In air pollution studies, it’s difficult to perform traditional science. Normally, we can’t stop running a city’s transportation system or power plants to assess the impact on our daily activities. But, inadvertently, we do perform some accidental experiments.
One occurred during the power plant blackout in the eastern U.S. in 2003. Another was observed during ‘The Day of Atonement’ – a traditional holiday in Israel, when nearly all transportation ceases for 24 hours. A third occurred just before and during the Beijing Olympics, in an effort by China to clear the air for the games.
All of these events witnessed a dramatic drop in emissions of nitric oxide—a major urban air pollutant, which is thought to be a precursor to other health hazards, like ozone. In Beijing, the decline in nitric oxide was accompanied by a decline in airborne particulate matter, which is increasingly recognized as a serious health hazard.
In the presence of sunlight and volatile organic compounds, nitric oxide forms ozone. But, interestingly, during the 2003 blackout and during the holiday in Israel, large reductions in nitric oxide did not result in large reductions in ozone. This could reflect an incomplete understanding of airborne chemical reactions. Or it could be that residual nitric oxide concentrations, even during reduced daily activity, were high enough to form ozone.
Atmospheric chemists have their work cut out for them. But, these natural experiments generally support the notion that human activities, if not regulated by pollution controls, can result in harmful levels of pollutants in the air we breathe.
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Photo, taken on August 7, 2008, courtesy of Open Democracy via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.