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排序方式: 共有619条查询结果,搜索用时 31 毫秒
171.
2016年3月31日,深圳市及其周边地区出现典型的区域性空气污染事件,多数地区的AQI超过了100.主要污染物浓度和气象要素的逐小时变化表明,该次污染天气主要是在不利气象条件下,由污染物区域传输和二次污染物生成共同导致的.进一步的后向轨迹分析表明,污染日抵达深圳市的气团可能从东莞、广州和佛山等地区携带了大量污染物,并且移动速度缓慢,造成了深圳较为严重的污染天气,而污染日前和污染日后抵达深圳市的气团有利于污染物的稀释扩散,因此空气质量较好. 相似文献
172.
This study was designed to examine the responses of soil CO2 efflux to precipitation pulses of varying intensities using precipitation simulations in two subtropical forests [i.e., mixed
and broadleaf forests (MF and BF)] in southern China. The artificial precipitation event was achieved by spraying a known
amount of water evenly in a plot (50 × 50 cm2) over a 30 min period, with intensities ranging from 10, 20, 50 and 100 mm within the 30 min. The various intensities were
simulated in both dry season (in December 2007) and wet (in May 2008) season. We characterized the dynamic patterns of soil
CO2 efflux rate and environmental factors over the 5 h experimental period. Results showed that both soil moisture and soil CO2 efflux rate increased to peak values for most of the simulated precipitation treatments, and gradually returned to the pre-irrigation
levels after irrigation in two forests. The maximum peak of soil CO2 efflux rate occurred at the 10 mm precipitation event in the dry season in BF and was about 3.5 times that of the pre-irrigation
value. The change in cumulative soil CO2 efflux following precipitation pulses ranged from −0.68 to 1.72 g CO2 m−2 over 5 h compared to the pre-irrigation levels and was generally larger in the dry season than in the wet season. The positive
responses of soil CO2 efflux to precipitation pulses declined with the increases in precipitation intensity, and surprisingly turned to negative
when precipitation intensity reached 50 and 100 mm in the wet season. These findings indicated that soil CO2 efflux could be changed via pulse-like fluxes in subtropical forests in southern China as fewer but extreme precipitation
events occur in the future. 相似文献
173.
Priadi C Bourgeault A Ayrault S Gourlay-Francé C Tusseau-Vuillemin MH Bonté P Mouchel JM 《Journal of environmental monitoring : JEM》2011,13(5):1470-1479
In order to obtain representative dissolved and solid samples from the aquatic environment, a spectrum of sampling methods are available, each one with different advantages and drawbacks. This article evaluates the use of discrete sampling and time-integrated sampling in illustrating medium-term spatial and temporal variation. Discrete concentration index (CI) calculated as the ratio between dissolved and solid metal concentrations in grab samples are compared with time-integrated concentration index (CI) calculated from suspended particulate matter (SPM) collected in sediment traps and labile metals measured by the diffusive gel in thin films (DGT) method, collected once a month during one year at the Seine River, upstream and downstream of the Greater Paris Region. Discrete CI at Bougival was found to be significantly higher than at Triel for Co, Cu, Mn, Ni and Zn, while discrete metal partitioning at Marnay was found to be similar to Bougival and Triel. However, when using time-integrated CI, not only was Bougival CI significantly higher than Triel CI, CI at Marnay was also found to be significantly higher than CI at Triel which was not observed for discrete CI values. Since values are time-averaged, dramatic fluctuations were smoothed out and significant medium-term trends were enhanced. As a result, time-integrated concentration index (CI) was able to better illustrate urbanization impact between sites when compared to discrete CI. The impact of significant seasonal phenomenon such as winter flood, low flow and redox cycles was also, to a certain extent, visible in time-integrated CI values at the upstream site. The use of time-integrated concentration index may be useful for medium- to long-term metal studies in the aquatic environment. 相似文献
174.
