PM2.5 Pollution and Temperature Inversions: A Case Study in St. Louis, MO

Johnson, Hannah
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Wintertime temperature inversions are partially responsible for some of the worst historical air pollution events as cold air pools are favorable for prolonged poor air quality episodes. The St. Louis metropolitan area in Missouri-Illinois has relevant problems with particulate pollution yet is under-studied. This case study examines the characteristics of an inversion layer along with additional meteorological parameters and their effects on PM2.5 air quality in St. Louis from November 22 to December 3, 2015. During the selected period, November 26 to December 1 PM2.5 Air Quality Index (AQI) daily values often exceeded levels the Environmental Protection Agency classifies as unhealthy for sensitive groups. Shallow surface temperature inversions were most common on less polluted days while strong temperature inversions with a base height around 950 mb persisted on more heavily polluted days. Variability in surface wind speed, wind direction, and relative humidity occurred mostly on less polluted days while values were consistent on more heavily polluted days. Precipitation only happened on the most heavily polluted days but showed no great impact of reducing pollution. Winds from the south on November 26 suggested transport of excess particulate pollutant was the cause of unhealthy PM2.5 levels that day, not temperature inversions. Strong temperature inversions contained these pollutants in St. Louis on November 27 to November 30. A surface pressure minimum north of St. Louis on December 1 produced a substantial change in wind direction on November 30, influencing eventual dispersion of pollutants. Further research is necessary to help fill in the knowledge gaps about air quality in the Midwest.