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Air and precipitation samples were collected and analyzed for 91 pesticides or metabolites from May to September 2004 at St. Damase, an agricultural site located in Yamaska basin in Québec, Canada. A broad range of pesticides was detected during this experiment where 40 different compounds were measured. Most of the samples showed more than 10 simultaneous pesticide detections and sometimes reaching 19 simultaneous detections. The most detected pesticides in air were trifluralin, metolachlor and captan, which were found in all the samples during the 5 months of measurements. For the detected compounds, the average concentrations ranged from 4 pg/m3 to 8 ng/m3. Some of the pesticides detected in air were found in precipitation samples as well showing that wet deposition can occur and have an impact on aquatic ecosystems. The most important pesticides detected were related to corn and soya cultivations, the two main cultures in this region highlighting that the major sources come from local applications. On the other hand, the detection of some pesticides in precipitation which were undetectable in air implies that some compounds may have a long range transport origin.

Long-term monitoring data of total gaseous mercury (TGM) concentrations from the Canadian Atmospheric Mercury Measurement Network (CAMNet) were analysed for temporal trends, seasonality and comparability within the network and compared to other network and model results. Data collected from 11 Canadian measurement sites between 1995 and 2005 were analysed. Sites within CAMNet were characterized by principle component analysis (PCA) into four main categories. For the first time since automated TGM measurements have been made within CAMNet, this paper reveals statistically significant decreasing TGM concentrations from rural locations in Canada during this time period. The largest declines were observed close to the urban areas of Toronto and Montreal, where levels fell by 17% at Point Petre, and 13% at St. Anicet, respectively. Many of the TGM changes are comparable with the overall trends observed in total mercury concentrations in precipitation, for similar time periods, at co-located or nearby National Atmospheric Deposition programme's Mercury Deposition Network (NADP-MDN) sites. The results show that these changes are mostly driven by local or regional changes in mercury emissions. Other sites within CAMNet reflect reported changes in hemispherical global background concentrations of airborne mercury, where slight decreases or no statistically significant trend in TGM concentrations exist over the same time period.

This paper, and its companion (that dealt with lindane and endosulfan) review available data on the presence of currently used pesticides (CUPs) in air and precipitation in Canada, since the late 1980s. Pesticides usage/sales are also given when available. Data from local studies/initiatives, region-wide monitoring networks and remote locations are compiled to summarize atmospheric levels of different CUP classes (e.g. acid herbicides, organophosphates, “new” organochlorines, triazines, etc.) and how this varies among regions and with time. Based on this information, and other parameters not specific to Canada, knowledge gaps are identified and ideas for further research work are proposed.

This paper, and its companion, review available data on the presence of currently used pesticides (CUPs) in air and precipitation of Canada, since the late 1980s. Pesticides usage/sales are also given when available. Two older CUPs—lindane, which shows a wealth of data, and endosulfan, one of the most abundant and ubiquitous organochlorine pesticides in the North American atmosphere today—are the focus of this first part. Data from local process studies, monitoring work in source and receptor regions, and modelling efforts are compiled to give an overall picture of the atmospheric levels and deposition and how this varies between regions and with time.

