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951.
为了研究大气中PM25污染特征以及其随时间变化规律,基于西安市2013年1月-2014年4月间SO2、NO2、CO、03、日最高温度(Tmax)、日最低温度(Tmin)、PM2.5、PM10等因素的监测数据.运用统计学原理和多元回归分析方法,分析了PM25的污染特征及相关因素对其产生的贡献度,进一步建立了四季的最优多元回归模型.研究结果表明,西安市年平均质量浓度124.9 μg/m3,四季的平均污染浓度从大到小依次为冬、春、秋、夏;春夏两季贡献较大的为SO2、CO;秋冬两季贡献较大的为NO2、CO;最终建立的模型的相关系数较高,模型很好地拟合了冬春两季PM2.5变化趋势,能较准确地反映了西安市PM2.5的污染特征,具有一定的理论和实用价值. 相似文献
952.
Nicholas A. Warner Gary Kozerski Jeremy Durham Martin Koerner Reinhard Gerhards Roy Campbell Debra A. McNett 《Chemosphere》2013
Contamination and analytical variation can significantly hinder trace analysis of cyclic methyl volatile siloxanes (cVMS); potentially resulting in the report of false positives at concentrations approaching detection limits. To assess detection and variation associated with trace cVMS analysis in environmental matrices, a co-operative laboratory comparison for the analysis of octametylcyclotetrasiloxane (D4), decamethylcylcopentasiloxane (D5), and dodecametylcyclohexasiloxane (D6) in sediment and biota from the Svalbard Archipelago was conducted. Two definitions of detection limits were evaluated in this study; method detection limits (MDL, matrix defined) and limits of detection (LOD, solvent defined). D5 was the only cVMS detected above both LOD (0.08–0.81 ng g−1 ww) and MDL (0.47–2.36 ng g−1 ww) within sediment by all laboratories where concentrations ranged from 0.55 to 3.91 ng g−1 ww. The percentage of positive detects for D5 decreased by 80% when MDL was defined as the detection limit. D5 was also detected at the highest frequency among all laboratories in fish liver with concentrations ranging from 0.72 to 345 ng g−1 ww. Similar to sediment, percentage of positive detects for D5 decreased by 60% across all laboratories for fish livers when using MDL (0.68–3.49 ng g−1 ww). Similar observations were seen with both D4 and D6, indicating that sample matrix significantly contributes to analytical response variation. Despite differences in analytical methods used between laboratories, good agreement was obtained when using MDL to define detection limits. This study shows the importance of incorporating variation introduced by sample matrices into detection limit calculations to insure data accuracy of cVMS at low concentrations. 相似文献
953.
954.
Crown defoliation of oak (Quercus robur and Q. petraea) was analysed in 808 trees during three forest condition surveys (1988, 1993, and 1999) in the southern Sweden. From 1988
to 1999 crown defoliation increased by more than 20%. Changes in crown defoliation were related to the pH in the upper 20–30 cm
of the mineral soils, which was closely connected to other measures of soil fertility (cation exchange capacity, CEC and C/N
ratio). Trees growing on soils with a high pH (≥4.00, in BaCl2 filtrate), high CEC and low C/N ratio had significantly lower crown defoliation than trees growing on more acid soils (pH
<4.00), indicating that less favourable soil conditions may further enhance oak decline. Age did not differentiate trees with
respect to crown defoliation, indicating that decline in crown condition was not due to an age-related increase in crown transparency.
Considering only trees younger than 100 years, a significant interaction was observed between changes in crown defoliation
and soil pH. Trees younger than 100 years old growing on more acidic soils had a greater increase in crown transparency than
trees on more basic soils between 1988 and 1999. Trees ≥100 years old had significantly higher defoliation on more acidic
than on more basic soils, however defoliation dynamics of these trees over 1988–99 was not related to soil acidity. Two biotic
agents (insect and fungal leaf infections) evaluated in this study did not prove to be important drivers of defoliation dynamics. 相似文献
955.
Salve PR Satapathy DR Katpatal YB Wate SR 《Environmental monitoring and assessment》2007,133(1-3):87-98
Stratospheric input and photochemical ozone formation in the troposphere are the two main sources determining the ozone levels
in the surface layer of the atmosphere. Because of the importance of ozone in controlling the atmospheric chemistry and its
decisive role in the heat balance of atmosphere, leading to climate change, the examination of its formation and destruction
are of great interest. This study characterized the distribution of Ground level Ozone (GLO) in Chandrapur district is lying
between 19°25′N to 20°45′N and 78°50′E to 80°10′E. Continuous ozone analyzer was used to quantify GLO at thirteen locations
fixed by Global Positioning System (GPS) during the winter of 2005–2006. The daily GLO at all the locations ranged between
6.4 and 24.8 ppbv with an average and standard deviation of 14.9 ± 6.5 ppbv. The maximum and minimum concentration occurs
during 1300–1600 h and 0300–0500 h may be due to high solar radiation facilitating photochemical production of O3 and downward mixing from the overlying air mass and in situ destruction of ozone by deposition and/or the reaction between
O3 and NO. GIS based spatial distribution of GLO in Chandrapur district is indicates that the central core of the district and
southern sites experienced elevated levels of GLO relative to the northern and western areas. The sites near by Chandrapur
city are particularly affected by elevated GLO. The average variation of GLO with temperature shows a significant correlation
of r = 0.55 indicating a direct relationship between GLO and temperature. Similarly an attempt has been made to compare the GLO
monitored data in Chandrapur district with the reported values for other locations in Indian cities. This generated database
helps regulatory agencies to identify locations where the natural resources and human health could be at risk. 相似文献
956.
