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[1] Atmospheric mercury speciation and deposition are critical to understanding the fate of mercury in the environment. The importance of atmospheric mercury speciation and deposition was investigated during an intensive field campaign in the Bay St. François wetlands in late summer 2002. Measured gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and particulate mercury (PM: 0.1-2.5 mm) concentrations were 0.85-2.16 ng/m 3 (average 1.38 ng/m 3 ), 0-22 pg/m 3 (average 3.63 pg/m 3 ), and 0.5-18 pg/m 3 (average 6.44 pg/m 3 ), respectively. PM and RGM represented <1% of the total mercury. We reported the first synchronized automated high-time-resolution mercury species fluxes. The average GEM flux was 32.1 ng/m 2 /h (positive sign means volatilization, and negative sign indicates deposition) with a maximum deposition value of 110 ng/m 2 /h and a maximum volatilization value of 278 ng/m 2 /h. The average RGM flux was À2.6 ng/m 2 /h with a maximum deposition value of 25.6 ng/m 2 /h and a maximum evasion value of 0.6 ng/m 2 /h. The average PM flux was À0.4 ng/m 2 /h with a maximum deposition value of 8.7 ng/m 2 /h and a maximum resuspension value of 32.7 ng/m 2 /h. RGM contributed over 90% to the total dry deposition of mercury (GEM, RGM, and PM). GEM evasion exceeded deposition of GEM, RGM, and PM, thus suggesting other sources of mercury to the mercury budget such as wet deposition through precipitation or soil. The median dry deposition velocities calculated from flux and concentration measurements were 0.19 cm/s (GEM) < 2.1 cm/s (PM) < 7.6 cm/s (RGM). The dry deposition velocity of PM is large and should be viewed as upper limits only. Although RGM should be rapidly depositing species, as predicted by its solubility, little RGM flux was observed at night. Time series of canopy wetness and RGM fluxes suggested that RGM fluxes are not driven by RGM solubility (in water) since the canopy was dry when larger RGM deposition periods were observed during daytime. It is suggested that the vegetation might directly uptake RGM and release elemental gaseous mercury during daytime. Our experimental data showed that photochemically reactive air masses could produce RGM, which is rapidly removed by dry deposition to the surfaces. Lifetime of RGM over vegetation canopy is on the order of a few hours.

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[1] Total gaseous mercury (TGM) air-water flux measurements were taken using a dynamic flux chamber (DFC) coupled with a gaseous mercury (Hg) analyzer at the Bay St. François (BSF) wetlands (Quebec, Canada) in summer 2003. The measured TGM fluxes over water exhibited a consistent diurnal pattern, with maximum emissions during daytime and minimum fluxes occurring at night. Pearson correlation analysis showed that solar radiation was the most influential environmental parameter in TGM air-water exchange. Significant correlations were also found between TGM fluxes and 1 hour timelagged water temperature, indicating the enhancement of fluxes by bacterial activities or chemical reactions. The concentrations of dissolved gaseous mercury (DGM) in water were measured during the 2003 sampling period and indicated that DGM was always supersaturated, which implied that the water body acted primarily as a source of mercury to the atmosphere. Several empirical models of mercury air-water gas exchange were developed and evaluated. Compared to the published models, these proposed models were capable of producing good results, leading to a better agreement between the measured and modeled fluxes (improvements by 48-98%). Among these empirical models, the ones linking TGM fluxes with net radiation were superior because of their strong predictive capability. Two preferred models were selected for air-water TGM flux estimation from Lake St. Pierre's surrounding wetlands. These two models yield a mean emission of 0.19-0.24 kg mercury during

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