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1.
A set of 152 vertical profiles of aerosol number concentration and size distribution with diameter ranging from 0.12 to 3.0 μm observed by the airborne optical spectrometer probe in Beijing, China, between February 2005 and September 2006 is analysed and discussed. The statistic of aerosol number concentration ( N a) reveals a high aerosol number density in this region with average surface level number concentration ( N 0) of about 6600 cm−3 (0.12–3.0 μm). The average vertical profile of N a approximately satisfies an exponential decline function with a scale height of 1419 m. The N a profiles are influenced by the structures of planetary boundary layer (PBL) significantly and two typical types of N a profile under different conditions of PBL are presented and parametrized in this study. The observations of aerosol size distribution show that, in most cases the aerosol size distributions are not very sensitive to altitude, with effective radii ranging from 0.16 to 0.28 μm. Comparison between aircraft-derived aerosol optical depth (AOD) and Moderate Resolution Imaging Spectroradiometer-derived AOD shows good agreement. The Mie model calculations suggest that the surface level number concentration, the PBL height and the structure of PBL can influence the AOD significantly.  相似文献   

2.
In this issue, Ramonet et al. revealed a positive trend in European, atmospheric CO2 concentrations relative to a marine, North Atlantic reference baseline, for the years 2001–2006. The observed build up mainly occurred during the cold season where it reaches a 0.8 ppm yr−1 at low-altitude stations to a 0.3 ppm yr−1 at mid-altitude stations. We explore the cause of this build-up using the mesoscale model CHIMERE. We first model the observed trends, using interannually varying fluxes and transport, then suppress the interannual variability in fluxes or aspects of transport to elucidate the cause. The run with no interannual variability in fluxes still matches observed trends suggesting that transport is the major cause. Separate runs varying either boundary layer height or winds show that changes in boundary layer height explain the trends at low-altitude stations within the continents while changes in wind regimes drive changes elsewhere.  相似文献   

3.
Wet‐only rainwater composition, acid‐precursor gas mixing ratios and aerosol loading were determined from weekly‐averaged samples at Petaling Jaya, Malaysia, over the five year period from March 1993 to March 1998. Annual deposition fluxes of acidic sulfur and nitrogen species estimated from these data show this site to be heavily impacted by acidic deposition, with total oxidised sulfur plus nitrogen deposition in the range 277–480 meq m−2 yr−1. Average contributions were 56% as sulfur species, 44% as nitrogen species, with wet deposition in this region of high rainfall accounting for 67% of total deposition. Thus total acid deposition fluxes were equivalent to levels that provided motivation for emissions reduction programs in both Europe and North America. The possibility of adverse environmental effects in Malaysia caused by acid deposition therefore merits serious consideration and assessment.  相似文献   

4.
In May–June 2006, airborne and ground-based solar (0.3–2.2 μm) and thermal infrared (4–42 μm) radiation measurements have been performed in Morocco within the Saharan Mineral Dust Experiment (SAMUM). Upwelling and downwelling solar irradiances have been measured using the Spectral Modular Airborne Radiation Measurement System (SMART)-Albedometer. With these data, the areal spectral surface albedo for typical surface types in southeastern Morocco was derived from airborne measurements for the first time. The results are compared to the surface albedo retrieved from collocated satellite measurements, and partly considerable deviations are observed. Using measured surface and atmospheric properties, the spectral and broad-band dust radiative forcing at top-of-atmosphere (TOA) and at the surface has been estimated. The impact of the surface albedo on the solar radiative forcing of Saharan dust is quantified. In the SAMUM case of 19 May 2006, TOA solar radiative forcing varies by 12 W m−2 per 0.1 surface-albedo change. For the thermal infrared component, values of up to +22 W m−2 were derived. The net (solar plus thermal infrared) TOA radiative forcing varies between −19 and +24 W m−2 for a broad-band solar surface albedo of 0.0 and 0.32, respectively. Over the bright surface of southeastern Morocco, the Saharan dust always has a net warming effect.  相似文献   

