Physical and optical characteristics of atmospheric aerosols during ICARB at Manora Peak, Nainital: A sparsely inhabited, high-altitude location in the Himalayas
U C Dumka1,∗, K Krishna Moorthy2, P Pant1, P Hegde1, Ram Sagar1 and K Pandey3
1Aryabhatta Research Institute of Observational Sciences, Nainital, India.
2Space Physics Laboratory, Vikram Sarabhai Space Center, Thiruvananthapuram 695 002, India.
3Department of Physics, DSB College, Nainital, India.
∗e-mail: dumka@aries.ernet.in

Abstract: Collocated measurements of the optical and physical properties of columnar and near-surface aerosols were carried out from Manora Peak, Nainital (a sparsely inhabited, high altitude location, ∼2 km above mean sea level, in the Himalayas), during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP). Under this, observational data of spectral aerosol optical depths (AOD), mass concentration of aerosol black carbon (MB), mass concentration (MT ) and number concentration (Nt) of composite (total) aerosols near the surface and meteorological parameters were collected during the period February 15 to April 30, 2006. Though very low (<0.1 at 500 nm) AODs were observed during clear days, as much as a fourfold increase was seen on hazy days. The ˚Angstr¨om exponent (α), deduced from the spectral AODs, revealed high values during clear days, while on hazy days α was low; with an overall mean value of 0.69 ± 0.06 for the campaign period. BC mass concentration varied between 0.36 and 2.87 μg m−3 and contributed in the range 0.7 to 1.8% to the total aerosol mass. Total aerosol number concentration and BC mass concentration showed diurnal variation with a midnight and early morning minimum and a late afternoon maximum; a pattern quite opposite to that seen in low altitude stations. These are attributed to the dynamics of the atmospheric boundary layer.


Influence of circulation parameters on the AOD variations over the Bay of Bengal during ICARB
Marina Aloysius, Mannil Mohan∗, S Suresh Babu, Vijayakumar S Nair,
K Parameswaran and K Krishna Moorthy
Space Physics Laboratory, Vikram Sarabhai Space Center, Thiruvananthapuram 695 022, India.
∗e-mail: mannil−mohan@vssc.gov.in

Abstract: MODIS (Moderate Resolution Imaging Spectroradiometer) level-3 aerosol data, NCEP (National Centers for Environmental Prediction) reanalysis winds and QuikSCAT ocean surface winds were made use of to examine the role of atmospheric circulation in governing aerosol variations over the Bay of Bengal (BoB) during the first phase of the ICARB (Integrated Campaign for Aerosols, gases and Radiation Budget) campaign (March 18–April 12, 2006). An inter-comparison between MODIS level-3 aerosol optical depth (AOD) data and ship-borne MICROTOPS measurements showed good agreement with correlation 0.92 (p < 0.0001) and a mean MODIS underestimation by 0.01. During the study period, the AOD over BoB showed high values in the northern/north western regions, which reduced towards the central and southern BoB. The wind patterns in lower atmospheric layers (> 850 hPa)  indicated that direct transport of aerosols from central India was inhibited by the presence of a high pressure and a divergence over BoB in the lower altitudes. On the other hand, in the upper atmospheric levels, winds from central and northern India stretched south eastwards and converged over BoB with a negative vorticity indicative of a downdraft. These wind patterns pointed to the possibility of aerosol transport from central India to BoB by upper level winds. This mechanism was further confirmed by the significant correlations that AOD variations over BoB showed with aerosol flux convergence and flux vorticity at upper atmospheric levels (600–500 hPa). AOD in central and southern BoB away from continental influences displayed an exponential dependence on the QuikSCAT measured ocean surface wind speed. This study shows that particles transported from central and northern India by upper atmospheric circulations as well as the marine aerosols generated by ocean surface winds contributed to the AOD over the BoB during the first phase of ICARB.



