An Eye on Megacities' Dirty Skies

New monitoring techniques are improving our understanding of pollution in the developing world

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Carbon dioxide emissions get all the hype. Global warming, sea level rise, melting ice caps, etc. But in this wide world, there are so many other emissions to worry about. For example, let’s not forget about the ozone- and smog-producing nitrogen oxides, NO and NO2. These nasty substances are mainly produced by the combustion engines that power the world’s automobiles, and are linked with severe health problems in the places they concentrate. Those places tend to be cities, especially cities in the developing world.

But unlike the more, well, popular carbon dioxide emissions, nitrogen oxides aren’t very well tracked. Scientists have a pretty solid idea about how much NOx there is, but they haven’t really had a good way to track its lifetime in the troposphere and how far it can travel. Now, researchers have developed a technique that’ll improve NOx monitoring on both fronts.

Dr. Steffen Beirle and colleagues have utilized new satellite data to monitor NOx emissions in developing megacities, and combined that information with wind data to track how far the emissions spread. Previous calculations didn’t calculate separately for different wind directions, creating instances where two opposing wind flows could be misinterpreted as cancelling each other out. But in reality, where the wind blows, the nitrogen oxides go.

Beirle and his team focused their research on the Saudi Arabian city of Riyadh. With a population of about 7 million, the greater region appears like other big cities as a bright red dot on a map of concentrated nitrogen oxide emissions. By monitoring concentrations at eight different wind directions, they could track how far the pollutants carried and how long they would persist in the troposphere. This research appears in the September 23 issue of Science.

It’s all a bit technical, but the implications are important. By being able to more fully understand concentrations of pollutants like nitrogen oxides, cities and regions can better respond to their threats. As global coverage of satellites increases, this type of more precise data will be available to more and more cities.

About the Author

  • Nate Berg is a freelance reporter and a former staff writer for CityLab. He lives in Los Angeles.