Monsoonal Transboundary Impact on Air Quality over Dhaka and Kolkata Region 

Air pollution has become a prime concern globally due to the escalation of anthropogenic activities and adverse meteorological conditions in recent years. The significant consequences of air pollution, manifesting in adverse ecosystem health effects and economic losses, highlight the urgency of assessing its impact on a regional to global scale. However, there is a lack of systematic investigations, particularly in the context of information deficiency on air pollution in Bangladesh. Therefore, this study aims to investigate the seasonal variations in air quality over Dhaka and Kolkata, with a specific focus on the summer monsoon (May-July). While winter pollution in these cities has been extensively explored in several studies, less attention has been given to understanding the dynamics of monsoon season. This study incorporates Copernicus Atmosphere Monitoring Service (CAMS) reanalysis data to evaluate the influences of both regional and global factors on air quality. Specific emphasis has given on determining the correlation between air pollutants (PM2.5, carbon monoxide, black carbon, sulfur dioxide, ozone, nitrogen dioxide) and meteorological parameters (temperature, humidity, wind components, atmospheric pressure, boundary layer height and precipitation). This understanding is crucial as it forms a strong foundation for developing effective control and prevention strategies of air pollution for this region. In addition, by correlating metrological conditions between Dhaka and Kolkata, the study aims to evaluate the transboundary effects on pollutant dispersion. The potential impact of Sahara fires on air quality of these two cities is investigated using concentration-weighted trajectory analysis (CWT), extending the geographical domain to include the entire South Asian region. The findings not only contribute to the scientific understanding of local air quality but also have broader implications for regional and global atmospheric interactions. The study's insights provide a basis for informed policymaking and facilitate more effective nature based mitigation and control management strategies during the summer monsoon season in these densely populated urban areas.