Studies on aerosol properties during ICARB–2006 campaign period at Hyderabad, India using ground-based measurements and satellite data
K V S Badarinath∗ and Shailesh Kumar Kharol
Atmospheric Science Section, Oceanography Division, National Remote Sensing Agency
(Department of Space, Govt. of India) Balanagar, Hyderabad 500 037, India.
∗e-mail: badrinath−kvs@nrsa.gov.in

Abstract: Continuous and campaign-based aerosol field measurements are essential in understanding fundamental atmospheric aerosol processes and for evaluating their effect on global climate, environment and human life. Synchronous measurements of Aerosol Optical Depth (AOD), Black Carbon (BC) aerosol mass concentration and aerosol particle size distribution were carried out during the campaign period at tropical urban regions of Hyderabad, India. Daily satellite datasets of DMSP-OLS were processed for night-time forest fires over the Indian region in order to understand the additional sources (forest fires) of aerosol. The higher values in black carbon aerosol mass concentration and aerosol optical depth correlated well with forest fires occurring over the region. Ozone Monitoring Instrument (OMI) aerosol index (AI) variations showed absorbing aerosols over the region and correlated with   ground measurements.


Aerosol characteristics at Patiala during ICARB–2006
Manjit Singh1, Darshan Singh1 and P Pant2
1Physics Department, Punjabi University, Patiala 147 002, Punjab, India.
2Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak,
Nainital 263 129, Uttaranchal, India.

Abstract: The spectral AOD measurements have been made for the first time over Patiala during multiplatform field campaign ICARB–2006 using a Multi-Wavelength Radiometer (MWR) along with the suspended particulate matter measurements with a high volume sampler. Spectral AOD has higher values in May in comparison to March and April. The monthly mean AOD values at 500 nm are 0.26 ± 0.08, 0.36 ± 0.19 and 0.58 ± 0.20 for the months of March, April and May respectively. The mean AOD is more during afternoon in comparison to forenoon at all wavelengths. The atmospheric turbidity is higher in May and is attributed to dust transported by southerly winds prevailing during this month. The ˚Angstr¨om parameter α varies between zero and 0.68 while β ranges from 0.1 to 0.9. The columnar water vapour content ranges from 0.12 to 2.92 cm, having a mean value of 1.06 ± 0.648 cm. The mean total suspended particulate matter is 334.41 ± 97.56 μgm/m3, an indication of high aerosol loading over Patiala during the campaign period.



On the marine atmospheric boundary layer characteristics  over Bay of Bengal and Arabian Sea during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)
Denny P Alappattu1,∗, D Bala Subrahamanyam1, P K Kunhikrishnan1,
K M Somayaji2, G S Bhat3, R Venkatesan2, C B S Dutt4,
A Bagavath Singh2, V K Soni5 and A S Tripathi6
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, Kerala, India.
2Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu, India.
3Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India.
4Indian Space Research Organization Head Quarters, Antariksh Bhavan, Bangalore 560 094, India.
5India Meteorological Department, Pune 411 005, India.
6India Meteorological Department, Mausam Bhavan, Lodhi Road, Delhi 110 003, India.
∗e-mail: dennyalp@gmail.com

Abstract: Detailed measurements were carried out in the Marine Atmospheric Boundary Layer (MABL) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) which covered both Arabian Sea and Bay of Bengal during March to May 2006. In this paper, we present the meteorological observations made during this campaign. The latitudinal variation of the surface layer turbulent fluxes is also described in detail.


Size segregated aerosol mass concentration measurements over the Arabian Sea during ICARB
Vijayakumar S Nair1, K Krishna Moorthy1, S Suresh Babu1, K Narasimhulu2,
L Siva Sankara Reddy2, R Ramakrishna Reddy2, K Rama Gopal2,
V Sreekanth3, B L Madhavan3 and K Niranjan3
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, India.
2Department of Physics, Sri Krishnadevaraya University, Anantapur 515 003, India.
3Department of Physics, Andhra University, Visakhapatnam 530 003, India.

Abstract: Mass concentration and mass size distribution of total (composite) aerosols near the surface are essential inputs needed in developing aerosol models for radiative forcing estimation as well as to infer the environment and air quality. Using extensive measurements onboard the oceanographic research vessel, Sagar Kanya, during its cruise SK223B in the second phase of the ocean segment of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), the spatial distribution of the mass concentration and mass size distribution of near-surface aerosols are examined for the first time over the entire Arabian Sea, going as far as 58◦E and 22◦N, within a span of 26 days. In general, the mass concentrations (MT ) were found to be low with the mean value for the entire Arabian Sea being 16.7 ± 7 μg m−3; almost 1/2 of the values reported in some of the earlier campaigns. Coarse mode aerosols contributed, on an average, 58% to the  total mass, even though at a few pockets accumulation mode contribution dominated. Spatially, significant variations were observed over central and northern Arabian Sea as well as close to the west coast of India. In central Arabian Sea, even though the MT was quite low, contribution  of accumulation aerosols to the total mass concentration was greater than 50%. Effective radius, a parameter important in determining scattering properties of aerosol size distribution, varied between 0.07 and 0.4 μm with a mean value of 0.2 μm. Number size distributions, deduced from the mass size distributions, were approximated to inverse power-law form and the size indices (ν) were estimated. It was found to vary in the range 3.9 to 4.2 with a mean value of 4.0 for the entire oceanic region. Extinction coefficients, estimated using the number-size distributions, were well-correlated with the  accumulation mode mass concentration with a correlation coefficient of 0.82.


