Atmospheric Environment (1967)最新文献

Large-scale spills of hazardous materials often produce gas clouds which are denser than air. The dominant physical processes which occur during dense-gas dispersion are very different from those recognized for trace gas releases in the atmosphere. Most important among these processes are stable stratification and gravity flow. Dense-gas flows displace the ambient atmospheric flow and modify ambient turbulent mixing. Thermodynamic and chemical reactions can also contribute to dense-gas effects. Some materials flash to aerosol and vapor when released and the aerosol can remain airborne, evaporating as it moves downwind, causing the cloud to remain cold and dense for long distances downwind. Dense-gas dispersion models, which include phase change and terrain effects have been developed and are capable of simulating many possible accidental releases. A number of large-scale field tests with hazardous materials such as liquefied natural gas (LNG), ammonia (NH₃), hydrofluoric acid(HF) and nitrogen tetroxide(N₂O₄) have been performed and used to evaluate models. The tests have shown that gas concentrations up to ten times higher than those predicted by trace gas models can occur due to aerosols and other dense-gas effects. A methodology for model evaluation has been developed which is based on the important physical characteristics of dense-gas releases.

Background trends of rainwater pH have been examined at ten BAPMoN stations in India for the period 1974–1984. The highest frequency of pH was observed in the range 6.5–7.0. The 621 pH values recorded were all lying between 5.18 and 9.00. At most of the stations the pH trend is decreasing towards the acid range. The overall probability of occurrence of acid rain was found to be about 2% (pH < 5.6). Very high pH values have also been observed at some stations, specially at Jodhpur, Allahabad and Srinagar, due to incursions of soil particles rich in Ca²⁺, Mg²⁺, Na⁺ and K⁺ ions.

A hydrostatic wind model used in conjunction with a grid-type air pollution model is applied to the diffusion experiments which were carried out by the Japan Atomic Energy Research Institute at Mt. Tsukuba, an 870 m mountain located to the north of Tokyo, Japan. The model can qualitatively simulate the flow pattern and concentration distribution, including divided plumes over the mountain. Even though the horizontal scale of the topography is theoretically not sufficiently larger than the vertical scale, the calculated concentration results are in no serious disagreement with those observed. The concentration distribution is quite sensitive to the surface soil temperature. This is as important as the ambient wind velocity and the vertical temperature profile.

A novel liquid Chromatographic method is presented. It saves both time and solvent. A1₂O₃ is used as the column packing material. A mixture of hexane and benzene (3:1 v/v) and benzene are used to develop the column sequentially. Alkane fraction, aromatics fraction (PAH) and polar component fraction are obtained. PAH is determined by Capillary Column Gas Chromatography. PAH in air paniculate matter of a Chinese city were determined by DCC. Recovery of 10 PAH is 81–99% (average 87.5%). The coefficient of variation of concentration is 4–21% (average 14%). This method is cost-effective; it takes $\text{1}\text{4}$ of the time and $\text{1}\text{10}$ solvent volume compared with conventional liquid chromatography.

The objective of this research was to measure the initial effective cleaning rates (ECRs) of selected air cleaners for removing nitrogen dioxide (NO₂) and six representative volatile organic compounds (VOC) from air. Four portable air cleaners, representing different principles of particle removal and incorporating activated carbon, were investigated. Experiments were conducted in a closed room-size environmental chamber using analyte concentrations similar to those reported in residences. Effects of relative humidity, temperature, filter particle loading and saturation of the adsorbents on the ECRs were not investigated in this preliminary study. However, the effect of extended usage was investigated for one air cleaner.

Two of the air cleaners were found to be reasonably effective initially in removing NO₂ and five of the six VOC. These two devices had relatively high flow rates and the greatest amounts of activated carbon. None of the devices removed dichloromethane, the VOC with the highest vapor pressure. One air cleaner emitted 1,1,1-trichloroethane and formaldehyde. After being used in a residence for 150 h, the ECRs for the air cleaner which had the highest initial values decreased to 50% or less of the initial ECRs. This use was only about 15% of the recommended filter lifetime. Conversion of NO₂ to NO was also observed for this device but only after it had been used in the residence.