Eight years of gaseous elemental mercury (GEM) concentration measurements from Alert, Nunavut, Canada (between 1995 and 2002) is presented. The annual time series shows a distinct repeating seasonal pattern with an overall annual median concentration for this time period of 1.58 (S.D.=0.04 ng m(-3)). Strong seasonal variation was observed throughout the years with springtime displaying strong variability in the GEM and overall lower median concentrations due to the so-called mercury depletion events (MDEs). Summer concentrations are higher than the annual average and show a decrease in variability. Fall and winter concentrations are distributed around the annual median concentrations and show little variability. The relationship between the springtime depression and the summer increase shows a change in the behaviour of mercury between 1995 and 2002. Preliminary results suggest that during this period an increasing amount of the mercury lost from the atmosphere in the spring is not returned to atmosphere in summer. A comparison of GEM concentration data from three sites--Alert (Canada), Amderma (Russia) and Kuujjuarapik (Canada)--demonstrated similar monthly distribution of GEM between Alert and Amderma, with the latter not showing as high summer concentrations. Monthly distribution of GEM at Kuujjuarapik varied considerably from the other two sites. MDEs were found to occur at each site in the spring yet displayed different characteristics. MDEs appear to start at Alert shortly after polar sunrise but in Amderma their initiation is delayed approximately 2 months following polar sunrise. MDEs occur in Kuujjuarapik in the springtime despite an incomplete development of the polar day-night cycle. In spring, as soon as air temperature attained temperatures consistently above 0 degrees C, MDEs ended immediately at all three sites. Continued studies into MDEs are warranted, but clearly an important component of future studies must focus on the origins of the variation of GEM behaviour at different sites.

Air and precipitation samples were collected in three stations located in Quebec between January 1993 and March 1996 to determine spatial and seasonal variations of several organochlorine pesticides and metabolites (alpha-HCH, gamma-HCH, HCB, gamma-chlordane, DDT, DDE, Mirex). alpha-HCH, gamma-HCH, and HCB were more or less measured in large amounts at all sites, whereas gamma-chlordane, DDT, and DDE concentrations were lower and Mirex was undetectable. Higher concentrations levels were observed in air during hot spring/summer periods except for HCB, indicating a probable temperature dependence. Ln concentrations vs reciprocal temperature plots and Henry's law determinations helped to highlight the contribution of soil and/or water volatilization of those compounds. Itwas observed that alpha-HCH came mainly from Atlantic Ocean volatilization at Mingan, whereas sources of gamma-chlordane and DDE were mostly due to volatilization from soils in southern Quebec. DDT may be present in the atmosphere by the way of transport from remote regions. Lindane sources were multiple: it may be found in the atmosphere bythe processes of transport and volatilization coming from soil or water. Finally, a negative correlation between HCB and air temperature implies that processes other than volatilization are involved in transport of this compound.

An intensive field campaign was conducted from 1 January to 31 December 2003 in St. Anicet (Quebec, Canada) using a set of Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A with 1130 and 1135 units) for the measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hg p ). This study is one of the first attempts to present the most extensive data sets of a year of continuous measurements of atmospheric mercury species. Average concentrations of GEM, RGM and Hg p in 2003 were 1.65±0.42 ng m −3 , 3±11 and 26±54 pg m −3 (mean±SD), respectively. On an average, the atmospheric mercury apportioned as follows: GEM (98.4%)>Hg p (1.4%)>RGM (0.2%). Regional atmospheric mercury sources contributed to the Southern Quebec atmospheric mercury contamination. The results showed large seasonality of GEM, RGM and Hg p (GEM: 0.37–10.4 ng m −3 ; RGM: 0–386 pg m −3 and Hg p : 0–1528 pg m −3 ). As a whole, mercury speciation concentrations are larger in wintertime than in summertime. RGM and Hg p concentrations showed the sharpest seasonal variations. Hourly variations were observed for the mercury species. Maximum RGM and Hg p concentrations were measured normally during mid-day with a Gaussian shape whereas GEM showed a bimodal shape with minimum values early in the morning. The backward trajectory model showed that atmospheric mercury speciation might be transported from local or regional sources. Also, it was observed that atmospheric mercury transformation times converting GEM to Hg p were short (∼4 h). However, atmospheric kinetics involving O 3 and OH radicals do not support such fast oxidation processes with normal concentrations.