Lidar observation of aerosol stratification in the lower troposphere over Pune during pre-monsoon season of 2006
P Ernest Raj∗, S K Saha, S M Sonbawne, S M Deshpande, P C S Devara,
Y Jaya Rao, K K Dani and G Pandithurai
Indian Institute of Tropical Meteorology, Pashan Road, Pune 411 008, India.
∗e-mail: ernest@tropmet.res.in

Abstract: Lidar observations of aerosol vertical distributions in the lower troposphere along with observations of horizontal and vertical winds from collocated UHF radar (Wind Profiler) over a tropical Indian station, Pune during the pre-monsoon season (March–May) of 2006 as part of an ISRO-GBP national campaign (ICARB) have been examined. Lidar vertical profiles showed high aerosol concentrations in the surface layers and a subsequent gradual decrease with height. Results showed the presence of an elevated stratified aerosol layer around 2000–3500m height which persisted throughout the months of March and April. Observed strong vertical gradients in both horizontal and vertical winds in the lower troposphere seem to be a possible cause for the formation of elevated aerosol layers. Further, high daytime temperatures accompanied by dry conditions at the surface help to enhance the aerosol loading in the lower layers over this location.



Analysis of marine aerosol optical depth retrieved from IRS-P4 OCM sensor and comparison with the aerosol derived from SeaWiFS and MODIS sensor
A K Mishra1, V K Dadhwal1 and C B S Dutt2
1Indian Institute of Remote Sensing (NRSA), P.B. 135, 4 Kalidas Road, Dehradun, Uttarakhand, India.
2Indian Space Research Organisation (ISRO), New BEL Road, Bangalore, India.

Abstract: 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%).


Characteristics of spectral aerosol optical depths over India during ICARB
S Naseema Beegum1, K Krishna Moorthy1, Vijayakumar S Nair1, S Suresh Babu1,
S K Satheesh2, V Vinoj2, R Ramakrishna Reddy3, K Rama Gopal3,
K V S Badarinath4, K Niranjan5, Santosh Kumar Pandey6, M Behera7,
A Jeyaram7, P K Bhuyan8, M M Gogoi8, Sacchidanand Singh9, P Pant10,
U C Dumka10, Yogesh Kant11, J C Kuniyal12 and Darshan Singh13
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, India.
2Centre of Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India.
3Department of Physics, Sri Krishnadevaray University, Anantapur 515 003, India.
4National Remote Sensing Agency, Balanangar, Hyderabad 500 037, India.
5Department of Physics, Andhra University, Visakhapatnam 530 003, India.
6ISTRAC Ground Station, Dolly Gunj, Port Blair 744 101, India.
7Regional Remote Sensing Service Centre, Indian Institute of Technology Campus, Kharagpur 721 302, India.
8Department of Physics, Dibrugarh University, Dibrugarh 786 004, India.
9National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110 012, India.
10Aryabhatta Research Institute of Observational Sciences, Nainital 263 129, India.
11Indian Institute of Remote Sensing, Dehra Dun 248 001, India.
12GB Pant Institute for Himalayan Environment and Development, Manali, Mohal-Kullu 175 126, India.
13Department of Physics, Punjabi University, Patiala 147 002, India.

Abstract: Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived ˚Angstr¨om parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The ˚Angstr¨om coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from the adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the ˚Angstr¨om exponent (α) remained significantly



Latitudinal and longitudinal variation in aerosol characteristics from Sun photometer and MODIS over the Bay of Bengal and Arabian Sea during ICARB
Sumita Kedia∗ and S Ramachandran∗∗
Space and Atmospheric Sciences Division, Physical Research Laboratory, Ahmedabad 380 009, India.
∗e-mail: sumita@prl.res.in
∗∗e-mail: ram@prl.res.in

Abstract: 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.



