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131.
132.
Craig Stroud Sasha Madronich Elliot Atlas Christopher Cantrell Alan Fried Brian Wert Brian Ridley Fred Eisele Lee Mauldin Richard Shetter Barry Lefer Frank Flocke Andy Weinheimer Mike Coffey Brian Heikes Robert Talbot Donald Blake 《Journal of Atmospheric Chemistry》2004,47(2):107-138
Local ozone production and loss rates for the arctic free troposphere (58–85° N, 1–6 km, February–May) during the TroposphericOzone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 kmlayer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratiosup to 300 pptv in February and for NOx mixing ratios up to 500 pptv in May. These NOx limits are an order of magnitude higher thanmedian NOx levels observed, illustrating the strong dependence ofgross ozone production rates on NOx mixing ratios for the majority of theobservations. The threshold NOx mixing ratio needed for netpositive ozone production was also calculated to increase from NOx 10pptv in February to 25 pptv in May, suggesting that the NOx levels needed to sustain net ozone production are lower in winter than spring. This lower NOx threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NOx neededto produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1–3 km layerand net ozone production for the 3–6 km layer throughout the campaign. 相似文献
133.
对大别-苏鲁造山带超高压变质岩矿物稳定同位素的系统研究发现,超高压变质过程中存在少量含水流体,但是流体的活动性很小,在不同岩相界面之间缺乏明显的流体渗透;超高压榴辉岩中的石英脉是蜂期变质后含水矿物降压分解和羟基出溶引起的流体流动结果,不是板块俯冲过程中进变质作用的产物;超高压变质岩经历了广泛的角闪岩相退变质作用,退变质流体主要来源于板块折返过程中超高压矿物中溶解经基的降压出溶。 相似文献
134.
135.
测定水中硫酸根方法的概述 总被引:16,自引:1,他引:16
介绍了测定水中硫酸根的方法和几种常用方法在水质分析中的应用。 相似文献
136.
Oxidation of Elemental Mercury in the Atmosphere; Constraints Imposed by Global Scale Modelling 总被引:1,自引:0,他引:1
We use the global mercury model published by Bergan et al. (1999) to evaluate the potential role of ozone and the hydroxyl radical as gas phase oxidants for the oxidation of elemental mercury in the atmosphere. The magnitude of natural and man-made mercury emissions are taken from recent literature estimates. We consider only two mercury reservoirs, elemental mercury, Hg0, and the more soluble divalent form, HgII. Wet and dry deposition of HgII is explicitly treated.Applying monthly mean fields of ozone for the oxidation of gas phase Hg0 and using the reaction rate by Hall (1995) yields a global transformation of Hg0 to HgII which is too slow to keep the simulated concentration of Hg0 near observed values. This shows that there must be additional important removal processes for Hg0 or that the reaction rate proposed by Hall (1995) is too slow. A simulation in which the oxidation rate was artificially increased, so that the global turn-over time of Hg0 is one year and the simulated average concentration of Hg0 realistic, produces latitudinal and seasonal variations in Hg0 that do not support the hypothesis that gas phase reaction with O3 is the major oxidation process for Hg0.Recent studies indicate that OH may be an important gas phase oxidant for Hg0 (Sommar et al., 2001). Using OH as the sole oxidantand applying the oxidation rate by Sommar et al., we calculate aconcentration of Hg0 well below (about a factor of three) the observations. By prescribing a slower rate, corresponding to a turn-over time of Hg0 of one year, we calculate concentrations of both Hg0 in surface air and HgII in precipitation which correspond reasonably well, both in magnitude and temporal variation, with seasonal observations in Europe and North America. This result supports the suggestion that the oxidation by OH is an important pathway for the removal of Hg0. In view of the uncertainties associated with our calculations, this conclusion should still be regarded as tentative. 相似文献
137.
138.
NUMERICAL MODELING OF CUMULUS CLOUD CHEMISTRY-PART Ⅱ:THE IMPACT OF CUMULUS CLOUD PROCESSES ON OZONE CHEMISTRY* 下载免费PDF全文
Ozone chemistry processes are analyzed during a cumulus cloud process with the model(lCCCM)described in Part Ⅰ.The simulation results show that entire cumulus cloud process can be well described with the development of vertical velocities and liquid water content which are the two most outstanding features of cumulus clouds.Ozone chemistry is strongly influenced by cumulus clouds.NOx can be transported upwards above 4 km in the first 20 minutes of the convection event and form a relative higher concentration area which enhances the production of ozone.Two areas appear during the convection event:area of net ozone production and area of net ozone depletion.The area of ozone depletion coincides with the area of liquid water within cloud.Results show that the aqueous phase(cloud water and rainwater)can alter gas ozone level through two ways:one is scavenging free radicals(HO2)from the gas phase and thereby inhibiting the reactions of transformation to NO2 from NO,which results in reduction of the gas source of ozone;the other is aqueous phase chemical reactions which consume ozone in the aqueous phase.Calculations reveal that the reaction O3+OH→HO2 is the main pathway of ozone depletion in gas phase during the process of cumulus clouds. 相似文献
139.
Using a relative rate method, rate constants have been measured for the gas-phase reactions of OH and NO3 radicals with pinonaldehyde, caronaldehyde and sabinaketone at 296 ± 2 K. The OH radical reaction rate constants obtained are (in units of 10–12 cm3 molecule–1 s–1): pinonaldehyde, 48 ± 8; caronaldehyde, 48 ± 8; and sabinaketone, 5.1 ± 1.4, and the NO3 radical reaction rate constants are (in units of 10–14 cm3 molecule–1 s–1): pinonaldehyde, 2.0 ± 0.9; caronaldehyde, 2.5 ± 1.1; and sabinaketone, 0.036 ± 0.023, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Upper limits to the O3 reaction rate constants were also obtained, of <2 × 10–20 cm3 molecule–1 s–1 for pinonaldehyde and caronaldehyde, and <5 × 10–20 cm3 molecule–1 s–1 for sabinaketone. These reaction rate constants are combined with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals and O3 to calculate tropospheric lifetimes and dominant transformation process(es) of these and other monoterpene reaction products. 相似文献
140.
海图上岛屿自动选取的一种模型 总被引:4,自引:0,他引:4
岛屿的自动选取是实现岛屿自动综合的前提,在分析岛屿选取特点的基础上,给出了岛屿自动选取模型。该模型采用了系统聚类和Vironoi图两项关键技术,在整体选取的基础上实施局部控制,使得岛屿选取更加趋向客观实际。 相似文献