Evidence for NO(x) control over nighttime SOA formation

Laboratory studies have established a number of chemical pathways by which nitrogen oxides (NO(x)) affect atmospheric organic aerosol (OA) production. However, these effects have not been directly observed in ambient OA. We report measurements of particulate organic nitrates in Bakersfield, California, the nighttime formation of which increases with NO(x) and is suppressed by high concentrations of organic molecules that rapidly react with nitrate radical (NO(3))--evidence that multigenerational chemistry is responsible for organic nitrate aerosol production. This class of molecules represents about a third of the nighttime increase in OA, suggesting that most nighttime secondary OA is due to the NO(3) product of anthropogenic NO(x) emissions. Consequently, reductions in NO(x) emissions should reduce the concentration of organic aerosol in Bakersfield and the surrounding region.     

Air-snow interactions and atmospheric chemistry

The presence of snow greatly perturbs the composition of near-surface polar air, and the higher concentrations of hydroxyl radicals (OH) observed result in a greater oxidative capacity of the lower atmosphere. Emissions of nitrogen oxides, nitrous acid, light aldehydes, acetone, and molecular halogens have also been detected. Photolysis of nitrate ions contained in the snow appears to play an important role in creating these perturbations. OH formed in the snowpack can oxidize organic matter and halide ions in the snow, producing carbonyl compounds and halogens that are released to the atmosphere or incorporated into snow crystals. These reactions modify the composition of the snow, of the interstitial air, and of the overlying atmosphere. Reconstructing the composition of past atmospheres from ice-core analyses may therefore require complex corrections and modeling for reactive species.     

Removal of Stratospheric O3 by Radicals: In Situ Measurements of OH, HO2, NO, NO2, ClO, and BrO

Simultaneous in situ measurements of the concentrations of OH, HO(2), ClO, BrO, NO, and NO(2) demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO(2) with ozone, accounted for nearly one-half of the total O(3) removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O(3); reactions involving BrO account for one-half of this loss. Catalytic destruction by NO(2), which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O(3) removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO(2) and ClO are inversely correlated with those of NO and NO(2). The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O(3) removal was inversely correlated with total NOx, loading.     

Observations of ozone formation in power plant plumes and implications for ozone control strategies

Data taken in aircraft transects of emissions plumes from rural U.S. coal-fired power plants were used to confirm and quantify the nonlinear dependence of tropospheric ozone formation on plume NO(x) (NO plus NO(2)) concentration, which is determined by plant NO(x) emission rate and atmospheric dispersion. The ambient availability of reactive volatile organic compounds, principally biogenic isoprene, was also found to modulate ozone production rate and yield in these rural plumes. Differences of a factor of 2 or greater in plume ozone formation rates and yields as a function of NO(x) and volatile organic compound concentrations were consistently observed. These large differences suggest that consideration of power plant NO(x) emission rates and geographic locations in current and future U.S. ozone control strategies could substantially enhance the efficacy of NO(x) reductions from these sources.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

O3与O3/H2O2两个体系降解除草剂2,4-D反应特性研究

分别采用O3、O3/H2O2体系降解苯氧羧酸类除草剂2,4-D,探讨了降解过程中反应温度、pH值、O3混合气流量、有机物初始浓度等操作条件的变化对降解动力学的影响。结果发现,温度和pH值的影响较大,O3流量影响最小,温度升高、pH值增大、臭氧流量增加、2,4-D初始浓度降低均有助于降解速率的提高。O3/H2O2体系中,H2O2能促进O3分解产生大量自由基,导致2,4-D反应活化能降低。和O3相比,O3/H2O2体系降解效果好,降解时间短,反应条件温和,操作费用低,是很有发展前景的高级氧化技术。     

Atmospheric hydroxyl radical production from electronically excited NO2 and H2O

Hydroxyl radicals are often called the "detergent" of the atmosphere because they control the atmosphere's capacity to cleanse itself of pollutants. Here, we show that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals. Using measured rate data, along with available solar flux and atmospheric mixing ratios, we demonstrate that the tropospheric hydroxyl contribution from this source can be a substantial fraction (50%) of that from the traditional O(1D) + H2O reaction in the boundary-layer region for high solar zenith angles. Inclusion of this chemistry is expected to affect modeling of urban air quality, where the interactions of sunlight with emitted NOx species, volatile organic compounds, and hydroxyl radicals are central in determining the rate of ozone formation.     

