| 24 Jul 2026
Contributions of Fine and Coarse Particles to Light Absorption at an Urban Traffic Site during Street Dust Season
Abstract. Light absorption by urban aerosols is dominated by fine particles (particulate matter ≤2.5 µm; PM2.5), particularly from traffic exhaust and residential combustion. However, coarse particles (2.5–10 µm; PM2.5–10) can also contribute during spring street dust events in northern countries. This study investigated size-resolved optical properties and chemical composition of PM in an urban street canyon during spring. Hourly PM₁₀ concentrations averaged 27.1 µg m⁻³, while PM2.5 and PM1 (≤1 µm) concentrations averaged 7.1 and 4.3 µg m⁻³, respectively. Light absorption across PM₁, PM₂.₅, and PM₇.₂ fractions was dominated by submicron particles, predominantly at short wavelengths, while coarse particles enhanced absorption during dust-resuspension events. Equivalent black carbon (eBC) showed strong size dependence, with PM1 capturing most combustion-derived BC despite low campaign-mean concentrations (0.49 µg m⁻³). Relative to PM₁, hourly eBC increased by 14 % in PM2.5 and 41 % in PM7.2. Absorption Ångström exponent analysis revealed size- and source-dependent spectra differences, with stronger wavelength dependence during high PM10 dust events and values closer to unity under traffic-exhaust-dominated conditions. The inclusion of coarse particles complicated the interpretation of the AAE470/950 and related biomass burning contribution estimates. Elemental analysis revealed elevated concentrations of Si, Fe, and Al in coarse PM, suggesting contributions from crustal material and/or non-exhaust emissions that may also influence optical properties. These findings demonstrate that quantification and source identification of urban aerosol light absorption requires consideration of the selected particle size cut-off.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Aerosol Research.
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