5.
利用2006年3～5月天空辐射计观测数据反演得到北京地区春季大气气溶胶光学性质参数,包括大气气溶胶光学厚度(0.5μm)、Angstrm指数、单次散射反射比和粒子谱分布特征。结果表明:北京地区春季气溶胶平均光学厚度0.67,Angstrm指数0.54,单次散射比0.88,粒子吸收性质较弱,粒子谱呈双峰形,以粗粒子为主,粗、细模态粒子粒径分别集中在0.17μm和7.7μm左右。相比2004年此次观测期间气溶胶粒径较大,粒子体积浓度较高,散射作用在其消光特性中的比重略有下降。光学厚度日变化呈单峰型,日间单次散射比随时间逐渐递减,Angstrm指数在上午递减趋势明显,午后变得稳定。对同时观测的天空辐射计与CE-318不同波长光学厚度结果进行比较,结果显示两者得到的光学厚度相关性很好,各波长小时平均结果的相对误差小于7%。  相似文献   

6.
This paper reports on the analysis of 24-h aerosol data measured during 2006, at 14 monitoring sites in China. Measurements included seven-wavelength Aethalometers, thermal/optical reflectance analyses of filter samples and determination of dust aerosols. Black (elemental) carbon (BC, EC) is found to be the principal light-absorbing aerosol over many parts of China; however, the fraction of apparent light absorption attributed to dust varied from 14% in winter, to 11% in spring, to 5% in summer to 9% in autumn. Aerosol light absorption in urban areas was larger than in rural areas by factors of 2.4 in winter, 3.1 in spring and 2.5 in both summer and autumn. These differences may lead to contrasts in radiative, thermal and cloud modification effects between urban and rural areas. Absorption 'hotspots' were located in the Sichuan Basin, the provinces south of Beijing, the Pearl Delta River regions and the Guanzhong Plain. The mass absorption coefficient for aerosol BC (σBC) based on Aethalometer data is estimated to be 11.7 m2 g−1 at 880 nm wavelength (λ) with inverse (λ−1) wavelength scaling, whereas the mass absorption coefficient for dust (σdust) is 1.3 m2 g−1 on average without significant wavelength dependence.  相似文献   

7.
Diurnal and annual variations of CO2, O3, SO2, black carbon and condensation nuclei and their source areas were studied by utilizing air parcel trajectories and tropospheric concentration measurements at a boreal GAW site in Pallas, Finland. The average growth trend of CO2 was about 2.5 ppm yr−1 according to a 4-yr measurement period starting in October 1996. The annual cycle of CO2 showed concentration difference of about 19 ppm between the summer minimum and winter maximum. The diurnal cycle was most pronounced during July and August. The variation between daily minimum and maximum was about 5 ppm. There was a diurnal cycle in aerosol concentrations during spring and summer. Diurnal variation in ozone concentrations was weak. According to trajectory analysis the site was equally affected by continental and marine air masses. During summer the contribution of continental air increased, although the southernmost influences decreased. During daytime in summer the source areas of CO2 were mainly located in the northern parts of the Central Europe, while during winter the sources were more evenly distributed. Ozone showed similar source areas during summer, while during winter, unlike CO2, high concentrations were observed in air arriving from the sea. Sulfur dioxide sources were more northern (Kola peninsula and further east) and CO2 sources west-weighted in comparison to sources of black carbon. Source areas of black carbon were similar to source areas of aerosols during winter. Aerosol source area distributions showed signs of marine sources during spring and summer.  相似文献   

8.
The major finding of this study is that aerosols over the tropical Indian Ocean enhance clear sky atmospheric solar heating significantly and decrease the surface solar heating by even a larger amount. The results presented here are based on aerosol chemical, microphysical, and optical and radiometric data collected at the island of Kaashidhoo (4.97°N, 73.47°E) during February and March of 1998, as part of the first field phase of the Indian Ocean experiment (INDOEX). The aerosol optical properties were integrated with a multiple scattering Monte Carlo radiative transfer model which was validated at the surface with broadband flux measurements and at the top of the atmosphere (TOA) with the clouds and earth's radiant energy system (CERES) radiation budget measurements. We consider both externally and internally mixed aerosol models with very little difference between the two models in the estimated forcing. For the February–March period, the aerosols increase the monthly mean clear sky atmospheric solar heating by about 12 W/m2(about 15% of the total atmospheric solar heating) and decrease the sea surface clear sky solar heating by about 16 W/m2 with a daily range from 5 to 23 W/m2. The net aerosol forcing at the top of the atmosphere is about −4 W/m2 with a daily range from −2 to −6 W/m2. Although the soot contributes only about 10% to the aerosol optical thickness, it contributes more than 50% to the aerosol induced atmospheric solar heating. The fundamental conclusion of this study is that anthropogenic aerosols over the tropical Indian Ocean are altering the clear sky radiation budget of the atmosphere and surface in a major manner.  相似文献   

