Gradients in PM2.5 over India: Five city study

Keeping in view the growing interest in the air pollution attributed morbidity and mortality, this study investigates the levels of ambient fine particulate matter over the rapidly developing and agglomerating Indian cities. Despite several measures and pollution mitigation strategies being implemented over Delhi, it recorded the highest PM2.5 among all the study cities, across all the seasons, in all the times of the day. The annual mean (±standard deviation) PM2.5 is found to be ~37 ± 17, 51 ± 23, 54 ± 36, 80 ± 67, 114 ± 86 over the cities of Chennai, Hyderabad, Mumbai, Kolkata and Delhi respectively. Winter season is the most hazardous among others, with almost all of its days exceeding the WHO threshold for daily mean PM2.5. On annual and seasonal basis, the daily mean PM2.5 values exhibited a northward increasing trend. A gradual change in the shape of the PM2.5 diurnal variations is noticed with change in space and time. The demographic factors influencing the concentrations and the modulations by weather and other natural phenomena were thoroughly discussed. The statistics and analysis presented in the manuscript are highly useful for the policy makers to strategize their region-specific mitigation efforts.