Synoptic scales of atmospheric aerosols in urban atmosphere of India: Implications for regional climate change

The physical (size) and chemical (composition) properties of aerosol particles over urban regions exhibit wide variability as they are emitted from a variety of sources. Aerosol size distribution is one of the crucial physical properties that govern the aerosol interaction with atmospheric radiation, cloud formation, transport and deposition, and health effects at regional and global level. With this, the different aspects of atmospheric aerosol particles has been carried out in term of carbonaceous aerosols (OC, EC, SOC and POC), morphology (size, shape, mixing states etc), and aerosol size distribution (number concentration) over urban region of India. Surface observation studies indicated that particulate mass (150-200 µg m^-3) levels are higher than Indian and WHO standards limit values. The aerosol size distributions exhibit two peaks, one between 0.39 and 0.42 μm, and another between 1.41 and 1.71 μm respectively. The measured aerosol number concentrations were higher, and the distribution patterns were different when compared to continental, urban, maritime and desert aerosol models. Contribution of N_fine (0.262-0.958 μm) and N_Coarse (1.070-9.575 μm) mode into total annual number concentration was ~ 66.5 % and ~33.5 %. Carbonaceous aerosol studies have revealed that being a high loading of OC (50-70 µg m^-3) and EC (10-15 µg m^-3) associated with fine particles in cities of India. The role of individual chemical species of aerosols in light extinction was estimated, the contributions of light scattering coefficient by particles (b_sp) were OC (45%), (NH₄)₂SO₄ (17%), NH₄NO₃ (8%) and coarse mass (12%) while, the contribution of light absorption coefficient by particle (b_ap) was 18% (EC). Morphological features of atmospheric particles indicated the synoptic changes in urban environment. The air mass backward trajectory clusters analysis was performed which supports the transport of aerosol mass from the long range transportation as well as dominance of local sources over varied Indian regions. Overall this attempt has been made to study the impact of atmospheric aerosols on regional climate as physical and chemical characteristics of atmospheric aerosol is one of the most uncertain aspect of aerosol science in estimating climatic and health impact of aerosols.