A University of Colorado at Boulder study has claimed that invisible and reactive gases hovering over the Earth's surface, form the bulk of organic haze in both urban and rural areas.
Till now, the scientists and health professionals had believed that sources that spew soot and other tiny particles directly into the air were the primary culprit in the formation of organic haze.
But the new study by researchers Qi Zhang and Jose-Luis Jimenez show aerosols formed chemically in the air account for about two-thirds of the total organic haze in urban areas and more than 90 percent of organic haze in rural areas.
Zhang and Jimenez compared concentrations of directly emitted, or primary, aerosols with chemically formed, or secondary aerosols. They surveyed urban areas, areas downwind of urban areas and rural areas from 37 sites in 11 countries.
According to Jimenez, there exists an extended source or continuous formation for the pollution, and both he and Zhang believe that this extended source of particle pollution is reactive, and can be identified as colourless gases called Volatile Organic Compounds (VOCs), the same gases that form smog.
"We think the gases react over a few days as the air travels downwind into more rural regions, producing more organic haze," Jimenez said.
Reactive gases are a diverse group of chemical compounds that include VOCs, surface ozone, nitrogen compounds and sulfur dioxide. All play a major role in the chemistry of the atmosphere and as such are heavily involved in inter-relations between atmospheric chemistry and climate.
According to Zhang, cars and trucks release VOCs, and he adds that gasoline evaporation occurs during gas station fill-ups, or during some industrial processes.
The U.S. Environmental Protection Agency does not currently regulate VOCs except for on-road vehicles and industrial settings, said Jimenez.
Jimenez and Zhang are now working on ways to better understand the relative importance of natural and human sources of VOCs in the production of secondary organic aerosol pollution, including which human sources significantly contribute to the problem.
The study was undertaken under the auspices of the university's Cooperative Institute for Research in Environmental Sciences, and is published in the July 7 online issue of Geophysical Research Letters.