Optical properties and chemical constituents of ambient fine particles in an urban environment in Korea

Aerosol optical properties, chemical constituents, and sources of ambient fine particles were measured in Seoul, Korea, from May to November 2016. Light scattering (σ_scat) and absorption (σ_abs) coefficients were measured with a photoacoustic extinctiometer (PAX) and a multiangle absorption photometer (MAAP), respectively. Chemical components of ambient fine particles were observed using a HR-ToF-AMS and their sources were identified using a positive matrix factorization model. During the study period, average mass concentration of fine particles, organic matter (OM), black carbon (BC), SO₄^2-, NO₃^-, NH₄⁺, and Cl^- were 27.4 (±16.9) μgm^-3, 13.0 (±8.3) μgm^-3, 1.7 (±1.0) μgm^-3, 5.0 (±3.6) μgm^-3, 4.7 (±4.9) μgm^-3, 2.9 (±2.3) μgm^-3, and 0.3 (±0.5) μgm^-3, respectively, and OM was a major component of fine particles. The observed σ_scat and σ_abs were 131.0 (±94.0) Mm^-1 and 13.6 (±8.2) Mm^-1, respectively. Both of the scattering and absorption coefficients showed unique diurnal patterns with high peaks during the morning and evening rush hours due to the peak emissions of vehicles and the unfavorable meteorological conditions for dispersion of the vehicle emissions. The average of single scattering albedo calculated was 0.9 (±0.1), representing that fine particles in the study area contain relatively high fraction of scattering chemical components. The average mass scattering efficiency of fine particles was 4.70 m²g^-1 and exhibited higher values in spring and lower values in fall, showing a similar trend to mass of fine particles. Multiple linear regressions were performed to investigate associations of chemical components of fine particles with extinction coefficient (b_ext). Results showed that OM contributed the most to b_ext, accounting for 51.3%, followed by (NH₄)₂SO₄, NH₄NO₃, and BC, 20.4%, 17.7%, and 9.7%, respectively. The PMF model identified four factors contributing to the OM, including low-volatile oxidized organic aerosol (LV-OOA), semi-volatile oxidized organic aerosol (SV-OOA), cooking influenced organic aerosol (COA), and hydrocarbon like organic aerosol (HOA). Among the identified four factors, secondary organic aerosol factors were the dominant contributors to b_ext.