Alabamians see clearer as air pollution plunges.
|Haze in Talladega National Forest.|
As aerosol emissions drop, Southeastern skies open up
January 29, 2015
By Brian Bienkowski
People in ‘Bama can see the light. And we're not talking about Alabama offense coordinator Lane Kiffin turning down the NFL to stay in Tuscaloosa.
Plunging atmospheric aerosol levels have spurred increased visibility over the past decade.
A team of researchers led by the National Oceanic and Atmospheric Administration (NOAA) recently reported that visibility in Alabama has improved based on decreasing soot.
The conclusion is based on findings that visibility over a national forest improved an estimated 3.4 percent per year from 2001 to 2013 thanks to decreasing aerosol mass.
In addition, fewer sulfates in the air particles led to an additional 1.1 percent per year improvement.
“We’ve had fairly significant drops in sulfur dioxide, especially from industrial sources,” said Leigh Bacon, chief of Alabama Department of Environmental Management’s meteorological section who was not involved in the study. “The study is less of a surprise and more of a validation.”
Aerosols are tiny atmospheric particles made up of air pollutants from volcanic eruptions, desert dust or human-made sources such as fossil fuel burning, especially coal plants. If they get big enough, they can scatter and absorb sunlight, which reduces visibility, making things appear hazy.
It’s not just good news for Alabama: The study, published in Geophysical Research Letters, said the forest is representative of the Southeastern U.S.
Human-caused aerosol outweighs natural sources, according to NASA, but levels have been declining. Over the past decade, emissions of sulfur dioxide – a major aerosol precursor and a component responsible for higher water absorption -- dropped about 10 percent per year in Alabama.
“Reductions in U.S. SO2 [sulfur dioxide] emissions that have led to changes in both dry aerosol mass and aerosol water mass are expected to continue in the future and may further reduce aerosol sulfate loading and mass fraction over the next decade,” the authors wrote.
The drops are due to federal regulations targeting the fossil fuel industry, kick started by 1990 Clean Air Act amendments, and the rise of natural gas and other energy sources that have further pinched the coal industry.
Coal as a percent of total electric generation in the Southeast has dropped from the mid-50s before 2009 to about 38 percent today.
Decreased sulfur dioxide emissions means more than more vibrant sunsets: the particles have been linked to health problems, such as asthma and heart disease, and play a role in altering the Earth’s climate.
The researchers measured the distance visible through aerosols in Alabama’s Talladega National Forest during the summer of 2013 and compared it to aerosol mass estimates from the past decade. They found aerosols are decreasing and “the composition is changing,” said Rebecca Washenfelder, a research scientist with NOAA who was a co-author of the study. “In the past, aerosol absorbed more water and grew larger.”
Less sulfur dioxide is a double win for people who like to see clearly: not only does it mean less aerosol forming; it means fewer sulfates in it. High sulfate aerosol absorbs more water, and, in turn, scatters more sunlight.
And the trend is nationwide: from 1990 to 2010 U.S. sulfur dioxide emissions were reduced by 60 percent.
Stacie Propst, executive director of GASP - an Alabama clean air advocate organization, said the reductions in sulfur dioxide are good news, however, were largely forced upon the state.
Propst pointed out that in 2006 – right in the middle of the new study’s timeframe – the U.S. Department of Justice forced the Alabama Power Company to bring one of its highest emitting coal-fired plants – the James H. Miller Plant – into Clean Air Act compliance.
The settlement reduced sulfur dioxide emissions by about 23,000 tons per year.
“If the state would have enforced the Clean Air Act from the beginning, this report (on decreased aerosol) would be even better,” Propst said.
Another aerosol precursor – volatile organic compounds – had a 63 percent decrease in emissions from cars and trucks in the United States from 1990 to 2010.
Aerosol impacts the Earth’s climate by reflecting solar radiation and cooling the planet. However, some types of particles, such as carbon soot, absorb the radiation and warm the atmosphere.
So the trend means “it could become slightly warmer in Alabama,” Washenfelder said.
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