温度/溶剂双梯度高效液相色谱法测定环境空气中的羰基化合物

该文建立了环境空气中13种碳数在1~8范围内的羰基化合物(6种脂肪醛、2种芳香醛、3种不饱和醛和2种酮)的温度/溶剂双梯度2,4-二硝基苯肼衍生/高效液相色谱分析方法。通过选择合适的色谱柱,优化柱温,用水和乙腈两元溶剂梯度基线分离了13种羰基化合物的衍生物。利用温度梯度解决了13种羰基化合物中C3组分(丙烯醛、丙酮和丙醛)和C4组分(丁烯醛、甲基丙烯醛、丁酮和正丁醛)难以分离的问题。优化的方法在各自的浓度范围内线性相关系数良好(r≥0.999 9);对于50.0L的空气样品检出限在0.04~0.19μg/m3(以羰基化合物计);该方法的相对标准偏差小于3.6%;加标回收率在95%~106%,适用于环境空气中羰基化合物的测定。     

Thermodynamic equilibrium and the inorganic origin of organic compounds

Theoretical and experimental support is presented for the hypothesis that many organic compounds may form under conditions of thermodynamic equilibrium. This possibility must be considered along with special effects of selective catalysts, radiation, and degradation from biological matter, in explaining the origin of organic compounds in carbonaceous chondrites. Similar considerations may apply to solar nebulas and planetary atmospheres. The equilibrium distribution of organic compounds at temperatures between 300 degrees K and 1000 degrees K and pressures of 10-(6) to 50 atm for the C-H-O system have been computed. At moderate temperatures and low pressures, conditions where graphite production is inhibited, aromatic compounds may form even in the presence of large excesses of hydrogen. Such conditions exist in the solar nebula and in the atmospheres of some of the major planets. Equilibrium concentrations of a large number of compounds at 1000 degrees K with nitrogen, sulfur, and chlorine added to the system have also been determined. In some cases, a limited equilibrium method is employed in which those few compounds which form with the most difficulty are excluded from the computations, while representatives of all other families of compounds are included. This approach is shown to be useful in the interpretation of certain experimental data in which complete equilibrium has not been attained. We have also found that gases, activated to the plasma state by a high-energy radio frequency field, recombine on cooling to yield product mixtures which are in qualitative agreement with those predicted by the equilibrium computations. We believe that such products can be profitably studied as if at a metastable limited equilibrium.     

夜间增温下施硅对稻田CH4好氧氧化及其氮响应的影响

【目的】研究硅肥对增温稻田甲烷(CH₄)好氧氧化速率的影响效应,为探索未来全球变暖背景下稻田温室气体减排措施提供科学依据。【方法】采用田间开放式增温系统对稻田土壤进行夜间增温,共设4个处理：夜间常温不施硅(CK)、夜间增温不施硅(NW)、夜间常温施硅(Si)和夜间增温施硅(NW+Si)。采集上述处理4年后的耕层根际土和非根际土,在无氮添加和氮添加(NH₄⁺、NO₃^-和尿素)条件下进行室内培养,采用¹³CH₄标记方法,研究稻田CH₄好氧氧化速率和固碳特征及其对氮肥的响应。【结果】Si处理稻田土壤的总有机碳和水溶性有机碳含量分别为23.2 g/kg和216.7 mg/kg,较CK稻田提高10.5%和26.7%;而NW处理的总有机碳和水溶性有机碳则分别较CK稻田降低11.9%和9.9%。施硅处理(Si和NW+Si)根际土的CH₄好氧氧化速率显著高于不施硅处理(CK和NW)(P<0.05),其...     

复合型人工湿地系统在农业面源污染水处理上的应用

利用复合型人工湿地系统净化处理农业面源污染,研究了湿地系统对营养物质、重金属的去除效果。结果表明,在低污染负荷的运行情况下,湿地系统对总氮、氨氮、硝态氮、亚硝态氮的去除率分别为44.11%、18.90%、52.86%和73.32%;对总磷、高锰酸盐指数和叶绿素a的去除率为49.46%、16.77%和75.82%;处理后的水质较处理前可提高1~2个水质等级。湿地系统对有机物的去除效果不明显,而对叶绿素的净化效果显著。湿地系统对重金属的去除有显著效果,对铜、锌、砷、硒、汞、铬、铅的去除率分别为74.7%、85.3%、21.2%、40.0%、30.4%、41.3%和33.5%。湿地系统对总磷和叶绿素a的去除呈极显著差异,对亚硝态氮和CODMn呈显著差异。经湿地系统处理后,出水水质完全达到温室蔬菜灌溉水环境质量标准的要求。     

复合型人工湿地系统在农业面源污染水处理上的应用

利用复合型人工湿地系统净化处理农业面源污染,研究了湿地系统对营养物质、重金属的去除效果。结果表明,在低污染负荷的运行情况下,湿地系统对总氮、氨氮、硝态氮、亚硝态氮的去除率分别为44.11%、18.90%、52.86%和73.32%;对总磷、高锰酸盐指数和叶绿素a的去除率为49.46%、16.77%和75.82%;处理后的水质较处理前可提高1~2个水质等级。湿地系统对有机物的去除效果不明显,而对叶绿素的净化效果显著。湿地系统对重金属的去除有显著效果,对铜、锌、砷、硒、汞、铬、铅的去除率分别为74.7%、85.3%、21.2%、40.0%、30.4%、41.3%和33.5%。湿地系统对总磷和叶绿素a的去除呈极显著差异,对亚硝态氮和CODMn呈显著差异。经湿地系统处理后,出水水质完全达到温室蔬菜灌溉水环境质量标准的要求。     