Atmospheric concentrations of α - and γ -hexachlorocyclohexane (HCH) were measured during 1993–1995 along the St. Lawrence River in Quebec, Canada. Average α - and γ -HCH concentrations (pg/m 3 ) were St. Anicet: 93–101; Villeroy: 92–42; Mingan: 96–20, respectively. α -HCH mean concentrations were similar in all sites and appeared to be more influenced by long-range transport than local sources. γ -HCH mean levels in St. Anicet were 2 and 5 times higher than in Villeroy and Mingan, respectively. The time-series of γ -HCH air concentrations at St. Anicet and Villeroy were characterised by highly elevated springtime episodes, which are in agreement with the γ -HCH usage in Quebec as corn seed dressing pesticide. No temporal trend was observed for the α -HCH in air. Clausius–Clapeyron plots (log conc. vs. 1/ T ) showed a stronger correlation between temperature and measured γ -HCH concentrations at St. Anicet and Villeroy than Mingan. On a regional scale, the influence of the local sources of γ -HCH implied a seasonal variability in air concentrations due to its short transport, while at the background site (Mingan), the observed α - and γ -HCH concentrations in air were the result of its long-range transport and/or water/air gas exchanges.

In order to better understand MDE chemistry, which are thought to happen in the presence of halogenated (chloride and bromide) species, we have led several kinetic experiments with gaseous mercury, ozone and chlorine in Teflon bags under polar atmospheric conditions. The chlorine was expected to produce, with natural solar radiation, the reactive chloride species assumed to play a role in the MDE mechanism. The aim of the first experiment was to study the reactivity between ozone and gaseous mercury: we obtained a rate constant of (13±6)x10 -20 cm 3 /molec/s, which is roughly comparable to constants given in the literature. Concerning the second experiment, for which chlorine has been introduced, a rate constant of (6.2 ±2.2))x10 -17 cm 3 /molec/s for the reactivity of gaseous mercury was obtained. This constant is too weak to recover the atmospheric lifetime of gaseous mercury during MDE. This difference is in discussion in this paper.

The combined effect of light and hydrogen peroxide on the ability of surface snow to scavenge atmospheric mercury was investigated in Kuujjuarapik, Nunavik, Canada (latitude 55°N). Mercury concentrations in the snowpack increased five-fold upon spiking with hydrogen peroxide under solar irradiation. Anion analysis of the snow revealed the presence of chloride, which may stabilize Hg(II). Measurements of total inorganic and organic carbon showed that both kinds of carbon content decreased in the spiked irradiated snow samples.

Mercury may be one of the best-documented hazardous substances utilised by man. Still the uncovering of the global human impacts on the environment through the use and mobilisation of mercury cannot be considered complete. Recent mercury depletion events observed in the Arctic have opened the horizon to numerous new aspects on mercury fate and cycling in the environment. This chapter browses various aspects of the extremely complex cycling and fate of mercury in the perspective of mercury as a global pollutant and discusses some new emerging research fields in mercury.

Volatilization of elemental Hg represents an important Hg flux for many aquatic systems. In order to model this flux accurately, it is necessary to measure elemental Hg concentrations in air and water, as well as meteorological variables. Up to now, temporal resolution of elemental Hg analysis has been low (0.5–1 h between data points) compared to other variables used in models (5 min between data points). Here we present an analytical system that allows for the near-real time measurement (every 5 min) of dissolved gaseous mercury (DGM). This system is automated and has a detection limit of 8.5 pg l−1. By using solar radiation as a predictor of DGM concentrations in aquatic systems, we demonstrate the fast response time of the analytical system to fluctuations in ambient DGM in the St. Lawrence river, at sunrise. Complete covering of the purge apparatus and tubing resulted in a 2.6-fold decrease in the slope of the DGM versus light relationship, revealing the importance of light shielding the instrumentation to obtain realistic values.

