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1.
A. P. Altshuller 《Journal of Atmospheric Chemistry》1991,12(1):19-61
The product distributions have been calculated for more abundant alkanes contributing most of the carbon atoms in the alkane fraction of an ambient air hydrocarbon mixture reasonably representative of U.S. emissions. The effects of ambient temperatures on product yields has been calculated for a range of temperatures from 250 to 330 K. The sensitivity of product yields to uncertainties in alkoxy radical process rate constants has been examined with emphasis on uncertainties in decomposition reactions. Chemical lifetimes are estimated at 300 K under summertime conditions for hydrocarbons and for products of alkane photooxidation in the atmosphere. The atmospheric distribution of alkanes and products is evaluated in terms of the extent to which reaction processes are likely to occur in the planetary boundary layer compared to the free troposphere.The calculations predict a substantial effect of temperature on product yields. A large decrease in alkyl nitrate yields and a smaller decrease in ketone yields occur with increasing temperature. The yields of the short-lived, more reactive aldehydes undergo substantial increases with increasing temperature. Lower yields of ketones and higher yields of aldehydes are associated with the use of higher compared to lower decomposition process rate constants. For the type of U.S. hydrocarbon mixture available from measurements, 16 oxygenated products account for more than 60% of the total alkane carbon atoms converted to products, with most of these carbon atoms accounted for by four products. The effects of increased temperature on product reactivity and radical production may also influence O3 production. 相似文献
2.
Ingvar Wängberg 《Journal of Atmospheric Chemistry》1993,17(3):229-247
The NO3 radical initiated oxidation of cyclopentene, cyclohexene and 1-methyl-cyclohexene has been studied. The products formed in an N2O5-NO2-N2-O2-cycloalkene-static reactor system, at 0.1 MPa and 296 K, were investigated using long path FTIR. The principal products were aldehydes formed via a ring opening process. The reactions also resulted in significant yields of three types of ring retaining nitrooxy-substituted compounds. The average yields of alkyl nitrates from, e.g., reactions with cycloalkene were 25.1% 2-oxo-cyclohexyl nitrate, 22.8% 2-hydroxy-cyclohexyl nitrate and 4.0% 1,2-cyclohexyl dinitrate. The mechanisms involved resembles those proposed for acyclic alkenes. In absence of NO, -oxo and -hydroxy-cycloalkyl nitrates are formed via self reactions of -nitrooxy substituted cycloalkyl peroxy radicals. Estimated branching ratios for the reactants leading to ring retaining products in the presence and in the absence of NO are given and the possible relevance of these reactions for cycloalkenes under tropospheric conditions is discussed. 相似文献
3.
Rate constants for the reaction of OH radicals with some branched alkyl nitrates have been measured applying a competitive technique. Methyl nitrite photolysis in synthetic air was used as OH radical source at 295±2 K and 1000 mbar total pressure. Using a rate constant of 2.53×10-12 cm3 s-1 for the reaction of OH radicals with n-butane as reference, the following rate constants were obtained (units: 10-12 cm3 s-1): isopropyl nitrate, 0.59±0.22; isobutyl nitrate, 1.63±0.20; 3-methyl-2-butyl nitrate, 1.95±0.15; 2-methyl-1-butyl nitrate, 2.50±0.15; 3-methyl-1-butyl nitrate, 2.55±0.35. These values have been combined with the literature data to recalculate the substituent factors F(X) for the different nitrate groups which can be used to predict OH rate constants for organic nitrates for which experimental data are not available.Preliminary measurements of the photolysis frequency of isopropyl nitrate have shown that for this nitrate as a model substance, OH reactions and direct photolysis are of equal importance under tropospheric conditions. 相似文献
4.
Alkyl nitrate yields from the NO x photooxidations of neopentane, 2-methylbutane and 3-methylpentane have been determined over the temperature and pressure ranges 281–323 K and 54–740 torr, respectively. The formation of the alkyl nitrates is attributed to the reaction pathway (1b) $${\text{RO}}_{\text{2}} + {\text{NO}}^{{\text{ }}\underrightarrow {\text{M}}} {\text{ RONO}}_{\text{2}}$$ and rate constant ratios k 1b/(k 1a+k 1b) are estimated, where (1a) is the reaction pathway (1a) $${\text{RO}}_{\text{2}} + {\text{NO}} \to {\text{RONO}}_{\text{2}} .$$ A method for estimating this rate constant ratio for primary, secondary and tertiary alkyl peroxy radicals is presented. 相似文献
5.