Airborne lead and other elements derived from local fires in the himalayas

The combustion of wood and yak dung for heating and cooking in a populated Nepal Himalayan valley contributes significantly to the ambient airborne concentrations of lead, copper, aluminum, magnesium, and elemental and organic carbon. A comparison of the concentrations of these elements in fresh snow with corresponding values in air suggests that the pollution aerosol is confined to the valley, with pristine air aloft.     

活性氧物种在环境污染物降解转化中的应用研究进展

利用活性氧物种这类具有氧化能力的含氧自由基或含氧的非自由基衍生物降解环境污染物是一种绿色高效的污染控制和环境修复手段,但活性氧物种在环境污染物降解转化过程的产生和作用机制有待深入研究。本文综述了近年来活性氧物种(羟基自由基、超氧阴离子自由基、单线态氧和过氧化氢)在环境污染物去除方面的最新研究进展,介绍了几类常见的活性氧物种的化学性质、产生途径和检测方法,归纳和总结了活性氧物种在大气环境净化、有机废水处理和有害微生物杀灭等方面的应用和深层作用机制,同时对在环境污染物降解转化中活性氧物种的产生技术开发、含量定量检测和协同降解效应等方面进行了展望。     

Dimethyl sulfide in the surface ocean and the marine atmosphere: a global view

Dimethyl sulfide (DMS) has been identified as the major volatile sulfur compound in 628 samples of surface seawater representing most of the major oceanic ecozones. In at least three respects, its vertical distribution, its local patchiness, and its distribution in oceanic ecozones, the concentration of DMS in the sea exhibits a pattern similar to that of primary production. The global weightedaverage concentration of DMS in surface seawater is 102 nanograms of sulfur (DMS) per liter, corresponding to a global sea-to-air flux of 39 x 10(12) grams of sulfur per year. When the biogenic sulfur contributions from the land surface are added, the biogenic sulfur gas flux is approximately equal to the anthropogenic flux of sulfur dioxide. The DMS concentration in air over the equatorial Pacific varies diurnally between 120 and 200 nanograms of sulfur (DMS) per cubic meter, in agreement with the predictions of photochemical models. The estimated source flux of DMS from the oceans to the marine atmosphere is in agreement with independently obtained estimates of the removal fluxes of DMS and its oxidation products from the atmosphere.     

Trace Gas Analysis of Power Plant Plumes Via Aircraft Measurement: O3, NOx, and SO2 Chemistry

The gaseouis plume from an isolated 1000-megawatt power plant was systematically examined from a single engine aircraft to determine the extent to which NO(x) and SO(2), chemistry occurs as a function of distance. The concentrations of ambient ozone, water vapor, and hydroxyl free radicals are indicated to be of major importance in defining the chemistry of power plant plumes during summertime conditions.     

The sulfur cycle

Even granting our uncertainties about parts of our model of the sulfur cycle, we can draw some conclusions from it: 1) Man is now contributing about one half as much as nature to the total atmospheric burden of sulfur compounds, but by A.D. 2000 he will be contributing about as much, and in the Northern Hemisphere alone he will be more than matching nature. 2) In industrialized regions he is overwhelming natural processes, and the removal processes are slow enough (several days, at least) so that the increased concentration is marked for hundreds to thousands of kilometers downwind. 3) Our main areas of uncertainty, and ones that demand immediate attention because of their importance to the regional air pollution question, are: (i) the rates of conversion of H(2)S and SO(2) to sulfate particles in polluted as well as unpolluted atmospheres; (ii) the efficiency of removal of sulfur compounds by precipitation in polluted air. And for a better understanding of the global model we need to know: (i) the amount of biogenic H(2)S that enters the atmosphere over the continents and coastal areas; (ii) means of distinguishing man-made and biogenic contributions to excess sulfate in air and precipitation; (iii) the volcanic production of sulfur compounds, and their influence on the particle concentration in the stratosphere; (iv) the large-scale atmospheric circulation patterns that exchange air between stratosphere and troposphere (although absolute amounts of sulfate particles involved are small relative to the lower tropospheric burden); (v) the role of the oceans as sources or sinks for SO(2).     