Chemical characteristics of PM10 aerosols and airmass trajectories over Bay of Bengal and Arabian Sea during ICARB
L A K Reddy1, U C Kulshrestha1,∗, J Satyanarayana1, Monika J Kulshrestha1
and K Krishna Moorthy2
1Indian Institute of Chemical Technology, Hyderabad 500 007, India.
2Space Physics Laboratory, Thiruvananthapuram 695 031, India.
∗e-mail: umesh−iict@rediffmail.com

Abstract: For the first time, chemical characterization of PM10 aerosols was attempted over the Bay of Bengal (BoB) and Arabian Sea (AS) during the ICARB campaign. Dominance of SO2− 4 , NH+ 4 and NO−3 was noticed over both the regions which indicated the presence of ammonium sulphate and ammonium nitrate as major water soluble particles playing a very important role in the radiation budget. It was observed that all the chemical constituents had higher concentrations over Bay of Bengal as compared to Arabian Sea. Higher concentrations were observed near the Indian coast showing influence of landmass indicating that gaseous pollutants like SO2, NH3 and NOx are transported over to the sea regions which consequently contribute to higher SO2− 4 , NH+ 4 and NO−3 aerosols respectively. The most polluted region over BoB was 13◦–19◦N and 70◦–90◦E while it was near 11◦N and 75◦E over AS. Although the concentrations were higher over Bay of Bengal for all the chemical constituents of PM10 aerosols, per cent non-sea salt (nss) fraction (with respect to Na) was higher over Arabian Sea. Very low Ca2+ concentration was observed at Arabian Sea which led to higher atmospheric acidity as compared to BoB. Nss SO2− 4 alone contributed 48% of total water soluble fraction over BoB as well as AS. Ratios SO2− 4 /NO−3 over both the regions (7.8 and 9 over BoB and AS respectively) were very high as compared to reported values at land sites like Allahabad (0.63) and Kanpur (0.66) which may be due to very low NO−3 over sea regions as compared to land sites. Air trajectory analysis showed four classes: (i) airmass passing through Indian land, (ii) from oceanic region, (iii) northern Arabian Sea and Middle East and (iv) African continent. The highest nss SO2− 4 was observed during airmasses coming from the Indian land side while lowest concentrations were observed when the air was coming from oceanic regions. Moderate concentrations of nss SO2− 4 were observed when air was seen moving from the Middle East and African continent. The pH of rainwater was observed to be in the range of 5.9–6.5 which is lower than the values reported over land sites. Similar feature was reported over the Indian Ocean during INDOEX indicating that marine atmosphere had more free acidity than land atmosphere.


Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB
P Murugavel, V Gopalakrishnan, Vimlesh Pant and A K Kamra
Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, NCL Post, Pune 411 008, India.

Abstract: Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20◦25N, 85◦83E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ∼100 km over land and ∼150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm−3 at 0.5 km level but are almost constant at ∼ 6000 cm−3 and ∼ 800 cm−3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm−3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal regions.



Aircraft measurements of aerosol black carbon from a coastal location in the north-east part of peninsular India during ICARB
S Suresh Babu1, S K Satheesh2, K Krishna Moorthy1, C B S Dutt3,
Vijayakumar S Nair1, Denny P Alappattu1 and P K Kunhikrishnan1
1Space Physics Laboratory, VSSC, Trivandrum 695 022, India.
2Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India.
3Indian Space Research Organisation Head Quarters, Antariksh Bhavan, New BEL Road,
Bangalore 560 094, India.

Abstract: During the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) over India, high-resolution airborne measurements of the altitude profiles of the mass concentrations (MB) of aerosol black carbon (BC) were made off Bhubaneswar (BBR, 85.82◦E, 20.25◦N), over northwest Bay of Bengal, in the altitude region upto 3 km. Such high-resolution measurements of altitude profiles of aerosols are done for the first time over India. The profiles showed a near-steady vertical distribution of MB modulated with two small peaks, one at 800m and the other at ∼2000m. High resolution GPS (Global Positioning System) sonde (Vaisala) measurements around the same region onboard the research vessel Sagar Kanya (around the same time of the aircraft sortie) revealed two convectively well mixed layers, one from ground to ∼700m with an inversion at the top and the other extends from 1200m to ∼2000m with a second inversion at ∼2200m and a convectively stable region in the altitude range 700–1200m. The observed peaks in the MB profile are found to be associated with these temperature inversions. In addition, long-range transport from the Indo- Gangetic Plain (IGP) and deserts lying further to the west also influence the vertical profile of BC. Latitudinal variation of MB showed a remarkable land ocean contrast at the 500m altitude (within the well mixed region) with remarkably lower values over oceans, suggesting the impact of strong sources over the mainland. However, above the ABL (at 1500m), the latitudinal variations were quite weak, and this appears to be resulting from the impact of long-range transport. Comparison of the altitude profiles of MB over BoB off BBR with those obtained during the earlier occasion over the inland stations of Hyderabad and Kanpur showed similarities above ∼500m, with MB remaining around a steady value of ∼1 μg m−3. However, large differences are seen within the ABL. Even though the observed MB values are not unusually high, their near constancy in the vertical column will have important implications to radiative forcing.


Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB): An overview
K Krishna Moorthy1, S K Satheesh2, S Suresh Babu1 and C B S Dutt3
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, India.
2Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India.
3Indian Space Research Organisation Head Quarters, New BEL Road, Bangalore 560 094, India.

Abstract: During March–May 2006, an extensive, multi-institution, multi-instrument, and multi-platform integrated field experiment ‘Integrated Campaign for Aerosols, gases and Radiation Budget’ (ICARB) was carried out under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP). The objective of this largest and most exhaustive field campaign, ever conducted in the Indian region, was to characterize the physico-chemical properties and radiative effects of atmospheric aerosols and trace gases over the Indian landmass and the adjoining oceanic regions of the Arabian Sea, northern Indian Ocean, and Bay of Bengal through intensive, simultaneous observations. A network of ground-based observatories (over the mainland and islands), a dedicated ship cruise over the oceanic regions using a fully equipped research vessel, the Sagar Kanya, and altitude profiling over selected regions using an instrumented aircraft and balloonsondes formed the three segments of this integrated experiment, which were carried out in tandem. This paper presents an overview of the ICARB field experiment, the database generated, and some of its interesting outcomes though these are preliminary in nature. The ICARB has revealed significant spatio-temporal heterogeneity in most of the aerosol characteristics both over land and ocean. Observed aerosol loading and optical depths were comparable to or in certain regions, a little lower than those reported in some of the earlier campaigns for these regions. The preliminary results indicate:
• low (< 0.2) aerosol optical depths (AOD) over most part of the Arabian Sea, except two pockets; one off Mangalore and the other, less intense, in the central Arabian Sea at ∼18◦N latitude;
• High ˚Angstr¨om exponent in the southern Arabian Sea signifying steep AOD spectra and higher abundance of accumulation mode particles in the southern Arabian Sea and off Mangalore;
• Remarkably low ˚Angstr¨om exponents signifying increased concentration of coarse mode aerosols and high columnar abundance in the northern Arabian Sea;
• Altitude profiles from aircraft showed a steady BC level up to 3 km altitude with structures which were associated with inversions in the atmospheric boundary layer (ABL);
• A surprisingly large increase in the BC mass fraction with altitude;
• Presence of a convectively mixed layer extending up to about 1 km over the Arabian Sea and Bay of Bengal;
• A spatial off shore extent of <100 km for the anthropogenic impact at the coast; and
• Advection of aerosols, through airmass trajectories, from west Asia and NW arid regions of India leading to formation of elevated aerosol layers extending as far as 400 km off the east coast.



Aerosol mass loading over the marine environment of Arabian Sea during ICARB: Sea-salt and non-sea-salt components
Susan K George and Prabha R Nair∗
Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, India.
∗e-mail: prabha−nair@vssc.gov.in

Abstract: Mass loading and chemical composition of atmospheric aerosols over the Arabian Sea during the pre-monsoon months of April and May have been studied as a part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB). These investigations show large spatial variabilities in total aerosol mass loading as well as that of individual chemical species. The mass loading is found to vary between 3.5 and 69.2 μg m−3, with higher loadings near the eastern and northern parts of Arabian Sea, which decreases steadily to reach its minimum value in the mid Arabian Sea. The decrease in mass loading from the coast of India towards west is estimated to have a linear gradient of 1.53 μg m−3/◦ longitude and an e−1 scale distance of ∼2300 km. SO2− 4 , Cl− and Na+ are found to be the major ionic species present. Apart from these, other dominating watersoluble components of aerosols are NO−3 (17%) and Ca2+ (6%). Over the marine environment of Arabian Sea, the non-sea-salt component dominates accounting to ∼76% of the total aerosol mass. The spatial variations of the various ions are examined in the light of prevailing meteorological conditions and airmass back trajectories.