9.
The equivalent wavelength ( λ E), at which the aerosol optical depth (AOD) is equal to broadband AOD (BAOD), can change in a wide range from 0.619 μm to 1.575 μm in the usual aerosol conditions. By using the least squares technique and some empirical corrections, a parameterized relationship of λ E with BAOD, Ångström wavelength exponent ( α ), solar zenith angle ( θ 0) and H2O amount is developed. Using this relationship, and based on the strong sensitivity of BAOD on θ 0 when θ 0>70°, the broadband extinction method to derive the spectral AOD and α is further proposed. As shown in comparative simulations to retrieve AOD by the present, Molineaux et al. and Gueymard methods, the present method has the best accuracy in most simulations using Junge, MODTRAN, log‐normal and Deirmendjian aerosol models. A key question of the pyrheliometer method to determine wavelength-dependent AODs is the effect of uncertainty in the aerosol size istribution. It is found that the AOD solution around λ E is less sensitive to the uncertainty. The wavelength exponent α is derived using an assumption of the stable atmospheric turbidity. If the pyrheliometer data from θ 0=85° to 70° are used and the change of the turbidity is ±10%, the error of solution α is usually within ±0.32. If the variation of the turbidity is random, the mean value of a lot of the measurements of α would be very reasonable.  相似文献   

10.
An aerosol dynamics model, AEROFOR2, is developed in the context of the BIOFOR project focussing on boreal forest aerosol. It is the second version of a Lagrangian type box model AEROFOR for investigating the formation and growth of particles under clear sky atmospheric conditions. Particles can consist of soluble and insoluble material and the particle population can be externally or internally mixed. AEROFOR2 includes gas phase chemistry and aerosol dynamics, and calculates the number and composition distributions of particles as functions of time. Observed growth rates of the nucleation mode particles after a typical nucleation event are 2–3 nm/h. The model simulations predict that 3·107 molecules cm−3 of insoluble organic vapour and less than 6·106 molecules cm−3 of soluble vapour condensing onto particles are enough to make them grow in good agreement with the observed growth rates. Then the source rate of the organic vapour must be an order of 105 molecules cm−3 s−1, and its saturation vapour density should be below 106 molecules cm−3. If the aerosol was initially an internal mixture of soluble (70%) and insoluble (30%) constituents it transformed to an externally mixed aerosol during the simulation. By applying the externally‐mixed aerosol based on measured soluble volume fractions, it was concluded that the modelled soluble fraction of the nucleation mode was too low in comparison with the measurements, and thus, a part of the condensable organic vapour must be water soluble.  相似文献   

11.
During the 1st Lagrangian experiment of the North Atlantic Regional Aerosol Characterisation Experiment (ACE‐2), a parcel of air was tagged by releasing a smart, constant level balloon into it from the Research Vessel Vodyanitskiy . The Meteorological Research Flight's C‐130 aircraft then followed this parcel over a period of 30 h characterising the marine boundary layer (MBL), the cloud and the physical and chemical aerosol evolution. The air mass had originated over the northern North Atlantic and thus was clean and had low aerosol concentrations. At the beginning of the experiment the MBL was over 1500 m deep and made up of a surface mixed layer (SML) underlying a layer containing cloud beneath a subsidence inversion. Subsidence in the free troposphere caused the depth of the MBL to almost halve during the experiment and, after 26 h, the MBL became well mixed throughout its whole depth. Salt particle mass in the MBL increased as the surface wind speed increased from 8 m s−1 to 16 m s−1 and the accumulation mode (0.1μm to 3.0 μm) aerosol concentrations quadrupled from 50 cm−3 to 200 cm−3. However, at the same time the total condensation nuclei (>3 nm) decreased from over 1000 cm−3 to 750 cm−3. The changes in the accumulation mode aerosol concentrations had a significant effect on the observed cloud microphysics. Observational evidence suggests that the important processes in controlling the Aitken mode concentration which, dominated the total CN concentration, included, scavenging of interstitial aerosol by cloud droplets, enhanced coagulation of Aitken mode aerosol and accumulation mode aerosol due to the increased sea salt aerosol surface area, and dilution of the MBL by free tropospheric air.  相似文献   

12.
The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE‐2). Very high cloud droplet number concentrations (almost 3000 cm−3) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150–3000 cm−3. The updraught velocity during the cloud formation was estimated to 2.2 m s−1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.  相似文献   

