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1.
Anthropogenic SO(2) emissions may exert a significant cooling effect on climate in the Northern Hemisphere through backscattering of solar radiation by sulfate particles. Earlier estimates of the sulfate climate forcing were based on a limited number of sulfate-scattering correlation measurements from which a high sulfate-scattering efficiency was derived. Model results suggest that cloud processing of air is the underlying mechanism. Aqueous phase oxidation of SO(2) into sulfate and the subsequent release of the dry aerosol by cloud evaporation render sulfate a much more efficient scatterer than through gas-phase SO(2) oxidation. 相似文献
2.
Photolysis of sulfuric acid vapor by visible solar radiation 总被引：1，自引：0，他引：1
Atmospheric field measurements and models of the stratospheric sulfate aerosol layer led to the suggestion that sulfuric acid (H2SO4) must photolyze at high altitudes. We propose that excitation of vibrational overtones of H2SO4 and its hydrate in the near-infrared and visible leads to photolysis, forming sulfur trioxide (SO3) and water. On the basis of absorption cross sections calculated with ab initio methods calibrated to experimental measurements, we estimated J values that are sufficient to explain stratospheric and mesospheric sulfur dioxide (SO2) concentrations and the observation of the sulfate layer. 相似文献
3.
Aerosol effect on cloud droplet size monitored from satellite 总被引：5，自引：0，他引：5
Aerosol concentration and cloud droplet radii derived from space-borne measurements are used to explore the effect of aerosols on cloud microphysics. Cloud droplet size is found to be largest (14 micrometers) over remote tropical oceans and smallest (6 micrometers) over highly polluted continental areas. Small droplets are also present in clouds downwind of continents. By using estimates of droplet radii coupled with aerosol load, a statistical mean relationship is derived. The cloud droplet size appears to be better correlated with an aerosol index that is representative of the aerosol column number under some assumptions than with the aerosol optical thickness. This study reveals that the effect of aerosols on cloud microphysics is significant and occurs on a global scale. 相似文献
4.
Polar stratospheric clouds (PSCs) are important for the chemical activation of chlorine compounds and subsequent ozone depletion. Solid PSCs can form on sulfuric acid tetrahydrate (SAT) (H2SO4·4H2O) nuclei, but recent laboratory experiments have shown that PSC nucleation on SAT is strongly hindered. A PSC formation mechanism is proposed in which SAT particles melt upon cooling in the presence of HNO3 to form liquid HNO3-H2SO4-H2O droplets 2 to 3 kelvin above the ice frost point. This mechanism offers a PSC formation temperature that is defined by the ambient conditions and sets a temperature limit below which PSCs should form. 相似文献
5.
Particulate air pollution has been shown to strongly suppress precipitation from convective clouds over land. New observations show that precipitation from similar polluted clouds over oceans is much less affected, because large sea salt nuclei override the precipitation suppression effect of the large number of small pollution nuclei. Raindrops initiated by the sea salt grow by collecting small cloud droplets that form on the pollution particles, thereby cleansing the air. Therefore, sea salt helps cleanse the atmosphere of the air pollution via cloud processes. This implies that over oceans, the climatic aerosol indirect effects are significantly smaller than current estimates. 相似文献
6.
Molina MJ Zhang R Wooldridge PJ McMahon JR Kim JE Chang HY Beyer KD 《Science (New York, N.Y.)》1993,261(5127):1418-1423
Polar stratospheric clouds (PSCs) play a key role in stratospheric ozone depletion. Surface-catalyzed reactions on PSC particles generate chlorine compounds that photolyze readily to yield chlorine radicals, which in turn destroy ozone very efficiently. The most prevalent PSCs form at temperatures several degrees above the ice frost point and are believed to consist of HNO(3) hydrates; however, their formation mechanism is unclear. Results of laboratory experiments are presented which indicate that the background stratospheric H(2)SO(4)/H(2)O aerosols provide an essential link in this mechanism: These liquid aerosols absorb significant amounts of HNO(3) vapor, leading most likely to the crystallization of nitric acid trihydrate (NAT). The frozen particles then grow to form PSCs by condensation of additional amounts of HNO(3) and H(2)O vapor. Furthermore, reaction probability measurements reveal that the chlorine radical precursors are formed readily at polar stratospheric temperatures not just on NAT and ice crystals, but also on liquid H(2)SO(4) solutions and on solid H(2)SO(4) hydrates. These results imply that the chlorine activation efficiency of the aerosol particles increases rapidly as the temperature approaches the ice frost point regardless of the phase or composition of the particles. 相似文献
7.
