As more of the world’s population moves into cities, air quality becomes an increasingly large problem. According to a new study from the National Center for Atmospheric Research, it isn’t just car exhaust from traffic jams that’s causing you to wheeze; it’s the way cities are constructed that keeps natural processes from cleaning up after us.
The study, which focused on the Houston area, used computer simulations and extensive measurements to figure out what kind of effect pavement has on breezes that we rely on to sweep away pollutants. Because pavement collects heat and stays warm overnight, the contrast between sea and land temperatures is reduced in the summer. That means there is a reduction in the evening winds that normally blow pollutants out to sea. At the same time, large urban structures interfere with winds and contribute to “stagnant afternoon weather conditions.”
If Houston were covered in cropland instead of pavement, a sea breeze would blow into the city during the afternoon, and a land breeze would blow pollution offshore at night.
“The developed area of Houston has a major impact on local air
pollution,” explained Fei Chen, lead author of the study, in a statement. “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.”
There are ways around this; adding more lakes, ponds, and green spaces could counteract the effect of pavement on weather. But every city has a different topology and climatology, so prescribing a quick fix for all coastal cities is impossible. Urban planners would be wise to take this study into account, though, when building up new cities (we’re looking at you, developing countries).