Identification of Upwind Source Regions Responsible for Pollution Episodes Over New Delhi During Premonsoon and Postmonsoon Seasons

Increasing air pollution poses rising concern, carrying the potential to significantly heighten the risk of disease and pose a severe threat to human well-being. This study aims to identify the potential source regions responsible for high levels of carbon monoxide (CO) and nitrogen oxides (NOx) over Delhi, India, using PSCF and CWT analyses based on backward trajectory modeling. The backward trajectories of air parcels arriving at Delhi at 500 m above ground level (AGL) were calculated using the Hybrid Single–Particle Lagrangian Integrated Trajectory (HYSPLIT) model for the premonsoon (MAM) and postmonsoon (SON) seasons in 2018. The trajectories were analyzed and correlated with in situ observations of CO and NOx to generate PSCF and CWT maps. The results of the PSCF and CWT analyses indicate that both local and regional sources play crucial roles in contributing to the concentrations of CO and NOx over Delhi, with variations observed between the pre-and postmonsoon seasons. These findings underscore the importance of considering both local and regional sources in understanding and addressing air pollution in Delhi. Overall, this research highlights the utility of PSCF and CWT analyses in identifying potential source regions and understanding the transport pathways of pollutants in Delhi. The outcomes emphasize the need for effective pollution control measures not only within Delhi but also in the surrounding regions to mitigate the impact of CO and NOx emissions on air quality in the area.