Measurements of size-fractionated concentration and bulk dry deposition of atmospheric particulate bound mercury

摘要

Daily samples of size-fractionated (18, 10, 2.5 and 1.0 μm) particulate-bound mercury Hg(p) were collected using Micro-Orifice Uniform Deposition Impactors (MOUDI), on randomly selected days each month between November 2010 and July 2011, at a traffic site (Hungkuang), a wetland site (Gaomei), and an industrial site (Quanxing) in central Taiwan. Bulk dry deposition was also collected simultaneously using a surrogate surface. The nine-month average (±standard deviation) Hg(p) concentrations were 0.57 (±0.90), 0.17 (±0.27), and 0.94 (±0.92) ng m~(-3) at Hungkuang, Caomei, and Quanxing, respectively. Concentrations in November and December were much higher than in the other months due to a combination of high local emissions and meteorological conditions. PM_(1.0) contributed more than 50% to the bulk concentration at the traffic and the industrial sites, but only contributed 25% at the wetland site. PM_(1.0-2.5) contributed 25%-50%, depending on location, to the bulk mass. Coarse fraction (PM_(2.5-18)) contributed 7% at Hungkuang, 25% at Gaomei, and 19% at Quanxing. Samples with very high bulk concentrations had large fine fractions. Annual dry deposition estimated from the surrogate surface measurements was in the range of 30-85 μg m~(-2) yr~(-1) at the three sites. Coarse particulate Hg(p) were estimated to contribute 50-85% of the total Hg(p) dry deposition. Daily dry deposition velocities (V_d) ranged from 0.01 to 7.7 cm s~(-1). The annual V_d generated from the total measured fluxes was 0.34, 0.60 and 0.29 cm s~(-1) at Hungkuang, Gaomei, and Quanxing, respectively. These values can be reasonably reproduced using a size-resolved model and measured size fractions.