Pliura A Baliuckiene A Baliuckas V 《Environmental pollution (Barking, Essex : 1987)》2008,156(1):152-161
Phenogenetic response of silver birch populations and half-sib families to separate and combined elevated ozone (O3) concentrations and ultraviolet-B (UV-B) radiation dozes was studied at juvenile age in the climatic chambers. Significant population and family effects were found for seedling height, lamina width, and leaf damage. The exposure to UV-B radiation decreased genetic variation at the stage of seed germination. Complex exposure to UV-B and O3 caused an increase of genetic variation at the stage of intensive seedling growth: seedling height genetic variation in separate treatments increased from 23.7–38.6 to 33.7–65.7%, the increase for lamina width was from 10.2–13.9 to 13.6–31.8%. Different populations and families demonstrated differing response to elevated complex UV-B and O3 exposure. Changes of genetic intra-population variation were population-specific. Such changes in genetic variation under the impact of stressors can alter adaptation, stability, and competitive ability of regenerating populations in a hardly predictive way. 相似文献
957.
A regression model based on the provincial energy consumption data was developed to calculate the monthly proportions of residential energy consumption compared to the total year volume. This model was also validated by comparing with some survey and statistical data. With this model, a PAHs emission inventory with seasonal variation was developed. The seasonal variations of different sources in different regions of China and the spatial distribution of the major sources in different seasons were also achieved. The PAHs emissions were larger in the winter than in the summer, with a difference of about 1.3-folds between the months with the largest and the smallest emissions. Residential solid fuel combustion dominated the pattern of seasonal variation with the winter-time emissions as much as 1.6 times as that in the summer, while the emissions from wild fires and open fire straw burning was mainly concentrated during the spring and summer. 相似文献
958.
Schipper AM Wijnhoven S Leuven RS Ragas AM Hendriks AJ 《Environmental pollution (Barking, Essex : 1987)》2008,151(1):17-26
Soil metal concentrations, inundation characteristics and abundances of 14 arthropod taxa were investigated in a moderately contaminated lowland floodplain along the Rhine River and compared to the hinterland. Internal metal concentrations were determined for the orders of Coleoptera (beetles) and Araneida (spiders) and were related to soil concentrations. The floodplain was characterized by larger arthropod abundance than the hinterland, in spite of recurrent inundations and higher soil metal concentrations. Most arthropod taxa showed increasing abundance with decreasing distance to the river channel and increasing average inundation duration. For Cd, Cu, Pb and Zn, significant relations were found between arthropod concentrations and concentrations in soil. Significant relations were few but positive, indicating that increasing soil concentrations result in increasing body burdens in arthropods. For arthropod-eating vertebrates, these results might imply that larger prey availability in the floodplain coincides with higher metal concentrations in prey, possibly leading to increased exposure to metal contamination. 相似文献
959.
We examined the effect of subsample size on the accuracy of information obtained from aquatic macroinvertebrate assemblage
samples. Subsamples containing 100 organisms or 300 organisms were compared on the bases of processing time and the ability
to discern ecological differences among samples. Independently of subsample size, assemblages differed between study streams,
primarily reflecting an intermittent vs. permanent stream difference, and between seasons at most streams. It required, on
average, two additional hours to process the larger subsamples. Larger subsamples gave significantly higher estimates of total
richness and Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness, but the relative abundances of many assemblage subsets
(e.g., EPT organisms and most functional feeding groups) were similar using both subsample sizes. Larger subsamples did not
typically enhance the ability to discriminate between samples from different seasons, but did more accurately distinguish
among streams when differences were subtle. They also appeared to avoid Type I error in comparisons of compositionally similar
reaches within a study stream. 相似文献
960.
It is significant to design best management practices (BMPs) and determine the proper BMPs placement for the purpose that
can not only satisfy the water quantity and water quality standard, but also lower the total cost of BMPs. The spatial rainfall
variability can have much effect on its relative runoff and non-point source pollution (NPSP). Meantime, the optimal design
and placement of BMPs would be different as well. The objective of this study was to discuss the relationship between the
spatial variability of rainfall and the optimal BMPs placements. Three synthetic rainfall storms with varied spatial distributions,
including uniform rainfall, downstream rainfall and upstream rainfall, were designed. WinVAST model was applied to predict
runoff and NPSP. Additionally, detention pond and swale were selected for being structural BMPs. Scatter search was applied
to find the optimal BMPs placement. The results show that mostly the total cost of BMPs is higher in downstream rainfall than
in upstream rainfall or uniform rainfall. Moreover, the cost of detention pond is much higher than swale. Thus, even though
detention pond has larger efficiency for lowering peak flow and pollutant exports, it is not always the determined set in
each subbasin. 相似文献