Effect of aerosol pollution on clouds and its dependence on precipitation intensity

In this study, simulations performed with a large-eddy resolving numerical model are used to examine the effect of aerosol on cumulus clouds, and how this effect varies with precipitation intensity. By systematically varying the surface moisture fluxes, the modeled precipitation rate is forced to change from weak to strong intensity. For each of these intensities, simulations of a high-aerosol case (a polluted case with a higher aerosol concentration) and a low-aerosol case (a clean case with a lower aerosol concentration) are performed. Whether or not precipitation and associated sub-cloud evaporation and convective available potential energy (CAPE) are large, liquid–water path (LWP) is larger in the high-aerosol case than in the low-aerosol case over the first two-thirds of the entire simulation period. In weak precipitation cases, reduction in aerosol content leads to changes in CAPE in the middle parts of cloud layers, which in turn induces larger LWP in the low-aerosol case over the last third of the simulation period. With strong precipitation, stronger stabilization of the sub-cloud layers in the low-aerosol case counters the CAPE changes in the middle parts of cloud layers, inducing smaller LWP in the low-aerosol case over the last third of the simulation period. The results highlight an interaction between aerosol effects on CAPE above cloud base and those in sub-cloud layers, and indicate the importance of a consideration of aerosol effects on CAPE above cloud base as well as those in sub-cloud layers. In the high-aerosol case, near the beginning of the simulation period, larger environmental CAPE does not necessarily lead to larger in-cloud CAPE and associated larger cloud intensity because aerosol-induced increase in cloud population enhances competition among clouds for the environmental CAPE. This demonstrates the importance of the consideration of cloud population for an improved parameterization of convective clouds in climate models.     

上海及周边地区气溶胶对云和降水的影响初探

利用2000年4月—2013年9月搭载于Aqua和Terra卫星上的中分辨率成像光谱仪(moderate-resolution imaging spectroradiometer,MODIS)遥感资料,首先分析上海及周边地区气溶胶光学厚度(AOD)的长期统计特性,而后配合地面自动气象站降水资料,分析气溶胶与不同类型云的特征参数和地面降水之间的关系,研究该地区气溶胶与云和降水的相互作用。结果表明:上海及周边地区AOD年均值从2000—2009年和2011—2013年分别呈现增强、减弱趋势,而2010年出现明显低值。随着气溶胶增多,该地区浅薄水云的发生频率减少15.5%~32.4%,而深厚混合云的发生频率增加2.1%~10.0%。气溶胶增多对水云云滴粒子有效半径变化的影响受环境水汽条件影响很大,当水汽条件充分(不足)时,气溶胶增多会导致水云云滴粒子有效半径增加(减弱)。深厚混合云的云顶温度随AOD增加而显著减少。气溶胶较多时,降雨量小于1.0 mm·h-1的较弱降水发生频率减少,而降雨量大于等于1.0 mm·h-1的较强降水发生频率增加,说明气溶胶增多会抑制弱降水发生而加强强降水发生。     

Compositions and source apportionments of atmospheric aerosol during Asian dust storm and local pollution in central Taiwan

A study has been carried out on water soluble ions, trace elements, as well as PM_2.5 and PM_2.5–10 elemental and organic carbon samples collected daily from Central Taiwan over a one year period in 2005. A source apportionment study was performed, employing a Gaussian trajectory transfer coefficient model (GTx) to the results from 141 sets of PM_2.5 and PM_2.5–10 samples. Two different types of PM₁₀ episodes, local pollution (LOP) and Asian dust storm (ADS) were observed in this study. The results revealed that relative high concentrations of secondary aerosols (NO₃⁻, SO₄²⁻ and NH₄⁺) and the elements Cu, Zn, Cd, Pb and As were observed in PM_2.5 during LOP periods. However, sea salt species (Na⁺ and Cl⁻) and crustal elements (e.g., Al, Fe, Mg, K, Ca and Ti) of PM_2.5–10 showed a sharp increase during ADS periods. Anthropogenic source metals, Cu, Zn, Cd, Pb and As, as well as coarse nitrate also increased with ADS episodes. Moreover, reconstruction of aerosol compositions revealed that soil of PM_2.5–10 elevated approximately 12–14% in ADS periods than LOP and Clear periods. A significantly high ratio of non-sea salt sulfate to elemental carbon (NSS-SO₄²⁻/EC) of PM_2.5–10 during ADS periods was associated with higher concentrations of non-sea-salt sulfates from the industrial regions of China. Source apportionment analysis showed that 39% of PM₁₀, 25% of PM_2.5, 50% of PM_2.5–10, 42% of sulfate and 30% of nitrate were attributable to the long range transport during ADS periods, respectively.     

