Characteristics of elevated aerosol layer over the Indian east coast, Kattankulathur (12.82oN, 80.04°E): A northeast monsoon region.

The elevated aerosol layer (EAL) plays a vital role in weather and climate by modifying the Earth's radiation budget. In the present study, the EAL occurrence and its characteristics in the pre-monsoon season using micropulse lidar (MPL) observations during 2016-2018 and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) during 2007-2018 over Kattankulathur is being reported. We have collected 147 days (101 cases) of MPL (CALIPSO) observations during clear sky conditions in the pre-monsoon 2016-2018 (2007-2018), out of which EAL is observed for 56 days (61 cases). The EAL width is generally found to be ~2.0 km and occurs between ~1.0 km and 5.0 km. Three different types of EALs are categorized based on their altitudinal occurrence using the zero-crossing method. The EALs with their base at ~1.0-1.5 km, ~1.5-2.0 km, and ~ 2.0-3.0 km are taken as types I, II, and III, which occur for 9, 20, and 27 days, respectively. The EAL significantly modifies the total columnar aerosol optical depth (AOD). It is found that AOD, in total, within ABL and EAL, are ~0.72 (0.61), 0.28 (0.25), and 0.45 (0.36) using MPL (CALIPSO), respectively. The aerosols within ABL contribute ~38 % (41 %) while EAL ~ 62 % (59 %) to the total AOD obtained using MPL (CALIPSO). We observed that the ABL and EAL are characterized by different aerosol subtypes, such as dust marine (31 %) and smoke (~ 27 %) aerosols. Other aerosol subtypes, such as dust and polluted dust, commonly occur within the ABL (54 %) and EAL (52 %).

Lead Isotope Evidence for Enhanced Anthropogenic Particle Transport to the Himalayas during Summer Months.

The Indo-Gangetic Plain (IGP) is one of the most highly polluted regions of the world, yet the temporal pattern of transport of anthropogenic aerosols from this region to the Himalayas is poorly constrained. On the basis of the seasonal variation of planetary boundary layer heights, air mass back trajectory analysis, and year-long time-series data for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, and 143Nd/144Nd from aerosols collected over a high-altitude station, we demonstrate that anthropogenic Pb transport to the glacierized catchment has a seasonal pattern. The Pb isotope data reveal that during winter, the thinned boundary layer traps up to 10 ± 7% more coal-derived Pb in the IGP. In contrast, in nonwinter months, a thicker boundary layer and enhanced subtropical westerly winds result in efficient Pb transport to the Himalayas. As Pb isotope ratios are robust conservative chemical tracers and Pb is predominantly derived from anthropogenic sources, these observations suggest that enhanced transport of anthropogenic aerosols to the glacierized catchment of the Himalayas coincides with higher near-surface temperatures in the summer, creating positive feedback that enhances melting. Our results further suggest that >50% of Pb in the Himalayan aerosols originates from the resuspension of historic Pb derived from phased out leaded gasoline, highlighting the importance of legacy Pb stored in the Indo-Gangetic Plains.