Science News - July 14, 2004

2003 blackout cleaned the air

When the power went out across the northeastern United States and southeastern Canada on August 14, 2003, University of Maryland researcher Russell Dickerson realized that he had the opportunity of a lifetime. Scientists have long speculated about how air quality would change if the power plants were shut down, he explains. And the shutdown of 100 power plants, most of which burn coal, gave Dickerson the ideal chance to find out. His team went up in an airplane to measure air quality 24 hours after the initial shutdown. They returned with the evidence that confirmed upwind power plants “play a dominant role in regional haze and ozone production.” These findings are slated to be published in the next issue of the journal Geophysical Research Letters.

NOAA/DMSP Nighttime satellite images show the Northeastern United States before (left) and after (right) lights went out in August 2003.

The team collected atmospheric measurements in three states: Pennsylvania, at the center of the blackout, and Maryland and Virginia, neither of which lost power. By comparing these measurements to data collected the previous summer when upwind plants were operating normally over the same locations under similar meteorological conditions, the researchers documented a dramatic drop in the pollutants associated with burning coal. On August 15, 2003, the levels of sulfur dioxide and ozone were 90 and 50% lower, respectively, in blacked-out Pennsylvania. Particle light scattering was down by 70%. The researchers estimated that NO_x and SO₂ emissions from power plants were down to 20% and 33%, respectively. Visibility increased by 20 miles. In the Washington, D.C., area, the skies were actually bluer, and a dangerous “code red” air quality rating that was predicted for that day never materialized, according to Dickerson.

Carbon monoxide levels and particle light absorption changed little. The researchers reasoned that cars and trucks are the primary source of airborne CO and soot and that vehicle use in upwind areas remained normal during the blackout. Dickerson could not confirm how many industry sites went down or if any were operating on independent power supplies that would have contributed some emissions.

The Maryland researchers’ unique observations are valuable, says John Seinfeld, an atmospheric chemist at the California Institute of Technology, because unambiguously fingerprinting the effect of a particular source on atmospheric concentrations is often quite difficult. He adds that the researchers “were able to quantify the effect of power plant emissions on downwind air quality in a way that does not require untangling the effects of these emissions from those of other sources in the predictions of a regional atmospheric model.”

Dickerson’s group believes their data could help to determine whether air quality models accurately represent the contributions of specific pollution sources in an area.

The Electrical Power Resource Institute declined to comment on this work. —RACHEL PETKEWICH