Robert J. Carley

Atmospheric mercury monitoring survey in Beijing, China.

With the aid of one industrial, two urban, two suburban, and two rural sampling locations, diurnal patterns of total gaseous mercury (TGM) were monitored in January, February and September of 1998 in Beijing, China. Monitoring was conducted in six (two urban, two suburban, one rural and the industrial sites) of the seven sampling sites during January and February (winter) and in four (two urban, one rural, and the industrial sites) of the sampling locations during September (summer) of 1998. In the three suburban sampling stations, mean TGM concentrations during the winter sampling period were 8.6, 10.7, and 6.2 ng/m3, respectively. In the two urban sampling locations mean TGM concentrations during winter and summer sampling periods were 24.7, 8.3, 10, and 12.7 ng/m3, respectively. In the suburban-industrial and the two rural sampling locations, mean mercury concentrations ranged from 3.1-5.3 ng/m3 in winter to 4.1-7.7 ng/m3 in summer sampling periods. In the Tiananmen Square (urban), and Shijingshan (suburban) sampling locations the mean TGM concentrations during the summer sampling period were higher than winter concentrations, which may have been caused by evaporation of soil-bound mercury in warm periods. Continuous meteorological data were available at one of the suburban sites, which allowed the observation of mercury concentration variations associated with some weather parameters. It was found that there was a moderate negative correlation between the wind speed and the TGM concentration at this suburban sampling location. It was also found that during the sampling period at the same site, the quantity of TGM transported to or from the sampling site was mainly influenced by the duration and frequency of wind occurrence from certain directions.

Detection and remediation of soil and aquifer systems contaminated with petroleum products: an overview

Fate of organic chemicals in the subsurface strata is not very well understood. It has only been a decade or two that environmental scientists are focusing their attentions on remediating sites that are contaminated with organic chemicals. Different routes of soil and groundwater contamination by petroleum hydrocarbon compounds and their partitioning into gaseous, aqueous and pure phases in the subsurface strata are discussed. A summary of the techniques used for treating hydrocarbon-contaminated soil and groundwater and their application limitations are presented. United States Environmental Protection Agencys (US-EPA) methods 8260, 8270 and 418.1 for detection and quantitation of petroleum range hydrocarbon in soil and aqueous samples and some recently developed mathematical models used to predict the fate and transport of petroleum range compounds in aquifer systems are briefly discussed. Results of some toxicological studies on light and heavy petroleum hydrocarbon are presented. It is concluded that reaching an environment free of hydrocarbon contamination needs broad public understanding of the risks associated with these compounds. Proper management and careful handling of petroleum products reduces the possibility of spills. Replacing old and leaking underground storage tanks with new double wall tanks equipped with leak detectors and cathodic protection could significantly improve the quality of our precious and fragile groundwater resources.

Atmospheric deposition of nitrogen along the Connecticut coastline of Long Island Sound: a decade of measurements

Four monitoring stations were established along the Connecticut coastline to study the atmospheric deposition of nitrogen into the Long Island Sound (LIS). Two stations at Bridgeport and Hammonasset were set up in 1991. Two additional ones have been in full operation since 1997 at Old Greenwich and Avery Point. Measurements were taken continuously from 1991 through 1994, and from 1997 through 1999. Nitrogen species including (nitrate/nitrite), ammonium, nitric acid gas and total nitrogen (since 1997) in air and precipitation were collected and used to infer ambient concentrations and dry and wet deposition flux densities, with independently collected meteorological data. Statistical procedures were employed to analyze the spatial and temporal variations of the weekly data and quarterly means for the two sampling periods of 1991–1994 and 1997–1999. The deposition flux densities of total nitrogen during 1991–1994 were 6.80 and 24.36 mg N m � 2 wk � 1 , respectively, for dry and wet forms averaged over the two sites of Bridgeport and Hammonasset. During 1997–1999, the overall mean weekly wet and dry depositions of total nitrogen over the four sites were 4.28 and 23.64 mg N m � 2 wk � 1 , respectively. In dry deposition, nitric acid gas was predominant and explained more than 70% of the total dry flux, while in wet deposition nitrate/nitrite was the major contributor (40–60%). Most of the collected nitrogen quantities were higher during warm months, especially from June through September, indicating higher emission rate, scavenging efficiency, and surface uptaking at warmer temperature. The ambient concentration and dry deposition peaked at Bridgeport, and the maximal wet deposition was observed at Old Greenwich. The spatial variation of the dry deposition quantities was affected by potential local emission sources, while the geographic gradient of the wet deposition was largely attributed to the proximities of the sites to the New York–New Jersey metropolitan area. Comparisons of nitrogen quantities between the two sampling periods revealed that the dry and total depositions at Hammonasset decreased, while there were no discernible changes at Bridgeport. r 2002 Elsevier Science Ltd. All rights reserved.

