Size Distribution and Source Apportionment of Trace Metal Elements in the Atmospheric Aerosols in a Coastal City, Northern China

Size-resolved aerosol samples of trace elements (TEs) were measured in a Chinese coastal city, from May 2015 to April 2016. Based on enrichment factors and positive matrix factorization (PMF), TEs were grouped into crustal (Al, Ba, Fe, Na, Ti, Co, Sc), anthropogenic (Zn, Pb, Cd), and mixed-source elements (K, Mn, Li, Cr, Cu). Crustal elements generally dominated the coarse mode (3.3–4.7 μm), with a notable shift toward larger particles (4.4–7.0 μm) in winter. Na exhibited seasonal distributions: tri-modal in summer (0.65–1.1, 3.3–4.7, and 7.0–11 μm), broad unimodal in spring (2.1–7.0 μm), and bimodal patterns in fall (2.1–3.3 and >11 μm) and winter (3.3–4.7 and 7.0–11 μm). Anthropogenic metals (Pb and Cd) generally peaked at 0.43–0.65 μm, with the peak shifting to 0.65–1.1 μm in summer. Mixed-source elements (K, Mn, Li) maintained a stable bimodal distribution (0.43–0.65 μm, 3.3–4.7 μm) across seasons. Dust events shifted peak positions and elevated overall loadings, while haze-fog (HF) conditions predominantly enhanced TEs concentrations in the fine mode. Chemical Mass Balance (CMB) model identified primary sources for PM1.1, PM2.1, PM2.1–10 and PM10, including industrial processes, construction dust, coal-fired plants, biomass burning, dust, shipping, road traffic, sea salt, and other unidentified sources, with contributions varying with particle size, season and weather conditions. Our results demonstrated that TEs size distribution were shaped by the combined effects of source and meteorology, and that derived log-normal parameterizations provided size-resolved constraints for aerosol transport, deposition, and health risk assessments.