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21.
NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P < 0.05) and negatively with soil moisture content (P < 0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N fromthe grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m3). 相似文献
22.
Pathogenic viruses in drinking water are great threats to public health. Visible-light-driven photocatalysis is a promising technology for virus inactivation. However, the existing photocatalytic antiviral research studies have mostly been carried out in single-component systems, neglecting the effect of natural organic matter, which exists widely in actual water bodies. In this paper, electrospun Cu-TiO2 nanofibers were prepared as photocatalysts, and their photocatalytic antiviral performance in the presence of humic acid (HA) was comprehensively studied for the first time. The properties of the reaction mixture were measured during the reaction. In addition, the safety, reliability and stability of photocatalytic disinfection in the mixed system were evaluated. The results showed that the virus removal efficiency decreased with the increase of the HA concentration. The type of reaction solution, such as PBS buffer solution or water, did not affect the removal efficiency noticeably. Under acidic conditions, the electrostatic forces between photocatalysts and viruses were strengthened, leading to higher virus removal efficiency. As the reaction time went on, the pH value in the solution increased first and then tended to be stable, the conductivity remained stable, and the dissolved oxygen increased first and then decreased. The safety test showed that the concentration of Cu ions released into the solution was lower than specified by the international standards. No photoreactivation was observed, and the addition of HA significantly reduced the reutilization efficiency of the photocatalysts. 相似文献
23.
基于本地污染源调查的杭州市大气污染物排放清单研究 总被引:4,自引:0,他引:4
基于实地调查数据并辅以统计数据,采用物料衡算法和排放因子法,估算了杭州市2015年大气污染物排放清单,并选取经纬度坐标、路网、航道、土地类型和人口等数据作为权重因子,研究了该地区各类排放源污染物排放空间分布特征.结果表明,杭州市2015年SO_2、NO_x、CO、VOCs、PM_(10)、PM_(2.5)和NH_3年排放总量分别为22.20×10~3、108.17×10~3、192.10×10~3、134.94×10~3、78.12×10~3、27.65×10~3和59.75×10~3t.工业源是杭州市SO_2排放的主要来源,移动源对NO_x和CO的排放贡献最为显著,扬尘源是杭州市PM_(10)和PM_(2.5)排放的最主要来源,其次为工业源;VOCs排放的主要来源依次为工业源、天然源和移动源;NH_3排放主要来自农业源.从空间分布来看,排放主要集中在中心城区及其周边的萧山、下沙、大江东、余杭和富阳等工业企业相对密集的区域.本研究建立的排放清单在污染源覆盖范围和排放因子方面仍然存在一定的不确定性,建议在后续研究中重点开展低、小、散企业及本地化排放因子调查研究工作,进一步提升大气污染物排放清单的准确度. 相似文献
24.
上海市城区春节和“五一”节期间大气挥发性有机物的组成特征 总被引:18,自引:2,他引:18
挥发性有机物(VOCs)是对流层臭氧和二次有机气溶胶等二次污染生成过程的关键前体物.研究VOCs的浓度水平、组成特征和反应活性对揭示复合型大气污染的形成机制具有重要意义.本研究利用在线气相-氢离子火焰法测量了2009年春节和"五一"节期间上海市城区大气中56种VOCs.结果表明,上海市城区大气受机动车尾气排放源影响明显,VOCs浓度日变化特征呈双峰状,与上下班交通高峰基本吻合.大气中VOCs平均体积分数为(28.39±18.35)×10-9;各组分百分含量依次为:烷烃46.6%,芳香烃27.0%,烯烃15.1%,乙炔11.2%.用OH消耗速率和臭氧生成潜势(OFP)评估了VOCs大气化学反应活性,结果表明,上海市城区大气VOCs化学反应活性与VOCs体积浓度相关性良好;VOCs活性与乙烯相当,平均化学反应活性较强;OH消耗速率贡献最大的物种是烯烃51.2%和芳香烃31.8%;OFP贡献最大的物种是芳香烃53.4%和烯烃30.2%;对臭氧生成贡献最大的关键活性物种为丙烯、乙烯、甲苯、二甲苯以及丁烯类物质. 相似文献
25.
