Two-year monitoring of gaseous elementary mercury in a typical iron–steel plant in Yangtze River Delta, China: Characterization and estimation of its dynamic oxidation

Abstract

A two-year gaseous elementary mercury (GEM) measurement was implemented at an iron–steel plant in Yangtze River Delta, China, which provided an excellent opportunity to investigate their dynamic cycling. The hourly GEM concentrations ranged between 0.78 and 113.8 ng m−3, with a mean value of 3.83 ± 2.53 ng m−3. Temporally, seasonal GEM contents decreased as winter ≈ spring > summer > autumn, while diurnal cycling was observed with a steady decrease at 14:00–17:00. GEM variations were found to be related to source emissions, meteorology and regional transportation. Three major oxidants (O3, Br and OH radicals) were used to evaluate GEM oxidation in the daytime, and the estimated GEM depletion rate was 70.8 ± 52.5 molecule cm−3 s−1 (0.09 ± 0.06 ng m−3 h−1). The GEM oxidized by Br radicals accounted for 83.4% of the total GEM oxidation rate, followed by O3 (13.8%). The estimated atmospheric lifetime of GEM was 22.9 to 345.2 days, which implies a major contribution of Br radicals to the GEM sink. These findings highlight the ability of iron–steel industry emissions and in–situ oxidation to affect daily local GEM cycling significantly.