The effect of changes in atmospheric carbon dioxide concentrations and sulphate aerosols on near-surface temperature is investigated using a version of the Hadley Centre atmospheric model coupled to a mixed layer ocea...
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The effect of changes in atmospheric carbon dioxide concentrations and sulphate aerosols on near-surface temperature is investigated using a version of the Hadley Centre atmospheric model coupled to a mixed layer ocean. The scattering of sunlight by sulphate aerosols is represented by appropriately enhancing the surface albedo. On doubling atmospheric carbon dioxide concentrations, the global mean temperature increases by 5.2 K. An integration with a 39% increase in CO2, giving the estimated change in radiative heating due to increases in greenhouse gases since 1900, produced an equilibrium warming of 2.3 K, which, even allowing for oceanic inertia, is significantly higher than the observed warming over the same period. Furthermore, the simulation suggests a substantial warming everywhere, whereas the observations indicate isolated regions of cooling, including parts of the northern midlatitude continents. The addition of an estimate of the effect of scattering by current industrial aerosols (uncertain by a factor of at least 3) leads to improved agreement with the observed pattern of changes over the northern continents and reduces the global mean warming by about 30%. Doubling the aerosol forcing produces patterns that are still compatible with the observations, but further increase leads to unrealistically extensive cooling in the midlatitudes. The diurnal range of surface temperature decreases over most of the northern extratropics on increasing CO2, in agreement with recent observations. The addition of the current industrial aerosol had little detectable effect on the diurnal range in the model because the direct effect of reduced solar heating at the surface is approximately balanced by the indirect effects of cooling. Thus, the ratio of the reduction in diurnal range to the mean warming is increased, in closer agreement with observations. Results from further sensitivity experiments with larger increases in aerosol and CO2 are presented. Although the aerosol
A detailed study of the physical properties and the chemical composition of spark-produced aerosol and corresponding erosion craters has been undertaken. A high repetition rate (1 kHz), electronically controlled wavef...
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Optimization of the Finnigan GCQ ion trap mass spectrometry (ITMS) system and a clean-up procedure were carried out in order to apply high-resolution gas chromatography-tandem mass spectrometry for the analysis of pol...
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Optimization of the Finnigan GCQ ion trap mass spectrometry (ITMS) system and a clean-up procedure were carried out in order to apply high-resolution gas chromatography-tandem mass spectrometry for the analysis of polychlorinated biphenyls (PCBs) in aerosols. Six ITMS operating parameters, including isolation time, excitation voltage, excitation time, "q" value, ion source temperature and electron energy were adjusted in order to optimize the instrument analytical performance. The adjustment of all parameters substantially increased the sensitivity of ITMS in the MS-MS mode. Changes in isolation time did not particularly affect ITMS sensitivity while ion source temperature had the strongest influence. After optimization, a limit of detection of 600 fg/mul with S/N varying from 8 up to 91 was achieved. The application of the optimized ITMS parameters conjointly with the developed clean-up procedure resulted in method detection limits of 10-20 fg/m(3) for the determination of PCBs, in the particulate and gas phase of the atmospheric aerosol of background areas in the Eastern Mediterranean and Sweden. (C) 2001 Elsevier Science B.V. All rights reserved.
Closure experiments were completed to compare measured and modeled aerosol optical properties and their dependence on controlled relative humidity (RH) and wavelength of light. NaCl, (NH4)(2)SO4, and NH4NO3 aerosol pa...
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Closure experiments were completed to compare measured and modeled aerosol optical properties and their dependence on controlled relative humidity (RH) and wavelength of light. NaCl, (NH4)(2)SO4, and NH4NO3 aerosol particles with approximate geometric mass mean diameters of 0.2 mum and geometric standard deviations of 1.7 were tested as part of this study. High evaporative losses (up to 40%) were observed for NH4NO3 aerosol at this particle size range due to heating, and the results from these tests have been excluded from the closure analysis. Aerosol optical properties were measured with a RH-scanning nephelometry system (humidograph) and modeled with a Mie-Lorentz light scattering model. Particle size distributions were measured with a scanning differential mobility analyzer. Closure between the measured and modeled values of the total light scattering coefficient (sigma(sp)), backscatter ratio (b), and Angstrom exponent (a) for dry (low RH) aerosols was achieved within 0.0%-5%, 4%-15%, and 3%-17%, respectively. The values of f(RH), hemispheric b, and a at 80% RH agreed within 2%-27%, 1%-27%, and 1%-28%, respectively. Correcting for nephelometer nonidealities, including a heating artifact, improved the agreement between the measured and predicted sigma(sp) values at RH = 80% from 35% to 13% for the TSI nephelometer at the maximum heating condition, and from 18% to 11% for the Radiance Research, Inc. (RR), nephelometer. Accurate quantification of the closure for these optical properties is important when establishing visibility standards, and assessing the progress toward meeting those standards, as well as reducing the uncertainties in estimating radiative forcing due to those aerosols.
