Vertically resolved black carbon measurements and associated heating rates obtained using in situ balloon platform

摘要

Vertically resolved Black Carbon (BC) measurements are obtained in situ up to 10 km during the summer monsoon season using a micro-aethalometer on-board balloon platform from Hyderabad (17.48 degrees N, 78.40 degrees E, 557 m msl), India. Simultaneous (on-board) aerosol size-segregated mass concentration measurements are made at particle sizes 0.5, 1.0, 2.5, 5.0 and 10.0 mu m using a Particle plus Optical Particle Counter for estimating the fractions of BC in size segregated (SS) PM2.5 and the fraction of SSPM2.5 in SSPM10. A prominent aerosol layer with large BC mass concentrations in the range of 10-25 mu g/m(3) is found below 4 km (above mean sea level) which matches well with the measured SSPM2.5 concentrations showing consistency in the two independent measurements. Thin layers of BC are also detected at mid-tropospheric region at altitude similar to 7 km and another between 8 and 10 km. FLEXPART analysis for back trajectories suggests that these high concentrations of BC are transported from over the west Asian region of Somalia, Gulf of Aden and Oman. Meteorological parameters along with ozone concentrations obtained simultaneously using radiosonde and ozonesonde together with BC concentrations are used to estimate the actual BC heating rates for the first time. Shortwave BC heating rates as high as 4 K/day are observed in the lower thick layer. It is suggested that this strong heating rate can act as a feedback in weakening the stable layer and well mixing of pollutants up to 4-5 km altitude. Heating rates obtained using standard tropical atmosphere model is found to be overestimated in this case suggesting the use of real time atmospheric conditions for actual estimates.