Measurement report: Intra-annual Variability of Black/Brown Carbon and Its Interrelation with Meteorological Conditions over Gangtok, Sikkim

Abstract

Abstract. Black carbon (BC) and brown carbon (BrC) have versatile nature, and they have apparent role in the climate variability and changes. As the anthropogenic activity is surging, the BC and BrC are also reportedly increasing. So, the monitoring of BC/BrC and observation of land use land cover changes (LULCC) at regional level are necessary for the various interconnected meteorological phenomenal changes. The current study investigates BC, BrC, CO2, BC from fossil fuels (BCff), BC from biomass burning (BCbb), LULCC, and their relationship to the corresponding meteorological conditions over Gangtok in Sikkim Himalayan region. The concentration of BC (BrC) 43.5 μg/m3 (32.0 μg/m3) is found to be highest during the March-2022 (April-2021). Surface pressure has been found to have a significant positive correlation with BC, BCff, BCbb and BrC. The boundary layer is calmer and more stable when the surface pressure is higher, which keeps contaminants deposited there. The wind, on the other hand, appears to represent the dispersion of pollutants with a strong negative correlation. The fact that all pollutants and precipitation have been shown to behave similarly points to moist scavenging of the pollutants. Despite the dense cloud cover, the area is not receiving convective precipitation, implying that orographic precipitation is occurring over the region. Most of Sikkim receives convective rain from May to September, indicating that the region has significant convective activity contributed from the Bay of Bengal during monsoon season. Furthermore, monsoon months have the lowest concentrations of BC, BCbb, BCff, and BrC, suggesting the potential of convective rain (as rain out scavenging) to remove most of the pollutants. Moreover, BC and BrC show positive radiative feedback.