Size-Resolved Characteristics and Source Influences of Airborne Microplastics in Central Los Angeles

Airborne microplastics (MPs) are increasingly recognized as atmospheric pollutants with potential implications for human exposure; however, their occurrence, temporal variability, and associations with urban particulate matter remain poorly understood. This study investigated MPs associated with PM10 in central Los Angeles across two seasonal sampling campaigns by integrating MP abundance, morphology, size distribution, PM10 chemical composition, and meteorological observations. MPs were detected in all samples, with concentrations ranging from 2.2-4.0 MP/m3 during the cool-season campaign and 2.2-3.4 MP/m3 during the warm-season campaign. Fibers remained the dominant morphology, while particles <100 µm, particularly the 5-50 µm and 50-100 µm fractions, consistently dominated the airborne MP population. Strong positive correlations (generally ρ ≥ 0.79) were observed between total MP concentrations and major crustal (Fe, Si, Mn, Ca, Al, and Mg), traffic-related (Ba, Cu, and Ni), and carbonaceous (OC and EC) tracers, indicating that MPs are closely associated with urban particulate mixtures influenced by resuspension and non-tailpipe traffic emissions. In contrast, short-term meteorological variability showed no consistent relationship with MP concentrations. These findings indicate that airborne MPs are a persistent component of the urban PM10 mixture rather than isolated contaminants, and provide new insight into their sources and behavior in densely populated urban environments.