GAW Report No. 205 - IGAC Project

CHAPTER 3 - ASIAAir Quality Index resultsUsing the methodology above, AQI was calculated for the period of August 2006 to June2010 utilizing the data for two stations across Delhi; (1) Income Tax Office (ITO) and (2) DelhiCollege of Engineering (DCE), where the PM monitoring data is available. For this analysis, AQI’sare calculated in 6 bins, explained in Table 6. The first three bins, at par with the national ambientair quality standards are considered “safe mode” or “clean air” days and the others “polluted” days[Guttikunda, 2010d].Table 6 - The AQI colour codes and their definitions"HEALTHY" – this range poses little or no risk tothe general public. No cautionary actions areprescribed."UNHEALTHY" - is borderline unhealthy,particularly for members of sensitive groups."VERY UNHEALTHY" - can trigger a health alert,meaning everyone may experience more serioushealth effects."MODERATE" - is acceptable for general public.However, unusually sensitive people should becautious."UNHEALTHY" - is considered unhealthy for mostof the public where everyone may begin toexperience some discomfort."HAZARDOUS" – this range triggers healthwarnings under emergency conditions, affecting allage groups.Of the six criteria pollutants – PM (coarse and fine), SO 2 , NO X , CO, and Ozone - the PMpollution is routinely above the daily average standards (Daily average national ambient air qualitystandards for PM 10 and PM 2.5 are 100 µg/m 3 and 60 µg/m 3 , respectively) and the conditionalpollutant for calculating the AQI for health impacts assessments – presenting the worst AQI. Figure21 presents estimated AQI due to PM 2.5 pollution at ITO and estimated AQI due to PM 10 pollution atDCE.Observations on AQI• At the monitoring sites, AQI is often morethan the healthy levels of 150. The ITO islocated at a traffic junction. On 19% of thedays the AQI is less than 100 and on 33% ofthe days less than 150. The DCE is abackground station in the north and tends tomeasure lower than the city averages and yetstruggled to stay in the green with only 24%of the days with an AQI less than 150.• In Figure 21(a) and 21(b), the winter months,which are highlighted with a blue box for eachyear, show the worst pollution each yearstarting in October and leading up toFebruary the following year.• A large portion of the AQI’s greater than 300(summary presented in Figure 21(c)) areassociated with the winter season.Figure 21 - (a) AQI based on PM2.5 measurements at ITO monitoringstation; (b) AQI based on PM10 measurements at DCE monitoringstation; (c) Frequency of AQI between July 2006 and August 201084