13.
利用MODIS光学厚度遥感产品研究北京及周边地区的大气污染   总被引：53，自引：2，他引：53  
对2001年在北京地区利用太阳光度计观测的气溶胶光学厚度和NASA发布的MODIS气溶胶产品进行了比较,验证了这一卫星遥感产品的可靠性;比较了2001年MODIS气溶胶光学厚度(AOD)产品和由空气污染指数(API)计算的每日平均可吸入颗粒物(PM10)浓度,得到了比较高的相关系数,证实该气溶胶产品可用于污染分析.将北京地区AOD与气象能见度观测资料进行比较,得到了不同季节的气溶胶"标高".利用统计的不同季节的气溶胶标高,从光学厚度的季节分布得到了能见度(能见距离)的季节分布.气溶胶光学厚度图像的个例分析表明,除局地排放外,周边区域(主要为西南和南向)的输送对北京市区的空气污染贡献份额较大.卫星遥感气溶胶可以比较直观地再现污染物的区域分布和输送,不仅为研究全球气候变化也为研究区域环境的空气质量提供了一种有效手段.  相似文献   

14.
Two airborne campaigns were carried out to measure the tropospheric concentrations and variability of CO2, CO and O3 over Siberia. In order to quantify the influence of remote and regional natural and anthropogenic sources, we analysed a total of 52 vertical profiles of these species collected in April and September 2006, every ∼200 km and up to 7 km altitude. CO2 and CO concentrations were high in April 2006 (respectively 385–390 ppm CO2 and 160–200 ppb CO) compared to background values. CO concentrations up to 220 ppb were recorded above 3.5 km over eastern Siberia, with enhancements in 500–1000 m thick layers. The presence of CO enriched air masses resulted from a quick frontal uplift of a polluted air mass exposed to northern China anthropogenic emissions and to fire emissions in northern Mongolia. A dominant Asian origin for CO above 4 km (71.0%) contrasted with a dominant European origin below this altitude (70.9%) was deduced both from a transport model analysis, and from the contrasted ΔCO/ΔCO2 ratio vertical distribution. In September 2006, a significant O3 depletion (∼–30 ppb) was repeatedly observed in the boundary layer, as diagnosed from virtual potential temperature profiles and CO2 gradients, compared to the free troposphere aloft, suggestive of a strong O3 deposition over Siberian forests.  相似文献   

15.
Using 5 yr (December 2000–November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency ( Eτ ) of aerosols during the morning Terra satellite overpass time over the global oceans (60°N–60°S). We calculate Eτ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes. Over the 5 yr, the global mean instantaneous Eτ between the methods is remarkably consistent and within 5 W m−2τ−1 with a mean value of –70 W m−2τ−1. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of <3 W m−2τ−1. These differences are largely due to assumptions in aerosol models and definition of clear sky backgrounds. Independent assessments of aerosol radiative effects from different satellite sensors and methods are extremely valuable and should be used to verify numerical modelling simulations.  相似文献   

16.
Long-term measurements of fine particle number-size distributions were carried out over 9.5 yr (May 1997–December 2006), in the urban background atmosphere of Helsinki. The total number of days was 3528 with about 91.9% valid data. A new particle formation event (NPF) is defined if a distinct nucleation mode of aerosol particles is observed below 25 nm for several hours, and it shows a growth pattern. We observed 185 NPF events, 111 d were clear non-events and most of the days (around 83.5%) were undefined. The observed events were regional because they were observed at Hyytiälä (250 km north of Helsinki). The events occurred most frequently during spring and autumn. The observed formation rate was maximum during the spring and summer (monthly median 2.87 cm−3 s−1) and the modal growth rate was maximum during late summer and Autumn (monthly median 6.55 nm h−1). The events were observed around noon, and the growth pattern often continued on the following day. The observation of weak NPF events was hindered due to pre-existing particles from both local sources. It is clear that regional NPF events have a clear influence on the dynamic behaviour of aerosol particles in the urban atmosphere.  相似文献   

