沙尘天气对大气生物气溶胶中微生物浓度、特性和分布的影响

生物气溶胶对全球气候、空气质量、大气过程和人体健康均具有重要影响。每年爆发的沙尘事件,使得生物气溶胶可借助沙尘进行长距离输运,从而影响到下风向地区生物气溶胶的浓度和性质。综述了沙尘天气下生物气溶胶中微生物的浓度、特性和分布特征的研究现状。已有研究显示,沙尘发生时,生物气溶胶中不同类别微生物的组成比例会有显著变化,细菌和真菌相对贡献随之改变。可培养细菌、真菌和总微生物浓度,均在沙尘天气下显著增加,但不同地区不同种类微生物在沙尘天气下的增加幅度相差很大。生物气溶胶中微生物主要分布于粗粒子中,其粒径分布受到沙尘天气的较大影响,而且不同种类微生物粒径分布的变化并不相同。沙尘发生时,生物气溶胶中的微生物群落结构与优势微生物也会发生明显改变。沙尘天气对生物气溶胶浓度、粒径分布、群落结构和活性的影响程度和影响机制,还需要进一步深入研究。     

天山乌鲁木齐河源1号冰川大气气溶胶的微观形貌及元素组成分析

为研究冰川区大气气溶胶单颗粒物的物理化学特征,使用带能谱的扫描电镜(SEM-EDX)对2007年在天山乌鲁木齐河源1号冰川东支积累区海拔4 130m(86°49′E,43°06′N)处采集的38个气溶胶样品中的38 861个单颗粒物进行了微观形貌和元素组成的分析.结果表明:天山乌鲁木齐河源1号冰川区大气气溶胶主要以粒径在0.6～2.5μm之间的不规则的非圆形矿物颗粒为主,其中以富含Si、Ca的粘土矿物颗粒为主,与人类活动密切相关的含S颗粒物及烟尘飞灰等含量较少.这与其它沙尘源区的气溶胶特征相似,其中含Ca颗粒多于其它沙尘源区,主要受西风带的影响.气团轨迹显示,来自于西面中亚地区的高空气流影响了1号冰川区的大气环境,表明天山乌鲁木齐河源1号冰川区的气溶胶主要代表了中亚沙尘源区对流层中上部大气的本底状况.     

2006年春季我国东部海域气溶胶光学厚度与沙尘天气

结合船基的太阳光度计观测资料和空基卫星遥感的MODIS气溶胶光学厚度资料,研究了我国东部海域气溶胶光学厚度与沙尘天气的关系。通过对不同天气条件下500 nm气溶胶光学厚度的分析,得出晴天(背景天气)、有云和浮尘以及只有浮尘时的平均值分别约为0.2、0.6和1.3以上;将MODIS的气溶胶光学厚度与船基观测资料进行对比之后发现,两者随时间的变化趋势非常一致,但前者在数值上明显偏高;利用订正后的MODIS资料,分析了2006年春季我国东部海域气溶胶光学厚度的时空分布特征,并与我国北方发生的沙尘天气进行了对比,发现两者之间关系密切。     

北极黄河站秋季气团传输影响下大气气溶胶数谱分布特征

2013 年9月在北极黄河站开展了气溶胶数谱（10~400nm）的短期观测实验。数浓度小时平均值主要出现在300~400cm^-3,平均值为350cm^-3,高于新奥尔松Zeppelin 全球大气本底站及环北极海洋大气7-9月航测报道的浓度。大气气溶胶的三个模态（核模态、爱根核模态和积聚模态）数浓度平均分别为35、122和193cm^-3。观测期间没有发生新粒子生成事件,平均数谱分布呈现双模态的分布特征,模态峰值分别出现在30nm和115nm,由积聚模态主导。平均数谱分布的几何中值粒径出现在约100~110nm。从单颗粒分析结果来看,观测期间黄河站地区大气气溶胶主要以海盐气溶胶为主,但是在来自挪威海域和北欧大陆的气团影响下,也观测到煤烟颗粒、富硫颗粒物和含碳颗粒物等人为气溶胶。     