Franziska Strauss Erwin Schmid Elena Moltchanova Herbert Formayer Xiuying Wang 《Climatic change》2012,111(3-4):641-664
Climate change affects major biophysical processes in agricultural crop production (e.g. evaporation of plants and soils, nutrient cycles, and growth of plants). This analysis aims to assess some of these effects by simulating regional climate projections that are integrated in the biophysical process model EPIC (Environmental Policy Integrated Climate). Statistical climate models have been developed for six weather parameters based on daily weather records of a weather station in the Austrian Marchfeld region from 1975 to 2006. These models have been used to estimate daily weather parameters for the period 2007–2038. The resulting projections have been compared to climate scenarios provided from the TYNDALL Centre for Climate Change Research, which are based on General Circulation Models (GCMs). The comparison indicates some differences, namely a smaller temperature increase and a higher precipitation amount in the TYNDALL data. Both climate datasets have been used to simulate impacts of climate change on crop yields, topsoil organic carbon content, and nitrate leaching with EPIC and thus to perform a sensitivity analysis of EPIC. Yield impacts have been assessed for four simulated crops, i.e. 6.2?t/ha for winter wheat for statistical climate projections compared to 5.7?t/ha for TYNDALL scenarios, 10.6?t/ha for corn compared to 10.5?t/ha, 3.9?t/ha for sunflower compared to 3.7?t/ha, and 4.5?t/ha for spring barley compared to 4.3?t/ha—all values as an average over the period 2007–2038. Smaller differences have been simulated for topsoil organic carbon content i.e. 55.1?t/ha for the statistical climate projections compared to 55.3?t/ha for the TYNDALL scenarios and nitrate leaching i.e. 7.1?kg/ha compared to 11.1?kg/ha. All crop yields as well as topsoil organic carbon content and nitrate leaching show highest sensitivity to temperature and solar radiation. 相似文献
6.
The reactions of the alkanes under atmospheric conditions and in the presence of oxides of nitrogen are reviewed and evaluated. Particular emphasis is placed upon their subsequent reactions after the initial OH radical reaction under conditions where the alkyl peroxy radicals produced react predominantly with NO, rather than with HO2 and/or RO2 radicals. Methods are discussed for estimating the overall OH radical rate constants, the number of molecules of NO consumed per alkane molecule reacted, and the products formed and their yields. 相似文献
7.
在过去的20多年里,中外对硫酸盐气溶胶做了大量的研究,对它在大气中的排放、含量、光学特征和辐射强迫有了深入的认识;由于硝酸盐气溶胶在大气中平均含量比硫酸盐低很多,因此过去人们对硝酸盐的研究没有给予重视。然而,近年来的研究表明,硝酸盐气溶胶的散射性质在某些波段甚至强于硫酸盐;同时,由于未来对人为硫酸盐前体物的减排,硫酸盐气溶胶排放会大幅度减少,而硝酸盐气溶胶的排放却增长迅速,其在人为气溶胶中所占的比重越来越高,将会导致其在未来造成的辐射强迫有可能超过硫酸盐,使得其在地区范围内和季节尺度上成为重要的辐射强迫和气候影响因子。中国是硝酸盐气溶胶排放量较大的地区,硝酸盐对未来中国气候和气候变化的影响显得越来越重要。因此,就近年来有关硝酸盐气溶胶的排放和在大气中的浓度变化、光学厚度分布特征及其辐射强迫的研究进展做了回顾和介绍,并对其未来的研究做了展望。 相似文献
8.
The room-temperature photodecomposition of acetone diluted with synthetic air was studied at nine wavelengths in the spectral region 250–330 nm. The quantum yields for the products CO2 and CO indicated that it was not possible to suppress secondary reactions sufficiently, even with acetone/air mixing ratios as low as 150 ppmv, to derive from these data primary acetone photodissociation quantum yields. The behavior of CO2 and CO formation nevertheless provides some insight into the mechanism of acetone photodecomposition. When small amounts of NO2 are added to acetone/air mixtures, peroxyacetyl nitrate (PAN) is formed. Quantum yields for PAN are reported. They are better suited to represent primary quantum yields for acetone photodissociation, because PAN is a direct indicator for the formation of acetyl radicals. The data were combined with absorption cross-sections for acetone measured at wavelengths up to 360 nm to calculate photodissociation coefficients applicable to the ground-level atmosphere at 40° northern latitude. Comparison with the rates for the reaction of acetone with OH radicals shows that both processes contribute almost equally to the total acetone losses in the lower atmosphere. The resulting atmospheric life time at 40° northern latitude is 32 days, on average. This value must be considered an upper limit, since it does not take into account acetone losses due to the reaction of excited triplet acetone with oxygen. 相似文献
9.