Evaluation of mercury speciation and removal through air pollution control
devices of a 190 MW boiler 总被引:1,自引:0,他引:1
Chengli Wu Yan Cao Zhongbing Dong Chinmin Cheng Hanxu Li Weiping Pan 《环境科学学报(英文版)》2010,22(2):277-282
Air pollution control devices (APCDs) are installed at coal-fired power plants for air pollutant regulation. Selective catalytic reduction
(SCR) and wet flue gas desulfurization (FGD) systems have the co-benefits of air pollutant and mercury removal. Configuration
and operational conditions of APCDs and mercury speciation a ect mercury removal e ciently at coal-fired utilities. The Ontario
Hydro Method (OHM) recommended by the U.S. Environmental Protection Agency (EPA) was used to determine mercury speciation
simultaneously at five sampling locations through SCR-ESP-FGD at a 190 MW unit. Chlorine in coal had been suggested as a factor
a ecting the mercury speciation in flue gas; and low-chlorine coal was purported to produce less oxidized mercury (Hg2+) and more
elemental mercury (Hg0) at the SCR inlet compared to higher chlorine coal. SCR could oxidize elemental mercury into oxidized
mercury when SCR was in service, and oxidation e ciency reached 71.0%. Therefore, oxidized mercury removal e ciency was
enhanced through a wet FGD system. In the non-ozone season, about 89.5%–96.8% of oxidized mercury was controlled, but only
54.9%–68.8% of the total mercury was captured through wet FGD. Oxidized mercury removal e ciency was 95.9%–98.0%, and there
was a big di erence in the total mercury removal e ciencies from 78.0% to 90.2% in the ozone season. Mercury mass balance was
evaluated to validate reliability of OHM testing data, and the ratio of mercury input in the coal to mercury output at the stack was from
0.84 to 1.08. 相似文献
26.
针对越江气体绝缘输电线路(GIL)综合管廊结构的特殊性,考虑内部混凝土支架与盾构隧道的动力相互作用,以及盾构隧道穿越地层的不同,建立了土?管廊结构非线性动力相互作用的整体计算分析模型,从结构变形、盾构管片张开量、结构地震损伤等方面详细分析了越江 GIL 综合管廊结构的抗震性能。结果表明:越江 GIL 管廊结构内部混凝土支架结构明显要先于外部盾构隧道发生地震损伤;当 GIL 管廊结构穿越相对较软土层时的地震损伤明显加重;受制于内部混凝土支架的约束作用,盾构隧道的下部管片张开量明显小于上部管片计算值,同时外侧残余张开量要明显大于管片内侧残余张开量。 相似文献
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30.
利用1963~2015年长江流域115个气象站点逐日降水数据,分析了不同极端降水指标的空间变化特点和时间变化趋势。结果表明,近53 a来,长江流域多年平均年极端降水量与年降水量从下游到上游逐渐递减,两者变化趋势大致呈现“增-减-增”的空间分布格局。年极端降水量对年降水量贡献(PEP)存在明显的空间分布差异,但贡献比例在流域内普遍呈现增加的趋势。持续1 d的极端降水事件的降水量分布及其变化趋势与年极端降水量的分布特征类似,其对年极端降水量的贡献比例高达65%以上,说明长江流域极端降水以持续1 d的极端降水事件为主。持续2 d及以上的极端降水事件主要集在中皖苏赣局部地区和四川中部地区,但其降水量对年极端降水量的贡献比例较小。从上游到下游,年最大日降水量(MDP)逐渐增大。其中,上游源头地区的沱沱河、曲麻莱和玉树3个站点MDP主要集中在0~25 mm之间,其他站点均以25~50 mm量级为主;长江流域中部地区的MDP大部分以50~100 mm的量级为主,处于100~150 mm之间的次之;长江流域东部地区主要以100~150 mm量级的MDP为主。
关键词: 极端降水;降水贡献;不同历时;长江流域 相似文献