东莞市黑碳气溶胶污染特征及来源分析

为探究珠江三角洲典型城市东莞市黑碳气溶胶(BC)的污染特征,对东莞市气象局站点2010年1月1日至2010年12月31日观测得到的BC数据进行了处理,并分析了东莞市2010年全年BC的分布特征、日变化规律以及污染来源。结果表明,(1)东莞站点BC浓度的频率分布为对数正态分布,BC的年均浓度为(3.98±3.42)μg/m~3,背景浓度为(1.14±1.04)μg/m~3。BC浓度湿季相对较低,干季相对较高。与国内各大城市相比,污染程度较轻,与背景站和一些国外城市相比,该站点处的BC污染问题较为严重;(2)BC浓度的日变化呈明显的两峰一谷型,表明BC浓度的日变化特征是由气象条件和交通源的日变化规律共同影响;(3)观测期间,370～950 nm波段的波长吸收指数(AAE_(370～950))的频率分布为对数正态分布,年均值为1.02,年变化呈现湿季减小、干季增大的变化趋势;(4)BC浓度和风速的关系表明,BC浓度随着风速的增大而减小,说明风对BC浓度起到稀释扩散的作用;(5)后向轨迹聚类分析结果表明,东莞站点的污染气团主要来自于局地排放、东南海岸线以及华中地区的长距离输送,南海吹来的气流对其污染的贡献占比较小。     

1961-2016年乌鲁木齐河流域气温和降水垂直梯度变化研究

新疆乌鲁木齐河流域高山区和平原区气候条件差异较大,对该流域气温和降水垂直梯度变化的研究,有利于了解不同地理要素之间的作用过程。利用乌鲁木齐河流域6个气象观测站数据,分析研究了气温和降水的变化趋势、气温和降水及其倾向率与海拔的关系,以及不同月份气温和降水随海拔的变化特征。结果表明：1961-2016年间,乌鲁木齐河流域气温和降水总体呈上升趋势,其中乌鲁木齐站气温和降水倾向率分别为0.189℃·（10a）^-1和28.83 mm·（10a）^-1,大西沟站气温和降水倾向率分别为0.268℃·（10a）^-1和18.85 mm·（10a）^-1;气温和降水与海拔关系密切,随海拔降低气温逐渐升高,而降水呈减少趋势;高海拔区气温升温倾向率总体大于低海拔区,降水倾向率随高度增加而明显增加;月气温变化速率随海拔升高呈“钟”形分布,并在5-8月达到最大;月降水变化速率随海拔变化表现为下降~上升~下降~上升,并在5-8月达到峰值。     

白龙江干流代表站径流变化特征及未来趋势预测

白龙江引水工程被列入国家确定的172项重大水利工程项目之一,分析研究白龙江干流代表站径流变化特征并进行未来趋势预测,为实施白龙江引水工程提供技术支撑。对白龙江干流白云、舟曲、武都、碧口4个代表站1956~2013年的实测径流系列资料进行分析,采用周期波均值外延叠加模型、谐波分析模型和逐步回归分析模型组合形成的加法模型对代表站未来径流变化趋势进行分析预测。结果表明:(1)该4站9月份多年平均流量占全年径流量比例最大,主汛期6~9月多年平均流量占全年径流量比例达到50%左右。(2)4个水文站多年径流量变化趋势呈现出逐渐缓慢减少的趋势,上游减少的幅度比下游小。(3)预测2015、2020、2025年年径流量的结果是:白云水文站均小于多年平均值,武都水文站均大于多年均值,舟曲和碧口水文站在多年均值上下浮动。     

临安一次沙尘暴过程影响气溶胶物理化学特性演变的初步分析

文章利用2002年3月29日～4月4日在浙江临安大气本底污染监测站观测的气溶胶粒子质量谱、离子与元素成分的数据,结合TOMS卫星的气溶胶指数资料和轨迹模式,重点分析在北方沙尘暴输送影响期间临安气溶胶质量浓度尺度分布的演变特点以及气溶胶化学成分与不同空气来源的关系。初步分析结果显示,受北方沙尘暴天气影响,临安气溶胶质量浓度、离子、元素浓度有明显的尺度分布演变。这种演变与污染物来源和大气污染物的气粒转化有关。沙尘影响前和结束后临安地区气溶胶主要以细粒子为主(<2.1μm),峰值粒径0.65～2.1μm,而受北方地区的沙尘暴影响,峰值粒径偏移到2.1～3.3μm,且在7～11μm间出现另一个峰值,同时临安气溶胶粗粒子中矿物元素显著增加。从离子成分看,在整个观测期间SO^2-₄与NH⁺₄在细粒子段有很好的一致性,而SO^2-₄,NO^-₃与Ca²⁺在粗粒子段有很好的相关,尤其是沙尘影响期间NO^-₃与Ca²⁺有很好的对应关系,表现出较明显的表面非均相反应特征     