为了构建具有科学可比性和客观实用性的干湿气候评判指标。基于广义的水分平衡原理, 从干燥度表达式出发, 通过细化参量和参数化处理, 恰当地加入降水有效性和前期气候影响的修正项, 构建了适用于云南高原山地评价气候干湿度的修正表示式; 应用典型相关分析, 找到了一个与气候蒸发量高度相关的特征量ST=S×T(T, S分别为平均气温、 日照时数), 简化了气候干湿指数表达式的重要参量——气候蒸发量的模拟求算, 实现了由实时常规气象要素观测值对气候干湿指数的简易估算。经业务应用, 提出的干湿指数可客观反映非灌溉区农田土壤湿度状况和变化趋势, 对典型春\, 夏季连旱年干雨季转换期的气候干湿空间分布和逐月变化模拟效果良好。 相似文献
10.
N. Galindo J.F. Nicols E. Yubero S. Caballero C. Pastor J. Crespo 《Atmospheric Research》2008,88(3-4):305-313
The present study was carried out between October 2003 and September 2004 at an urban background station near the Mediterranean coast in southeastern Spain. The sulfate and nitrate content was determined in 332 PM10 and PM2.5 daily samples. The results show that the seasonal variation of nitrate measured in PM10 does not correspond with what has been observed at other locations in the Iberian Peninsula, where the minima are reached during the summer months due to decomposition of ammonium nitrate at high temperatures. The recorded levels of PM10 nitrate were slightly higher in summer due to an increase in the concentrations of coarse mode nitrate. On the contrary, both the concentrations and the percentages of nitrate in PM2.5 were lowest from June to September. The sulfate levels in both PM10 and PM2.5 were maxima in summer because the oxidation rate of SO2 increases with solar radiation. An elevated correlation (0.72 < r < 0.92) between the monthly average concentrations and percentages of sulfate and solar radiation has been found. We have also investigated the influence that Saharan dust intrusions and high pollution episodes have upon the sulfate and nitrate concentrations. Both types of events increased NO3− and SO42− levels, particularly the high pollution episodes. 相似文献
11.
Summary Structures in atmospheric Integrated Water Vapor (IWV) have been studied for the three successive cyclones, Kerstin, Liane
and Monika, which controlled the meteorological conditions in the Baltic Sea catchment region in the period from 28 August
to 5 September 1995 (part of the PIDCAP observational campaign defined within BALTEX). Several model predictions of these
cyclones have been performed with a regional atmospheric general circulation model (RACMO). The impact of two different versions
of the model physics package (standard ECHAM4 and a revised version with modifications in the cloud and turbulence scheme)
has been investigated. Model predicted IWV has been evaluated with GPS station data from several stations in Sweden and Finland.
For the most strongly developed cyclone Monika, the revised scheme generates more pronounced IWV structures, with well defined
bands of high and low values of IWV curving into the center of the cyclone. In particular, the shape of the minima are in
better agreement with the GPS station data, and the consistency between two subsequent model forecasts is also larger with
the revised physics package. For the weaker systems, Kerstin and Liane, results from both model versions are very similar.
Received August 11, 2000 Revised February 13, 2001 相似文献
12.
Henry's law coefficients of 15 alkyl nitrates, keto-, hydroxy-, and dinitrates of atmospheric interest have been measured, mostly over the temperature range 1–25°C. The compounds are stable in aqueous solution. Where literature data were available, Henry's law coefficients are in very good agreement. It is concluded that dissolution in cloud and rain water is not an important loss process for alkyl mononitrates in the atmosphere. The residence times of the more soluble bifunctional organic nitrates, however, are significantly affected or even controlled by washout and rainout. Gas chromatographic analysis of bifunctional nitrates in preconcentrated atmospheric samples may be adversely affected by the adsorptive properties of these compounds. 相似文献
13.
