Atmospheric Environment (1967)最新文献

Secondary Ion Mass Spectrometry (SIMS) is used to study atmospheric particle production by an industrial source responsible for the acid precipitation phenomenon. A sampling network has been put in place at Rouyn-Noranda to collect local aerosols with cascade impactors. Aerosols have also been collected in the plume of the most important source of SO₂ in Quebec. Instruments have been developed and constructed to collect these samples. A multi-analytical technique approach permits physico-chemical analysis of individual aerosol: SIMS using a 1 μm ion probe and Scanning Electron Microscopy (SEM) coupled with an X-ray analyzer (EDAX) perform micro-analysis, whereas bulk analysis is provided by a SIMS using a 200 μm Argon ion probe. Devices used for localization of microparticles permit manipulation of samples without damaging them and allow analysis of individual aerosol particles with a SIMS after analysis with SEM-EDAX. Laser Microprobe Mass Analysis (LAMMA) is also possible. Negative and positive mass spectra, obtained with a SIMS-Ar⁺, have been analyzed with a multivariate statistical technique. Relations between these mass spectra and specific conditions existing during sampling have been determined.

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.

Major ion and trace metal (Zn, Cu, Cd, Pb, Fe, Mn) concentrations have been determined in 32 rainfall events at a North Sea coastal site over a period of 14 months (June 1987–July 1988). Precautions have been taken to avoid trace metal contamination. Trace metal depositions are positively correlated to excess sulphate deposition; the exception is Cd for which no clear relationship is evident. This is probably due to contamination of the samples with respect to Cd.

The highest trace metal concentrations are associated with small rainfall events and with the occurrence of fog and mist. Trace metal concentrations (volume weighted average) are in general agreement with earlier data. For Cd and Zn, however, they are lower and consequently it is suggested that estimates of annual deposition be revised downwards.

Oxidation reactions of SO₂ and NO₂ in clouds are considered important atmospheric acid formation processes. This paper evaluates the feasibility of detecting the occurrence of these oxidation reactions in natural clouds by means of field measurements. This evaluation is performed by calculating the changes expected in reagent and product concentrations resulting from these reactions in representative cloud types, and comparing those changes with concentration differences detectable by available analytical methods in the context of typical atmospheric variability. Four in-cloud oxidation reactions are considered: aqueous-phase reactions of SO₂ with O₃ and with H₂O₂, and gas-phase reactions of NO₂ with OH radical and with O₃, the latter leading to acid formation by reaction of N₂O₅ with cloud liquid water. The cloud types considered are fog, stratus, cumulus and mountain lee wave. This evaluation indicates that oxidation of SO₂ by H₂O₂ should be detectable in a wide variety of cloud conditions, but that oxidation of SO₂ by O₃ is unlikely to be detected by field measurements. Oxidation of NO₂ may be detectable in fog and stratus clouds, which provide long in-cloud residence times. The paper includes discussion of factors which favor or hinder detection of acid producing reactions in clouds, and reviews evidence from published field studies on the occurrence of these reactions.

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.

This paper describes the development of a severe SO² smog episode that occurred over central Europe during mid-January 1985. Data presented here summarize the knowledge about this episode as was available at an OECD workshop in October 1985. Spatial and temporal extent of the episode are assessed, emission reduction measures that were taken are described and their effectiveness is evaluated.