A GCM study of future climate response to aerosol pollution reductions

We use the global atmospheric GCM aerosol model ECHAM5-HAM to asses possible impacts of future air pollution mitigation strategies on climate. Air quality control strategies focus on the reduction of aerosol emissions. Here we investigate the extreme case of a maximum feasible end-of-pipe abatement of aerosols in the near term future (2030) in combination with increasing greenhouse gas (GHG) concentrations. The temperature response of increasing GHG concentrations and reduced aerosol emissions leads to a global annual mean equilibrium temperature response of 2.18 K. When aerosols are maximally abated only in the Industry and Powerplant sector, while other sectors stay with currently enforced regulations, the temperature response is 1.89 K. A maximum feasible abatement applied in the Domestic and Transport sector, while other sectors remain with the current legislation, leads to a temperature response of 1.39 K. Increasing GHG concentrations alone lead to a temperature response of 1.20 K. We also simulate 2–5% increases in global mean precipitation among all scenarios considered, and the hydrological sensitivity is found to be significantly higher for aerosols than for GHGs. Our study, thus highlights the huge potential impact of future air pollution mitigation strategies on climate and supports the need for urgent GHG emission reductions. GHG and aerosol forcings are not independent as both affect and are influenced by changes in the hydrological cycle. However, within the given range of changes in aerosol emissions and GHG concentrations considered in this study, the climate response towards increasing GHG concentrations and decreasing aerosols emissions is additive.     

A GIS based approach to back trajectory analysis for the source apportionment of aerosol constituents and its first application

A new method has been developed to combine back trajectory statistics with a detailed land cover analysis. It provides numeric proxies for the residence times of sampled air masses above certain land cover classes (marine, natural vegetation, agricultural lands, urban areas, and bare areas), as well as further meteorological parameters (mean trajectory length, solar radiation along trajectory, and local height of the boundary mixing layer). The method has been implemented into a GIS-enabled database system to allow for an efficient processing of large datasets with low computational demands. A principal component analysis was performed on a dataset including the modelled residence times, the modelled meteorological parameters, some measured meteorological parameters (wind speed and temperature), and the concentrations of 10 particle constituents (inorganic ions and organic and elemental carbon) in 5 particle size ranges for 29 winter- and summertime samples at an urban background site in Leipzig, Germany. Six principal components could be extracted which together explained about 80% of the total variance in the dataset. The factors could be attributed to the influence of meteorology to continental background pollution, secondary formation processes in polluted air masses, wood burning, aged sea-salt, local traffic, and long-range transported crustal material. The modelled residence times and the meteorological parameters were generally consistent with the existing knowledge of specific particle sources and thereby facilitated and strengthened the interpretation of the factors. Moreover, they allowed for a clear distinction between continental background pollution and secondary formation processes, which has not been possible in previous source apportionment studies. The results demonstrate that the combined usage of back trajectory, land cover, and meteorological data by the presented method yields valuable additional information on the history of sampled air masses, which can improve the quality of source apportionment of atmospheric aerosol constituents.     