The solubilities and hydrolysis rates of PAN (peroxyacetyl nitrate) and its homologues PPN (peroxypropionyl nitrate), PnBN (peroxy-n-butyl nitrate), PiBN (peroxy-isobutyl nitrate) and MPAN (peroxymethacryloyl nitrate) in liquid water have been studied at 20 °C. Temperature dependencies were measured for PAN and PPN. The solubilities of peroxyacyl nitrates decrease smoothly with increasing carbon-chain length fromH (293 K)=4.1 M atm–1 (PAN) toH (293 K)=1.0 M atm–1 (PiBN). Hydrolysis-rate constants, which cover the range fromk
h
(293 K)=(2.4–7.4)×10–4 s–1, do not show a systematic chain-length dependency. Solubilities of PAN and PPN in solutions which mimic the composition and ionic strength of sea water are 15% and 20% lower than in pure water. The hydrolysis rate constants are not affected. 相似文献
14.
This paper reports the results of a study on the transformation of benzene in the presence of solid nitrate salts (NaNO3, NH4NO3) under irradiation in a gas-solid photoreactor. Sodium and ammonium nitrate have been chosen as representative of the composition
of atmospheric particulate, benzene as a model aromatic molecule. The purpose is to simulate the transformations that aromatic
compounds undergo on the surface of dispersed particles in the atmosphere. Irradiation of sodium nitrate causes hydroxylation
and nitration of benzene, yielding phenol and nitrobenzene. This is most likely due to the generation of •OH and •NO2 radicals upon nitrate photolysis, with •OH + O2 leading to the formation of phenol and •OH + •NO2 yielding nitrobenzene. The percentage of oxygen in the reaction environment influences the transformation pathways, with
phenol formation being favoured and nitrobenzene formation depressed by high O2 concentration. In the presence of hematite (α-Fe2O3, another component of atmospheric particulate) very relevant formation of nitrobenzene takes place even with 21% oxygen (simulated
air), indicating that the interaction between hematite and nitrate can lead to the formation of aromatic nitroderivatives
on the surface of atmospheric particulate. The effect of hematite is possibly due to protonation of peroxynitrite, formed
upon nitrate photoisomerisation, to peroxynitrous acid, a powerful nitrating agent. A similar effect leads to relevant formation
of nitrobenzene under atmospheric conditions upon irradiation of the acid salt ammonium nitrate. 相似文献
15.
Miquel Gay 《Atmospheric Research》2007,83(2-4):201-210
Considering the number of dead people, the worst tornado in the last two centuries in Spain is presented. The words used to describe the phenomenon have hidden it to the general public and the specialist The coetaneous press and other printed sources have been revised, and this has let us know the true sense of those words as well as the sequence of the tornadic event.The synoptic situation that was presented by some European Meteorological Offices in 1886 has been revised when all available data and some indirect information have been included.Tornado track and force have been plotted on the actual map of the city following the available information in the newspapers and other documents. Other subjective comments made by the paper writers have allowed us to find out some psychological and sociological aspects used to enhance the tragic perception of their readers. 相似文献
16.
采用EFAST方法和SCE-UA算法优化WheatSM模型参数,采用区域模拟和单站插值的方法对2013—2017年鹤壁市冬小麦各发育期日数和产量进行模拟修订,为WheatSM作物模型在豫北地区的业务应用提供参考。研究发现:区域模拟方法对鹤壁地区冬小麦生育期开始日期的模拟效果除出苗期、越冬期的外,其他均好于单点插值方法的。单点插值方法对越冬期的模拟效果明显好于区域模拟方法的。冬小麦产量的模拟效果区域模拟方法也比单点插值方法好,但两种结果的相对误差均较大。通过对WheatSM模型得到的冬小麦气象产量模拟结果进行修订,可以明显提高模型产量模拟结果。2013—2017年鹤壁地区模拟产量的误差为-17. 92%～-2. 98%,RMSE为1114. 9 kg/hm~2,NMSE为12. 59,模拟效果较好。利用区域模拟方法可以对区域内单个站点的冬小麦生长发育和产量进行模拟,但对越冬期开始时间的模拟需要参考单点插值方法的相应结果。 相似文献
17.