The main objectives of this paper were to report total gaseous mercury (TGM) concentrations at four stations along the St. Lawrence River in 1998 and to give some insights regarding their fate. The TGM network stretches from latitudes 45 degrees N to 50 degrees N. TGM and ozone concentrations (used as complementary pollutant) were presented. The median TGM concentrations throughout the network varied from 1.62 to 1.79 ng/m3. Sites close to Montreal had larger TGM concentrations. Montreal surroundings appeared to be a source of TGM. The TGM concentrations were maximum in wintertime and minimum in summertime throughout the sites. However, the diurnal variations were site specific. St. Anicet and L'Assomption were more variable in terms of large concentrations, whereas Mingan and Villeroy were more variable in terms of low concentrations. Ozone and TGM concentrations were positively correlated at some sites (Villeroy, Mingan and St. Anicet) whereas they were not at L'Assomption (closest site to Montreal). Local TGM and ozone precursor sources would affect the correlation.

The paper presents an analysis of a set of data that includes both Hg profiles and modeled fluxes over water surface (using the two-layer model) and develops some insights regarding mercury water−air exchanges in Lake Ontario and the Upper St. Lawrence River (USLR). This paper presents the first in situ estimation of the water−air Hg gas exchange in Lake Ontario. It shows that water−air exchange fluxes over Lake Ontario and the Upper St. Lawrence River contributed to atmospheric mercury built-up over water bodies. TGM concentrations over Lake Ontario were significantly higher on the South shore than on the North shore, whereas the degree of saturation was higher on the North shore. Moreover TGM concentrations over water bodies were significantly higher than the reference station located on the ground surface (St. Anicet) indicated. TGM gradient measurements suggested that the South shore of Lake Ontario was mostly in evasion mode, whereas on the North shore and the Upper St. Lawrence River, both evasion a...

Abundances of heavy metals and Pb and Sr isotope ratios have been determined in precipitation collected between December 1997 and June 1999 at St. Anicet and L'Assomption, near Montreal, Canada. Median enrichment factors for the heavy metals, relative to upper crustal abundances, are all »10 indicative of an anthropogenic origin. The 206Pb/207Pb values exhibit a large variation at both stations, with values of 1.170–1.190 and 1.130–1.150 recorded during the winter and summer seasons, respectively. The Pb isotope systematics defined by most of the samples from both stations may be explained by mixing of anthropogenic emissions from U.S. and Canadian sources. Comparison of Pb isotope ratios and heavy metal abundances between the same, individual precipitation events from both stations, however, do not systematically yield similar values and may be attributable to significant, local anthropogenic sources. The 87Sr/86Sr values for precipitations also exhibit a seasonal variation at both stations with the least radiogenic values being recorded, in general, during the winter months (

Elemental Hg (Hg0) is a volatile species that is responsible for water-to-air transfer of Hg in Lake Ontario and the St. Lawrence River. We conducted two cruises in 1998 to identify spatial and temporal patterns in Hg0 levels in these systems and performed field and laboratory experiments on redox transformations of Hg. Elemental Hg concentrations were higher in Lake Ontario than in the St. Lawrence River. At stations in Lake Ontario, Hg0 levels were higher at the bottom of the water column than at the surface, whereas they were homogeneous throughout the water column of the river. Elemental Hg concentrations were generally higher in July than in September and, in contrast with experiments on inland lakes, were relatively constant during the day except for a narrow peak at sunrise. Field and laboratory experiments showed that photoreduction of Hg(II) in St. Lawrence River water was substrate limited and was influenced by visible and ultraviolet radiation. Pseudo first-order kinetics best described photoreduction, with k values between 1 and 2·h-1.

The potential source contribution function (PSCF) has been used to study the source–receptor relationships for total gaseous mercury (TGM) found in air collected at two sites along the St. Lawrence River valley, namely at St. Anicet and Mingan. TGM concentrations have been measured with high time-resolution analysers (Tekran instrument). The source–receptor analyses have been applied with regards to the seasonality of TGM. Median TGM concentrations are significantly less (χ2: α=0.01) during the summertime than other periods at both sites. A total of 12 225 trajectory end-points for St. Anicet and 4480 trajectory end points for Mingan have been used to create potential source area maps. This study identifies preferred potential sources of TGM at St. Anicet during wintertime with strongest probability stretching from the Gulf of Mexico to the southern tip of Greenland. This pattern mimics, the North American anthropogenic Hg emission inventory. Furthermore, some Eurasian mercury air mass intrusions are suggested at Mingan during wintertime. The summertime period at Mingan points out some potential sources stretching from the american mid-west to the St. Lawrence River valley as well as areas around the southern tip of the Hudson Bay.

