Long-term regional air pollution characteristics in and around Hyderabad, India: Effects of natural and anthropogenic sources

Abstract

India is experiencing a rapid urban growth in recent decades modifying the regional air quality around urban agglomerations. Hyderabad, the capital city of Telangana state in India, has been experiencing significant urbanization of about 17 % growth in urban agglomeration over the past two decades. We investigated the long-term pollution characteristics along with the meteorology in and around Hyderabad (300 km × 300 km) using satellite-based remote sensing, and reanalysis data. Columnar aerosol loading was highest during the Spring while the positive trend was more during the Winter. The northeastern and southeastern parts of the study domain experienced higher aerosol loading. A significant increasing linear trend in AOD and PM_2.5 is observed over the urban region as well as the northern and eastern parts. The NO₂ and SO₂ columnar concentrations showed considerable enhancement over the northeast sub-region where numerous thermal power plants are located, and over the urban centre. The SO₂ concentration and SSA values were higher during the Autumn, while the NO₂ values peaked along with lower SSA values during the Spring. The observed spatio-temporal features in air pollutants are further investigated using rainfall information, transport pathways, vegetation index, and fire events. Higher surface temperature and the polluted northeasterlies caused the comparative enhancement of NO₂ concentration during Spring. The investigation on the NDVI and the fire events in different sub-regions points to the possibility of enhanced human settlement, and thereby the associated anthropogenic activities are notable over the West and South parts of Hyderabad. However, the presence of thermal power plants in the northeast and natural gas plants along the coast act as persistent regional sources for aerosols and pollutant gases irrespective of the wet removal.