Saharan aerosol and fractionated soil samples have been analysed with X-ray diffraction in order to compare the aerosol mineral composition with its source material. The soil samples used for this study contained only...
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Saharan aerosol and fractionated soil samples have been analysed with X-ray diffraction in order to compare the aerosol mineral composition with its source material. The soil samples used for this study contained only particles with radii r ⩽ 5 μ m generated by a dry fractionation procedure. This soil size fraction can be expected as most relevant for atmospheric processes such as long-range transport, radiation balance, formation and composition of precipitation. The mineral constituents of both types of samples turned out to be rather similar in composition. Even the aerosol samples from the interior of the desert did not show any significant differences which can be attributed to different or typical source regions. The homogeneity of the aerosol composition is obviously due to the fact that the aerosol over the desert itself is already well mixed as a product of continuous deposition and uptake of material from the ground. The composition of the individual soil samples reflects the major petrography. High contents of calcite and palygorskite in samples of the northern desert are the only significant deviations from the average composition. Therefore, calcite and polygorskite can be considered as tracers for atmospheric mineral dust derived from the northern Sahara.
Simultaneous measurements of the water-soluble organic nitrogen (WSON) in the aerosols and rainwater were conducted to clarify the deposition pathway of the atmospheric WSON. In the aerosols, about 10% of the water-so...
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Simultaneous measurements of the water-soluble organic nitrogen (WSON) in the aerosols and rainwater were conducted to clarify the deposition pathway of the atmospheric WSON. In the aerosols, about 10% of the water-soluble total nitrogen (WSTN) was in an organic form, and a large portion (about 81% on average) of the WSON was distributed in the fine-mode range. Concentrations of the fine-mode WSON were associated with the acidity of the fine particles, suggesting the secondary production of the WSON in the acid fine particles. On the other hand, it was suggested that the coarse-mode WSON was derived from bio-particles, such as plant debris, although its concentrations were low and widely scattered. Dry deposition amounts of the WSON estimated from the concentrations and dry deposition velocities of the particulate WSON suggested that almost all of the dry deposition of the particulate WSON was derived from the coarse-mode particles. The contribution of the fine mode particles to the dry deposition was negligible. About 10% of the WSTN in the bulk precipitation was in an organic form. The bulk deposition amounts of the WSON were largely dependent on the rainfall amounts and coarse-mode WSON concentrations. Although about 30% of the WSON in the bulk deposition was from the dry deposition, the wet deposition significantly contributed to the WSON deposition, especially in the rainy season. Wet deposition is the major removal process of WSON from spring to autumn;however, in winter, dry and wet deposition are comparable.
The current understanding of the climate effects of mixed-type aerosols is an open question. The optical and radiative properties of the anthropogenic, mixed-type, and dust aerosols were studied using simultaneous obs...
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The current understanding of the climate effects of mixed-type aerosols is an open question. The optical and radiative properties of the anthropogenic, mixed-type, and dust aerosols were studied using simultaneous observations of a sun photometer and a depolarization lidar over the Semi-Arid Climate and Environment Observatory of LanzhouUniversity (SACOL), northwestern China. The aerosol radiative effect was calculated using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model and was in good agreement with theAerosolRobotic Network (AERONET) product. The anthropogenic, mixed-type, and dust aerosols were identified mainly based on the lidar-measured depolarization ratio, which was supported by the airmass back trajectories. The mixed-type aerosols exhibit lower (higher) extinctions below (above) 1.5 km above the ground, indicating anthropogenic pollution from the atmospheric boundary layer and dust aerosols above. The dust aerosols exhibit the highest absolute radiative effect because of the highest aerosol loading. However, the mixed-type aerosols are effective in both scattering and absorbing solar radiation, leading to the highest cooling efficiency at the bottom of the atmosphere (BOA), 7.4% and 6.5% higher than those of the anthropogenic and dust aerosols, respectively. Themixed-type aerosols exhibit the highest warming efficiency in the atmosphere (ATM), 20.8% and 28.2% higher than the anthropogenic and dust aerosols, respectively. The mixed-type aerosols also show the lowest cooling efficiency at the top of the atmosphere (TOA). The results suggest the necessity of carefully characterizing the mixed-type aerosols in atmospheric numerical models to more precisely assess the energy budget of the Earth-atmosphere system.