The spatial and temporal variability of SO₄²⁻ concentrations in precipitation over the eastern U.S. during the period 1981–1986 was examined through the use of principal component analysis. Application of Kaiser's Varimax orthogonal rotation led to the delineation of seven contiguous subregions, each displaying statistically unique SO₄²⁻ concentration characteristics. These seven statistically significant modes of variability, which together accounted for 74.2% of the total variance, corresponded well with major SO_x emission patterns. Examination of the time series associated with each subregion revealed a general seasonality in which periods of high concentrations are more likely during the summer, while periods of low concentration are more likely during the winter. This seasonal cycle, however, was more prevalent in those subregions which contained few major emissions, and was less prevalent and often obscured by perturbations in those subregions which contained major emissions.

The effects of including a parameterization of subgrid-scale dispersion and chemical processes in the Eulerian-Lagrangian transport model of Hess are investigated. A case chosen to maximize the subgrid-scale effects is studied, and it is found that the predicted change in maximum O₃ when subgrid-scale processes are included is small (∼5%) compared with predictions based on direct injection of point emissions. It is also found for this model that the parameterization of subgrid-scale processes is not necessary to provide numerical stability in calculating the chemical kinetics.

Ozone concentrations were monitored above a 30 m Douglas-fir canopy at Cedar River, Washington from 1 April to 30 September in 1986 and 1987. Maximum average hourly ozone concentrations were similar in both years. Ozone concentrations exceeded 0.12 ppm on 2 days in 1986 and 1 day in 1987. Fifteen and 14 days had ozone concentrations greater than or equal to 0.08 ppm in 1986 and 1987, respectively. Ozone concentrations were positively related to daily radiation and maximum daily air temperature. However, only 46 per cent of the variance in ozone concentration in 1986 could be explained by solar radiation and even less was explained by maximum temperature (26%). In 1987, 51 and 54 per cent of the variation in ozone concentration was explained by solar radiation and temperature, respectively. Maximum average hourly ozone concentrations peaked near 1500 h (Pacific Standard Time) for days > 0.06 ppm with minimum values near 0600 h. Highest concentrations were observed when the wind was blowing from the northwest from the Seattle area indicating that photochemical oxidation of NO_x was a major source of elevated ozone. If the data represent current levels of ozone some potential for forest damage exists in Puget Sound forests.

The impact of a large NO_x point source on photochemical smog in Melbourne is examined through the use of a numerical model described by Hess. Over most of the Melbourne Airshed the NMHC/NO_x ratio is found to be less than 10, in agreement with the results of Evans et al. For these cases trajectories passing through the Newport Power Station exhibit a decrease in ozone (compared to background values) of about 0.02 ppm and an increase in nitrogen dioxide of about the same amount due to Newport's emissions. This result confirms a preliminary finding by Form and Substance (1982).

However, worst case scenarios have not been previously studied. Measurements indicate that any trajectory that links the high NO_x from Newport and the high NMHC from Pt Cook will result in a worst case. The windfield observations reported here show the existence of a topographically generated mesoscale eddy in the airshed, as proposed by Spillane (1978, Clean Air12, 50–56.), and its location tends to link Newport and Pt Cook. Simulation of two cases indicates that under worst case conditions Newport's emissions increase the ozone concentration by 0.01–0.04 ppm. These conditions are estimated to occur on one day in four to one day in three of high oxidant days in Melbourne.

This study was performed primarily to account for the differences between ice forming activity of fly ashes from different sources.

Ten samples of fly ash from ten various power plants on our territory were examined by X-ray powder diffraction to determine the contents of quartz, mullite and hematite. The quartz content varied in the range 5–17% depending on the type of coal and mullite contents varied from 0 to 22%.

The amounts of crystalline phases were compared with data about composition of ashes obtained by elemental chemical analysis. The distribution of silica and aluminia between crystalline phases and amorphous phase is discussed in connection with the origin of fly ash and with the differences observed in the ice forming activity. A direct relationship between the freezing temperatures and the contents of crystalline fractions in the samples does not exist but the presence of mullite and/or hematite in the concentrations found in samples could account for the observed freezing temperatures of droplets containing some of the samples.