The role of pollution state on urban heat islands in the Midwestern United States

Concentrations of anthropogenic greenhouse gases and other pollutants are magnified in urban areas and likely affect urban heat islands (UHIs). UHIs are defined by temperatures in the urban core that are warmer relative to nearby rural areas. These warmer temperatures alter atmospheric stability, cloud and precipitation formation, and increase photochemical smog production. However, the air quality-UHI link remains unquantified. Here we assess the chemical contribution of pollution state to the UHI. We focus on small to medium-sized (population ranging from 300,000 to 1.2 million) cities in the Great Plains, a region known for its springtime extreme weather and good to moderate air quality. We investigate the urban pollution state using satellite and ground-based observations for aerosol optical depth (AOD), nitrogen dioxide (NO₂ ; an important anthropogenic precursor for ozone formation), and ozone (O₃; a greenhouse gas). To isolate the chemical effects of urban pollution on the UHI, we simulate an isolated supercell thunderstorm crossing the Oklahoma City urban area using the WRF-Chem model. One simulation includes the physical effects of the UHI over Oklahoma City during a severe convective event. The second simulation further incorporates the radiative effects of greenhouse gases and aerosols to determine the chemical contribution to the UHI. Through these simulations with and without atmospheric chemistry, we assess the chemical contribution to the UHI and the formation and sustenance of this severe weather event.