Aircraft measurements of aerosol black carbon from a coastal location in the north-east part of peninsular India during ICARB

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 $(M_B)$ of aerosol black carbon (BC) were made off Bhubaneswar (BBR, $85.82^oE$, $20.25^oN$), 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 $\sim 2000m$. 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 $\sim 700m$ with an inversion at the top and the other extends from 1200m to $\sim 2000m$ with a second inversion at $\sim 2200m$ 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 $M_B$ 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 $M_B$ over BoB off BBR with those obtained during the earlier occasion over the inland stations of Hyderabad and Kanpur showed similarities above $\sim 500m$, with MB remaining around a steady value of $\sim 1 \mu g m^{−3}$. However, large differences are seen within the ABL. Even though the observed $M_B$ values are not unusually high, their near constancy in the vertical column will have important implications to radiative forcing