A regional scale modeling study of atmospheric transport and transformation of mercury. I. Model development and evaluation

Abstract A three-dimensional regional scale air quality model was developed to study the atmospheric transport, transformation and deposition of mercury (Hg) by formulating and incorporating mercury chemistry, cloud processes, and air–surface exchanges into the framework of Sarmap Air Quality Model (SAQM). Three mercury species were included: elemental mercury Hg(0), divalent mercury Hg(II), and particulate mercury Hg(p). Precipitating clouds, co-existing non-precipitating clouds, and fair weather clouds were considered in modeling the in-cloud transformation processes. A formulation of bi-directional air-surface exchange of elemental mercury was used for emission from, and dry deposition to, natural surfaces. Preliminary evaluation of the model was conducted by comparing six major weekly output variables, including ambient Hg concentrations and Hg concentration in precipitation, with corresponding measurements at eight monitoring stations in Connecticut for a summer week and a winter week. Model predictions of surface-level gaseous Hg concentrations were close to measured levels, agreeing to within 12% on average, about half the estimated error in measurements. The predicted Hg concentrations in precipitation were 50% higher than measured values on average, slightly lower than the estimated 60% error in measurements. The model was shown to be capable of predicting hourly concentrations and deposition fields of the three Hg species as well as in-cloud transformation of Hg(0) by each of the three cloud types, and useful in analyzing the effects of various controlling factors on the transport and transformation of Hg species in the atmosphere.

A regional scale modeling study of atmospheric transport and transformation of mercury. II. Simulation results for the northeast United States

Abstract This paper presents the results of a simulation study of the transport, transformation, and deposition of atmospheric mercury (Hg) in the northeastern United States for 5 consecutive days in summer 1997, using the newly developed regional scale air quality model described in part I. Hourly ambient concentrations, in-cloud transformations, and deposition fluxes were predicted for each of the three mercury species: Hg(0), Hg(II), and Hg(p). The simulation results showed that surface level Hg concentrations over the land varied diurnally with the boundary layer structure. The Hg concentrations over the coastal ocean water were strongly influenced by the concentrations over land because of atmospheric advection by the prevailing westerly winds in the region. Over 90% of the ambient air concentration of Hg was in the form of Hg(0) vapor. Approximately half of the total Hg in wet deposition originated from ambient Hg(0), while the predominant species in dry deposition was Hg(II). The simulation predicted more dry deposition ( 31 kg day −1 ) than wet deposition ( 18 kg day −1 ) over the region for the simulation period. The re-emission of Hg(0) from land and water surfaces ( 46 kg day −1 ) was of the same magnitude as the total anthropogenic emission ( 55 kg day −1 ) within the region. Both precipitating and non-precipitating clouds were shown to be important media for in-cloud transformation of Hg(0). It was predicted that transformation and redistribution caused a net gain of Hg(p) at the upper troposphere during rain events. Over the region of simulation, the amount of Hg(0) transformation in non-precipitating clouds was 30% higher than in precipitating clouds. In co-existing non-precipitating clouds, the amount of Hg(0) transformation in the lower and upper troposphere was approximately equal.

Long-term investigation of atmospheric mercury contamination in Connecticut

Atmospheric mercury was monitored from January 1997 through the end of December 1999 in eight sampling locations in Connecticut. Four sampling locations were chosen along the shores of Long Island Sound and four were chosen in interior sections of Connecticut. Sampling locations were chosen to represent both rural and urban sectors. Average concentrations of gaseous and particulate mercury were found to be 2.06 ng/m3 and 10.5 pg/m3, respectively. The weekly average wet deposition fluxes of mercury and methylmercury over the three-year sampling period were measured to be 611 and 11 microg/ha/week, respectively. Concentrations of gaseous, particulate and wet flux of mercury were found to be significantly higher in urban areas than the rural sampling locations. There was, however, no significant difference between the mean gaseous and particulate concentrations of mercury in coastal and inland sampling locations. No significant difference was observed either between the wet fluxes of total mercury in coastal and inland sampling locations and there was no spatial gradient for mercury concentration and deposition. The data of this study suggest that vehicular traffic and localized emission sources in urban areas play a significant role in determining the atmospheric concentration of mercury in Connecticut.

Relationships between Concentrations of Mercury in Largemouth Bass and Physical and Chemical Characteristics of Connecticut Lakes

Abstract Concentrations of total mercury were determined for axial muscle tissue of 438 largemouth bass Micropterus salmoides from 46 lakes representing five regions in Connecticut to determine relationships between mercury concentrations and lake characteristics and to assess regional differences in mercury concentrations. Expected concentrations of mercury (EHg) predicted for a length of 356 mm for each population ranged from 0.103 to 0.795 μg/g wet weight. Principal components analysis revealed that, in general, two types of lakes were represented in the data set and were grouped based on hydrologic characteristics. Type-II lakes (artificial impoundments) had a significantly lower mean retention time than type-I lakes (natural drainage lakes) and a significantly larger mean watershed area, watershed area : surface area ratio, watershed area: lake volume ratio, and shoreline development index. Mean EHg was approximately 20% higher in type-II lakes (0.514 μ/g wet weight) than in type-I lakes (0.410 μg/g ...