The paper presents one year of results (1995–1996) of an on-going research study in southern Quebec with regard to mercury in precipitation. A modified rain water collector (MIC-B1) coupled to a data logger is used, in order to be able to select individual events from a remote site. A peristaltic pump coupled with an enclosed Teflon system train separates `in situ' the particulate and the dissolved phases of mercury. QA/QC sampling protocol including memory effect, percentage of recovery as well as field blanks are applied to maintain the high standards of quality. Total mercury concentrations in both phases are measured by Cold Vapour Atomic Fluorescence Spectrophotometry (CVAFS). The volume-weighted mean of total Hg concentration is 6.98 ng.l−1 (the median concentration is 6.58 ng.l−1 and the arithmetic mean is 8.26 ng.l−1). The annual total mercury deposition is about 7.6 μg.m−2. The particulate fraction accounts for a median of 26% of the total mercury concentration. According to Henry's Law, the truly dissolved mercury accounts for less than 0.5% whereas most of the dissolved fraction is expected to be in molecular complexes or colloidal form (

In order to evaluate and understand the processes of water-air and soil-air exchanges involved at background sites, an intensive field measurement campaign has been achieved during the summer of 1995 using high-time resolution techniques (10 min) at two sites (land and water) in southern Quebec (Canada). Mercury flux was measured using a dynamic flux chamber technique coupled with an automatic mercury vapour-phase analyser (namely, Tekran®). The flux chamber shows that the rural grassy site acted primarily as a source of atmospheric mercury, its flux mimicked the solar radiation, with a maximum daytime value of ∼ 8.3 ng m−2 h−1 of TGM. The water surface location (St. Lawrence River site located about 3 km from the land site) shows deposition and evasion fluxes almost in the same order of magnitude (−0.5 vs 1.0 ng m−2 h−1).The latter is influenced to some extent by solar radiation but primarily by the formation of a layer of stable air over the water surface in which some redox reactions might promote evasion processes over the water surface. This process does not appear over the soil surface. As a whole, soil-air exchange rate is about 6–8 fold greater than the water-air exchange.

Total Gaseous Mercury (TGM) data (n = 5125) measured from September 9 to November 30, 1994 in Southern Quebec with an automatic TGM analyser (Tekran®) are used to study the behaviour of TGM with ozone and the water vapour mixing ratio. Results show, as a whole, no straight-forward correlation between TGM and ozone concentrations. A significant correlation between TGM and water vapour mixing ratio was measured. Some back reduction of Hg(II) to Hgo in the aqueous phase and subsequent evaporation of Hg0 according to Henry's Law is expected. The latter correlation seems to be partly ozone dependent since under ‘clean conditions’ (ozone > 30 ppbv) the slope of TGM vs the water vapour mixing ratio is twice that during ‘polluted conditions’ (ozone > 30 ppbv) which suggests some compensation effects under polluted conditions (counteracting the back-reduction of Hg(II) to Hgo in the aqueous phase). Oxidation of TGM by ozone during high moisture conditions (water vapour mixing ratio ∼14g/kg) seems to appear at the threshold ozone concentration ⩾ 30 ppbv.

A fugacity-based model to explain the partitioning of contaminants in the environment is evaluated. Using emission inventories, air and water concentrations predicted by the model for the southwestern Quebec region generally agree with field data for phenanthrene, α-HCH, lindane, and DDT. For pyrene, air concentrations are in agreement but water concentrations were in error by a factor of nearly 20. There is also a possibility for using the model to predict emissions from known air and water concentrations. The model was run over 120 times each for phenanthrene, HCB, and lindane while randomly varying the input parameters each time. A Principal Components Analysis and a partial correlation analysis indicate that certain input parameters are more important for some compounds than for others and that log Kow is the physical-chemical property of greatest importance.

