Atmospheric Environment. Part A. General Topics最新文献

We explored the seasonal characteristics in wet deposition chemistry for two sites located at different elevations along the east slope of the Colorado Front Range in Rocky Mountain National Park. Seasonally separated precipitation was stratified into highly concentrated (high salt), dilute (low salt), or acid-dominated precipitation groups. These groups and unstratified precipitation data were related to mean easterly or westerly zonal winds to determine direction of local transport. Strong acid anion associations were also determined for the stratified and unstratified precipitation data sets. We found that strong acid anions, acidity, ammonium, and high salt concentrations originate to the east of Rocky Mountain National Park, and are transported via up-valley funneling winds or convective instability from differential heating of the mountains and the plains to the east. These influence the composition of precipitation at Beaver Meadows, the low elevation site, throughout the year, while their effect on precipitation at Loch Vale, the high elevation site, is felt most strongly during the summer. During the winter, Loch Vale precipitation is very dilute, and occurs in conjunction with westerly winds resulting from the southerly location of the jet stream.

Wetfall and bulkfall were collected on Mt Carmel, Israel, for three hydrological years, 1989–1992, using an acid precipitation sampler equipped with a moving cover. The analysis of 40 rain events indicated that in more than 65% of the events the pH was acid (<5–6) and in nearly 40% of the events strongly acid. Only in 12% of the events was the pH distinctly alkaline. Bulkfall collected on the same site had a higher pH, due to much higher Ca²⁺ and K⁺ concentrations, suggesting the effects of local aerosols emanating from calcareous soils. The relatively high Na⁺ and Cl⁻ levels and their Na⁺/Cl⁻ ratio of 0.866 indicated the marine origin of the major portion of dissolved salts. Alkaline wetfall, strongly enriched in K⁺, Cl⁻ and Na⁺, was associated with duststorms. X-ray and chemical analysis of the dryfall (dust) showed the presence of quartz, carbonates, clay minerals, feldspar, halite and gypsum. SO₄²⁻, responsible for the acidity of the wetfall, appears to be imported from Central or Eastern Europe, via the Mediterranean Sea, as suggested by back-trajectories of 26 rain events.

The use of lead as an additive in petrol decreased in Europe from the 1970s and particularly from 1988 in France. It is attempted in this paper to evaluate the impact of such a decrease on a northwestern Mediterranean coastal environment. The atmospheric Pb concentrations measured at Cap Ferrat in 1986 and 1987 are compared with the 1991–1992 results (aerosol + rainwater) obtained at the same sampling site. The 50% decrease in the leaded gasoline consumption is expressed by Pb levels reduced of 24 and 30% in aerosol and rainwater, respectively. This decrease of Pb concentrations in the atmospheric aerosol is up to 2-fold higher in urban areas, where airborne Pb is almost totally due to automotive exhaust. Indeed, most of anthropogenic Pb should deposit close to its emission area.

Blank values of 30 elements in 19 different filter types from Gelman, Millipore, Nuclepore and Whatman have been compared. The filter media were extracted with dilute nitric acid and the element contents determined by ICP-MS. Large differences in blank values were observed between different filter materials. Glass fiber filters showed high blank values for a number of elements, whereas PTFE filters were generally the cleanest. However, most filter types showed high blank values of one or more elements of environmental interest.

Galvanized steel specimens varying in size, shape, orientation angle and previous exposure history (weathered specimens) were exposed at Research Triangle Park, NC, in the absence of natural precipitation. The soluble corrosion products were assumed to represent the effects of dry deposition of airborne substances. The statistical analysis of their variability in relation to atmospheric conditions suggested that these substances included sulfur dioxide, nitric acid, hydrochloric acid, and calcium (presumably from coarse particles). The specimen characteristic most influencing inferred dry deposition was previous exposure history. Deposition of gases depended on surface condition (wetness), wind speed, temperature, and to a lesser extent, orientation angle. Deposition of particles depended on orientation angle. Loss of soluble zinc from specimens varied with specimen size to the −0.2 power, even though Reynolds numbers based on average wind speeds and specimen length were well below those classically expected to produce turbulent flow.

Businger and Oncley (1990; Flux measurement with conditional sampling, J. Atmos. Ocean Technol.7, 349–352) proposed a method to measure fluxes of scalar quantities by determining the mean concentration difference between air samples collected selectively during updrafts. This method has been tested for carbon dioxide over a growing cotton field where the fluxes were large. Simultaneous direct flux measurements were made using the eddy-correlation technique. These two techniques gave fluxes which were mostly within 20% on one of the two experiment days; however, the other day had cases with large differences. These differences are suspected to have been caused by a failure of the infra-red absorption sensor used to make the fast carbon dioxide measurements for the eddy-correlation technique.

Fifteen hazardous gas models were evaluated using data from eight field experiments. The models include seven publicly available models (AFTOX, DEGADIS, HEGADAS, HGSYSTEM, INPUFF, OB/DG and SLAB), six proprietary models (AIRTOX, CHARM, FOCUS, GASTAR, PHAST and TRACE), and two “benchmark” analytical models (the Gaussian Plume Model and the analytical approximations to the Britter and McQuaid Workbook nomograms). The field data were divided into three groups—continuous dense gas releases (Burro LNG, Coyote LNG, Desert Tortoise NH₃-gas and aerosols, Goldfish HF-gas and aerosols, and Maplin Sands LNG), continuous passive gas releases (Prairie Grass and Hanford), and instantaneous dense gas releases (Thorney Island freon). The dense gas models that produced the most consistent predictions of plume centerline concentrations across the dense gas data sets are the Britter and McQuaid, CHARM, GASTAR, HEGADAS, HGSYSTEM, PHAST, SLAB and TRACE models, with relative mean biases of about ±30% or less and magnitudes of relative scatter that are about equal to the mean. The dense gas models tended to overpredict the plume widths and underpredict the plume depths by about a factor of two. All models except GASTAR, TRACE, and the area source version of DEGADIS perform fairly well with the continuous passive gas data sets. Some sensitivity studies were also carried out. It was found that three of the more widely used publicly-available dense gas models (DEGADIS, HGSYSTEM and SLAB) predicted increases in concentration of about 70% as roughness length decreased by an order of magnitude for the Desert Tortoise and Goldfish field studies. It was also found that none of the dense gas models that were considered came close to simulating the observed factor of two increase in peak concentrations as averaging time decreased from several minutes to 1 s. Because of their assumption that a concentrated dense gas core existed that was unaffected by variations in averaging time, the dense gas models predicted, at most, a 20% increase in concentrations for this variation in averaging time.

The aerial deposition of Cd, Cr, Cu, Ni, Pb and Zn to the tidal surface of the Severn Estuary in southwest Britain was determined using the nonlinear isoplething of point data from 11 bulk-deposition sampling stations operated between January 1989 and March 1990. Previous surveys based on crude spatial bulking of deposition data from coastal sites had generated overestimates of aerial deposition of metals. The distribution of aerial deposition away from the dominant source around Avonmouth was related to weather variables. Down-estuary deposition gradients were steepest in wet westerly on-shore airflows.