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191.
To better understand the potential causes of visibility impairment in autumn and winter in Chengdu, relative humidity(RH), visibility, the concentrations of PM_(2.5) and its chemical components were on-line measured continuously in Chengdu from Nov. 2016 to Jan. 2017.Six obvious haze episodes occurred in Chengdu, with the total time of haze episodes accounted for more than 90% of the total observation period, and higher NO_2 concentrations and RH were related to the high particle concentrations in haze episodes. The visibility decreased in a non-linear tendency under different RH conditions with the increase of PM_(2.5) concentrations, which was more sensitive to RH under lower PM_(2.5) concentrations. The threshold concentration of PM_(2.5) got more smaller with the increase of RH. During the entire observation period, organic matter(OM) was the largest contributor(31.12% to extinction coefficient(bext)), followed by NH_4NO_3 and(NH_4)_2SO_4 with 28.03% and 23.01%, respectively.However, with the visibility impairment from Type I(visibility 10 km) to Type IV(visibility ≤ 2 km), the contribution of OM to bextdecreased from 38.12% to 26.77%, while the contribution of NH_4NO_3 and(NH_4)_2SO_4 to bextincreased from 19.09% and 20.20% to 34.29% and 24.35%, respectively, and NH_4NO_3 became the largest contributor to bextat Type IV. The results showed that OM and NH_4NO_3 were the key components of PM_(2.5) for visibility impairment in Chengdu, indicating that the control of precursors emissions of carbonaceous species and NH_4NO_3 could effectively improve the visibility in Chengdu. 相似文献
192.
在流动注射测定挥发酚的过程中,会出现基线不稳、噪声信号增加、流量不稳定、准确度和精密度降低等现象,分析测试结果表明溶液有气泡、流通池pH、冷却水温度、到阀时间、周期时间等因素均会导致上述现象的发生。通过研究,对检测时间条件及前处理等方面进行调整。在调整流通池pH到9.8~10.2、设置到阀时间为350 s、周期时间为200 s,并且将试剂脱气方式调整为氦气脱气后,测试准确度和精密度均有较大提高。 相似文献
193.
194.
Environmental scanning electron microscopy as a new technique to determine the hygroscopic behaviour of individual aerosol particles 总被引:2,自引:0,他引:2
Martin Ebert Marion Inerle-Hof Stephan Weinbruch 《Atmospheric environment (Oxford, England : 1994)》2002,36(39-40)
The hygroscopic behaviour of NaCl, (NH4)2SO4, Na2SO4 and NH4NO3 particles in the size range of 0.1–20 μm was studied by environmental scanning electron microscopy (ESEM). This technique allows the in-situ observation of individual aerosol particles while changing the temperature and/or relative humidity (RH) in the sample chamber. The hygroscopic behaviour of these particles (e.g., deliquescence, adsorption of water on the particle surface) becomes directly observable with a lateral resolution of the order of 8–15 nm. The deliquescence relative humidities (DRH) of the different salts, the temperature dependence of the DRH for NH4NO3, and the growth factors (at increasing relative humidities) for NaCl were determined. Generally, a good agreement between the values obtained by ESEM and those found in literature was achieved. However, the DRH of NaCl determined by ESEM is systematically higher (approximately 2%, absolute) than the values obtained by other techniques, which can be explained by the observed strong absorption of water onto the crystal surface prior to droplet formation. The efflorescence behaviour of individual particles can be studied only qualitatively due to influences of the sample substrate. Furthermore, it is demonstrated that the activation of soot can be studied at high resolution by ESEM. 相似文献
195.
196.
An alternative method of estimating relative demand among nonconsumptive uses of wildlife and among wildlife species is proposed. A demand intensity score (DIS), derived from the relative extent of an individual's involvement in outdoor recreation and conservation activities, is used as a weighting device to adjust the importance of preference rankings for wildlife uses and wildlife species relative to other members of a survey population. These adjusted preference rankings were considered to reflect relative demand levels (RDLs) for wildlife uses and for species by the survey population. This technique may be useful where it is not possible or desirable to estimate demand using traditional economic means. In one of the findings from a survey of municipal conservation commission members in Massachusetts, presented as an illustration of this methodology, poisonous snakes were ranked third in preference among five groups of reptiles. The relative demand level for poisonous snakes, however, was last among the five groups. 相似文献
197.
198.
SOIL EROSION AND SEDIMENT YIELD PREDICTION ACCURACY USING WEPP1 总被引:1,自引:0,他引:1
John M. Laflen Dennis C. Flanagan Bernard A. Engel 《Journal of the American Water Resources Association》2004,40(2):289-297
ABSTRACT: The objectives of this paper are to discuss expectations for the Water Erosion Prediction Project (WEPP) accuracy, to review published studies related to WEPP goodness of fit, and to evaluate these in the context of expectations for WEPP's goodness of fit. WEPP model erosion predictions have been compared in numerous studies to observed values for soil loss and sediment delivery from cropland plots, forest roads, irrigated lands and small watersheds. A number of different techniques for evaluating WEPP have been used, including one recently developed where the ability of WEPP to accurately predict soil erosion can be compared to the accuracy of replicated plots to predict soil erosion. In one study involving 1,594 years of data from runoff plots, WEPP performed similarly to the Universal Soil Loss Erosion (USLE) technology, indicating that WEPP has met the criteria of results being “at least as good with respect to observed data and known relationships as those from the USLE,” particularly when the USLE technology was developed using relationships derived from that data set, and using soil erodibility values measured on those plots using data sets from the same period of record. In many cases, WEPP performed as well as could be expected, based on comparisons with the variability in replicate data sets. One major finding has been that soil erodibility values calculated using the technology in WEPP for rainfall conditions may not be suitable for furrow irrigated conditions. WEPP was found to represent the major storms that account for high percentages of soil loss quite well—a single storm application that the USLE technology is unsuitable for—and WEPP has performed well for disturbed forests and forest roads. WEPP has been able to reflect the extremes of soil loss, being quite responsive to the wide differences in cropping, tillage, and other forms of management, one of the requirements for WEPP validation. WEPP was also found to perform well on a wide range of small watersheds, an area where USLE technology cannot be used. 相似文献
199.
本文应用云南省“95计划”期间改造过的14个数字化高精度水温资料,对数字化改造前后的资料进行对比研究,分析其异常特征及映震效能。结果表明,数字化改造后观测质量有所提高,信息量更大,对应云南地区5级以上中强地震的能力较好。 相似文献
200.
本文应用云南省“95计划”期间改造过的14个数字化高精度水温资料,对数字化改造前后的资料进行对比研究,分析其异常特征及映震效能。结果表明,数字化改造后观测质量有所提高,信息量更大,对应云南地区5级以上中强地震的能力较好。 相似文献