青藏高原及其周边地区降水的水汽来源变化研究进展

近几十年来,随着全球气候变暖,青藏高原降水整体呈现增加趋势,气候暖湿化趋势明显;与此同时,位于青藏高原东南缘的中国西南地区整体上呈现暖干化趋势,干旱事件频发。探讨青藏高原及其周边地区降水的水汽来源变化、揭示降水趋势性变化的原因已经成为当前研究热点。本文评述了近年来青藏高原降水的水汽来源研究,重点关注青藏高原变湿、西南地区变干的水汽来源变化原因以及青藏高原南北水汽来源差异,讨论了尚未解决的科学问题,展望了未来研究方向。现有研究表明,青藏高原以西的西风带控制区蒸散发贡献的水汽整体呈现减少趋势,青藏高原以南和以东的季风控制区蒸散发贡献的水汽整体呈现增加趋势,上述水汽源区贡献变化导致了青藏高原及其周边不同区域降水趋势性变化的差异。展望未来,水汽来源分析的模型和数据需要进一步验证及减少不确定性,青藏高原下垫面和蒸散发变化对周边地区降水的影响机制研究有待加强,全球变化与青藏高原降水水汽来源变化的关系尚需深入分析。     

Resources of the ionized atmosphere as an aerosol source

The potential resources on the ion-stimulated syntheses effects of aerosol particles of lower troposphere in test sites in the arctic, mountain, arid and forest areas as the function of irradiation time and gas-precursor concentration were experimentally and theoretically evaluated. The dust-free outdoor air was irradiated with an ionization current of 10^− 6 A by α-rays from isotope ²³⁹Pu. The total output of radiolytic aerosols (RA) with a diameter of 3–1000 nm was found to be 0.05–0.1 molecules per 1 eV of absorbed radiation, while the physical upper limit is 0.25–0.4 molecules/eV. In an interval of exposition time from 6 to 800 s (adsorbed energy is 3 · 10¹²–10¹⁴ eV/cm³) the RA mass concentration at different sites was increased from 1–10 to 50–500 μg/m³. According to the liquid chromatography data the major RA material is the H₂O/HNO₃ solution with acid concentration  25%. The used physical model presents new aerosols as a product from small and intermediate ion association through formation of neutral clusters and describes adequately some of the peculiarities in field experiment data. Introducing SO₂, NH₃, and also hydrochloric, nitric and sulphuric acid vapours with concentration 0.1–1 mg/m³ in the irradiated air stimulated an increase of mass aerosol concentration by a factor of 8–30. The mean size also decreased by a factor of 3–5. These facts allowed us to expect that the chemical composition of radiolytic aerosols generated in outdoor air would noticeably differ after addition of the gas-precursors.     

齐次积分方程数值求解法及在反演气溶胶谱分布上的应用

本文论述了一个数值求解齐次的第一类Fredholm积分方程的方法,并以消光系数和体积散射系数综合反演气溶胶谱分布为例,说明采用比值通道以反演气溶胶谱分布有利于消除多次散射等系统误差.本文还证明了在Junge谱分布下,不同波长的体积消光系数、散射相函数等Mie散射光学参数之比与折射率无关的特性,指出了采用比值通道能够有效地消除折射率的不确定性对于消光——小角散射法反演气溶胶谱分布的影响.     

Application of particle induced X-ray emission to aerosol long-range transport studies—transport pathways of pollution aerosol over the Atlantic ocean and Europe

Particle induced X-ray emission analysis (PIXE) has been applied to aerosol long-range transport studies. The combination of a size fractionating sampler and a multi-element technique has enabled the identification of the transport pathways of individual constituents over the Atlantic Ocean and Europe. Chemical and size distribution data were obtained for aerosols collected at different sampling sites for the ground layer and the free atmosphere. Evaluation of these data under the aspect of air mass history extended the elemental determination in long range transport. A statistical technique was introduced and used to succeed in the semi-quantitative determination of transported pollutants.     

Source terms and source strengths of the carbonaceous aerosol in the tropics

Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6°N, 5°W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (¹³C/¹²C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 20×10¹² g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics.     

