Spatial variability of concentrations of gaseous pollutants across the National Capital Region of Delhi, India

Özet

This study presents a systematic evaluation of a year-long, continuous, real-time measurements ofgaseous pollutants including oxides of nitrogen (NOx ¼ NO þ NO2), carbon monoxide (CO), and ozone(O3) in the National Capital Region (NCR) of Delhi. Data are available from seven air quality monitoringstations (AMS) and meteorological parameters were measured at three meteorological observatories(MO). The daily mean concentrations of NOx and CO across NCR of Delhi (average of all seven AMSs) were37.1 ± 11.6 ppb (NO: 18.3 and NO2: 18.8 ppb), and 2.3 ± 0.6 ppm, respectively. The highest diurnal COconcentrations were observed during midnight (21:00 to 01:00 h LT) due to nocturnal boundary conditions.The daily mean O3 concentration was 37.5 ± 11.0 ppb. The diurnal variations of O3 concentrationswere characterized by the high concentrations during the daytime (07:00 to 17:00 h LT: 43.6 ppb) andlow concentrations during the late evening and early morning hours (18:00 to 06:00 h LT: 31.1 ppb).From 07:00 h onwards, the O3 concentrations start increasing gradually after sunrise coinciding with theincreasing solar radiation. The highest concentrations (51.7 ppb) were observed around 15:00 h.Thereafter, it is decreased. Local sources of gaseous pollutants were identified by analyzing the surfacewind patterns. The annual resultant wind vector were 338 (57%) and 288 (27%) at the Hindon andPalam MOs, respectively. Local NO emissions substantially reduced the urban ozone concentrations asseen by the observed untitrated NO concentrations.