Mercury in the Arctic atmosphere: an analysis of eight years of measurements of GEM at Alert (Canada) and a comparison with observations at Amderma (Russia) and Kuujjuarapik (Canada)

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.     

The Northeast States and Eastern Canadian Provinces mercury study: a framework for action: summary of the Canadian chapter

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. 210Pb-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 microg/m2/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.     

Mémorisation de textes chez des élèves du primaire et du secondaire.

Examined immediate and delayed recall of a narrative and an informative text by 5th, 9th, and 12th graders. The younger Ss produced shorter recall than the 2 older groups. Informative text led to shorter recall than narrative text at all 3 scholastic levels. Long-term results indicated the same effects for type of text. In the short term, 5th graders produced less similar propositions than did the 2 older groups, suggesting that they had more difficulty accepting the idea that a rewording could be semantically equivalent to a literal sentence. This finding indicates that the capacity to produce synonyms and paraphrases, necessary for the elaboration of summaries, increases with age. This tendency also increased with the passage of time. Differences were found in the quantity of these types of production between the 2 high-school groups, with the 9th graders producing less similar propositions than the 12th graders. (French & English abstracts) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ebullition of hydrogen, carbon monoxide, methane, carbon dioxide and total gaseous mercury from the Cornwall Area of Concern

This paper reports the first ebullitive fluxes of hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and total gaseous mercury (TGM) from the Cornwall Area of Concern (CAC). Although sediments were contaminated with mercury, bubbling was a negligible source of mercury for the global atmosphere. Indeed, the average emission of TGM through ebullition was 0.04 pg m(-2) h(-1). Measurements of H2, CO, CH4 and CO2 trapped gas concentrations and fluxes were used as indicators of diagenesis processes. The CAC represented a significant regional source of CH4 since the estimated ebullitive fluxes (3.5 mg m(-2) h(-1)) were similar to the CH4 emissions measured above typical flooded freshwater wetlands. As molecular diffusion is known as the main pathway of CO2 transport from water to the atmosphere, CO2 ebullitive fluxes were weak (0.39 mg m(-2) h(-1)). Bubbling of CO (1.6 microg m(-2) h(-1)) was 10 folds less important than CO fluxes measured over flooded freshwater wetlands. Finally, H2 emissions (0.001 microg m(-2) h(-1)) were negligible since the level of this trace gas is tightly regulated by microorganisms in anaerobic environments.     

Atmospheric particle evolution during a nighttime atmospheric mercury depletion event in sub-Arctic at Kuujjuarapik/Whapmagoostui, Québec, Canada

During a field experiment at Kuujjuarapik/Whapmagoostui (55.31 degrees N, 77.75 degrees W), Quebec, we observed increases of concentrations of particles with diameters larger than 0.3 microm in the ambient air during a nighttime atmospheric mercury depletion event (AMDE). These increases were strongly correlated with decreases of ozone and atmospheric mercury, and we also observed a change in the particle size distribution during this AMDE. Assuming that these phenomena imply either a chemical link or an association through transport, we also studied the nature of this AMDE. We hypothesize that the observed AMDE was a result of an influx of already depleted air masses and that it was not a product of local chemical reactions.     

Dissolved gaseous mercury concentrations and mercury volatilization in a frozen freshwater fluvial lake

In situ mesocosm experiments were performed to examine dissolved gaseous mercury (DGM), mercury volatilization, and sediment interactions in a frozen freshwater fluvial lake (Lake St. Louis, Beauharnois, QC). Two large in situ mesocosm cylinders, one open-bottomed and one close-bottomed (no sediment diffusion), were used to isolate the water column and minimize advection. Mercury volatilization over the closed-bottom mesocosm did not display a diurnal pattern and was low (mean = -0.02 ng m(-2) h(-1), SD = 0.28, n=71). Mercury volatilization over the open-bottom mesocosm was also low (mean = 0.24 ng m(-2) h(-1), SD = 0.08, n=96) however a diurnal pattern was observed. Low and constant concentrations of DGM were observed in surface water in both the open-bottomed and close-bottomed mesocosms (combined mean = 27.6 pg L(-1), SD = 7.2, n=26). Mercury volatilization was significantly correlated with solar radiation in both the close-bottomed (Pearson correlation = 0.33, significance = 0.005) and open-bottomed (Pearson correlation = 0.52, significance = 0.001) mesocosms. However, DGM and mercury volatilization were not significantly correlated (at the 95% level) in either of the mesocosms (significance = 0.09 in the closed mesocosm and significance = 0.9 in the open mesocosm). DGM concentrations decreased with depth (from 62 to 30 pg L(-1)) in the close-bottomed mesocosm but increased with depth (from 30 to 70 pg L(-1)) in the open-bottomed mesocosm suggesting a sediment source. DGM concentrations were found to be high in samples of ice melt (mean 73.6 pg L(-1), SD = 18.9, n=6) and snowmelt (mean 368.2 pg L(-1), SD = 115.8, n=4). These results suggest that sediment diffusion of mercury and melting snow and ice are important to DGM dynamics in frozen Lake St. Louis. These processes may also explain the lack of significant correlations observed in the DGM and mercury volatilization data.     

