Spatio-temporal variability of near-surface air pollutants at four distinct geographical locations in Andhra Pradesh State of India

Abstract

India is highly vulnerable to air pollution in the recent decade, especially urban areas with rapidly growing urbanisation and industrialisation. Here, we present spatio-temporal variability of air pollutants at four distinct locations in Andhra Pradesh State of India. The mean concentrations of air pollutants were generally higher at Visakhapatnam site than Amaravati, Rajahmundry, and Tirumala sites. The mean concentration of particulate matter of diameter less than 2.5 μm (PM2.5) was higher at Visakhapatnam site (48.5 ± 27.3 μg/m3) by a factor of about 1.6 as compared to Tirumala site (29.5 ± 17 μg/m3). On the contrary, the mean concentrations of oxides of nitrogen (NOx, 70.3 ± 28.1 μg/m3) and ammonia (NH3, 20.5 ± 9.2 μg/m3) were higher at Tirumala by a factor of about 1.4 and 1.9, respectively, as compared to Visakhapatnam (49 ± 5 μg/m3 and 10.7 ± 5 μg/m3). This was mainly attributed to higher vehicular emissions at Tirumala site. PM2.5, carbon monoxide (CO), NOx, and sulfur dioxide (SO2) showed distinct seasonal variation, with higher concentrations in winter followed by post-monsoon, pre-monsoon and monsoon. The Concentration Weighted Trajectory analysis of PM2.5 based on 5-days backward air mass trajectories showed that all sites experienced northeast air mass flow indicative of the outflow from Indo-Gangetic Plain, particularly in the post-monsoon and winter seasons. The Continuous Wavelet Transform analysis further showed that higher variations in PM2.5 concentrations occurring at a regular interval from a week to 16 days at both Tirumala and Visakhapatnam sites, while weekly periods are dominant over Amaravati and Rajahmundry sites with 95% significance during post-monsoon and winter seasons. Overall, our results underline heterogeneity in air pollution emission sources and influx of pollutants from distant sources, which would be useful when formulating the policies and mitigation procedures for this region.