濮阳市秋冬季大气细颗粒物污染特征及来源解析 总被引:8,自引:8,他引:0
濮阳市作为京津冀周边地区大气污染传输通道城市之一,秋冬季重污染天气频发,空气污染问题严峻.为了研究濮阳市秋冬季大气细颗粒物污染特征及其主要来源,于2017年10月15日至2018年1月13日在濮阳市3个国控点对PM_(2.5)进行了手工膜采样与化学组分分析,并结合PMF受体模型,开展了细颗粒物来源解析研究.结果表明,濮阳市2017年秋冬季PM_(2.5)平均质量浓度为94. 16μg·m~(-3),濮水河管理处的污染状况最严重,进入采暖季后3站点均表现为重度及严重污染事件频发,轻度污染发生频率降低,重污染发生时NO_2与CO浓度升高明显. PM_(2.5)中的主要组分为水溶性离子(52. 33%)、碳质组分(25. 32%)和地壳元素(0. 08%),NO_3~-的含量高而SO_4~(2-)的浓度水平较低.重污染发生时,PM_(2.5)中水溶性离子、OC、EC和K浓度都出现了明显的升高,而地壳元素浓度降低.采样期间濮阳市的硫氮转化率水平较高,大气氧化性较强,硫氮转化促进了重污染的发生.濮阳市2017年NOx、CO和VOCs排放量较高,来源解析结果表明,濮阳市秋冬季PM_(2.5)主要来源分别为二次无机盐(37%)、工业源(16%)、二次有机气溶胶SOA(14%)、生物质燃烧源(12%)、移动源(9%)、燃煤源(7%)和扬尘源(4%).可见,二次转化在濮阳重污染的形成过程中起到重要作用,要减轻大气细颗粒物污染,需要重点控制工业源、生物质燃烧、移动源和民用散煤燃烧的排放. 相似文献
175.
Mitch Serpas Yunfei Chu Juergen Hahn 《Journal of Loss Prevention in the Process Industries》2013,26(3):443-452
This paper develops a new approach for fault detection which involves soft sensors for process monitoring. Unlike existing approaches, which compare current measurements, or linear combinations thereof, to values of these measurements representing normal operations, the methodology presented here deals directly with the state estimates that need to be monitored. The advantage of such an approach is that the effect of abnormal process conditions on the state variables can be directly observed and that it is possible to include nonlinear relationships between measurements and states. At the same time, this type of approach has the drawback that the variances of the unmeasured states are not equal to the variances of the actual process variables due to the use of a soft sensor. However, for many popular soft sensor techniques, such as Kalman filters and related approaches, it is possible to compute variances of the predicted states that correspond to normal operating conditions. This paper presents a general framework for using soft sensors for process monitoring, i.e., soft sensor design and computation of the statistics that represent normal operating conditions, and illustrates this framework in three specific applications. It should be pointed out that the contribution of this work does not lie with the soft sensor design or the computation of the statistics itself as either part has individually already been addressed in the existing literature. However, the authors are not aware of any studies where both tasks are combined for process monitoring, which forms the contribution of this work. 相似文献
176.
p-Dichlorobenzene (p-DCB) was eluted through a compacted ferruginous clay with dilute aqueous solutions of methanol, ethanol, n- and i-propanols, and n- and i-butanols. The presence of the alcohols results in very marked increases in the concentrations of p-DCB in the effluents from the clay-packed columns. Flux of p-DCB through the columns increases with increasing chain length of the alcohol, and normal alcohols increase the flux somewhat more than corresponding branched alcohols. Flux increases with increasing mole fraction of the alcohol. Flux enhancement is due almost exclusively to enhancement of the solubility of p-DCB. 相似文献
177.
