric Administration (NOAA) reached the surprising conclusion after assessing the source of chemicals that reacted in the air to form fine particles and other lung-damaging pollutants in the US city of Los Angeles.
「As transportation gets cleaner, those other sources become more and more important,」 said Brian McDonald, the project leader. 「The stuff we use in our everyday lives can impact air pollution.」
The findings were released at the start of the American Association for the Advancement of Science annual meeting in Austin and also published in the journal Science.
Alastair Lewis, professor of atmospheric chemistry at York University in the UK, who was not involved in the study, said the results 「would be broadly applicable to most cities in the developed world」.
「People have assumed that the consumer sector is relatively unimportant as a contributor to air pollution,」 he said. 「I think this study is a very helpful reminder that there』s much more to pollution than road transport.」
The NOAA researchers focused on volatile organic compounds (VOCs) found in everyday products which reacted in the atmosphere, particularly in sunlight, to form smog.
They found that VOCs are emitted from consumer and industrial sources at levels up to three times greater than previous estimates from authorities such as the US Environmental Protection Agency.
In Los Angeles, 42 per cent of the most dangerous fine particles in the air originated from consumer products, 19 per cent from industrial products, and the remaining 39 per cent from vehicle emissions, filling stations and fuel storage.
「Fuel is stored in closed, hopefully airtight containers and its VOCs are burnt for energy,」 said Jessica Gilman, another member of the NOAA team. 「But volatile chemical products used in common solvents and personal care products are literally designed to evaporate. You wear perfume or use scented products so that you or your neighbour can enjoy the aroma. You don』t do this with gasoline.」
The Lancet medical journal last year estimated that air pollution killed 6m people a year worldwide, with tiny airborne particles generated by VOCs posing the greatest health risk.
The NOAA study found that people were often exposed to concentrations of volatile chemicals, such as limonene from cleaning products, which are 10 times higher inside their homes than outdoors.
Yet while the indoor pollution may pose health risks, 「VOCs become more harmful when they get outside and react in sunlight with nitrogen oxides to generate a wide range of pollutants」, Prof Lewis noted.
He added that regulators may need to turn their attention to household products that have been ignored as potential pollution sources.
「Since the Volkswagen [emissions] scandal, people have had something of a one-track mind, focusing on vehicles,」 he said. 「You can take your eye off the ball when things become politicised.」
Some consumer products could be reformulated to reduce VOC emissions, as has already happened with the transition from oil-based to water-based paint. But the study said more research was needed to discover which chemicals within household products are most liable to cause air pollution.
「We don』t know yet which compounds are most important,」 said Chris Cappa, professor of environmental engineering at the University of California, Davis. For now, he added, the best advice for consumers is: 「Use the least amount of any product that you need to get the job done.」