ORGANIC ACIDS IN THE ATMOSPHERE AND BULK DEPOSITION OF HONG KONG

摘要

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 Kowloon and 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 acids for bulk deposition samples collected on a daily basis, with pH < 5.0, were 17 and 14%, respectively. The concentrations of these acids were significantly correlated with each other, but not with pH. Higher organic acid concentrations were found in the dry, winter season, and for the synoptic weather system types: approaching cyclone and cold front. Oxalate levels were generally higher in bulk deposition samples for northortheasterly 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 acids are reported.