乌鲁木齐河源1号冰川积累区气溶胶和表层雪中SO2-4的季节变化及成因分析

2003年12月至2004年12月,在天山乌鲁木齐河源1号冰川(以下简称1号冰川)积累区海拔4 130 m处共采集了53个气溶胶和55个表层雪样品.结果表明:气溶胶和表层雪中的SO2-4在年内的浓度变化形式大致相同,均有两个高值区出现,分别出现在春末和夏末秋初,表明年内表层雪中SO2-4浓度变化基本上反映了大气中SO2-4的浓度变化情况.通过对不同季节气溶胶和表层雪中的SO2-4浓度相关性分析表明,秋冬季最好,春季次之,夏季最差.这可能与SO2-4不同季节的来源,干沉降过程以及淋溶过程有关.     

天山高山区与郊区降水中颗粒物特征的比较

以天山乌鲁木齐河流域为例,运用参数比较法、相关分析法,对降水中粉尘颗粒物特征在高山区和郊区随时间变化特征及其差异进行研究.结果表明,降水中颗粒物的浓度、粒径分布及化学要素组成在两个取样点都具有明显的季节变化.颗粒浓度表现为冬-春季节升高而夏-秋季节降低,与降水量成反向变化,反映了降水受中亚沙尘活动的影响明显.颗粒在冬-...     

Trends in aerosol optical properties over Eastern Europe based on MODIS-Aqua

This study provides characteristics of aerosol columnar properties, measured over ten countries in Eastern Europe from 2002 to 2019. Aerosol optical depth (AOD) and Ångström exponent (AE) were obtained with the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6.1 merged Dark Target and Deep Blue aerosol product. The product is validated using ground-based Aerosol Robotic Network (AERONET) situated at Minsk, Belsk, Moldova and Kyiv. The results showed that 76.15% of retrieved AOD data are within the expected error. It was established that 64.2% of AOD points are between 0 and 0.2 and 79.3% of all AE points are over 1. Mean AOD values in the region vary from 0.130 ​± ​0.04 (Moldova) to 0.193 ​± ​0.03 (Czech Republic) with mean value in the region 0.162 ​± ​0.05. Seasonal mean AOD (AE) values were at the maximum during the summer from 0.231 ​± ​0.05 (1.482 ​± ​0.09 in winter) to minimum 0.087 ​± ​0.04 during the winter (1.363 ​± ​0.17 in summer). Gradual AOD reduction is observed in all countries with annual trend from −0.0050 (Belarus) to −0.0029 (Russia). Finally, the relationship between AOD and AE was studied to classify various aerosol types and showed seasonal non-uniformity of their contribution depending on variation in sources. The entire region is under significant impact of various aerosol types, including clean continental (СС), mixed (MX) and anthropogenic/burning (AB) aerosols types that are at 59.77%, 24.72%, and 12.97% respectively. These results form an important basis for further regional studies of air quality and distribution of sources of pollution.     

Characterization of aerosol type based on aerosol optical properties over Baghdad,Iraq

