The optical and physical properties of atmospheric aerosols over the Indian Antarctic stations during southern hemispheric summer of the International Polar Year 2007-2008

The properties of background aerosols and their dependence on meteorological, geographical and human influence are examined using measured spectral aerosol optical depth (AOD), total mass concentration (MT) and derived number size distribution (NSD) over two distinct coastal locations of Antarctica; Maitri (70° S, 12° E, 123 m m.s.l.) and Larsemann Hills (LH; 69° S, 77° E, 48 m m.s.l.) during southern hemispheric summer of 2007–2008 as a part of the 27th Indian Scientific Expedition to Antarctica (ISEA) during International Polar Year (IPY). Our investigations showed comparable values for the mean columnar AOD at 500 nm over Maitri (0.034±0.005) and LH (0.032±0.006) indicating good spatial homogeneity in the columnar aerosol properties over the coastal Antarctica. Estimation of Angstrom exponent α showed accumulation mode dominance at Maitri (α~1.2±0.3) and coarse mode dominance at LH (0.7±0.2). On the other hand, mass concentration (MT) of ambient aerosols showed relatively high values (≈8.25±2.87 μg m−3) at Maitri in comparison to LH (6.03±1.33 μg m−3)

Characterizing the hygroscopicity of growing particles in the Canadian Arctic summer

The impact of aerosols on clouds is a well-studied, although still poorly constrained, part of the atmospheric system. New particle formation (NPF) is thought to contribute 40 %-80 % of the global cloud droplet number concentration, although it is extremely difficult to observe an air mass from NPF to cloud formation. NPF and growth occurs frequently in the Canadian Arctic summer atmosphere, although only a few studies have characterized the source and properties of these aerosols. This study presents cloud condensation nuclei (CCN) concentrations measured on board the CCGS Amundsen in the eastern Canadian Arctic Archipelago from 23 July to 23 August 2016 as part of the Network on Climate and Aerosols: Addressing Uncertainties in Remote Canadian Environments (NETCARE). The study was dominated by frequent ultrafine particle and/or growth events, and particles smaller than 100 nm dominated the size distribution for 92 % of the study period. Using kappa-Kohler theory and aerosol size distributions, the mean hygroscopicity parameter (kappa) calculated for the entire study was 0.12 (0.06-0.12, 25th-75th percentile), suggesting that the condensable vapours that led to particle growth were primarily slightly hygroscopic, which we infer to be organic. Based on past measurement and modelling studies from NETCARE and the Canadian Arctic, it seems likely that the source of these slightly hygroscopic, organic, vapours is the ocean. Examining specific growth events suggests that the mode diameter (D-max) had to exceed 40 nm before CCN concentrations at 0.99 % supersaturation (SS) started to increase, although a statistical analysis shows that CCN concentrations increased 13-274 cm(-3) during all ultrafine particle and/or growth times (total particle concentrations > 500 cm(-3 ), D-max < 100 nm) compared with background times (total concentrations < 500 cm(-3)) at SS of 0.26 %-0.99 %. This value increased to 25-425 cm(-3) if the growth times were limited to times when D-max was also larger than 40 nm. These results support past results from NETCARE by showing that the frequently observed ultrafine particle and growth events are dominated by a slightly hygroscopic fraction, which we interpret to be organic vapours originating from the ocean, and that these growing particles can increase the background CCN concentrations at SS as low as 0.26 %, thus pointing to their potential contribution to cloud properties and thus climate through the radiation balance.Peer reviewe

Aerosol total mass concentration and optical depth during IPY 2007-2008 at Maitri and Larsemann Hills Station

The properties of background aerosols and their dependence on meteorological, geographical and human influence are examined using measured spectral aerosol optical depth (AOD), total mass concentration (Mt) and derived number size distribution (NSD) over two distinct coastal locations of Antarctica; Maitri (70°S, 12°E, 123 m m.s.l.) and Larsemann Hills (LH; 69°S, 77°E, 48 m m.s.l.) during southern hemispheric summer of 2007-2008 as a part of the 27th Indian Scientific Expedition to Antarctica (ISEA) during International Polar Year (IPY). Our investigations showed comparable values for the mean columnar AOD at 500 nm over Maitri (0.034±0.005) and LH (0.032±0.006) indicating good spatial homogeneity in the columnar aerosol properties over the coastal Antarctica. Estimation of Angstrom exponent a showed accumulation mode dominance at Maitri (alpha ~1.2±0.3) and coarse mode dominance at LH (0.7±0.2). On the other hand, mass concentration (M(T)) of ambient aerosols showed relatively high values (~8.25±2.87 µg/m**3) at Maitri in comparison to LH (6.03±1.33 µg/m**3)