Previous studies have suggested that hydroxymethanesulfonate ion (HMSA) can be an important species in fog and cloud water. Formation of HMSA explains observed excesses of sulfur in the S(IV) state (+4 oxidation state) and formaldehyde (CH(2)O) in fogs and clouds. HMSA was determined in fog water by a novel ion-pairing chromatographic technique. Concentrations in samples collected in Bakersfield, California, within 5 kilometers of major sources of sulfur dioxide (SO(2)), were as high as 300 micromoles per liter. Total CH(2)O and S(IV) concentrations, which were measured independently, ranged from 10 to 200 and 5 to more than 300 micromoles per liter, respectively. Concentrations of CH(2)O, S(IV), and HMSA at Buttonwillow, California, which is 15 kilometers from the nearest source of SO(2), were less than those at Bakersfield but not absent. These data confirm that HMSA forms in atmospheric water droplets and can reach appreciable concentrations. HMSA represents an important source of acidity for water droplets and may also play a role in long-distance transport and transformation of SO(2). 相似文献
8.
《Science (New York, N.Y.)》1983,220(4595):360
In the report "Cloud droplet deposition in subalpine balsam fir forests: Hydrological and chemical inputs" by G. M. Lovett et al. (24 Dec., p. 1303), two errors appeared in Table 2 on page 1304. The cloud deposition of SO(4)(2-), incorrectly reported as 275.8 kg ha(-1) year(-1), should have been 137.9 kg ha(-1) year(-1). The percentage of the sum contributed by clouds, reported as 81 for SO(4)(2-), should have been 68. 相似文献
9.
10.
Phytoplankton and cloudiness in the Southern Ocean 总被引：1，自引：0，他引：1
The effect of ocean biological productivity on marine clouds is explored over a large phytoplankton bloom in the Southern Ocean with the use of remotely sensed data. Cloud droplet number concentration over the bloom was twice what it was away from the bloom, and cloud effective radius was reduced by 30%. The resulting change in the short-wave radiative flux at the top of the atmosphere was -15 watts per square meter, comparable to the aerosol indirect effect over highly polluted regions. This observed impact of phytoplankton on clouds is attributed to changes in the size distribution and chemical composition of cloud condensation nuclei. We propose that secondary organic aerosol, formed from the oxidation of phytoplankton-produced isoprene, can affect chemical composition of marine cloud condensation nuclei and influence cloud droplet number. Model simulations support this hypothesis, indicating that 100% of the observed changes in cloud properties can be attributed to the isoprene secondary organic aerosol. 相似文献
11.
[目的]探讨浓硫酸和GA3浸种及其交互作用对榛种子萌发的影响。[方法]以平榛为试材,将榛种子置于浓硫酸中分别浸种0、10、20和30 min,对酸蚀处理的种子,分别用0、100、300和500 mg/L赤霉素浸种24 h,经与用湿沙自然层积3个月后在恒温箱中催芽。[结果]浓硫酸酸蚀可提高榛种子发芽率,且随着浓硫酸酸蚀时间的延长,榛子的出苗率逐渐升高,但酸蚀时间过长则容易使种胚受伤,影响发芽,以20 min的酸蚀效果较好。GA3能有效打破榛种子休眠,以300 mg/LGA3处理效果较好。浓硫酸和GA3对促进种子萌发有显著的交互作用,以浓硫酸酸蚀20 min和300 mg/L GA3的处理组合对种子发芽率的提高效果最为显著(P<0.05)。[结论]浓硫酸酸蚀榛种子配合赤霉素浸种能够打破榛子的休眠,提高发芽率。 相似文献
12.
