Gerald J. Keeler

Isotopic Composition and Fractionation of Mercury in Great Lakes Precipitation and Ambient Air

Atmospheric deposition is a primary pathway by which mercury (Hg) enters terrestrial and aquatic ecosystems; however, the chemical and meteorological processes that Hg undergoes from emission to deposition are not well understood. Hg stable isotope geochemistry is a growing field used to better understand Hg biogeochemical cycling. To examine the atmospheric Hg isotopic composition in the Great Lakes, precipitation and ambient vapor-phase Hg samples were collected in Chicago, IL, Holland, MI, and Dexter, MI, between April 2007 and September 2009. Precipitation samples were characterized by negative mass-dependent fractionation (MDF) (δ(202)Hgu2009=u2009-0.79‰ to 0.18‰), while most vapor-phase samples displayed positive MDF (δ(202)Hgu2009=u2009-0.59‰ to 0.43‰). Positive mass-independent fractionation (MIF) (Δ(199)Hgu2009=u20090.04‰ to 0.52‰) was observed in precipitation, whereas MIF was slightly negative in vapor-phase samples (Δ(199)Hgu2009=u2009-0.21‰ to 0.06‰). Significant positive MIF of (200)Hg up to 0.25‰ was also measured in precipitation. Such MIF of an even-mass Hg isotope has not been previously reported in natural samples. These results contrast with recent predictions of the isotopic composition of atmospheric Hg and suggest that, in addition to aqueous photoreduction, other atmospheric redox reactions and source-related processes may contribute to isotopic fractionation of atmospheric Hg.

Indoor and outdoor concentrations of inorganic acidic aerosols and gases.

Annular denuder-filter pack sampling systems were used to make indoor and outdoor measurements of aerosol strong H+, SO4(2-), NH4+, NO3- and NO2-, and the gaseous pollutants SO2, HNO3, HONO and NH3 during summer and winter periods in Boston, Massachusetts. Outdoor levels of SO2, HNO3, H+ and SO4(2-) exceeded their indoor concentrations during both seasons. Winter indoor/outdoor ratios were lower than during the summer, probably due to lower air exchange rates during the winter period. During both monitoring periods, indoor/outdoor ratios of aerosol strong H+ were 40-50 percent of the indoor/outdoor SO4(2-) ratio. Since aerosol strong acidity is typically associated with SO4(2-), this finding is indicative of neutralization of the acidic aerosol by the higher indoor NH3 levels. Geometric mean indoor/outdoor NH3 ratios of 3.5 and 23 respectively were measured for the summer and winter sampling periods. For HONO, NH3, NH4+ and NO2-, indoor concentrations were significantly higher than ambient levels. Indoor levels of NO3- were slightly less than outdoor concentrations.

Dry deposition of semivolatile organic compounds to lake michigan.

The Lake Michigan Urban AirToxics Study(LMUATS) was carried out from July 8 to August 9, 1991, in the southern Lake Michigan basin. The investigation was the first aimed at assessing the impact of the Chicago/Gary urban plume on the deposition of hazardous air pollutants (HAPs) to Lake Michigan. The concentrations of a large number of semivolatile organic compounds (SOCs) were measured at four locations (Kankakee, IL ; Chicago, IL ; over Lake Michigan onboard the R/V Laurentian ; and South Haven, Ml). These sites were chosen as they are often linked by air mass transport with air masses reaching South Haven, after passing through Chicago, often having an over-water path to the downwind site. The University of Michigan R/V Laurentianwas also deployed off-shore of Chicago to measure the concentrations of HAPs as they were transported out over the water. A hybrid-receptor deposition (HRD) modeling approach, which utilized measured atmospheric concentrations ata a receptor site together with observed meteorological data in a lagrangian dispersion modeling framework, was used to estimate both gas exchange across the air-water interface and particle dry deposition of SOCs to Lake Michigan. The atmospheric concentrations of selected pesticides, PCBs, and PAHs measured during the LMUATS were used as input to the HRD model. The comparison between the measured and calculated ambient concentrations gives reasonable results with measured/calculated concentration ratios in the range of 0.3-1.9 for pesticides, 0.9-2.6 for PCBs, and 0.5-3.8 for PAHs. A comparison of deposition fluxes obtained in this study with those found in literature reveals large differences for some compounds, especially for those that are primarily in the particle phase. This finding suggests that assuming constant values of critical parameters controlling the transfer processes of gaseous and particulate SOCs from the atmosphere to the water surface may result in estimates with large uncertainties.