Aerosol optical depth (AOD), Angstrom exponent (AE), and ozone monitoring instrument aerosols index (OMI-AI) data, derived from MODerate Resolution Imaging Spectroradiometer (MODIS) and OMI sensor on board NASA’s Aqua satellite and NASA-Aura satellite platforms, have been analyzed and classified over Baghdad, Iraq, for an 8-year period (2008–2015). In order to give an obvious understanding of temporal inconsistency in the characteristics and classification of aerosols during each season separately, PREDE POM-02 sky radiometer measurements of AOD, carried out during a 2-year period (2014–2015), were compared with MODIS–Aqua AODs. On seasonal bases, MODIS–Aqua AODs corroborate well with ground-based measurements, with correlation coefficients ranging between 0.74 and 0.8 and RMSE ranging from 0.097 to 0.062 during spring and autumn seasons respectively. The overall satellite- and ground-based measurement comparisons showed a good agreement with correlation coefficients of 0.78 and RMSE of 0.066. These results suggest that MODIS–Aqua gives a good estimate of AOD. Analysis of MODIS–Aqua data for the 8-year period showed that the overall mean AOD, AE, and OMI-AI over Baghdad were 0.44?±?0.16, 0.77?±?0.29, and 1.34?±?0.33 respectively. AOD records presented a unique peak which was extended from mid-spring (April) to mid-summer (July) while the AE annual variability indicated a more complicated behavior with minimum values during the period from late spring (May) to early autumn (September). The maximum AOD and OMI-AI values occurred during summer while their minimum values occurred during winter. The AE showed an opposite behavior to that of AOD such that the highest AE values occurred during autumn and winter and the lowest values happened during spring and summer. This behavior may be attributed to the domination of coarse aerosol particles during autumn and winter seasons and fine aerosol particles during spring and summer seasons. A Hybrid Single-Particle Lagrangian Integrated Trajectory model was utilized to determine the source of air mass transport and to recognize the variability of aerosol origin regions. Finally, AOD, AE, and OMI-AI values have been employed to identify several aerosol types and to present seasonal heterogeneity in their contribution based on their origins.     

Detection of marine aerosols with IRS P4-Ocean Colour Monitor

The atmospheric correction bands 7 and 8 (765nm and 865nm respectively) of the Indian Remote Sensing Satellite IRS P4-0CM (Ocean Colour Monitor) can be used for deriving aerosol optical depth (AOD) over the oceans. A retrieval algorithm has been developed which computes the AOD using band 7 data by treating the ocean surface as a dark background after removing the Rayleigh path radiance in the sensor-detected radiances. This algorithm has been used to detect marine aerosol distributions at different coastal and offshore locations around India. A comparison between OCM derived AOD and the NOAA operational AOD shows a correlation ∼0.92 while that between OCM derived AOD and the ground-based sun photometer measurements near the coast of Trivandrum shows a correlation of ∼0.90.     

Impact of dust events on aerosol optical properties over Iraq

The spatial and temporal characteristics of aerosol optical properties (AOP) were analyzed in order to find out the hotspot aerosol sources over Iraq and surrounding regions. The correlation of AOP with the frequency of dust events (dust storm (DS), rising dust (RD), suspended dust (SD)) over 12 Iraqi stations is evaluated during the study period (January 2005–December 2014). The AOP: aerosol absorption optical depth (AAOD), aerosol extinction optical depth (AOD), and aerosol single scattering albedo (SSA) at 388 and 500 nm and aerosol index (AI), are derived from the Ozone Monitoring Instrument (OMI) on board the Aura satellite. Three well-known spatial interpolation techniques: inverse distance weighting, radial basis function with three sub-types, and kriging with three sub-types, are examined in ArcGIS software. Statistical analysis is applied to compute the station probability of dust events and its correlation with AOP. Results showed that the spline with the lowest RMSE and MPE near zero is the optimum method for estimating AOP. The spatial mean of AAOD, AOD, and AI (SSA) have the same pattern with high (low) mean values over the south and northwest of Iraq, Kuwait, and the northeast of Saudi Arabia. The seasonal variability of AAOD and AOD over the Iraqi stations showed that high (low) values occurred during spring and summer (winter) and concluded that AAOD is a responsible component for variation in AOD. DS and RD probability is higher over stations in the middle and south of Iraq than the stations in the north. High SD probability is over Mosul, Baghdad, and Nasiriya stations. The correlation of AOP with dust events suggests that the AAOD component is more important in the study of DS than SSA and AI while AI is a good index for the study of RD and SD in the study region.     

