This graph shows strong seasonal variation in PM2.5. November through February are the months with the highest concentration of PM2.5, March through June are characterized by PM2.5 levels that hover near the daily limit set by the Indian government, and July through October have the lowest levels of the year. Between January 2015 through January 2016, PM2.5 reached its peak reading of 976μg/m3 on November 12th at 1:00AM, during Diwali, a holiday which is celebrated in India by setting off firecrackers. Notably, over these 13 months, the weekly mean PM2.5 was below the daily WHO limit of 25μg/m3 for only three weeks, and was below the less stringent daily Indian government limit of 60μg/m3 for only 17 weeks. The weekly variation in PM2.5 is also high, often varying over several hundreds of μg/m3 over the course of a week.
Means present weekly averages of hourly observations. Similarly, weekly minimums and maximums are displayed using bars, and 25th and 75th percentiles are displayed using horizontal markers. Data are from the US Embassy, Chanakyapuri, New Delhi.
This graph has been published in Plos One, “An experiment with air purifiers in Delhi during winter 2015-2016.”