Abiotic source of reactive organic halogens in the sub-arctic atmosphere?

Recent theoretical studies indicate that reactive organic iodocarbons such as CH2I2 would be extremely effective agents for tropospheric Arctic ozone depletion and that iodine compounds added to a Br2/BrCl mixture have a significantly greater ozone (and mercury) depletion effect than additional Br2 and BrCl molecules. Here we report the first observations of CH2I2, CH2IBr, and CH2ICl in Arctic air, as well as other reactive halocarbons including CHBr3, during spring at Kuujjuarapik, Hudson Bay. The organoiodine compounds were present atthe highest levels yet reported in air. The occurrence of the halocarbons was associated with northwesterly winds from the frozen bay, and, in the case of CHBr3, was anticorrelated with ozone and total gaseous mercury (TGM), suggesting a link between inorganic and organic halogens. The absence of local leads coupled with the extremely short atmospheric lifetime of CH2I2 indicates that production occurred in the surface of the sea-ice/overlying snowpack over the bay. We propose an abiotic mechanism for the production of polyhalogenated iodo- and bromocarbons, via reaction of HOI and/or HOBr with organic material on the quasi-liquid layer above sea-ice/snowpack, and report laboratory data to support this mechanism. CH2I2, CH2IBr, and other organic iodine compounds may therefore be a ubiquitous component of air above sea ice where they will increase the efficiency of bromine-initiated ozone and mercury depletion.     

Polycyclic aromatic hydrocarbons in the air in the St. Lawrence Basin (Québec)

High-volume air samples were collected from 1993 to 1996 in rural areas of Québec to investigate on the levels and the vapor-particle partitioning of polycyclic aromatic hydrocarbons (PAHs). Ranges for the mean concentrations of total PAHs (ng m(-3)) were as follows: Villeroy, 3.31-18.92; St. Anicet, 7.57-22.84; and Mingan, 0.50-0.53. Lower molecular weight PAHs predominated at all locations. Particle-gas partition coefficients (Kp) were in good correlation with their vapor pressures (r2 = 0.79-0.97) with slopes deviating from the expected value of -1. The curve of the fractions of PAHs on particles in St Anicet in 1995 fell on that of Lake Superior. In St. Anicet, fractions of phenanthrene, fluoranthene, pyrene, and chrysene on particles were close to those calculated from the soot-air partition coefficient (KSA). At all sites the mean ratios of particulate PAH of the same molecular weight but of very different reactivities were similar during the same sampling days, suggesting that particle-bearing PAHs in Villeroy and Mingan were of the same nature as those found in St. Anicet where adsorption onto soot particles was the major mechanism. Furthermore, the enthalpies of desorption for the predominant PAHs were close at all sites.     

Pesticides in fluvial wetlands catchments under intensive agricultural activities

A survey on pesticides (73 compounds) in the Bay St. Fran?ois wetland and its catchment (part of the wetlands of Lake St. Pierre area [St. Lawrence River, Québec]) was achieved in 2006. The metabolites as well as the active ingredients of pesticides (11 compounds) were detected in the wetland and its catchment. This wetland ecosystem was active in the degradation of agricultural pesticides (e.g., atrazine). The measured pesticides were individually below the criteria for aquatic species in natural water, except chlorpyrifos. Overall, the pesticides lost from agricultural field towards the streams were <1% of the quantity applied. The environmental fates of the pesticides were found to vary according to the size of the watershed. Over large catchments, half-life times were important in terms of global loss from the agricultural lands to wetlands whereas over small catchments, soil organic carbon/water distribution coefficient (Koc) was an important term for pesticides losses to water system since half-life times were not limiting factors.     

Pesticides in the atmosphere across Canadian agricultural regions

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.