Particulate Matter 2.5 (PM_2.5): Persistence and Trends in the Air Quality of Five India Cities

Poor air quality in India has sparked our interest in studying the time series dynamics of PM2.5 in India's five most populous cities (Mumbai, New Delhi, Hyderabad, Chennai, and Kolkata). Daily data for the period 2014-2023 are examined in the paper. Using fractional integration methods, we analyze the persistence, seasonality, and time trends of the data. The results indicate that all series display fractional degrees of integration, being smaller than 1 and thus presenting mean reversion. Moreover, only for New Dehli and Kolkata the time trends are significantly negative, implying a continuous reduction in the level of pollution. These findings suggest that targeted interventions, such as stricter emission regulations, improved urban planning, and the promotion of clean technologies, are essential to sustain and amplify the observed improvements in air quality. The study also highlights the need for consistent and long-term efforts to address pollution in Mumbai, Hyderabad, and Chennai, where no significant reductions have been observed, emphasizing the importance of adapting policies to regional conditions. The paper's findings can serve as a guide for air pollution management and for policymakers at the Central Pollution Control Board (CPCB) the governmental body responsible for monitoring and regulating environmental pollution in India.