Spatio-temporal variations in aerosol properties over the oceanic regions between coastal India and Antarctica

Measurements of aerosol optical depth (AOD), mass concentrations of black carbon (MB) and composite aerosols (MT) in the marine atmospheric boundary layer (MABL) were made during onward [Dec 2007 to Jan 2008; Northern Hemispheric (NH) winter] and return (Mar–Apr 2008; NH spring) legs of the trans-continental cruise of 27th Indian Scientific Expedition to Antarctica (ISEA) during International Polar Year of 2007–2008. Large latitudinal gradients are seen; with AOD decreasing from coastal India (AOD~0.45) to coastal Antarctica (AOD~0.04) during NH winter. The measurements also evidenced a strong seasonality of AOD over all regions, with a decrease of the values and gradient in NH spring. BC concentration in the MABL decreases exponentially from 3800 ng m−3 (over 10°N) to 624 ng m−3 near equator and much lower values (&#60; 100 ng m−3) over southern oceanic region. Seasonality in the latitudinal gradients of AOD, MB and MT exists over regions north of 20°S. Multi campaign [Pilot Expedition to Southern Ocean (2004), Special Expedition to Larsemann Hills (2007) and Tropical Indian Ocean cruise (2010)] analysis over these oceanic regions showed that the pattern over the regions (south of 20°S) remained the same. Seasonality of AOD exists over Atlantic Ocean as well. Temporal variation of AOD at different latitudes derived from AERONET data also showed marked seasonality and latitudinal variation in northern hemisphere than in southern Hemisphere. Satellite retrieved AOD showed good correlation with the ship borne measurements; while GOCART retrieved AOD underestimates but gives a measure of the spatial variations

Black carbon aerosols over coastal Antarctica and its scavenging by snow during the Southern hemispheric summer

Mass concentrations of aerosol black carbon (BC) and of the composite (total) aerosols (MB and MT, respectively) were measured over two Antarctic locations, Maitri [70&#176;S, 12&#176;E, 123 m mean sea level (msl)] and Larsemann Hills (LH; 69&#176;S, 77&#176;E, 48 m msl) as a part of the twenty-eighth Indian Scientific Expedition to Antarctica during the Southern Hemispheric summer of 2009. Despite being very low compared to Northern Hemisphere locations, MB and its mass mixing ratio to the total aerosols were much high over Maitri (~75 ng m-3 and 2%) compared to LH (13 ng m-3 and 0.2%). At both locations, MB fell abruptly after blizzards, after which the values reduced to nearly half the pre-blizzard values. This BC scavenging by snow can lead to change in snow albedo and has strong climate implications. The Angstrom exponent (&#945;abs) estimated from the spectral values of absorption coefficients (&#963; abs) is found to vary from 0.5 to 1, indicating higher a BC-to-organic carbon ratio typical of fossil fuel origin

Absorption characteristics of aerosols over the northwestern region of India: distinct seasonal signatures of biomass burning aerosols and mineral dust

Continuous measurements of aerosol black carbon (BC) mass concentrations made over a period of 3 years from a semi-arid, near-coastal, remote and sparsely inhabited location along with satellite-based data of aerosol absorption index, optical depth and extinction profiles in western India are used to characterize the distinct nature of aerosols near the surface and in the free troposphere and their seasonality. Despite being far remote and sparsely inhabited, significant levels of BC are observed in the ambient during winter (1.45 ± 0.71 μg m−3) attributed to biomass burning aerosols, advected to the site from the north and west; while during summer the concentrations are far reduced (0.23 ± 0.11 μg m−3) and represent the apparent background concentrations. The spectral absorption coefficients suggest the BC during summer be mostly of fossil fuel combustions. The strong convective boundary layer dynamics produces significant diurnal variation during winter and modulates to a lesser extent the seasonal variation. Examination of aerosol (absorption) index from OMI data for the study period showed a seasonal pattern that is almost opposite to that seen at the surface; with high aerosol index in summer, showing a significant difference between the surface and columnar aerosol types in summer. MISR and MODIS-derived columnar AOD follow the OMI pattern. Analysis of the vertical profiles of aerosol extinction and volume depolarization ratio (VDR), derived from CALIPSO data indicates the presence of strong dust layers with VDR ∼ 0.3 in the altitude region 4–6 km, contributing to the high aerosol index in the OMI data, while the surface measurements show absorptive properties representing fossil fuel BC aerosols