CO2和O3浓度倍增对作物影响的研究进展 总被引：14，自引：0，他引：14
文中利用自行设计的OTC - 1型开顶式气室进行了 9a的田间试验 ,取得了一批质量可靠的试验数据 ,分析了CO2 浓度倍增对大豆、冬小麦、棉花、玉米、春小麦和谷子的生物量、产量及品质的影响 ,结果表明CO2 浓度倍增对上述 6种作物的生物量及产量的影响均是正效应 ,对冬小麦、棉花和谷子品质的影响可能是有利的 ,对玉米品质的影响可能是不利的 ,对大豆的影响不大 ;分析了O3 浓度倍增对冬小麦、水稻、油菜和菠菜生物量、产量及品质的影响 ,结果表明O3 浓度倍增对上述 4种作物生物量的影响均是负效应 ,对冬小麦和水稻的产量影响是负效应 ,但是冬小麦和水稻籽粒中粗蛋白和 17种氨基酸含量都有所增加 ;分析了CO2 和O3 浓度复合倍增对大豆生物量、产量及品质的影响 ,结果是生物量和产量呈增加趋势 ,说明了CO2 的正效应大于O3 的负效应。采用作物模型数值模拟方法 ,分析了CO2 和O3 浓度倍增对冬小麦生物量及产量的影响。 相似文献
18.
We analyze the response of Kenyan maize yields to near-term climate change and explore potential mitigation options. We model county level yields as a function of rainfall and temperature during a period of increased regional warming and drying (1989–2008). We then do a counter factual analysis by comparing existing maize yields from 2000 to 2008 to what yields might have been if observed warming and drying trends had not occurred. We also examine maize yields based on projected 2026–2040 climate trends. Without the observed warming and drying trends, Eastern Kenya would have had an 8% increase in maize yields, which in turn would have led to a net production increase of 500,000 metric tons. In Western Kenya, the magnitude of change is higher but the relative changes in predicted values are smaller. If warming and drying trends continue, we expect future maize yields to decline by 11% in Eastern Kenya (vs. 7% in Western Kenya). We also examine whether these future losses might be offset through agricultural development. For that analysis, we use a household panel dataset (2000, 2005) with measurements of individual farm plot yields, inputs, and outputs. We find that under a scenario of aggressive adoption of hybrid seeds and fertilizer usage coupled with warming and drying trends, yields in Western Kenya might increase by 6% while those in Eastern Kenya could increase by 14%. This increase in yields might be larger if there is a corresponding increase in usage of drought-tolerant hybrids. However, wide prediction intervals across models highlight the uncertainty in these outcomes and scenarios. 相似文献
19.
本文应用帕尔默旱度模式的基本原理,选取平凉等11个站点的资料,建立了适用于黄土高原西北部地区的修正的帕尔默旱度模式。并用此模式分析了本区的干旱特征。结果表明,此模式是分析本区干旱的一个良好工具。 相似文献
20.
A. Plewka T. Gnauk E. Brüggemann C. Neusüss H. Herrmann 《Journal of Atmospheric Chemistry》2004,48(2):131-156
Inorganic ions, organic carbon (OC), elemental carbon (EC) and a variety of organic single species in airborne particles have been determined at the research station of the Leibniz – Institut für Troposphärenforschung (IfT) in Melpitz (Germany) in autumn 1997.Samples of eight selected measurement events were divided in two groups in order to investigate differences in the chemical composition of particles originating from southwesterly (SW – developed EU countries) or from easterly directions (E – less developed eastern countries). Differences between these two groups were tested statistically by Student's t-test.Five stage cascade impactor samples show nitrate as most abundant in the accumulation mode in the SW group. EC and sulphate show the most abundant mass fractions in the E group. That can be considered as a consequence of domestic coal heating and coal-fired power plant emissions in the region of westerly Poland, northern Czech Republic and easterly Germany. Higher nitrate concentrations in the SW group can be explained by stronger NO
x
emissions caused by the leeward plume of the conurbation of Leipzig, as well as by the still higher traffic density in western Germany.The methane sulphonic acid (MSA) mass fraction was higher for SW air masses in accumulation mode particles, probably indicating marine origin. Succinic acid also showed higher mass fractions for the SW group. This could be caused by primary emission in automobile exhaust gases and photochemical formation during transport from SW. Indeed, during SW sampling, solar radiation intensity was higher than during E sampling.The observed differences in the particle composition are an expression of the still existing technology gradient in Europe. Future campaigns could show the development to a joint economy with smaller differences in anthropogenic emissions. 相似文献