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311.
为提高重污染天气应对的科学性和精准度,2019年7月生态环境部制定重污染天气应对“绩效分级、差异化管控”措施.为应对9月底至10月初的重污染过程,京津冀及周边共68个城市启动重污染预警,该措施得以首次实践.通过时间序列断点回归方法对该措施效果进行评估发现,空气质量改善存在滞后的现象,SO2、 NO2和CO这3个气态污染物改善速度较快,对涉及二次生成的O3和PM2.5两个污染物见效速度相对较慢. 10月1日恰逢在北京举办庆祝中华人民共和国成立70周年阅兵式,对10月1日当天进行评估,发现与假如不采取措施的情形相比,重污染应急措施使北京市PM2.5、 NO2和CO日均浓度显著下降,下降幅度分别为54.1%、 62.4%和25.8%.如果不采取重污染应急措施,北京10月1日上午可能出现中重度污染,但实际上空气质量保持在良的水平.区域启动预警的68城市PM2.5、 PM10、 NO2、 SO 相似文献
312.
为研究CO2驱替CH4过程中注气压力对气体解吸特性的影响,采用自主搭建的驱替实验平台,在0.6,0.8,1.0 MPa不同注气压力下进行驱替实验,研究CO2驱替CH4过程中煤层温度、气体浓度、置换效率和渗透率等变化规律。实验结果表明:提高CO2注气压力可提高CO2置换驱替煤层CH4的效果。随着注气压力增大,CH4累计解吸量增大,CO2突破时间越短,CO2封存量越大,置换效率升高,驱替比下降。注气压力为0.6,0.8,1.0 MPa时,CH4累计解吸量分别为90.2,94.1,97.8 L;CO2封存量分别为19.73,19.92,20.21 mL/g;置换效率由76.9%上升到80.2%再到82.9%,驱替比由3.28下降到3.17再到3.09。注气驱替CH4过程中煤层温度升高,可分为低速升温、高速升温和趋于平缓阶段。煤层温度最高变化量分别为9.4,11.5,12.7 ℃。同一注气压力下,煤层渗透率变化可分为缓慢增长、急剧下降和趋于稳定阶段。 相似文献
313.
1949—1994年中国洪水灾害成灾面积的时序分形特征 总被引:24,自引:3,他引:24
作者应用1949~1994年中国洪水灾情资料,重构了其嵌入相空间序列,探讨了其时序的分形特征,计算得到了分维数。研究表明:洪水灾害成灾面积的时序分布具有分形特征。研究结果为建立洪水灾害成灾面积的时序预测预报模型提供依据。 相似文献
314.
焦荣华 《湖南环境生物职业技术学院学报》2009,15(3):24-27
分析了湖南衡阳地区乙型肝炎病毒基因型分布特征,并探讨HBV各基因型与血清HBVDNA水平之间的关系.采用荧光定量PCR结合TaqmanMGB探针技术,对湖南衡阳地区164份乙型肝炎患者血清中的HBVDNA进行基因分型和定量检测.结果164例血清中,C型110A.(67.1%),B、C型37人(22.3%),B型8人(5.1%),D型1人(0.6%),A型1人(0.6%).C型与B、C混合型在HBVDNA水平上存在显著差异(t=2.433,P〈0.05),B、C混合型的HBVDNA水平明显高于C型.由此得出湖南衡阳地区HBV基因型以C型为主、B、C混合型次之,B型较少,D型、A型极少;B、C混合型患者的HBVDNA数量水平显著高于C型.表1.参11. 相似文献
315.
Curtis G. Cude 《Journal of the American Water Resources Association》2001,37(1):125-137
ABSTRACT: The Oregon Water Quality Index (OWQI) is a single number that expresses water quality by integrating measurements of eight water quality variables (temperature, dissolved oxygen, biochemical oxygen demand, pH, ammonia+nitrate nitrogen, total phosphorus, total solids, and fecal coliform). Its purpose is to provide a simple and concise method for expressing the ambient water quality of Oregon's streams for general recreational use, including fishing and swimming. The OWQI, originally developed in the 1970s, has been updated based upon improved understanding about water quality behavior. This report describes the historical basis of the OWQI and defines the improved design of the present OWQI. The index allows users to easily interpret data and relate overall water quality variation to variations in specific categories of impairment. This report demonstrates the value of the OWQI in presenting spatial and temporal water quality information. The OWQI improves comprehension of general water quality issues, communicates water quality status, and illustrates the need for and effectiveness of protective practices. 相似文献
316.