Estimation of wet, dry and bulk deposition of atmospheric nitrogen in Connecticut

Atmospheric nitrogen species including NO3-, NH4+ and total nitrogen in air and precipitation samples were collected with low-volume filter packs and wet deposition collectors from March 1999 through the end of December 2000 in seven sampling locations in Connecticut. Three sampling locations were chosen along the shores of Long Island Sound and four were chosen in interior sections of Connecticut. Sampling sites were chosen to represent both rural and urban sectors. Wet deposition flux of nitrogen species was calculated using wet concentrations, the volume of collected precipitation and the opening surface area of the Aerochemetrics wet deposition collector. The dry deposition flux of nitrogen species was estimated with the application of the dry deposition inferential model (DDIM). Bulk deposition of nitrogen was collected with the aid of a device based on the Swedish IVL Sampler. The dry deposition fluxes of NO3-, NH4+ and total nitrogen were found to be significantly higher in urban areas than the rural sampling locations. There was, however, no significant difference between the wet deposition fluxes of different nitrogen species in rural and urban sampling locations. When inland and coastal sites were compared, the dry deposition fluxes of NH4+ and total nitrogen were significantly higher in inland locations and there was no significant difference between coastal and inland sampling locations for wet deposition fluxes of nitrogen species. No significant difference was observed between the bulk deposition and the sum of the wet and dry deposition fluxes of total nitrogen at rural sampling locations. In urban sampling locations, the bulk deposition flux of total nitrogen was significantly lower than the sum of dry and wet deposition fluxes. There appears to be a similar seasonal trend in wet and dry deposition fluxes of total nitrogen in Connecticut with high and low deposition fluxes occurring in summer and winter periods, respectively.

A sensitivity analysis on the atmospheric transformation and deposition of mercury in north-eastern USA

This paper presents the results of a sensitivity analysis on the factors that affect dry and wet deposition of atmospheric mercury (Hg), using a regional scale air quality model. Simulations were conducted for the north-eastern USA during a summer week and a winter week in 1997. Simulation results for the summer week and the winter week in general showed similar responses to changes in emission, environmental conditions, and alternative chemical mechanisms. Reduction of the ambient concentrations of soot or ozone was shown to reduce the wet deposition of Hg. When averaged over the summer and the winter week, the total deposition to the simulation domain would be reduced by 26% by reducing Hg emission from anthropogenic sources within the domain by 50%. For individual grids, however, only locations near local sources obtained noticeable reductions in ambient concentration and wet deposition due to the influence of re-emission from the natural surfaces and regional/global scale transport. The reduction in deposition would reach 36% if all Hg(II) emitted from anthropogenic sources were attached to particles. The total deposition was predicted to decrease by 22% when the gas phase Hg(II)-Hg(p) partitioning was included in the model. Only small changes in total deposition were observed by including the gas-phase ozone-Hg(0), reaction and the aqueous phase chlorine-Hg(0), reaction, and by lowering ambient concentrations of Hg(II) and Hg(p) at the upper lateral boundaries. During the summer week, Hg(II) deposition contributed 40% or more to the total deposition. The contribution increased to 70% in the winter week.

The effect of precipitation amount and atmospheric concentrations on wet deposition fluxes of oxidized and reduced nitrogen species in Connecticut

The effects of precipitation amount and atmospheric concentrations of inorganic nitrogen species on precipitationconcentrations and wet fluxes of oxidized and reduced nitrogen inConnecticut were studied for a period of 152 weeks (7 February,1997 through 31 December, 1999). The annual volume weighted mean(VWM) concentration in precipitation of oxidized and reducednitrogen varied with precipitation amount between sites andyears. To investigate the effect of varying precipitation amountand mean monthly temperatures on concentrations of inorganicnitrogen species in precipitation, the precipitation events wereclassified into seven groups and each year was divided into twowarm and cold sampling periods. Increasing precipitation amounthad a substantial decreasing effect on the VWM concentration ofnitrate and ammonium ions in precipitation. The highest VWMconcentrations of oxidized and reduced nitrogen in precipitationwere found in the lower weekly precipitation range of 0 to 0.5 cm. The results of this study indicated that precipitationamount was one of the main factors affecting volume weighted meanconcentrations and fluxes of oxidized and reduced nitrogen. Chemical composition of inorganic nitrogen species in theatmosphere showed that during warm and cold sampling periodsreduced nitrogen was the predominant atmospheric specie, andoxidized nitrogen was the predominant wet specie in precipitationat all sampling sites.