Earth System Science Center and Department of Atmospheric Science at The University of Alabama in Huntsville

UAH studies ‘natural’ air pollution

A southern forest near Huntsville, Ala., going about its business and generating hydrocarbons.

HUNTSVILLE, Ala. (Oct. 26, 2015) — Scientists at The University of Alabama in Huntsville (UAH) and Rice University in Houston will use data from satellites in an attempt to better estimate how much air pollution in the eastern U.S. is natural, and therefore isn’t subject to government regulations.

Supported by a $1 million NASA research grant, over the next three years the group led by UAH’s Arastoo Pour-Biazar, with Daniel Cohan from Rice, will study the natural supply of chemicals that combine in the atmosphere to produce ozone (O3), a pollutant that irritates lung and mucous tissue, and can also harm plants.

As the Environmental Protection Agency considers reducing the acceptable level of ozone in the air in cities across the U.S., it becomes more important to know how much natural ozone is found in the atmosphere under different weather conditions. To do that, scientists need to know how much of the components needed to produce ozone is created naturally.

The dominant source of ozone pollution is the reaction of hydrocarbons, also known as volatile organic compounds (VOCs), with nitrogen oxide (NOx). Both are created as byproducts of human activity: NOx from the burning of fossil fuels and VOCs from several sources, including vehicle exhausts and the evaporation of paints, solvents and cleaning compounds. You just add a bit of sunshine to power the reaction.

Both NOx and VOCs, however, are also created naturally. NOx is formed by lightning and by microbial activity in the soil, while VOCs are produced by trees and other plants. In the heavily-forested eastern U.S., most of the VOCs in the region are released by trees.

“In the eastern U.S., if we’re looking at the whole region, I would say more than 70 percent of the total summertime VOCs come from trees,” Pour-Biazar said. “Over Atlanta and other major metro areas, it would be a much smaller part of the total. The human contribution is a much higher percentage of the total in those urban areas.”

Because the natural contribution to ozone pollution varies from region to region, it can make creating air pollution strategies challenging. Much of the national strategy for combating ozone came from strategies developed to combat smog in southern California.

“In southern and central California (where there are few forests), the strategy of cutting hydrocarbon emissions has worked,” Pour-Biazar said. “In those dry areas of California, there is a limited supply of natural VOCs, so reducing the manmade contribution is effective.”

In the eastern U.S., less so.

“In Alabama we don’t have controls on hydrocarbons,” Pour-Biazar said, “but in Georgia they do. For instance, they have annual car inspections, where you are required to take your car to an inspection center to make sure you aren’t putting out too much hydrocarbon.”

Does all of that hassle accomplish anything in reducing ozone?

“No,” he said. “In the eastern U.S., and especially in the southeast, ozone is NOx limited. With the exception of a few major urban areas, there is simply too much natural hydrocarbon in the air to make significant reductions in ozone by reducing manmade VOCs.”

The next step is collecting data that can be used to power computer models of regional air pollution, to create more effective air pollution strategies.

Further complicating the issue are pollutants that float from city to city, or even from continent to continent, making it that much more difficult for cities and states to meet their air pollution goals.

“We use NASA assets to look at air pollution as a global problem,” Pour-Biazar said. “And as it becomes more of a global problem, NASA assets become more relevant.”

The UAH-Rice team is working with several air quality control agencies on this project, including EPA’s Atmospheric Modeling Division, the California Air Resources Board, the Bay Area Air Quality Management District, the Texas Commission on Environmental Quality, and the Georgia Environmental Protection Division.

Arastoo Pour-Biazar teaching a atmospheric science class at The University of Alabama in Huntsville.

Arastoo Pour-Biazar teaching a atmospheric science class at The University of Alabama in Huntsville.

A southern forest near Huntsville, Ala., going about its business and generating hydrocarbons.

A southern forest near Huntsville, Ala., going about its business and generating hydrocarbons.

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