Messing With the Local Air Currents
It's already pretty obvious to anyone who's ever been in a city on a smoggy day that air quality can get quite bad in urban areas, but we're still finding new reasons why that is so. The most obvious ones are the density of pollutant sources, the lack of vegetation to filter the air, the 'heat island' effect, etc. To this list we can add the effect of paved areas on local weather patterns that prevents polluted air from being blown out to sea (this applies to coastal cities, obviously).
Photo: Flickr, CC
The research team combined extensive atmospheric measurements with computer simulations to examine the impact of pavement on breezes in Houston. They found that, because pavement soaks up heat and keeps land areas relatively warm overnight, the contrast between land and sea temperatures is reduced during the summer. This in turn causes a reduction in nighttime winds that would otherwise blow pollutants out to sea.
In addition, built structures interfere with local winds and contribute to relatively stagnant afternoon weather conditions.
"The developed area of Houston has a major impact on local air pollution," says scientist Fei Chen of the National Center for Atmospheric Research in Boulder, Colo. and lead author of the new study. "If the city continues to expand, it's going to make the winds even weaker in the summertime, and that will make air pollution much worse." (source)
The practical implications are that urban development should take this effect into account and try to include more parks and green areas that will help keep night-time temperatures lower. This'll be more comfortable for the local residents, but it'll also allow for polluted air to be evacuated by air currents created by the temperature differentials.
Via AGU, GCC
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