Organic Acids in the Atmosphere and Bulk Deposition of Hong Kong

Abstract

Results from the first study in Hong Kong, Southern China, to investigate the concentrations of organic acids in bulk deposition, aerosol and gas phase samples are presented. 57 daily bulk deposition samples were collected in central Kowloonand analyzed by ion chromatography, from May 1999 to May 2000. The volume-weighted (vw) mean concentrations for formate, acetate, propanoate and oxalate were 6.1, 4.5, 0.4 and 1.4 μeq dm-3, respectively, with vw mean pH being 4.65.The maximum acidity contributions by formic and acetic acidsfor bulk deposition samples collected on a daily basis, withpH < 5.0, were 17 and 14%, respectively. The concentrationsof these acids were significantly correlated with each other, butnot with pH. Higher organic acid concentrations were foundin the dry, winter season, and for the synoptic weather systemtypes: approaching cyclone and cold front. Oxalate levels weregenerally higher in bulk deposition samples for north/northeasterly air masses, higher surface windspeeds, and low rainfall amounts. Formic and acetic acids were present at higher concentrations in the gas phase (mean concentrations at two sites were in the range from 3.2 to 6.5 μg m-3, with formate usually < acetate), than in aerosols (mean concentration of formate, acetate or oxalate ≤2.2 μg m-3). Higher levels of organic acids both in aerosols and in the gas phase were found at a busy roadside site than at a residential site. Deposition fluxes for formic and acetic acidsare reported.