Particle and Aerosol Research Vol. 9, No. 1, March 2013 |
ISSN : 1738-8716 (Print) ISSN : 2287-8130 (Online) |
Characteristic of Size-Resolved Water-Soluble Organic Carbon in Atmospheric Aerosol Particles Observed during Daytime and Nighttime in an Urban Area
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Abstracts
Twelve-hour size-resolved atmospheric aerosols were measured to determine size distributions of water-soluble organic carbon(WSOC) during daytime and nighttime, and to investigate sources and formation pathways of WSOC in individual particle size classes. Mass, WSOC, NO3-, K+, and Cl- at day and night showed mostly bimodal size distributions, peaking at the size range of 0.32-0.55§(condensation mode) and 3.1-6.2§(coarse mode), respectively, with a predominant condensation mode and a minor coarse mode. While NH4+ and SO42- showed unimodal size distributions which peaked between 0.32 and 0.55§. WSOC was enriched into nuclei mode particles(<0.1§) based on the WSOC-to-mass and WSOC-to-water soluble species ratios. The sources and formation mechanisms of WSOC were inferred in reference to the size distribution characteristics of inorganic species(SO42-, NO3-, K+, Ca2+, Na+, and Cl-) and carbon monoxide. Nuclei mode WSOC was likely associated with primary combustion sources during daytime and nighttime. Among significant sources contributing to the condensation mode WSOC were homogeneous gas-phase oxidation of VOCs, primary combustion emissions, and fresh(or slightly aged) biomass burning aerosols. The droplet mode WSOC could be attributed to aqueous oxidation of VOCs in clouds, cloud-processed biomass burning aerosols, and small contributions from primary combustion sources. From the correlations between WSOC and soil-related particles, and between WSOC and sea-salt particles, it is suggested that the coarse mode WSOC during daytime is likely to condense on the soil-related particles(K+ and Ca2+), while the WSOC in the coarse fraction during nighttime is likely associated with the sea-salt particles(Na+).
Keywords£ºSize distribution, water-soluble organic carbon(WSOC), sources and formation mechanisms of WSOC, coarse mode WSOC
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