Modifications in aerosol physical,optical and radiative properties during heavy aerosol events over Dushanbe,Central Asia

The location of Central Asia,almost at the center of the global dust belt region,makes it susceptible for dust events.The studies on atmospheric impact of dust over the region are very limited despite the large area occupied by the region and its proximity to the mountain regions(Tianshan,Hindu Kush-Karakoram-Himalayas,and Tibetan Plateau).In this study,we analyse and explain the modification in aerosols'phys-ical,optical and radiative properties during various levels of aerosol loading observed over Central Asia utilizing the data collected during 2010-2018 at the AERONET station in Dushanbe,Tajikistan.Aerosol epi-sodes were classified as strong anthropogenic,strong dust and extreme dust.The mean aerosol optical depth(AOD)during these three types of events was observed a factor of～3,3.5 and 6.6,respectively,higher than the mean AOD for the period 2010-2018.The corresponding mean fine-mode fraction was 0.94,0.20 and 0.16,respectively,clearly indicating the dominance of fine-mode anthropogenic aerosol during the first type of events,whereas coarse-mode dust aerosol dominated during the other two types of events.This was corroborated by the relationships among various aerosol parameters(AOD vs.AE,and EAE vs.AAE,SSA and RRI).The mean aerosol radiative forcing(ARF)at the top of the atmosphere(ARFTOA),the bottom of the atmosphere(ARFBOA),and in the atmosphere(ARFATM)were-35±7,-73±16,and 38±17 Wm-2 during strong anthropogenic events,-48±12,-85±24,and 37±15 Wm-2 during strong dust event,and-68±19,-117±38,and 49±21 Wm-2 during extreme dust events.Increase in aerosol loading enhanced the aerosol-induced atmospheric heating rate to 0.5-1.6 K day-1(strong anthropogenic events),0.4-1.9 K day-1(strong dust events)and 0.8-2.7 K day 1(extreme dust events).The source regions of air masses to Dushanbe during the onset of such events are also identified.Our study con-tributes to the understanding of dust and anthropogenic aerosols,in particular the extreme events and their disproportionally high radiative impacts over Central Asia.     

A MODIS-based modeling scheme for the estimation of downward surface shortwave radiation under cloud-free conditions

Atmospheric aerosol optical depth (AOD) plays an important role in radiation modeling and partly determines the accuracy of estimated downward surface shortwave radiation (DSSR). In this study, Iqbal’s model C was used to estimate DSSR under cloud-free conditions over the Koohin and Chitgar sites in Tehran, Iran; the estimated DSSR was based on (1) our proposed hybrid modeling scheme where the AOD is retrieved using the Simplified Aerosol Retrieval Algorithm (SARA), ground-based measurements at the AERONET site in Zanjan and (2) the AOD from the Terra MODerate-resolution Imaging Spectroradiometer (MODIS) sensor. Several other Terra MODIS land and atmospheric products were also used as input data, including geolocation properties, water vapor, total ozone, surface reflectance, and top-of-atmosphere (TOA) radiance. SARA-based DSSR and MODIS-based DSSR were evaluated with ground-based DSSR measurements at the Koohin and Chitgar sites in 2011 and 2013, respectively; the averaged statistics for SARA-based DSSR [R ² ≈ 0.95, RMSE ≈ 22 W/m² (2.5% mean value), and bias ≈ 3 W/m²] were stronger than those for MODIS-based DSSR [R ² ≈ 0.79, RMSE ≈ 51 W/m² (5.8% mean value), and bias ≈ 34 W/m²]. These results show that the proposed hybrid scheme can be used at regional to global scales under the assumption of future access to spatially distributed AERONET sites. Additionally, the robustness of this modeling scheme was exemplified by estimating the aerosol radiative forcing (ARF) during a dust storm in Southwest Asia. The results were comparable to those of previous studies and showed the strength of our modeling scheme.     

Surface water and aerosol spatiotemporal dynamics and influence mechanisms over drylands

