Size distribution and seasonal variation of size-segregated particulate matter in the ambient air of Raipur city, India

In this study, size-segregated particulate matter samples were collected in Raipur, India from July 2009 to June 2010 by using eight-stage cascade impactor sampler. The annual average concentrations and associated standard deviation of PM10, PM2.5–10, PM2.5, and PM1 were 270.5 ± 105.5, 119.6 ± 44.6, 150.9 ± 78.6, and 72.5 ± 39.0 μg/m3, respectively. The PM10 and PM2.5 levels at Raipur, India were well above the annual National Ambient Air Quality Standards of India of 60 and 40 μg/m3 for PM10 and PM2.5, respectively. Particulate matter concentrations in winter were higher than those in summer and monsoon. Increased energy use and dry atmospheric conditions contributed to increasing particulate matter concentrations in winter, while increased rainfall precipitation contributed to decreasing particulate matter levels in the monsoon. Spearman correlation analysis between PM10 and PM2.5 revealed high correlation coefficients (r = 0.85), implying that PM10 and PM2.5 may have the same source of regions or that they are influenced by the same local conditions. The highest monthly values of air quality index occur in winter and spring, while they are reduced in summer and monsoon. The analysis showed that 25.0% of the days was unhealthy for sensitive people, 47.4% was unhealthy or very unhealthy, while 4.1% was considered as hazardous. A comparison of the exceedance factors indicated that PM10 and PM2.5 was the most significant polluting agent, causing maximum deterioration in the ambient air quality of Raipur, India.