17.
The effect of anthropogenic emissions from China on global burdens of ozone, sulphate, organic carbon (OC) and black carbon (BC) aerosols is examined, using the three-dimensional chemistry transport model Oslo CTM2. Two model simulations were performed, the first with global present-day emissions and the second with the anthropogenic emissions from China set to their pre-industrial levels. The global radiative forcing for these species is then calculated. Industrial emissions from China are found to account for a 4–5% increase in the global burden of OC aerosol, the change in secondary organic aerosol being slightly less than that of primary organic aerosol. A 10% increase in the global sulphate aerosol burden is calculated, and the increase in BC is 23%. The global radiative forcing of aerosols from China was calculated to be −62, −3.7, −13 and 89 mW m−2, for sulphate, secondary organic, primary organic and BC aerosols, respectively. The increase in ozone causes a forcing of 77 mW m−2.  相似文献   

18.
The impact of land use on the global carbon cycle and climate is assessed. The Bern carbon cycle-climate model was used with land use maps from HYDE3.0 for 1700 to 2000 A.D. and from post-SRES scenarios for this century. Cropland and pasture expansion each cause about half of the simulated net carbon emissions of 188 Gt C over the industrial period and 1.1 Gt C yr−1 in the 1990s, implying a residual terrestrial sink of 113 Gt C and of 1.8 Gt C yr−1, respectively. Direct CO2 emissions due to land conversion as simulated in book-keeping models dominate carbon fluxes due to land use in the past. They are, however, mitigated by 25% through the feedback of increased atmospheric CO2 stimulating uptake. CO2 stimulated sinks are largely lost when natural lands are converted. Past land use change has eliminated potential future carbon sinks equivalent to emissions of 80–150 Gt C over this century. They represent a commitment of past land use change, which accounts for 70% of the future land use flux in the scenarios considered. Pre-industrial land use emissions are estimated to 45 Gt C at most, implying a maximum change in Holocene atmospheric CO2 of 3 ppm. This is not compatible with the hypothesis that early anthropogenic CO2 emissions prevented a new glacial period.  相似文献   

19.
During the ACE‐2 field campaign in the summer of 1997 an intensive, ground‐based physical and chemical characterisation of the clean marine and continentally polluted aerosol was performed at Sagres, Portugal. Number size distributions of the dry aerosol in the size range 3–10 000 nm were continuously measured using DMPS and APS systems. Impactor samples were regularly taken at 60% relative humidity (RH) to obtain mass size distributions by weighing the impactor foils, and to derive a chemical mass balance by ion and carbon analysis. Hygroscopic growth factors of the metastable aerosol at 60% RH were determined to estimate the number size distribution at a relative humidity of 60%. A size segregated 3‐way mass closure study was performed in this investigation for the first time. Mass size distributions at 60% RH derived from number size distribution measurements and impactors samples (weighing and chemical analysis) are compared. A good agreement was found for the comparison of total gravimetrically‐determined mass with both number distribution‐derived (slope=1.23/1.09; R2>0.97; depending on the parameters humidity growth and density) and chemical mass concentration (slope=1.02; R2= 0.79) for particles smaller than 3 μm in diameter. Except for the smallest impactor size range relatively good correlations (slope=0.86–1.42) with small deviations (R2=0.76–0.98) for the different size fractions were found. Since uncertainties in each of the 3 methods are about 20% the observed differences in the size‐segregated mass fractions can be explained by the measurement uncertainties. However, the number distribution‐derived mass is mostly higher than the chemically and gravimetrically determined mass, which can be explained by sampling losses of the impactor, but as well with measurement uncertainties as, e.g., the sizing of the DMPS/APS.  相似文献   

20.
Concentrations of organic carbon (OC), elemental carbon (EC), selected trace elements and water-soluble (WS) ions were determined for samples collected from August 2004 to February 2005 to assess the aerosol background at two remote sites in China. The OC and EC concentrations in PM10 from near the Tibetan Plateau at Zhuzhang (ZUZ) were comparable with other background sites, averaging 3.1 and 0.34 μg m−3, respectively, with no pronounced seasonality. At Akdala (AKD) on northern margin of the Zhungaer Basin, the average concentrations were similar (mean OC = 2.9 μg m−3 and EC = 0.35 μg m−3), but the concentrations were higher in winter. The aerosol mass at both sites was dominated by OC and SO42−, but a stronger contribution from soil dust was observed at AKD. At ZUZ, NO3− showed a unique weather-related fluctuation in PM10 with a periodicity of ∼1 week. Anthropogenic sources in the Sichuan Basin and southeastern Yunnan Province evidently influence ZUZ in summer and autumn while pollutants from Russia and the China–Mongolia border affect AKD nearly all year. The identification of these upwind sources demonstrates that transboundary transport needs to be taken into account when assessing air quality in remote parts of China.  相似文献   

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