通过对2008年4月21日河北省正定1次飞机探测气溶胶垂直分布和云微物理结构的资料进行分析,结果表明：探测的气溶胶数浓度为10^2～10^3个／cm^3,平均直径为0．19～0．70μm;云滴数浓度为10^0～10^2／cm^3,云滴平均直径为4～15μm。边界层是气溶胶和云凝结核（CCN）最密集处,云区为1176～2465m,云底云滴数浓度低,蒸发释放核膜态粒子使得气溶胶进入云层后数浓度减少幅度较小,另云滴对CCN有消耗作用。气溶胶平均谱基本为双峰型,高层云区云滴增加促使气溶胶由核膜态向积聚模态、粗模态转变。云滴谱较复杂,具有单峰型和双峰型,云顸平均谱最宽。 相似文献
13.
Ultraviolet spectroscopy of the Venus cloud tops reveals absorption features attributed to sulfur dioxide in the atmosphere above the cloud tops. Measurements of scattered sunlight at 2663 angstroms show evidence for horizontal and vertical inhomogeneities in cloud structure. Images of the planet at SO(2) absorption wavelengths show albedo features similar to those seen at 3650 angstroms from Mariner 10. Airglowv emissions are consistent with an exospheric temperatuire of approximately 275 K, and a night airglows emission has been detected, indicating the precipitation of energy into the dark thermosphere. 相似文献
14.
Berndt T Böge O Stratmann F Heintzenberg J Kulmala M 《Science (New York, N.Y.)》2005,307(5710):698-700
We investigated the formation of new particles in a laboratory study, starting from H2SO4 produced in situ through the reaction of OH radicals with SO2. Newly formed particles were observed for H2SO4 concentrations above 7 x 10(6) per cubic centimeter. At 293 kelvin, a rough estimate yielded a nucleation rate of 0.3 to 0.4 particles per cubic centimeter per second for approximately 10(7) particles per cubic centimeter of H2SO4 (particle size >/= 3 nanometers). These findings are in agreement with observations from the atmosphere. The results demonstrate that under laboratory conditions similar to the atmosphere, particle formation occurs at atmospheric H2SO4 concentration levels. 相似文献
15.
Bell JF Crisp D Lucey PG Ozoroski TA Sinton WM Willis SC Campbell BA 《Science (New York, N.Y.)》1991,252(5010):1293-1296
Near-infrared spectra of a bright and a dark thermal emission feature on the night side of Venus have been obtained from 2.2 to 2.5 micrometers (microm) at a spectral resolution of 1200 to 1500. Both bright and dark features show numerous weak absorption bands produced by CO(2), CO, water vapor, and other gases. The bright feature (hot spot) emits more radiation than the dark feature (cold spot) throughout this spectral region, but the largest contrasts occur between 2.21 and 2.32 microm, where H(2)SO(4) clouds and a weak CO(2) band provide the only known sources of extinction. The contrast decreases by 55 to 65 percent at wavelengths longer than 2.34 microm, where CO, clouds, and water vapor also absorb and scatter upwelling radiation. This contrast reduction may provide direct spectroscopic evidence for horizontal variations in the water vapor concentrations in the Venus atmosphere at levels below the cloud tops. 相似文献
16.
Phase changes in stratospheric aerosols were studied by cooling a droplet of sulfuric acid (H(2)SO(4)) in the presence of nitric acid (HNO(3)) and water vapor. A sequence of solid phases was observed to form that followed Ostwald's rule for phase nucleation. For stratospheric partial pressures at temperatures between 193 and 195 kelvin, a metastable ternary H(2)SO(4)-HNO(3) hydrate, H(2)SO(4) . HNO(3) . 5H(2)O, formed in coexistence with binary H(2)SO(4) . kH(2)O hydrates (k = 2, 3, and 4) and then transformed to nitric acid dihydrate, HNO(3) . 2H(2)O, within a few hours. Metastable HNO(3) . 2H(2)O always formed before stable nitric acid trihydrate, HNO(3).3H(2)O, under stratospheric conditions and persisted for long periods. The formation of metastable phases provides a mechanism for differential particle growth and sedimentation of HNO(3) from the polar winter stratosphere. 相似文献
17.