Acid aerosol measurements at a suburban Connecticut site

Abstract Atmospheric acidity data were gathered during a year-long field project investigating the possible health effects of acid aerosol in a rural community in southwestern Connecticut. This site was chosen because the air quality is frequently influenced by pollutants transported from the New York-New Jersey corridor as well as from the Midwest U.S. An annular denuder filter-pack system utilized to obtain daily measurements of gaseous HNO 3 , HONO, SO 2 , and NH 3 ; plus fine particle SO 4 2− , NO 3 − , and H + . Fine particle mass ( d ⩽ 2.1 μm ) and PM10 (particles d ⩽ 10 μm ) were also measured. Ozone concentrations and basic meteorological data were also obtained continuously. The atmosphere was acidic with average concentrations of HONO (16 nmol m –3 ), HNO 3 (42 nmol m −3 ), and H + (42 nmol m −3 ), observed from May to September 1988. Atmospheric ammonia concentrations were fairly low averaging 34 nmol m −3 during the same period, and suggesting the neutralizing capacity of the air was significant to neutralize all the acidic species present. Neutralization of acidic particles by reactions on the filter media after collection resulted in a loss of approximately 10% of the measured particle strong acidity for the summertime period investigated. Concentrations of ozone and acidic gases tended to peak with mixed layer flow from the south-southwest while particulate acidity was highest with flow predominantly from the west-soutwest. Hourly ozone concentrations greater than 100 ppb were observed on 31 different days during the monitoring, and concentrations greater than 150 ppb measured on 14 days. HNO 3 and aerosol strong acidity (H + ) concentrations reached 174 and 199 nmol m −3 , respectively during the summer months.

Acid rain and atmospheric chemistry at Allegheny Mountain

Rain chemistry was measured in August 1983 on Allegheny Mountain and Larel Hill in southwester Pennsylvania. The average composition approximated an H/sub 2/SO/sub 5//HNO/sub 3/ mixture with a volume-weighted average pH of 3.5 and an SO/sub 4//sup 2 -//NO/sub 3//sup -/ mole ratio of 1.8. There was very little undissociated (weak) acidity and very little S(IV). The acidic rains were associated with air masses traversing SO/sub 2/ source regions west of the sites; stagnation and intervening precipitation were important influences. The geographic scale for a halving of rain SO/sub 4//sup 2 -/ concentration downwind of SO/sub 2/ sources was approx.440 km. Scavenging ratios were inferred for SO/sub 2/, aerosol SO/sub 4//sup 2 -/, and HNO/sub 3/. On average about half of the rain SO/sub 4//sup 2 -/ resulted from scavenging of SO/sub 2/, the rest from scavenging of SO/sub 4//sup 2 -/. The rain H/sup +/ was attributed about 25% to HNO/sub 3/, 55% to scavenging of SO/sub 2/, and 20% to scavenging of aerosol acid SO/sub 4//sup 2 -/. Cumulative deposition totals in rain were compared with deposition in fog and with dry deposition in the same experiment. A crude acid-deposition budget was calculated as follows: 47%, H/sub 2/SO/submorexa0» 4/ in rain; 23%, SO/sub 2/ dry deposition without dew; 16%, HNO/sub 3/ in rain; 11%, HNO/sub 3/ dry deposition without dew; 2%, HNO/sub 3/ and H/sub 2/SO/sub 4/ in fog and dew; 0.5%, aerosol dry deposition without dew. 86 references, 4 figures, 8 tables.«xa0less

Dry deposition of trace elements to lake michigan: a hybrid-receptor deposition modeling approach.

