We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm–3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m–3. Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.

Long‐term measurements of the light absorption coefficient (babs) obtained with a particle soot absorption photometer (PSAP), babs (PSAP), have been previously reported for Barrow, Alaska, and Ny‐Ålesund, Spitsbergen, in the Arctic. However, the effects on babs of other aerosol chemical species coexisting with black carbon (BC) have not been critically evaluated. Furthermore, different mass absorption cross section (MAC) values have been used to convert babs to BC mass concentration (MBC = babs/MAC). We used a continuous soot monitoring system (COSMOS), which uses a heated inlet to remove volatile aerosol compounds, to measure babs (babs (COSMOS)) at these sites during 2012–2015. Field measurements and laboratory experiments have suggested that babs (COSMOS) is affected by about 9% on average by sea‐salt aerosols. MBC values derived by COSMOS (MBC (COSMOS)) using a MAC value obtained by our previous studies agreed to within 9% with elemental carbon concentrations at Barrow measured over 11 months. babs (PSAP) was higher than babs (COSMOS), by 22% at Barrow (PM1) and by 43% at Ny‐Ålesund (PM10), presumably due to the contribution of volatile aerosol species to babs (PSAP). Using babs (COSMOS) as a reference, we derived MBC (PSAP) from babs (PSAP) measured since 1998. We also established the seasonal variations of MBC at these sites. Seasonally averaged MBC (PSAP) decreased at a rate of about 0.55 ± 0.30 ng m−3 yr−1. We also compared MBC (COSMOS) and scaled MBC (PSAP) values with previously reported data and evaluated the degree of inconsistency in the previous data.

[1] First ever in-situ measurements of black carbon (BC) aerosols in the troposphere (up to 9 km) made over central India and the resulting atmospheric impact as revealed by the environment lapse rate are presented. The altitude distribution of BC showed multiple peaks; two surprisingly large peaks, one at ∼4.5 km, and another above 8 km. Associated with these, rapid decrease in the environmental lapse rate and a sharp increase in the atmosphere stability were observed, probably caused by the atmospheric warming by the BC layers. This important observation calls for extensive high altitude profiling of BC to quantify the resultant warming, increase in stability and consequent increase in BC lifetime. Citation: Babu, S.

Abstract. Ship-borne observations of spectral aerosol optical depth (AOD) have been carried out over the entire Bay of Bengal (BoB) as part of the W-ICARB cruise campaign during the period 27 December 2008-30 January 2009. The results reveal a pronounced temporal and spatial variability in the optical characteristics of aerosols mainly due to anthropogenic emissions and their dispersion controlled by local meteorology. The highest aerosol amount, with mean AOD 500 >0.4, being even above 1.0 on specific days, is found close to the coastal regions in the western and northern parts of BoB. In these regions theÅngström exponent is also found to be high (∼1.2-1.25) indicating transport of strong anthropogenic emissions from continental regions, while very high AOD 500 (0.39±0.07) and α 380−870 values (1.27±0.09) are found over the eastern BoB. Except from the large α 380−870 values, an indication of strong fine-mode dominance is also observed from the AOD curvature, which is negative in the vast majority of the cases, suggesting dominance of an anthropogenic-pollution aerosol type. On the other hand, clean maritime conditions are rather rare over the region, while the aerosol types are further examined through a classification scheme based on the relationship between α and dα. It was found that even for the same α values the fine-mode dominance is larger for higher AODs showing the strong continental influence over the marine environment of Correspondence to: S. Kumar Kharol (shaileshan2000@yahoo.co.in) BoB. Furthermore, there is also an evidence of aerosol-size growth under more turbid conditions indicative of coagulation and/or humidification over specific BoB regions. The results obtained using OPAC model show significant fraction of soot aerosols (∼6 %-8 %) over the eastern and northwestern BoB, while coarse-mode sea salt particles are found to dominate in the southern parts of BoB.

Deposition of black carbon (BC) aerosol in the Arctic lowers snow albedo, thus contributing to warming in the region. However, the processes and impacts associated with BC deposition are poorly understood because of the scarcity and uncertainties of measurements of BC in snow with adequate spatiotemporal resolution. We sampled snowpack at two sites (11 m and 300 m above sea level) at Ny‐Ålesund, Spitsbergen, in April 2013. We also collected falling snow near the surface with a windsock from September 2012 to April 2013. The size distribution of BC in snowpack and falling snow was measured using a single‐particle soot photometer combined with a characterized nebulizer. The BC size distributions did not show significant variations with depth in the snowpack, suggesting stable size distributions in falling snow. The BC number and mass concentrations (CNBC and CMBC) at the two sites agreed to within 19% and 10%, respectively, despite the sites' different snow water equivalent (SWE) loadings. This indicates the small influence of the amount of SWE (or precipitation) on these quantities. Average CNBC and CMBC in snowpack and falling snow at nearly the same locations agreed to within 5% and 16%, after small corrections for artifacts associated with the sampling of the falling snow. This comparison shows that the dry deposition was a small contributor to the total BC deposition. CMBC were highest (2.4 ± 3.0 μg L−1) in December–February and lowest (1.2 ± 1.2 μg L−1) in September–November.

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Atmospheric aerosols over south Asia constitute a major environmental and climate issue. Thus, extensive land and cruise campaigns have been conducted over the area focusing on investigating the aerosol properties and climate implications. Except from the ground-based instrumentation, several studies dealt with analyzing the aerosol properties from space, focusing mainly on the spatial distribution of the aerosol optical depth (AOD) and possible feedbacks of aerosols on the monsoon system. However, except from some works using ground-based instrumentation or satellite observations over a specific region, there is lack of studies dealing with monitoring of the aerosol trend over south Asia. The present work analyzes the variations and trends in aerosol load over south Asia using Terra-MODIS AOD₅₅₀ data in the period 2000–2009. Overall, an increasing trend of 10.17 % in AOD is found over whole south Asia, which exhibits large spatio-temporal variation. More specifically, the AOD₅₅₀ increasing trend is more pronounced in winter, and especially over northern India. The present study shows an evidence of a decreasing AOD₅₅₀ trend over the densely-populated Indo-Gangetic Plains (IGP) during the period April–September, which has never been reported before. This decreasing trend is not statistically significant and leads to an AOD change of −0.01 per year in June, when the dust activity is at its maximum. The AOD decrease seems to be attributed to weakness of dust activity in the northwest of India, closely associated with expansion of the vegetated areas and increase in precipitation over the Thar desert. Similarly, GOCART simulations over south Asia show a pronounced decreasing trend in dust AOD in accordance with MODIS. However, much more analysis and longer dataset are required for establishing this evidence

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