Severe air pollution events were observed frequently in north India in recent years especially at its capital, Delhi. Criteria air pollutants data at 10 sites for 2017 in Delhi were analyzed. The results show annual fine particulate matter (PM2.5) concentrations exceeded the National Ambient Air Quality Standards (NAAQS) of 60mug/m(3) at all sites from 105.51 (site 10) to 143.23mug/m(3) (site 7). Sub-urban sites (site 8, 9, and 10) had lower PM2.5 concentrations than urban sites. Coarse PM (PM10) and ozone (O3) were also important with annual averages of 399.56mug/m(3) and 75.69ppb, respectively. Peak PM2.5 occurred at the Diwali in early November and Christmas. Only PM10 showed a significant weekly difference with a weekdays/weekends ratio of approximately 1.5. PM2.5/PM10 ratio in episode days with PM2.5 of >60mug/m(3) was higher than non-episode days. Pearson correlation coefficients show O3 was negatively related with CO, SO2, and NO2, while PM2.5 was positively related to these pollutants. Analysis of two extreme events from Nov. 6th to Nov. 14th and Dec. 18th to Dec. 26th shows that meteorological conditions with low wind speed and warm temperature kept PM2.5 concentrations at a high level during these events. Backward trajectory and cluster analysis show the wind coming from northwest of Delhi, where massive anthropogenic emissions were generated, led to high concentrations of air pollutants to Delhi. Health risk analysis reveals that PM2.5 and PM10 were the two major pollutants threatening public health among the six criteria pollutants.