Aerosol black carbon characteristics over Central India: Temporal variation and its dependence on mixed layer height

In a first of its kind study over the Indian region, concurrent and extensive measurements of black carbon (BC) concentration and atmospheric boundary layer parameters are used to quantify the role of atmospheric boundary layer in producing temporal changes in BC. During this study, 18months (2011–12) data of continuous measurements of BC aerosols, made over a semi-urban location, Nagpur, in Central India are used along with concurrent measurements of vertical profiles of atmospheric thermodynamics, made using weekly ascents of GPS aided Radiosonde for a period of 1year. From the balloon data, mixed layer heights and ventilation coefficients are estimated, and the monthly and seasonal changes in BC mass concentration are examined in the light of the boundary layer changes. Seasonally, the BC mass concentration was highest (~4573±1293ngm−3) in winter (December–February), and lowest (~1588±897ngm−3) in monsoon (June–September), while remained moderate (~3137±1446ngm−3) in pre-monsoon (March–May), and post-monsoon (~3634±813ngm−3) (October–November) seasons. During the dry seasons, when the rainfall is scanty or insignificantly small, the seasonal variations in BC concentrations have a strong inverse relationship with mixed layer height and ventilation coefficient. However, the lowest BC concentrations do not occur during the season when the mixed layer height (MLH) is highest or the ventilation coefficient is the highest; rather it occurs when the rainfall is strong (during summer monsoon season) and airmass changes to primarily of marine origin. •Black carbon (BC) characteristics from Central India for the first time•Association between BC and mixed layer height from year-around measurements•Wet removal as the main sink of atmospheric BC at near surface level