Snowden SL Mebold U Hirth W Herbstmeier U Schmitt JH 《Science (New York, N.Y.)》1991,252(5012):1529-1532
The detection by the Roentgen satellite (ROSAT) x-ray telescope of a shadow in the 1/4-kiloelectron volt (C band, 0.1 to 0.284 kiloelectron volt) cosmic diffuse background is reported. The location and morphology of the local minimum in x-rays are in clear agreement with a discrete H I cloud. The shadow is very deep with a minimum level at 50 percent of the surrounding emission; therefore, a minimum of 50 percent of the observed off-cloud flux must originate on the far side of the cloud. The analysis of H I velocity components links the cloud with the Draco nebula (distance approximately 600 parsecs); it then follows that there is significant 1/4-kiloelectron volt x-ray emission at a large distance (>400 parsecs) from the galactic plane along this line of sight. The extent of the distant emission region is uncertain, and, if it indicates the existence of a hot galactic corona, it must be patchy in nature. 相似文献
18.
19.
落叶前根外追肥对苹果休眠期营养状况的影响 总被引：3，自引：0，他引：3
本文于落叶前向苹果树根外追施矿质肥料,落叶后采样测定了氨基酸、可溶性糖和Ｐ、Ｋ、Ｂ、Ｃａ的含量。结果表明,喷含Ｃａ２＋、Ｋ＋、ＳＯ２－４、Ｈ２ＰＯ－４、ＮＯ－３及尿素等肥料均使粗根中氨基酸含量下降,除ＳＯ２－４外其它肥料能促进氨基酸由长枝下运至根系;ＫＮＯ３、Ｂ使根枝中可溶性糖含量增加,而Ｋ２ＳＯ４、ＣａＳＯ４、Ｃａ（ＮＯ３）２、ＫＨ２ＰＯ４使其含量下降;根外追肥促进Ｐ在粗根和枝条中贮存,其效果依次是：ＫＨ２ＰＯ４＞Ｋ２ＳＯ４＞尿素＞ＫＮＯ３,ＫＨ２ＰＯ４、尿素促进Ｃａ在短枝中的贮藏;Ｂ在喷肥后略有减少;根外追肥对Ｋ＋在粗根贮藏影响不显著。 相似文献
20.
[目的]筛选出4Na2SO4.2H2O2.NaCl加合物的适宜稳定剂。[方法]通过测定不同稳定剂的稳定度筛选出适合加入4Na2SO4.2H2O2.NaCl加合物的复合稳定剂。[结果]不同的稳定剂对4Na2SO4.2H2O2.NaCl的稳定效果不同。就单一稳定剂而言,多基络合剂(EDTA、TEA、DTPA)对4Na2SO4.2H2O2.NaCl的稳定效果较好,4Na2SO4.2H2O2.NaCl的稳定度在95.21%~96.91%,所以单一稳定剂应该首选有机多基络合剂。复合稳定剂比单一稳定剂的稳定效果好,选择无机和有机物作为复合稳定剂时,首先要选择有利于环境保护和无毒的物质。在其他制备条件不变的情况下,随着稳定剂使用量的增加,4Na2SO4.2H2O2.NaCl的稳定度增大。当稳定剂的加入量达0.16 g时,4Na2SO4.2H2O2.NaCl的稳定度达97.2%。稳定剂的加入量超过0.16 g时,4Na2SO4.2H2O2.NaCl的稳定度几乎不变。[结论]该研究有利于促进4Na2SO4.2H2O2.NaCl的开发和应用。 相似文献