Atmospheric Environment (1967)最新文献

A theoretical approach is presented for the evaluation of laboratory and field performances of denuder tubes. The Differential Technique, Asymptotic Differential Technique and Absolute Differential Technique are described as solutions to the problem of measuring a reactive species in real conditions. A method, based on the analysis of the analyte deposition pattern, is proposed for an accurate determination of the denuder loading capacity and for the formulation of sound hypothesis on the structure of the deposition function and the behaviour of the interfering species (high and low reactivity inteiferents, paniculate matter). An example of the application of this method to a field data set concerning HNO₃ collection on nylon denuders is reported. The causes of the deviation of these experimental data from the model of the Gormley and Kennedy equation are identified and discussed. The method proves to be a powerful tool for prediction of the denuder behaviour in different experimental conditions and for the interpretation of field results.

Rain water and aerosol samples were collected at a few locations representative of urban and non-urban regions in India. Also, rain water samples were collected in and around a coal-fired power plant. All the rain water and aerosol samples were analyzed for major chemical components along with pH. The rain water at all the places of measurement, except near the industrial sources, has been found to be alkaline and was characterized by the presence of excess cations, particularly by Ca²⁺. The acid rain near the industrial sources was associated with excess anions, especially SO₄²⁻. The atmospheric aerosols at all the places of measurement were found rich with basic components, suggesting that the alkaline soil dust and fly ash are responsible at present for preventing the spread of acid rain in India.

During the night of 25 to 26 April 1986, the most severe nuclear accident occurred at the Chernobyl power station, about 150km north of Kiev, in the Ukraine. It resulted in the irradiation of 237 workers at dose levels justifying medical care. The most severe cases (115) were hospitalized in Moscow, with 20 patients with doses higher than 6 Gy. In most cases, the treatment was classical, based on transfusion of red cells and platelets, and heavy supportive therapy. For 19 patients with severe aplasia, transplantations of bone marrow (13) or foetal liver (6) were decided. Of these patients only one survived, which justifies the statement from U.S.S.R. physicians: after an accident the indications of grafting are limited and its risks may not justify its use. Most of the complications were related to radiation burns which involved 56 victims and resulted in fatal outcomes in at least 19 patients. The population was evacuated from a 30 km zone around the site; based on direct measurements and calculations, the collective dose was evaluated at 1.6 × 10⁴ man Sv, with an individual average lower than 250 mSv. The European part of U.S.S.R. with 75 million persons is supposed to have received a collective dose likely to increase the natural mortality by less than 0.1%. The numbers with cancer in the Northern Hemisphere might increase by 0.004% over the next 50 years.

Research Triangle Institute (RTI) has recently evaluated several sampling devices for the collection of selected volatile and toxic organic compounds and have shown the stainless steel canister to be the best overall for whole-air sampling. The toxic organics collected in the canisters were analyzed using a automated cryogenic preconcentration followed by gas chromatography with a selective detector. Stability studies of selected organics in a passivated “SUMMA” stainless steel canister revealed that the compounds are stable over a 2-week period. The design of the sample collection system, collection and analysis procedures and stability data were described.

A photochemical model has been used to quantify the sensitivity of the tropospheric oxidants O₃ and OH to changes in CH₄, CO and NO emissions and to perturbations in climate and stratospheric chemistry. Coefficients of the form ∂1n[O₃]/∂1n[X] and ∂1n[OH]/∂1n[X], where [X] = flux of CH₄, CO, NO; stratospheric O₃ and H₂O have been calculated for a number of “chemically coherent” regions (e.g. nonpolluted continental, nonpolluted marine, urban) at low and middle latitudes. Sensitivities in O₃ and OH vary with regional emissions patterns and are nonlinear within a given region as [X] changes. In most cases increasing CH₄ and CO emissions will suppress OH (negative coefficients) and increase O₃ (positive coefficients) except in areas where NO and O₃ influenced by pollution are sufficient to increase OH. Stratospheric O₃ depletion will tend to decrease O₃ (except in high NO_x areas) and increase OH through enhanced u.v. photolysis. Increased levels of water vapor (one possible outcome of a global warming) will also decrease O₃ and increase OH. We conclude that in most regions, NO, CO and CH₄ emission increases will suppress OH and increase O₃, but these trends may be opposed by stratospheric O₃ depletion and climate change. A regional survey of OH and O₃ levels suggests that the tropics have a pivotal role in determining the earth's future oxidizing capacity.

A simple General Finite Line Source Model (GFLSM), based on the Gaussian diffusion equation is formulated so that it could be used for any orientation of wind direction with roadway and also does not have the infinite line source constraint of the General Motors (GM) model. The GFLSM is also modified to predict particulate concentrations by incorporating some simple corrections. The GFLSM, along with some other models viz. GM, CALINE-3 and HIWAY-2, has been applied to predict carbon monoxide (CO) concentrations near two traffic junctions in Bombay city. Staistical analysis of the predicted and observed (coilected by Municipal Corporation of Greater Bombay) CO levels reveals that the GFLSM performs better than other models when the line source is relatively finite in length. The modified GFLSM for particulates along with the GM model has been evaluated against the data base prepared by the New York State Department of Environmental Conservation and it is observed that the new model gives satisfactory results.

Urban particulate matter (PM10) concentrations often include a large contribution from secondary aerosols, i.e. sulfate, nitrate and organic aerosols, which are formed in situ by chemical reactions of their gas phase precursors, SO_x, NO_x and reactive organic gases (ROG), respectively. For secondary organic aerosols, the results of smog chamber experiments are used to estimate the fraction of ROG that is converted into aerosols, called the fractional aerosol coefficient. An ‘emission parameter’ for secondary organic aerosol can thus be calculated for each ROG. This emission parameter is simply taken as the product of the ROG emission factor and the fractional aerosol coefficient. The secondary organic aerosol emission parameters thus estimated can then be modeled as if secondary organic aerosols formed photochemically in urban air were primary emissions.

The General Motors mobile Atmospheric Research Laboratory was situated in rural western Massachusetts in the Berkshire Mountains for 62 days during the summer of 1984. One purpose of this study was to determine the source regions of wet acid deposition for this northeastern U.S. location. First, to apportion the precursors (sulfate, sulfur dioxide and nitrate) to source regions, daily ambient air samples were analyzed for the precursors as well as for tracer species that are associated with particular sources. Factor and trajectory analyses were then used to deduce the contributions of the Midwest and the Northeast to these precursors. Finally, the contribution of the precursors to precipitation acidity was estimated by analyzing the chemical constituents in the rain during seven precipitation events. Averaged over the entire duration of the study, the data show that Northeast sources accounted for about 60% of the precipitation sulfate and nitrate, while Midwest sources accounted for about 30%. The balance (~ 10%) was accounted for by background sulfate. A more useful way of examining the data is according to the type of storm that caused the wet deposition. The site was affected by two basic types of storms: coastal low-pressure systems that traveled up the Atlantic Coast, and cold fronts that approached from the west. During the coastal lowpressure events, the Midwestern contribution to precipitation acidity was zero, as easterly flows from the Atlantic Ocean dominated. The cold front events, however, were all associated with southwesterly flows, and the Midwest contributions exceeded the Northeast contributions. During these events, the average Midwest contribution to precipitation acidity was about 50%. For all events, the ratio of sulfate to nitrate was approximately 2:1 on an equivalent basis. During the coastal lows, the relative nitrate contributions were the highest. It was estimated that particulate sulfate scavenging was responsible for about half of the sulfate in the rain, while the other half was due to in-cloud oxidation of gaseous sulfur dioxide.