Ion Beam Analysis (IBA) techniques were used to assign nine years of PM2.5 observations to seven source types, at Lucas Heights, a topographically complex urban fringe site of Sydney. The highest contributions to tota...
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Ion Beam Analysis (IBA) techniques were used to assign nine years of PM2.5 observations to seven source types, at Lucas Heights, a topographically complex urban fringe site of Sydney. The highest contributions to total PM2.5 were from motor vehicles (Autos, 263%), secondary sulfur (2ndryS, 23.7%), a mixture of industry and aged sea air (IndSaged, 20.6%), and smoke (Smoke, 13.7%). The Autos contribution was highest in winter, whereas 2ndryS was highest in summer, indicating that mitigation measures targeting SO2 release in summer and vehicle exhaust in winter would be most effective in reducing the PM2.5 concentrations at this site. Since concentrations of particulate matter can be significantly affected by local meteorology, generalised additive model (GAM) techniques were employed to investigate relationships between PM2.5 source types and meteorological conditions. The GAM predictors used included: time (seasonal to inter-annual variations), mixing layer depth, temperature, relative humidity, wind speed, wind direction, and atmospheric pressure. Meteorological influences on PM2.5 variability were found to be 58% for soil dust, 46% for Autos, 41% for total PM2.5, and 35% for 2ndryS. Effects were much smaller for other source types. Temperature was found to be an important variable for the determination of total PM2.5, 2ndryS, IndSaged, Soil and Smoke, indicating that future changes in temperature are likely to have an associated change in aerosol concentrations. However, the impact on different source types varied. Temperature had the highest impact on 2ndryS (sometimes more than a factor of 4 increase for temperatures above 25 degrees C compared to temperatures under 10 degrees C) and IndSaged, being predominantly secondary aerosols formed in the atmosphere from precursors, whereas wind speed and wind direction were more important for the determination of vehicle exhaust and fresh sea salt concentrations. The marginal effect of relative humidity on 2ndryS increase
作者：
Tao, Wei-KuoChen, Jen-PingLi, ZhanqingWang, ChienZhang, ChidongNASA
Lab Mesoscale Atmospher Proc Goddard Space Flight Ctr Greenbelt MD 20771 USA Natl Taiwan Univ
Dept Atmospher Sci Taipei 10617 Taiwan Univ Maryland
Earth Syst Sci Interdisciplinary Ctr College Pk MD 20740 USA Univ Maryland
Dept Atmospher & Ocean Sci College Pk MD 20740 USA MIT
Dept Earth Atmospher & Planetary Sci Cambridge MA 02139 USA Univ Miami
Rosenstiel Sch Marine & Atmospher Sci Miami FL 33149 USA Beijing Normal Univ
Coll Global Change & Earth Syst Sci State Key Lab Earth Surface Proc & Resource Ecol Beijing 100875 Peoples R China
aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. ...
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aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosol effects on clouds could further extend to precipitation, both through the formation of cloud particles and by exerting persistent radiative forcing on the climate system that disturbs dynamics. However, the various mechanisms behind these effects, in particular, the ones connected to precipitation, are not yet well understood. The atmospheric and climate communities have long been working to gain a better grasp of these critical effects and hence to reduce the significant uncertainties in climate prediction resulting from such a lack of adequate knowledge. Here we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes from theoretical analysis of microphysics, observational evidence, and a range of numerical model simulations. In addition, the discrepancies between results simulated by models, as well as those between simulations and observations, are presented. Specifically, this paper addresses the following topics: (1) fundamental theories of aerosol effects on microphysics and precipitation processes, (2) observational evidence of the effect of aerosols on precipitation processes, (3) signatures of the aerosol impact on precipitation from large-scale analyses, (4) results from cloud-resolving model simulations, and (5) results from large-scale numerical model simulations. Finally, several future research directions for gaining a better understanding of aerosol-cloud-precipitation interactions are suggested.
The hygroscopic properties of the organic fraction of aerosols are poorly understood. The ability of organic aerosols to absorb water as a function of relative humidity (RH) was examined using data collected during th...
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The hygroscopic properties of the organic fraction of aerosols are poorly understood. The ability of organic aerosols to absorb water as a function of relative humidity (RH) was examined using data collected during the 1999 Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). (On average, organics accounted for 22% of fine particulate matter with an aerodynamic diameter less than 2.5 mum (PM2.5) mass). Hourly RH exceeded 80% only 3.5% of the time and averaged 44%. BRAVO aerosol chemical composition and dry particle size distributions were used to estimate PM2.5 light scattering (Bsp) at low and high ambient RH. Liquid water growth associated with inorganic species was sufficient to account for measured Bsp for RH between 70 and 95%.
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