Invisible gases form most organic haze in urban, rural areas

July 9, 2007
San Bernadino Sunset and Haze
Organic haze at sunset over the San Bernadino Valley, Calif. Credit: Mike Cubison, CU-Boulder

A new study involving the University of Colorado at Boulder shows that invisible, reactive gases hovering over Earth's surface, not direct emissions of particulates, form the bulk of organic haze in both urban and rural areas around the world.

Many science and health professionals have believed sources that spew soot and other tiny particles directly into the air were the primary culprit in the formation of organic haze. But a new study by researchers at CU-Boulder's Cooperative Institute for Research in Environmental Sciences 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.

The study was led by Qi Zhang, a former CIRES scientist now at the Atmospheric Sciences Research Center at State University of New York, Albany and CIRES researcher Jose-Luis Jimenez. The study was published in the July 7 online issue of Geophysical Research Letters.

The scientists 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.

"What we're seeing is that concentrations of secondary organic aerosols decrease little downwind from urban areas," said Jimenez, also an assistant professor in CU-Boulder's chemistry and biochemistry department. "That tells us there has to be an extended source or continuous formation for the pollution."

The scientists believe the extended source of particle pollution is reactive, colorless gases called Volatile Organic Compounds, or VOCs, the same gases that form smog. Jimenez said he believes VOCs emitted in urban and regional areas immediately begin undergoing a chemical transformation that causes them to stick to particles and increase such pollution.

"We think the gases react over a few days as the air travels downwind into more rural regions, producing more organic haze," he 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 interrelations between atmospheric chemistry and climate.

VOCs are released by cars and trucks, gasoline evaporation that occurs during gas station fill-ups, and some industrial processes, said Zhang. VOCs also are produced naturally by vegetation.

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 working 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.

"One question is whether we could improve air quality if we directly targeted VOC emissions and not just particle emissions," said Zhang. "Until we understand the breakdown between human-caused and natural VOC emissions, and between different human sources, we won't have an answer to that question."

Source: University of Colorado at Boulder

Explore further: Clean smell doesn't always mean clean air

Related Stories

Clean smell doesn't always mean clean air

October 29, 2014

Some of the same chemical reactions that occur in the atmosphere as a result of smog and ozone are actually taking place in your house while you are cleaning. A researcher in Drexel's College of Engineering is taking a closer ...

Japan's Panasonic to give China expats 'pollution pay'

March 13, 2014

Japanese electronics giant Panasonic said Thursday it would give employees sent to China a wage premium to compensate for the country's hazardous air pollution, in a possible first for an international company.

China's Wuhan city covered in mysterious haze

June 11, 2012

Young and old residents of the Chinese metropolis of Wuhan were advised to stay indoors on Monday after a thick haze blanketed the city of nine million people, official media said.

Recommended for you

New study sheds light on end of Snowball Earth period

August 24, 2015

The second ice age during the Cryogenian period was not followed by the sudden and chaotic melting-back of the ice as previously thought, but ended with regular advances and retreats of the ice, according to research published ...

Earth's mineralogy unique in the cosmos

August 26, 2015

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.