Issue Date: December 4, 2006
Using newly available satellite data, scientists in the U.S. and Germany have shown that atmospheric concentrations of NOx—the combination of NO and NO2 central to the production of near—surface ozone and smog-have declined over the Ohio River Valley by about 40% since 1999 (Geophys. Res. Lett., DOI: 10.1029/2006GL027749).
In-stack NOx measurements from power plants fitted with emissions controls have been indicating declining NOx emissions, but it has taken atmospheric transport and chemistry models to get pictures of the larger, regional consequences. Now, Si-Wan Kim, Stuart McKeen, Gregory Frost, and Michael Trainer of the National Oceanic & Atmospheric Administration and their colleagues have turned to orbiting sensors to measure those regional NOx trends more directly.
"We have used satellite-borne measurement to demonstrate that the reduction of NOx by power plants has been effective" in the Ohio River Valley, Kim says. Similar declines in NOx levels did not show up along the Northeast Corridor, where cars and other mobile sources, rather than power plants, are the dominant NOx sources.
Computer models of near-surface ozone production suggest that the diminishing NOx levels should be reflected by 4-10% reductions in ozone in the Ohio River Valley and nearby regions, the researchers report. Preliminary on-ground ozone measurements confirm that simulation result, comments Kenneth L. Schere of EPA's Atmospheric Sciences Modeling Division.
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