Add time:08/13/2019         Source:sciencedirect.com

Aerosol samples were collected at the summit of Mt. Fuji in July–August 2009 and analyzed for diacids and related compounds together with major ions to decipher the sources and formation process of organic aerosols in the free troposphere. Molecular distributions of diacids showed the predominance of oxalic acid (C2) followed by succinic (C4) and malonic (C3) acids. The average concentration of total diacids is ten times higher in whole-day samples than night-only samples due to the uplift of planetary boundary layer in daytime, suggesting the daytime formation of diacids in the uplifted ground-level air mass along the mountain slope. A strong correlation is found between C4 and levoglucosan in whole-day and nighttime samples. Liquid water content (LWC) shows strong correlations in nighttime with anthropogenic and biogenic secondary organic aerosol (SOA) tracers (e.g., adipic (0.90, p < 0.05) and phthalic acids (0.93, p < 0.05) and 3-methyl 2,3,4-trihydroxy-1-butene (0.95, p < 0.05), suggesting that aqueous-phase chemistry is important for the formation of water-soluble organic aerosols in the free troposphere. In whole-day samples, LWC is strongly correlated with organic carbon (r = 0.97, p < 0.05), and isoprene-SOA tracers such as methylthreitol (0.96, p < 0.05), methylerythritol (0.97, p < 0.05), 2-methylglyceric acid (0.94, p <0 .05) and glycolic acid (0.98, p < 0.05), suggesting that daytime SOAs are mainly from the oxidation of isoprene emitted from the regional forests on the foothill of Mt. Fuji. A strong correlation between LWC and glycolic acid further suggests that isoprene is the main precursor for the production of oxalic acid via glycolic acid as intermediate. This study supports the heterogeneous formation of diacids in the free troposphere.

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