This paper presents a year of data on certain persistent organic pollutants and heavy metals in the atmosphere over a St.Lawrence River valley site (Villeroy) in 1992. These results are compared with other sites in North America: most of the concentration levels found here are characteristic of a rural site. The specific behaviours of certain species are presented and discussed with regard to physical and chemical laws as well as with the potential source and transport in the atmospheric compartment of the environment.

The southern Ontario oxidant study (SONTOS) is one of the scientific responses to the problem of ozone exceedences in the Windsor/Quebec City corridor, the strip extending from Windsor in the extreme southwest of Ontario, along the north shores of Lake Erie and Lake Ontario and down the St Lawrence valley. This corridor includes the two major metropolitan areas of Toronto and Montreal and experiences more exceedences of the Canadian ozone guideline per year than any other part of the country. The overall objective of SONTOS is to elucidate the factors which lead to these high levels. The study design is based on intensive measurements made at a site to the NNW of Toronto, with supplementary measurements at other sites and on board an aircraft. This paper, and the seven which follow, describe and interpret the measurements made in the summer of 1992. Although this summer was noteworthy for generally very low ozone concentrations, a number of interesting observations have been made which have a bearing on the oxidant phenomenon in southern Ontario. In particular, this paper describes two specific events. In one, which occurred on 6 August 1992, the intensive measurement site experienced the impact of a polluted air mass, which had apparently travelled to the site from Toronto, by way of Lake Ontario. This case has been contrasted with an event in the last week of August, in which large-scale, organised southwesterly flow led to the conditions which more typically give rise to widespread ozone episodes in the province. Events similar to the 6 August episode occurred on several occasions during the study period, and underline the very important role of the Great Lakes in ozone transport and delivery in southern Ontario.

Statistical analysis of observations made between 7 and 31 August 1992 at a rural site in Southern Ontario, Canada, is presented using principal component analysis (PCA), as well as rank and partial correlation analyses. Data for ozone, CO, SO 2 , NO, NO y (NO + NO 2 including NO x , PAN and HNO 3 ), ethane, ethylene, propane, acetylene and isoprene are employed, as well as such meteorological information as temperature, relative humidity, wind speed and direction. The analysis involved several scenarios classifying the data according to daytime, nighttime and wind direction. A normal correlation analysis suggests that isoprene might be important in the build-up of ozone in the S-W sector, whereas it is not important in the N-E wind sector. PCA show that the chemical and the meteorological variables interact differently within the different scenarios. Finally, the relationships between ozone and isoprene for both wind sectors are found to be the same when the data are subjected to a partial correlation analysis including the meteorological parameters and it is concluded that the S-W ozone-isoprene relationship might be biased by temperature.

The Canadian Atmospheric Network for Currently Used Pesticides (CANCUP) was the first comprehensive, nationwide air surveillance study of pesticides in Canada. This paper presentsthe atmospheric occurrence and distribution of pesticides including organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), acid herbicides (AHs), and neutral herbicides (NHs) during the spring to summer of 2004 and 2005 across agricultural regions in Canada. Atmospheric concentrations of pesticides varied within years and time periods, and regional characteristics were observed including the following: (i) highest air concentrations of several herbicides (e.g., mecoprop, triallate, and ethalfluralin) were found at Bratt's Lake, SK, a site in the Canadian Prairies; (ii) the west-coast site at Abbotsford, BC, had the maximum concentrations of diazinon; (iii) the fruit and vegetable growing region in Vineland, ON, showed highest levels for several insecticides including chlorpyrifos, endosulfan, and azinphos-methyl; (iv) high concentrations of atrazine and metolachlor were measured at St. Anicet, QC, a corn-growing region; (v) the Kensington site in PEI, Canada's largest potato-producing province, exhibited highest level of dimethoate. Analysis of particle- and gas-phase fractions of air samples revealed that most pesticides including OCPs, OPPs, and NHs exist mainly in the gas phase, while AHs exhibit more diversity in particle-gas partitioning behavior. This study also demonstrated that stirred up soil dust does not account for pesticides that are detected in the particle phase. The estimated dry and wet deposition fluxes indicate considerable atmospheric inputs for some current-use pesticides (CUPs). This data set represents the first measurements for many pesticides in the atmosphere, precipitation, and soil for given agricultural regions across Canada.