Integrating lidar and satellite optical depth with ambient monitoring for 3-dimensional particulate characterization 总被引:3,自引:0,他引:3
Jill A. Engel-Cox Raymond M. Hoff Raymond Rogers Fred Dimmick Alan C. Rush James J. Szykman Jassim Al-Saadi D. Allen Chu Erica R. Zell 《Atmospheric environment (Oxford, England : 1994)》2006,40(40):8056-8067
A combination of in-situ PM2.5, sunphotometers, upward pointing lidar and satellite aerosol optical depth (AOD) instruments have been employed to better understand variability in the correlation between AOD and PM2.5 at the surface. Previous studies have shown good correlation between these measures, especially in the US east, and encouraged the use of satellite data for spatially interpolating between ground sensors. This work shows that cases of weak correlation can be better understood with knowledge of whether the aerosol is confined to the surface planetary boundary layer (PBL) or aloft. Lidar apportionment of the fraction of aerosol optical depth that is within the PBL can be scaled to give better agreement with surface PM2.5 than does the total column amount. The study has shown that lidar combined with surface and remotely sensed data might be strategically used to improve our understanding of long-range or regionally transported pollutants in multiple dimensions. 相似文献
178.
Aquaculture has a long history,and has achieved rapid development from 1950 to 2010,especially since the 1990s.Nevertheless,aquaculture has also seen a series of problems emerge.Inevitably,aquaculture interacts with the environment and society.Rapid development requires that close attention be paid to potential environmental and social impacts and their prevention or mitigation.The development and management of aquaculture is related closely with a variety of legal and institutional arrangements.Thus,aquaculture raises numerous legal and institutional issues.This paper explores actual legal and institutional practices of global representative aquaculture countries and provides a comprehensive account of the legislation and policies of different countries.Further,this paper reveals that the optimal legal framework for aquaculture is in line with related international regulations(especially the soft laws)and strictly operational,and the corresponding policy framework should establish early access and warning,as well as post assessment and feedback mechanisms. 相似文献
179.
本研究利用发光细菌急性毒性实验测定了长江口及其邻近海域表层沉积物中有机污染物的复合毒性,同时运用气相色谱-质谱联用仪测定了沉积物中16种美国环境保护局(United States Environmental Protection Agency, US EPA)规定的优先控制的多环芳烃(polycyclic aromatic hydrocarbons, PAHs)的浓度。在此基础上,分析其时空分布特征及多环芳烃毒性贡献,并评估其环境风险。结果表明,2019年长江口及邻近海域表层沉积物中16种PAHs总浓度范围为32.84~283.47 ng·g(-1);2020年浓度范围为66.93~132.64 ng·g(-1);2020年浓度范围为66.93~132.64 ng·g(-1)。在空间分布上,2019年长江口表层沉积物中PAHs在靠近渔港的区域呈现较高浓度(S3=(283.47±29.94) ng·g(-1)。在空间分布上,2019年长江口表层沉积物中PAHs在靠近渔港的区域呈现较高浓度(S3=(283.47±29.94) ng·g(-1)),而2020年在靠近舟山岛的区域呈现较高浓度(L6=(132.64±9.95) ng·g(-1)),而2020年在靠近舟山岛的区域呈现较高浓度(L6=(132.64±9.95) ng·g(-1))。与2019年相比,2020年多环芳烃的平均浓度有所降低,且其细胞毒性量化指标——生物分析当量浓度(BEQ_(bio))的平均值(66.62 mg·kg(-1))。与2019年相比,2020年多环芳烃的平均浓度有所降低,且其细胞毒性量化指标——生物分析当量浓度(BEQ_(bio))的平均值(66.62 mg·kg(-1))远低于2019年(128.20 mg·kg(-1))远低于2019年(128.20 mg·kg(-1))。在长江口沉积物毒性当量浓度中PAHs所占比例较小,2019年和2020年由PAHs引起的细胞毒性的平均占比分别为4.46%和4.25%。该结果表明,检测到的PAHs仅能解释所观察到的复合毒性效应的一小部分,因此,还需要进一步对其他未检测的化学物质进行测试分析。 相似文献
180.
Chen Juxiang Dai Caiqiong Zhu Yanping Gao Yuqiong Chu Wenhai Gao Naiyun Wang Qiongfang 《Environmental science and pollution research international》2022,29(36):54407-54420
Environmental Science and Pollution Research - Sulfadiazine (SDZ) is a typical persistent sulfonamide antibiotic, which has been widely detected in natural drinking water sources. The degradation... 相似文献