A hybrid-receptor deposition modeling approach was utilized to estimate the dry deposition flux of size segregated particles to Lake Michigan during the Lake Michigan Urban Air Toxics Study (LMUATS) from July 8 to August 9, 1991. The model estimated the flux of trace elements associated with particles in the fine (<2.5 μm) and PM10-coarse (2.5-10 μm) size range to Lake Michigan using ambient concentration measurements. The ensemble average deposition velocities for fine particles traversing Lake Michigan were found to vary considerably, by factors of 3-15. The average deposition velocities for PM10-coarse particles vary by factors of <1-3. The ratios of observed to estimated ambient concentrations ranged from 0.75 to 2 for fine fraction elements and from 0.8 to 3.6 for elements in the PM10-coarse fraction. The ratios of the estimated deposition fluxes of Ca and Pb with those measured by surrogate surfaces over Lake Michigan during the same period ranged from 0.75 to 1 for the fine fraction and from 1.4 to 2.2 for the PM10-coarse fraction. Si (517 x 10 3 kg) had the highest deposition flux among trace elements primarily of soil or crustal origin, followed by Ca (250 x 10 3 kg), Fe (208 x 10 3 kg), Al (143 x 10 3 kg), and K (73 x 10 3 kg). Trace elements primarily of anthropogenic origin had the following deposition fluxes : S, 53 x 10 3 kg ; Zn, 3.8 x 103 kg ; Mn, 2.4 x 10 3 kg ; Cu, 2.2 x 10 3 kg ; Pb, 1.01 x 10 3 kg ; Se, 1.0 x 10 3 kg ; Ni, 0.86 x 10 3 kg ; Cr, 0.5 x 10 3 kg ; and Br, 0.35 x 10 3 kg. This paper discusses the effect of mi-crometeorological parameters, particle size distributions, water wave dynamics, and the type and location of measurement sites on the estimate of dry deposition fluxes.

Transported acid aerosols measured in southern Ontario

Abstract During the period 29 June 1986–9 August 1986, a field health study assessing the acute health effects of air pollutants on children was conducted at a summer girls camp on the northern shore of Lake Erie in SW Ontario. Continuous air pollution measurements of SO 2 , O 3 , NO x , particulate sulfates, light scattering, and meteorological measurements including temperature, dew point, and wind speed and direction were made. Twelve-hour integrated samples of size fractioned particles were also obtained using dichotomous samplers and Harvard impactors equipped with an ammonia denuder for subsequent hydrogen ion determination. Particulate samples were analyzed for trace elements by X-ray fluorescence and Neutron Activation, and for organic and elemental carbon by a thermal/optical technique. The measured aerosol was periodically very acidic with observed 12-h averaged H + concentrations in the range −3 . The aerosol H + appeared to represent the net strong acidity after H 2 SO 4 reaction with NH 3 (g). Average daytime concentrations were higher than night-time for aerosol H + , sulfate, fine mass and ozone. Prolonged episodes of atmospheric acidity, sulfate, and ozone were associated with air masses arriving at the measurement site from the west and from the southwest over Lake Erie. Sulfate concentrations measured at the lakeshore camp were more than twice those measured at inland sites during extreme pollution episodes. The concentration gradient observed with onshore flow was potentially due to enhanced deposition near the lakeshore caused by discontinuities in the meteorological fields in this region.

Stochastic simulation of meteorological variability for long-range atmospheric transport—II. Long-term statistical models

Methods are developed for simulating meteorological inputs for statistical atmospheric transport models. Stochastic models are presented for the annual mean wind vector, the horizontal diffusion coefficient, the fraction of time it is raining, and the quantity of precipitation. The models are derived by aggregating the statistical models for short-term meteorological processes given in the companion paper of Small and Samson (Atmospheric Environment, 1989, 23, 2813–2824). Normal distributions are used for each variable. The normal distribution is derived directly for the mean wind vector based on the normality of short-term winds, and serves as an acceptable approximation for the other variables given their low interannual coefficient of variation. Correlation between variables is considered, including correlation between winds and precipitation, between the fraction of time it is raining and the total quantity of precipitation at a site, and between the annual precipitation quantity at multiple sites. Development and confirmation of the interannual distributions is supported by long-term meteorological data, including a nine-year backward trajectory record computed for a site in western Pennsylvania. Application of the method is demonstrated with a statistical atmospheric LRT model used to predict distributions of annual precipitation sulfates in eastern North America. Predicted interannual coefficients of variation of wet SO42− concentrations range from about 10 to 15 per cent, similar to the level of interannual variation inferred from long-term data sets.