Identifying and Quantifying the Impacts of Advected North African Dust on the Concentration and Composition of Airborne Fine Particulate Matter in Houston and Galveston, Texas

Every summer, large-scale dust plumes emerge from the west coast of North Africa, cross the Atlantic, enter the Caribbean Basin, and on occasion pass over the southern United States. We show that such dust events significantly increase the concentration and alter the chemical composition of ambient fine particulate matter (PM2.5) in southern Texas. Between 1 August and 13 September 2014, PM2.5 was sampled daily at Clinton Drive, an industrial location in Houston, and at Galveston located on the Gulf of Mexico coast that is not directly/significantly impacted by local and regional pollution sources. Between 17-25 August, average PM2.5 concentrations nearly doubled when a large dust-laden African air mass moved through the region. Using ground-based measurements, satellite observations, and modeling tools, we demonstrate that this massive influx of mineral dust greatly reduced the relative abundance of pollutants in Houston where aerosols are otherwise dominated by local and regional emissions. Chemical mass balance modeling estimated that African dust contributed 19-48% of PM2.5 during the 9-day dust episode. Moreover, African dust was present throughout the measurement period even on days outside the main dust event contributing an estimated similar to 8% of PM2.5 which suggests that it may be a normal summertime component in this region. These measurements agree closely with inferences of "fine dust" based on a generic soil composition in the IMPROVE (National Interagency Monitoring of Protected Visual Environments) network. Our detailed protocol supports the conclusion that African dust affects a wide region of the South, Southeast, and East Coast United States.