Interannual and Intraseasonal Variability in Fine Mode Particles over Delhi: Influence of Meteorology

Fine mode particles (i.e., PM2.5) were collected at Delhi, India, for three consecutive years from January 2007 to December 2009 and were statistically analyzed. Daily mean mass concentration of PM2.5 was found to be 108.81 +/- 75.5 mu g m(-3) ranged from 12 to 367.9 mu g m(-3), which is substantially higher than the Indian National Ambient Air Quality Standards (NAAQS). Among the measurements, similar to 69% of PM2.5 samples exceeded 24 h Indian NAAQS of PM2.5 level (mu g m(-3)); however, similar to 85% samples exceeded its annual level (40 mu g m(-3)). Approximately 30% of PM2.5 mass was in the range of 40-80 mu g m(-3), indicating abundance of fine particles over Delhi. Intraseasonal variability of PM2.5 indicates highest mass concentration during postmonsoon (154.31 +/- 81.62 mu g m(-3)), followed by winter (150.81 +/- 74.65 mu g m(-3)), summer (70.86 +/- 29.31 mu g m(-3)), and monsoon (45.06 +/- 18.40 mu g m(-3)). In interannual variability, it was seen that in 2008, the fine mode particle was similar to 23% and similar to 36% higher as compared to 2007 and 2009, respectively. Significantly negative correlation was found between PM2.5 and temperature ( 0.59) as well as wind speed ( 0.38). Higher concentration of PM2.5 (173.8 mu g m(-3)) was observed during calm conditions whereas low concentration (79.18 mu g m(-3)) was observed when wind speed was >5 Km/hr. In winter, greater exposure risk is expected, as the pollutant often gets trapped in lower atmosphere due to stable atmospheric conditions.