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Summer 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

July 19, 2011


Washington’s improving air quality

When summer's heat roasts the Washington area, air quality tends to worsen — but compared with a decade ago, it has improved.

"We still get bad days," says Timothy Canty, an atmospheric scientist at the University of Maryland, "but it's getting better." A 2002 EPA regulation required states to reduce emissions of nitrogen oxides (NOx). On hot, stagnant days, NOx and volatile organic compounds (VOCs) produce ozone (O3).

"Ozone is a good thing at high altitudes, where it blocks damaging ultraviolet rays," says Canty, "but at ground level, ozone inflames the lungs." It causes acute respiratory problems, reduces lung capacity and impairs the body's immune system. "In some cases," says Canty, "high ozone levels can lead to death." Ozone can also damage vegetation, including crops, and it will degrade rubber and plastic.

Since 2002, U.S. power plants have cut their overall emissions of NOx by around 40 percent; ozone levels have dropped significantly.

Alerting the public to air-quality dangers, the Metropolitan Washington Council of Governments (MWCG) issues a daily air-quality forecast, which gauges the presence of ozone and aerosols, airborne particles resulting from combustion, especially from industry and vehicles.

Air quality ratings for the District.

SOURCES: Environmental Protection Agency, District Department of the Environment, Metropolitan Washington Council of Governments, Clean Air Partners