Francesco Lisi Vigilio Villi 《Journal of the American Water Resources Association》2001,37(2):271-279
ABSTRACT: This paper considers the problem of forecasting the discharge time series of a river by means of a chaotic approach. To this aim, we first check for some evidence of chaotic behavior in the dynamic by considering a set of different procedures, namely, the phase portrait of the attractor, the correlation dimension, and the largest Lyapunov exponent. Their joint application seems to confirm the presence of a nonlinear deterministic dynamic of chaotic type. Second, we consider the so‐called nearest neighbors predictor and we compare it with a classical linear model. By comparing these two predictors, it seems that nonlinear river flow modeling, and in particular chaotic modeling, is an effective method to improve predictions. 相似文献
317.
Connie A. Woodhouse 《Journal of the American Water Resources Association》2001,37(3):561-569
ABSTRACT: Water resource planning is based primarily on 20th century instrumental records of climate and streamflow. These records are limited in length to approximately 100 years, in the best cases, and can reflect only a portion of the range of natural variability. The instrumental record neither can be used to gage the unusualness of 20th Century extreme low flow events, nor does it allow the detection of low‐frequency variability that may underlie short‐term variations in flow. In this study, tree rings are used to reconstruct mean annual streamflow for Middle Boulder Creek in the Colorado Front Range, a semi‐arid region of rapid growth and development. The reconstruction is based on a stepwise regression equation that accounts for 70 percent of the variance in the instrumental record, and extends from 1703–1987. The reconstruction suggests that the instrumental record of streamflow for Middle Boulder Creek is not representative of flow in past centuries and that several low flow events in the 19th century were more persistent than any in the 20th century. The 1840s to early 1850s period of low flow is a particularly notable event and may have coincided with a period of low flow in the Upper Colorado River Basin. 相似文献
318.
Lawrence A. J. Fennessey Arthur C. Miller James M. Hamlett 《Journal of the American Water Resources Association》2001,37(4):899-912
ABSTRACT: In the last 30 years, the National Resource Conservation Service's TR‐55 and TR‐20 models have seen a dramatic increase in use for stormwater management purposes. This paper reviews some of the data that were originally used to develop these models and tests how well the models estimate annual series peak runoff rates for the same watersheds using longer historical data record lengths. The paper also explores differences between TR‐55 and TR‐20 peak runoff rate estimates and time of concentration methods. It was found that of the 37 watersheds tested, 25 were either over‐ or under‐predicting the actual historical watershed runoff rates by more than 30 percent. The results of this study indicate that these NRCS models should not be used to model small wooded watersheds less than 20 acres. This would be especially true if the watershed consisted of an area without a clearly defined outlet channel. This study also supports the need for regulators to allow educated hydrologists to alter pre‐packaged model parameters or results more easily than is currently permitted. 相似文献
319.
320.
1999年5月—2001年10月在北京观象台对紫外线指数(UVI)进行了长期观测,结果表明:UVI季节差异明显,春、夏、秋、冬季的最大值分别为7 85,9 87,4 92,2 99;正午时的平均值分别为3 52,5 31,2 17,1 24。在UVI高峰时段(10:00—15:00),秋、冬季的UVI基本在0~2范围,对人体危害不大;而0~2,3~4,5~6,大于7的各级UVI的平均累积日照时间春季分别为159,87,47,2min,夏季分别为75,99,93,29min,春、夏季紫外线辐射对人体危害较大。另外,UVI的累积分布显示,春、秋、冬季的UVI多数集中在各季节平均值以下,而夏季正午前后的UVI多分布在其季节平均值以上。 相似文献