夏季3种生境森林内空气颗粒物变化特征

研究不同生境类型城市森林内空气颗粒物的变化特征及其影响因素,为休闲保健型城市森林的营造提供理论依据。于2015年夏季对深圳园山山麓(SL)、河谷(HG)和山脊(SJ)3种典型生境类型城市森林内的空气颗粒物(TSP、PM₁₀、PM_2.5、PM₁)进行昼夜24h监测,并同步观测气象因子,分析3种森林内颗粒物质量浓度的变化规律及影响因素。结果表明:1)深圳园山3种生境城市森林内TSP、PM₁₀质量浓度日均值都达到二类环境功能区质量要求,其中HG、SJ的TSP质量浓度甚至达到一类环境功能区质量要求(120μg/m3);PM_2.5质量浓度日均值都达到一类环境功能区质量要求(35μg/m3)。2)不同生境林地内各粒径颗粒物质量浓度存在差异,4种粒径颗粒物日均质量浓度在SJ均为最低(分别为85.51、58.82、14.29、5.13μg/m3);TSP、PM₁₀质量浓度在SL最高(分别为162.19、95.39μg/m3);PM_2.5、PM₁质量浓度在HG最高(分别为21.76、8.29μg/m3)。3)3种林地内4种粒径颗粒物质量浓度总体表现为白天低、夜间高的特点,高峰出现在01:00—07:00,低谷出现于11:00—15:00。4)3种林地间相对湿度、风速、气压等气象因子存在差异;林内4种粒径颗粒物质量浓度与温度、风速表现为显著负相关,与相对湿度呈显著正相关,颗粒物质量浓度变化受多种气象因子共同影响。基于上述研究认为,深圳园山3种生境类型城市森林均为人们提供了一个相对健康的森林游憩环境,人们在11:00—15:00进行森林游憩最为适宜。      

Activation of alkanes with organotransition metal complexes

Alkanes, although plentiful enough to be considered for use as feedstocks in large-scale chemical processes, are so unreactive that relatively few chemical reagents have been developed to convert them to molecules having useful functional groups. However, a recently synthesized iridium (lr) complex successfully converts alkanes into hydridoalkylmetal complexes (M + R-H --> R-M-H). This is a dihydride having the formula Cp(*)(L)lrH(2), where Cp(*) and L are abbreviations for the ligands (CH(3))(5)C(5) and (CH(3))(3)P, respectively. Irradiation with ultraviolet light causes the dihydride to lose H(2), generating the reactive intermediate Cp(*)lrL. This intermediate reacts rapidly with C-H bonds in every molecule so far tested (including alkanes) and leads to hydridoalkyliridium complexes Cp(*)(L)lr(R)(H). Evidence has been obtained that this C-H insertion, or oxidative addition, reaction proceeds through a simple three-center transition state and does not involve organic free radicals as intermediates. Thus the intermediate Cp(*)lrL reacts most rapidly with C-H bonds having relatively high bond energies, such as those at primary carbon centers, in small organic rings, and in aromatic rings. This contrasts directly with the type of hydrogen-abstraction selectivity that is characteristic of organic radicals. The hydridoalkyliridium products of the insertion reactions can be converted into functionalized organic molecules-alkyl halides-by treatment with mercuric chloride followed by halogens. Expulsion (reductive elimination) of the hydrocarbon from the hydridoalkyliridium complexes can be induced by Lewis acids or heat, regenerating the reactive intermediate Cp(*)lrL. Oxidative addition of the corresponding rhodium complexes Cp(*)RhL to alkane C-H bonds has also been observed, although the products formed in this case are much less stable and undergo reductive elimination at -20 degrees C. These and other recent observations provide an incentive for reexamining the factors that have been assumed to control the rate of reaction of transition metal complexes with C-H bonds-notably the need for electron-rich metals and the proximity of reacting centers.     

沉箱填料强化MBR工艺脱氮的试验研究

[目的]研究沉箱填料强化MBR工艺对有机物和氮的去除效果.[方法]通过向MBR反应池投加沉箱填料处理生活污水,研究沉箱填料强化MBR工艺对有机物和氮的去除效果.[结果]未加填料和已投填料的出水COD均值分别为26.8、24.7 mg/L,投加填料比未加填料的脱氮效果要好,对NH3-N去除率均值分别为98.44％、96.37％;对TN去除率均值分别24.03％、16.43％.出水COD和NH3-N浓度低于《城镇污水处理厂污染物排放标准》(GB18918-2002)一级A标准.出水TN主要以NO3-N形式存在(98.06％),NH3-N和NO2-(-0N所占的比例很小,只占整个TN的1.22％和0.72％.对反硝化脱氮研究的进一步建议:①沉箱填料与反应池体积比重增至4％～5％;②更换单个体积较小,内部纤维量较多的填料;③适量减少曝气量,使MBR反应池内的DO减少到1.5 ～3.0 mg/L.[结论]该研究为今后的工程实践提供了理论依据.