Under the background of global warming and excessive human activities, much surface water in drylands is experiencing rapid degradation or shrinkage in recent years. The shrinkage of surface water, especially the degradation of lakes and their adjacent wetlands in drylands, may lead to the emergence of new salt dust storm hotspots, which causes greater danger. In this paper, based on high spatial resolution global surface water (GSW) and multiangle implementation of atmospheric correction (MAIAC) AOD data, we systematically analyze the dynamic characteristics of surface water and aerosols in typical drylands (Central Asia, CA) between 2000 and 2018. Simultaneously, combined with auxiliary environment variables, we explore the driving mechanisms of surface water on the regional salt/sand aerosols on different spatial scales. The results show that the seasonal surface water features an increasing trend, especially a more dramatic increase after 2015, and the permanent surface water indicates an overall decrease, with nearly 54.367 % at risk of receding and drying up. In typical lakes (Aral Sea and Ebinur Lake), the interannual change feature of the surface water area (WA) is that a continuous decrease during the study period occurs in Aral Sea area, yet a significant improvement has occurred in Ebinur Lake after 2015, and the degradation of Ebinur Lake takes place later and its recovery earlier than Aral Sea. The aerosol optical depth (AOD) in CA shows obvious seasonal variation, with the largest in spring (0.192 ± 0173), next in summer (0.169 ± 0.106), and the smallest in autumn (0.123 ± 0.065). The interannual variation of AOD exhibits an increase from 2000 to 2018 in CA, with high AOD areas mainly concentrated in the Taklamakan Desert and some lake beds resulting from lake degradation, including Aral Sea and Ebinur Lake. The AOD holds a similar trend between Aral Sea and Ebinur Lake on an interannual scale. And the AOD over Ebinur Lake is lower than that over Aral Sea in magnitude and lags behind in reaching the peak compared with Aral Sea. The WA change can significantly affect aerosol variation directly or indirectly on the aerosol load or mode size, but there are obvious differences in the driving mechanisms, acting paths, and influence magnitude of WA on aerosols on different spatial scales. In addition, the increase of WA can significantly directly suppress the increase of Ångström exponent (AE), and the effects of WA on AOD are realized majorly by an indirect approach. From the typical lake perspective, the effects of WA on aerosol in Aral Sea are achieved via an indirect path; and the decrease of WA can indirectly promote the AOD rise, and directly stimulate the AE growth in Ebinur Lake.     

Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent ‘α’ had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ～ 33.0% during March and by ～ 9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.     

Analysis of marine aerosol optical depth retrieved from IRS-P4 OCM sensor and comparison with the aerosol derived from SeaWiFS and MODIS sensor

Aerosol optical depth is regularly derived from SeaWiFS and MODIS sensor and used by the scientific community in various climatic studies. In the present study an attempt has been made to retrieve the aerosol optical depth using the IRS-P4 OCM sensor data and a comparison has been carried out using few representative datasets. The results show that the IRS-P4 OCM retrieved aerosol optical depth is in good agreement with the aerosols retrieved from SeaWiFS as well as MODIS. The RMSE are found to be ±0.0522 between OCM and SeaWIFS and ±0.0638 between OCM and MODIS respectively. However, IRS-P4 OCM sensor retrieved aerosol optical depth is closer to SeaWiFS (correlation = 0.88, slope = 0.96 and intercept = ?0.013) compared to MODIS (correlation = 0.75, slope = 0.91 and intercept = 0.0198). The mean percentage difference indicates that OCM retrieved AOD is +12% higher compared to SeaWiFS and +8% higher compared to MODIS. The mean absolute percentage between OCM derived AOD and SeaWiFS is found to be less (16%) compared to OCM and MODIS (20%).     

Latitudinal and longitudinal variation in aerosol characteristics from Sun photometer and MODIS over the Bay of Bengal and Arabian Sea during ICARB

Spatial variations in aerosol optical properties as function of latitude and longitude are analysed over the Bay of Bengal and Arabian Sea during ICARB cruise period of March–May 2006 from in situ sun photometer and MODIS (Terra, Aqua) satellite measurements. Monthly mean 550 nm aerosol optical depths (AODs) over the Bay of Bengal and Arabian Sea show an increase from March to May both in spatial extent and magnitude. AODs are found to increase with latitude from 4°N to 20°N over the Bay of Bengal while over Arabian Sea, variations are not significant. Sun photometer and MODIS AODs agree well within ±1σ variation. Bay of Bengal AOD (0.28) is higher than the Arabian Sea (0.24) latitudinally. Aerosol fine mode fraction (FMF) is higher than 0.6 over Bay of Bengal, while FMF in the Arabian Sea is about 0.5. Bay of Bengal α(～1) is higher than the Arabian Sea value of 0.7, suggesting the dominance of fine mode aerosols over Bay of Bengal which is corroborated by higher FMF values over Bay of Bengal. Air back trajectory analyses suggest that aerosols from different source regions contribute differently to the optical characteristics over the Bay of Bengal and Arabian Sea.