The objective of this paper is to give an overview of the findings of the Canadian chapter of the Northeast States and Eastern Canadian Provinces Mercury Study, which was conducted between 1995 and 1998. The Canadian chapter provided information on mercury emissions, sources and levels in air, water, biota and humans. Industry, governments and universities provided information for the Canadian chapter. The study showed that the Northeast States and Eastern Canadian Provinces (NES/ECP) is a region impacted by airborne mercury. Annual mercury emissions for the NES/ECP region are estimated to be approximately 19 t (12%) of the combined Canadian and US national anthropogenic mercury emissions of 155 t/year. 210 Pb-dated lake sediment cores from Atlantic Canada showed a mercury enrichment factor of 2.5 for coastal sites with mercury increases starting in 1860. Regional mercury wet deposition for the NES/ECP region was 7–11 μg/m 2 /year. Provincial and federal fish health advisories have been updated in the ECP for children and women of child-bearing age limiting the consumption of freshwater fish, as well as fresh or frozen shark, tuna or swordfish.

Diffuse anthropogenic and naturally mercury-enriched areas represent long- lived sources of elemental mercury to the atmosphere. The Nevada Study and Tests of the Release of Mercury From Soils (STORMS) project focused on the measurement of mercury emissions from anaturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury-enriched substrate were made September 1-4, 1997, using four micrometeorological methods and seven field flux chambers. Ambient air mercury concentrations ranged from 2 to nearly 200 ng m- 3 indicating that the field site is a source of atmospheric mercury. The mean day time mercury fluxes, durin p conditions of no precipitation, measured with field chambers were 50 to 360 ng m -2 h - , and with the micrometeorological methods we re 230 to 600 ng m- 2 h -1. This wide range in mercury emission rates reflects differences in method experimental designs and local source strengths. Mercury fluxes measured by many field chambers were significantly different (p < 0.05) but linearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and site heterogeneity had a significant influence on the magnitude of mercury fluxes. Data developed during the field study demonstrated that field flux chambers are ideal for assessment of the physicochemical processes driving mercury flux and development of an understanding of the magnitude of the influence of individual factors on flux. In general, mean mercury fluxes measured with micrometeorological methods during day time periods were nearly 3 times higher than me an fluxes measured with field flux chambers. Micrometeorological methods allow for derivation of a representative mercury flux occurring from an unconstrained system and provide an assessment of the actual magnitude and variability of fluxes occurring from an area.

An international intercomparison of micrometerological techniques and dynamic flux chamber methods applied to measure mercury fluxes was conducted from September 1 to 4, 1997, during the Nevada Study and Tests of the Release of Mercury From Soils (STORMS) in Reno, Nevada. Nine research groups from four countries met in the Steamboat Springs, Nevada Geothermal Area, to participate in the first international flux intercomparison ever attempted for mercury. The highly heterogeneous soil Hg concentrations and complex landscape within the study area (4 ha) were unfavorable for spatial intercomparison of Hg fluxes between the research groups. However, reliable and correlated Hg fluxes were measured between our micrometerological technique and a dynamic flux chamber method (r2 = 0.29), run side by side (5 m). Hg fluxes and their relationships with environmental factors were complex. After ∼90 days of dry condition, a series of storm events impacted the site and increased the soil moisture from