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971.
M. L. Cox G. A. Sturrock P. J. Fraser S. T. Siems P. B. Krummel S. O'Doherty 《Journal of Atmospheric Chemistry》2003,45(1):79-99
There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences 相似文献
972.
D. Oettl R. A. Almbauer P. J. Sturm G. Pretterhofer 《Stochastic Environmental Research and Risk Assessment (SERRA)》2003,17(1-2):58-75
Although the strict legislation regarding vehicle emissions in Europe (EURO 4, EURO 5) will lead to a remarkable reduction
of emissions in the near future, traffic related air pollution still can be problematic due to a large increase of traffic
in certain areas. Many dispersion models for line-sources have been developed to assess the impact of traffic on the air pollution
levels near roads, which are in most cases based on the Gaussian equation. Previous studies gave evidence, that such kind
of models tend to overestimate concentrations in low wind speed conditions or when the wind direction is almost parallel to
the street orientation. This is of particular interest, since such conditions lead generally to the highest observed concentrations
in the vicinity of streets. As many air quality directives impose limits on high percentiles of concentrations, it is important
to have good estimates of these quantities in environmental assessment studies. The objective of this study is to evaluate
a methodology for the computation of especially those high percentiles required by e.g. the EU daughter directive 99/30/EC
(for instance the 99.8 percentile for NO2). The model used in this investigation is a Markov Chain – Monte Carlo model to predict pollutant concentrations, which performs
well in low wind conditions as is shown here. While usual Lagrangian models use deterministic time steps for the calculation
of the turbulent velocities, the model presented here, uses random time steps from a Monte Carlo simulation and a Markov Chain
simulation for the sequence of the turbulent velocities. This results in a physically better approach when modelling the dispersion
in low wind speed conditions. When Lagrangian dispersion models are used for regulatory purposes, a meteorological pre-processor
is necessary to obtain required input quantities like Monin-Obukhov length and friction velocity from routinely observed data.
The model and the meteorological pre-processor applied here, were tested against field data taken near a major motorway south
of Vienna. The methodology used is based on input parameters, which are also available in usual environmental assessment studies.
Results reveal that the approach examined is useful and leads to reasonable concentration levels near motorways compared to
observations.
We wish to thank Andreas Schopper (Styrian Government) for providing air quality values, M. Kalina for providing the raw
data of the air quality stations near the motorway and J. Kukkonen for providing the road site data set from the Finish Meteorological
Institute (FMI). The study was partly funded by the Austrian science fund under the project P14075-TEC. 相似文献
973.
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976.
C/B法城镇污水处理技术简介 总被引:1,自引:0,他引:1
目前我国城市污水处理普遍采用的工艺为普通活性污泥法、氧法沟法、SBR法及AB法等。这些工艺虽然运行稳定,达到可靠,但投资大、运行费用高。鉴于我国的经济发展水平与发达国家有较大的差距,污染治理的资金投入有限,提出必须研究适合我国国情的高效、低耗、低成本的城市污水处理技术。阐述了C/B法的C段和B段污水处理技术,指出由于该技术是化学强化处理技术与生物滤池技术的有机结合,综合了化学处理与生物处理技术的优点,具有可分阶段实施、投资省、运行费用低、占地少、有效去除磷、氨、氮等优点。 相似文献
977.
石家庄市地下水盐污染时空演化规律 总被引:2,自引:0,他引:2
石家庄市地下水盐污染研究具有典型示范性。在对石家庄市地下水污染特征分析的基础上,对盐污染随时空演化的规律进行了研究。结果表明,石家庄市盐污染随时间呈加重之势;在空间上形成从北向南逐渐加重的趋势。 相似文献
978.
生活垃圾对环境的污染,主要表现为垃圾渗滤液对地面水、地下水、土壤等的污染。其污染评价涉及污染物指标、污染物标准值的确定和计算模式的建立等内容。本文在总结现行环境指数评价法的基础上,探讨性地提出一套将基于生活垃圾填埋场环境监测技术标准(CJJ/T3037—95)中涉及地面水、地下水、土壤等的相关监测项和垃圾中的其他常见重要污染物,一并确定出的污染评价指标,再根据相关有毒物急性毒性分级,结合阈限值和部分浸出毒性鉴别标准值等分为5类污染指标。并在污染物的标准值确定后,进行对应于5类污染物的不同数学模式计算,得到5个分类污染指数,再比较判别这5个分类污染指数,选出最大者作为总污染指数的组合型评价垃圾污染的方法。经实例应用分析,该方法对各种污染物数据分布情况的适宜性优于现行其他常用方法。 相似文献
979.
四平市由于没有合理开发利用地下水资源,从而导致了区域性的地下水位下降。同时水质遭受污染,生态环境失去平衡,由此给四平市造成了巨大的经济损失,文章最后从多方面,不同角度论述了合理开发利用地下水的有效措施及其重要意义。 相似文献
980.
中国煤中的铀、钍和放射性核素 总被引:14,自引:0,他引:14
中国煤中的铀平均含量为3mg/kg,在某地富铀煤中检测到的最高值达25660mg/kg,其赋存状态主要是与有机质相结合的方式;钍平均含量6 mg/kg,没有发现异常现象.南方一些地区的石煤中含有较多的放射性核素,并且容易在灰渣中富集,综合利用时应加强监控,以避免产生危害. 相似文献