东亚沙尘源区与下游地区气溶胶光学特性比较

利用AERONET观测资料从气候学的角度比较分析了2001-2011年东亚地区沙尘天气发生时沙尘源区和下游区大气气溶胶光学特性。结果表明：沙尘期间沙尘源区气溶胶光学厚度明显大于下游区,而Angstr?m波长指数却小于下游区,当沙尘暴出现时会降至零甚至负值。气溶胶粒子尺度体积谱分布除敦煌为单峰外,其余各站均呈双峰分布,香河和北京的细粒子浓度明显大于西北地区,这可能是由细的沙尘粒子和污染气溶胶共同造成。在440-1020 nm范围内,中国地区气溶胶单次散射反照率平均值为0.93,韩国和日本站分别为0.93和0.94。沙尘源区与下游区相比,复折射指数实部偏大,虚部偏小。总体来说,沙尘天气下东亚地区在4个波段内平均不对称因子为0.70。     

Framing the way to relate climate extremes to climate change

The atmospheric and ocean environment has changed from human activities in ways that affect storms and extreme climate events. The main way climate change is perceived is through changes in extremes because those are outside the bounds of previous weather. The average anthropogenic climate change effect is not negligible, but nor is it large, although a small shift in the mean can lead to very large percentage changes in extremes. Anthropogenic global warming inherently has decadal time scales and can be readily masked by natural variability on short time scales. To the extent that interactions are linear, even places that feature below normal temperatures are still warmer than they otherwise would be. It is when natural variability and climate change develop in the same direction that records get broken. For instance, the rapid transition from El Ni?o prior to May 2010 to La Ni?a by July 2010 along with global warming contributed to the record high sea surface temperatures in the tropical Indian and Atlantic Oceans and in close proximity to places where record flooding subsequently occurred. A commentary is provided on recent climate extremes. The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.     

大气气溶胶浓度及其谱分布的某些特征

本文简要描述了光电仪器测量大气气溶胶粒子的工作原理;根据实测结果对不同大气条件下气溶胶粒子的浓度、谱分布特征进行了分析。结果表明,对于洁净大气和浑浊大气而言,气溶胶粒子的浓度和谱分布都有着明显的差别,相对变化最大的是那些半径处于0.2—1.0微米范围内的粒子;实际大气中粒子谱的演变过程是复杂的,并且具有多峰分布特征;相对湿度对气溶胶粒子物理特征的影响是明显的,并且这种影响主要是改变粒子的谱分布和折射指数。     

2000—2013年北京及周边地区大气气溶胶光学厚度时空变化特征及气象影响因素分析

利用NASA Terra卫星搭载的MODIS传感器观测到的2000—2013年气溶胶光学厚度数据和河北省142个观测站同期的气象数据,对北京及周边区域大气气溶胶的时空变化特征进行了分析,并通过研究光学厚度与各气象要素的关系,对影响大气气溶胶时空变化的关键气象因素进行探讨。结果表明：北京以南区域的气溶胶光学厚度在夏季最大,其次为春季,秋冬季相对较低,河北省西北部低于东南部;坝上地区的光学厚度年际变化小于其他地区,平原区与沿海地区的年际变化基本一致,春夏高于秋冬。春季相对湿度是影响光学厚度值的重要因素,气溶胶光学厚度的高值出现在5—7月,并伴随较高的相对湿度、较低的能见度、南风、较低的地面风速和稳定的大气层结。北京以南的河北省各台站污染程度与北京类似,南部站点的光学厚度高于东北部,这与人为气溶胶的排放主要集中于北京南部的工业城市,以及南风控制的污染物扩散方向有关。     

Investigation of the effects of high atmospheric aerosol pollution on the development of the high-depth cumulonimbus cloud

