Abstract. As part of an international Hg flux intercomparison at the Steamboat Springs, Nevada, geothermal area, several dynamic soil flux chambers and micrometeorological gradient systems were operated over desert soils in early September 1997. A series of unanticipated convective rain cells impacted the site with the first rainfall in -90 days, and the initial 4-cm rainfall increased soil moisture from -0.01 to 0.06% (vol/vol). Several chambers were operating prior to the events, and two were deployed over wet soils following rainfall. Rainfall resulted in an immediate and steep rise in ambient air Hg concentrations and soil Hg emissions which persisted for 12-24 hours. Fluxes increased most quickly and to a greater degree over the wettest soils, and the rate of increase was related to chamber design and flushing rate. The flux response was also apparent in the micrometeorological data. In general, soil emissions increased by an order of magnitude following the rain, and reached levels -6 times above those at the same time the previous day. These fluxes were significantly correlated with temperature, radiation, humidity, wind speed, and soil moisture. After drying for -40 hours, selected soil plots were manually irrigated with low-Hg-distilled water. Mercury emissions responded similarly across the

[1] Field measurements of mercury air-surface exchange from natural settings were made in various Canadian landscapes. Soil and water samples were analyzed for mercury concentrations, and air-surface exchange fluxes from these substrates were determined using dynamic chamber, micrometeorological, or modeling methods. Environmental variables, including air and soil/water temperature, solar radiation, humidity, and wind speed, were monitored concurrently with the air-surface exchange to better understand the processes affecting the environmental cycling of mercury. Average mercury fluxes from aquatic landscapes ranged from 0.0 to 5.0 ng m À2 h À1 with total mercury concentration in water ranging from 0.3 to 6.5 ng L À1 . A significant correlation (R 2 = 0.47) was found between gaseous Hg fluxes and total Hg concentration in water. Mean gaseous Hg fluxes from forest soils varied from À0.4 to 2.2 ng m À2 h À1, while those from agricultural fields ranged from 1.1 to 2.9 ng m À2 h À1. Non-mineralized bedrock, sand, and till sites yielded fluxes ranging from À0.03 to 5.9 ng m À2 h À1 . Mean fluxes from mercuriferous geological substrates at various locations were large compared to nonmercuriferous sites, ranging from 9.1 to 1760 ng m À2 h À1 , and represent natural emissions. The corresponding total mercury substrate concentrations ranged from 0.360 to 180 ppm. A significant correlation (R 2 = 0.66) was found between Hg fluxes and total Hg concentrations in mineralized and non-mineralized substrates. These gaseous Hg flux measurements represent a significant contribution to understanding natural mercury cycling, but there are still insufficient data and knowledge of processes to properly scale up fluxes from natural sources in Canada.

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A residential washing machine was studied in order to determine the extent of chloroform formation following the application of a laundry bleach containing sodium hypochlorite. A dynamic model was also developed to estimate chloroform formation, mass transfer, and gaseous emissions during a typical wash cycle. A series of 22 experiments was completed to determine model parameters, including chemical reaction and mass transfer rate coefficients, as well as headspace air exchange rates. Three additional experiments were completed to evaluate model performance. Experimental and model results suggest that washing machine environments are very conducive to chloroform formation, with chloroform levels frequently exceeding 1 mg/L in washwater. Chloroform stripping efficiencies were observed to be greater than those previously reported for ethanol, but less than those reported for radon. Mass emissions of chloroform to indoor air during a ten-minute wash cycle were predicted to be between 5.3 and 9.8 mg. On a unit activity basis, chloroform emissions associated with hypochlorite-containing bleach addition to washing machines far exceeded emissions from showers. Each source was estimated to emit similar quantities of chloroform on an annual basis. Finally, it was estimated that the use of hypochlorite-containing laundry bleaches may contribute a significant fraction of chloroform mass loadings to municipal wastewater.

Abstract. The potential for the use of a laboratory gas exchange system to estimate of mercury emissions from naturally and anthropogenically mercury-enriched areas was assessed by comparison of mercury fluxes measured from the same substrate in situ and in the laboratory. In general, mercury emissions measured with the laboratory chamber for daytime conditions were of the same magnitude as mean mercury emissions measured in situ with field chambers. Mercury emissions measured with both the field chamber and laboratory chamber were lower than those measured with micrometeorological methods. Within the controlled experimental regime of the laboratory chamber, data were developed that demonstrated that substrate mercury concentrations and light are important parameters in controlling mercury emissions. However, with light and other parameters interacting with the soil, the correlation between mercury fluxes and substrate mercury concentrations declined. Mercury emissions from a variety of substrates in the dark were -25% of those emissions measured in the light at the same soil surface temperature. IntroductionAlthough the ultimate goal of quantifying mercury (Hg) fluxes from naturally and anthropogenically enriched terrains is to provide reliable, spatially representative data, achieving this goal is not always easy. This often requires numerous in situ monitoring campaigns in rugged, remote terrains, which in practice are difficult, expensive, and labor-intensive. This paper explores the viability of using a cost-effective laboratorybased approach to augment field studies, by comparing Hg emissions data obtained in the field with data obtained using a controlled gas-exchange laboratory system.