Chemical characteristics of aerosols in MABL of Bay of Bengal and Arabian Sea during spring
inter-monsoon: A comparative study
Ashwini Kumar, A K Sudheer andM M Sarin∗
Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India.
∗e-mail: sarin@prl.res.in

Abstract: The chemical composition of aerosols in the Marine Atmospheric Boundary Layer (MABL) of Bay of Bengal (BoB) and Arabian Sea (AS) has been studied during the spring and inter-monsoon (March–May 2006) based on the analysis of water soluble constituents (Na+, NH+ 4, K+, Mg2+, Ca2+, Cl−, NO−3 and SO2− 4 ), crustal elements (Al, Fe, and Ca) and carbonaceous species (EC, OC). The total suspended particulates (TSP) ranged from 5.2 to 46.6 μg m−3 and 8.2 to 46.9 μg m−3 during the sampling transects in the BoB and AS respectively. The water-soluble species, on average, accounted for 44% and 33% of TSP over BoB and AS respectively, with dominant contribution of SO2− 4 over both the oceanic regions. However, distinct differences with respect to elevated abundances of NH+ 4 in the MABL of BoB and that of Na+ and Ca2+ in AS are clearly evident. The non-sea-salt component of SO2− 4 ranging from 82 to 98% over BoB and 35 to 98% over AS; together with nss-Ca2+/nss-SO2− 4 equivalent ratios 0.12 to 0.5 and 0.2 to 1.16, respectively, provide evidence for the predominance of anthropogenic constituents and chemical transformation processes occurring within MABL. The concentrations of OC and EC average around 1.9 and 0.4 μg m−3 in BoB and exhibit a decreasing trend from north to south; however, abundance of these carbonaceous species are not significantly pronounced over AS. The abundance of Al, used as a proxy for mineral aerosols, varied from 0.2 to 1.9 μg m−3 over BoB and AS, with a distinctly different spatial pattern – decreasing north to south in BoB in contrast to an increasing pattern in the Arabian Sea.



Aerosol characteristics at a remote island: Minicoy in southern Arabian Sea
V Vinoj1, S K Satheesh1 and K Krishna Moorthy2
1Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India.
2Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India.

Abstract: Extensive measurements of aerosol optical and microphysical properties made at a remote island, Minicoy in southern Arabian Sea for the period (February 2006–March 2007) are used to characterize their temporal variability and Black Carbon (BC) mass mixing ratio. Large decrease in aerosol BC (from ∼800 ng m−3 to ∼100 ng m−3) was observed associated with change in airmass characteristics and monsoon rains. The total aerosol mass varied between ∼80 and 20 μg m−3. Though the total mass fell drastically, a slight increase in super micron mass was observed during the June–August period associated with high winds. The mass fraction of Black Carbon aerosols during the prevalence of continental airmass is found to be ∼1.2% of the composite aerosols, which is much lower than the values reported earlier for this region.



Temporal characteristics of aerosol physical properties at Visakhapatnam on the east coast of India during ICARB – Signatures of transport onto Bay of Bengal
K Niranjan∗, V Sreekanth, B L Madhavan, T Anjana Devi and B Spandana
Department of Physics, Andhra University, Visakhapatnam 530 003, India.
e-mail: niranjankandula@hotmail.com

Abstract: Realizing the importance of aerosol physical properties at the adjoining continental and coastal locations in the airmass pathways onto the oceanic region, extensive measurements of aerosol physical properties were made at Visakhapatnam (17.7◦N, 83.3◦E), an eastern coastal location in peninsular India during the ICARB period. The temporal variations of aerosol optical depth, near surface aerosol mass size distributions and BC mass concentrations show significantly higher aerosol optical depth and near surface mass concentrations during the first and last weeks of April 2007. The mean BC mass fraction in the fine mode aerosol was around 11%. The aerosol back scatter profiles derived from Micro Pulse Lidar indicate a clear airmass subsidence on the days with higher aerosol optical depths and near surface mass fraction. A comparison of the temporal variation of the aerosol properties at Visakhapatnam with the MODIS derived aerosol optical depth along  the cruise locations indicates a resemblance in the temporal variation suggesting that the aerosol transport from the eastern coastal regions of peninsular India could significantly affect the aerosol optical properties at the near coastal oceanic regions and that the affect significantly reduced at the farther regions.