Considered is a case of the development of the cumulonimbus cloud (Cb) in the southwestern part of Saudi Arabia under the conditions of heavy pollution of atmosphere with natural aerosol. Using the ground-based radar and satellite radiometric instruments, the characteristics of the Cb are obtained for the cloud top height of more than 14 km and maximum reflectivity of 58 dBZ. To measure the precipitation rate using the radar data, the Z-I ratio obtained for the area under study was applied. To compute the precipitation rate, the results of the sounding with the SEVERI radiometer installed on the Meteosat-8 satellite were also used. Carried out are numerical experiments on the simulation of aerosol effects on the evolution of the cloud under study. The development of the cloud at the presence of background aerosol was simulated as well as at high aerosol concentration. Three cases are considered: aerosol is a passive admixture; aerosol has hygroscopic properties; aerosol has ice-forming properties. It is demonstrated that the most considerable effects on the cloud evolution are caused by the intensification of ice formation under the influence of aerosol; not only the time distribution of precipitation rate changes but also the amount of precipitation increases.     

Associations between the size of hurricane rain fields at landfall and their surrounding environments

This study examines relationships between the extent of hurricane rain fields, storm size, and the environment surrounding the storm. A Geographic Information System is employed to measure the extent of the rain fields in each quadrant of 31 hurricanes at landfall-time. After correlating the extents with measures of storm size, multiple linear regression models are developed to determine which atmospheric forcing(s) at 0, 12, and 24 h prior to landfall are most highly related to rain field size in each quadrant. Results show that the radius of the outermost closed isobar encompasses the rain fields in 90% of the observations. Strong vertical wind shear from the southwest correlates with a larger (smaller) rain field extent toward the northeast (southwest), while higher relative humidity values correlate with a larger extent toward the northwest, southwest, and southeast. Storm intensity and location also exhibit statistically significant correlations with rain field size.     

Parameterization of the CCN-humidity spectrum in dependency on nucleation conditions and aerosol size distribution

Summary Atmospheric CCN-humidity spectra (describing the CCN-number concentration as function of supersaturation) are derived as the integral over given particle size distributions. In that concept the finite boundary, representing the limiting activated particle size, results from the critical values of the Köhler-curve. As utilization of this general outcome different representative aerosol size distributions of the power law type as well as the log-normal type are chosen for case studies which are compared to empirical results. The dependency on temperature of the limiting activated particle size is shown to provide a non-negligible influence on the number of activated particles.With 3 Figures     

Estimation of aerosol deposition rate from the data of geochemical studies and atmospheric radioactive pollution monitoring

The aerosol deposition rate is computed for some chemical elements from the resuits of studies on the elemental composition of atmospheric aerosol and snow cover in the background and anthropogenic areas in the Primorskii krai as well as for the radionuclide ¹³⁷Cs and suspended matter from the data of atmospheric radioactive pollution monitoring. Taking into account the differences in sampling methods, the rather close values of deposition rate were obtained for chemical elements and radionuclide.     

Ship measurements of submicron aerosol size distributions over the Yellow Sea and the East China Sea

During the spring of 2005, the total particle concentrations and the submicron aerosol size distributions were measured on board the research vessel over the south sea of Korea and the Korean sector of the Yellow Sea. Similar measurements were made over the East China Sea in autumn 2005. The aerosol properties varied dynamically according to the meteorological conditions, the proximity to the land masses and the air mass back trajectories. The average total particle concentration was the lowest over the East China Sea, 4335 ± 2736 cm^− 3, but the instantaneous minimum, 837 cm^− 3, for the entire ship measurement was recorded during the Yellow Sea cruise. There was also a long (more than 6 h) stretch of low total particle concentrations that fell as low as 1025 cm^− 3 during the East China Sea cruise when the ship was the farthest from the shores and the air mass back trajectories resided long hours over the sea. These observations lead to the suggestion of ~ 1000 cm^− 3 as the background total particle concentration over the marine boundary layer in the studied region of the Yellow Sea and the East China Sea, implying significant anthropogenic influence even for the background value. In the mean time, average aerosol size distributions were unimodal and the mode diameter ranged between 52 and 86 nm, excluding the fog periods, which suggests that the aerosols measured in this study experienced relatively less aging processes within the marine boundary layer.