Identifying External Sources of High PM2.5
Concentrations
at Urban Air Monitors: An Application to North-Central Texas, U.S.
Paul F. Hudak
Abstract This objective of this study was to identify external sources of high particulate concentrations at a monitoring station in north-
central Texas, U.S. Concentrations of particulate matter finer than 2.5 microns (PM2.5), averaged over 24 hours, were plotted over a five-year period, from 2018 through 2022. PM2.5 concentrations ranged from 0.2 μg/m3 to 52.0 μg/m3, with a mean of 7.4 μg/m3 and standard deviation of 4.1 μg/m3. For 23 PM2.5 samples (of 1,667 total samples) with concentrations above 20 μg/ m3, backward atmospheric transport trajectories and satellite data were used to identify likely external sources. Saharan dust
affected all but two of the 23 samples with the highest PM2.5 concentrations. Smoke from wildfires in the Pacific Northwest and Great Plains (Oklahoma and Kansas) affected the other two of 23 elevated samples. Results illustrate a substantial influence of
Saharan dust on PM2.5 concentrations, especially in summer months, near the western edge of its westward transport trajectory. Monitoring and forecasting Saharan dust incursions should help inform regional air quality advisories.
Keywords: PM2.5, Saharan dust, smoke, north-central Texas
Introduction Windblown dust is an important process
in the rock cycle, as evident throughout much of the geologic record. Transported dust both benefits and potentially harms ecosystems and humans. Other natural sources of air pollution include volcanic eruptions and wildfires. Human activities producing air pollutants include transportation, electric power production, agriculture, and other industrial activity. Many pollution sources emit both gases and particulate matter (PM) to the atmosphere. PM, comprising solids and small liquid droplets, consists of numerous directly emitted and secondary forms created through chemical reactions of sulfur dioxide, nitrogen oxides, and other chemicals (EPA, 2022).
Air quality has improved in the U.S.
(EPA, 2022), but many cities periodically have unhealthy airspace. Both local and external sources affect air quality in urban complexes. PM in external events such as dust storms can originate hundreds
34 TPG •
Jul.Aug.Sep 2024
or thousands of kilometers away from a metropolitan area. The objective of this study was to identify external sources of elevated 24-hour concentrations of PM less
than 2.5 microns (PM2.5) at a monitoring station in north-central Texas, U.S. over a five-year period.
Background PM affects human health, the
environment, and climate. Fine PM can lodge deeply in human lungs, enter the bloodstream, and harm the cardiovascular system (Anderson et al., 2012). Some forms of transported PM carry nutrients to ecosystems; however, PM can also transport infectious diseases, block sunlight and reduce photosynthesis, and increase sedimentation and eutrophication in water bodies (Tong et al., 2023). PM affects weather and climate by serving as cloud condensation nuclei (Twomey, 1974; Yu et al., 2006); altering the capability of the atmosphere to absorb, reflect, and scatter solar radiation (Ginoux, 2017; Myhre et
al., 2013; Sokolik and Toon, 1996); and decreasing the albedo of snow and ice surfaces (Drake, 1981). PM also damages machinery and reduces solar energy production (Tong et al., 2023).
External events such as dust storms and
smoke from wildfires affect air quality far away from source areas (Kaulfus et al., 2017; Varga, 2020). Worldwide, dust from wind erosion makes up about 40% of aerosols in the troposphere (WMO, 2022). Globally, the main sources of desert dust are northern Africa (Sahara), the Arabian Peninsula, Central Asia, and China (WMO, 2022). The Sahara contributes more than half of global mineral dust emissions (Rocha-Lima et al., 2018; Varga, 2020).
Saharan dust is regularly transported
westward, northward, and eastward (Goudie and Middleton, 2001), but the westward trajectory over the North Atlantic is most voluminous (Toure et al., 2012). Typically, Saharan dust takes about five to seven days to reach the Caribbean; however,
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