AMOUNT AND SIZE DISTRIBUTION OF LEAF-LEVEL PARTICULATE MATTER FROM AN EMITTER IN SW OHIO USING SEM/EDS: IMPLICATIONS FOR THE SPATIAL FOOTPRINT OF A POLLUTION POINT SOURCE

Despite continued actions to abate harmful air pollutant emissions (e.g., PM10 and PM2.5), air pollution is still a worldwide concern, yet apportioning individual shares of responsibility for pollution can be relatively challenging. Atmospheric particulate matter (PM) can be efficiently trapped by trees and serve as an important environmental medium for recording pollution. Certain PM groups are known to have characteristic chemical compositions and morphologies, reflecting possible sources. Here, we present a spatially distributed approach to trace PM emissions potentially related to a steel manufacturing plant in Middletown, Ohio, using imaging techniques. To this aim, the leaves from evergreen species (Juniperus communis) were collected 1.5-2 m above ground in the fall of 2023 in three sites situated ~2 km downwind and 18 km and 32 km upwind from the steel plant. PM retained on the leaf surfaces was rinsed using the ultrasonic cleaning method. The relative abundance and size range of spherical Fe-rich particles were tracked as indicators of the steel factory's emissions. A Zeiss Supra 35 VP field emission scanning electron microscope (FESEM) equipped with an EDAX Genesis 2000 energy dispersive spectroscopy (EDS) detector was used to investigate the particle morphology and chemical composition of the wash-off PM from leaves. The abundance and diameter of spheres were quantified on representative images of each location. Microscopy investigations reveal the presence of spherical Fe-rich particles in all three sites, but the amount (10-fold variation) and mean particle size (particle equivalent diameters from 10 to 1 µm) showed a clear decreasing trend with distance. The spatial footprint indicates that emitted particles can influence air quality in areas >30 km upwind from the point source and are likely more abundant and larger along the predominant wind direction. Generating spatial emission footprints can help facilitate future pollution reduction endeavors.