Investigation into relationships among NO, NO2, NOx, O-3, and CO at an urban background site in Delhi, India
Tiwari, S; Dahiya, A; Kumar, N
High resolution concentrations of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), and Ozone (O-3) were measured at a urban site (urban background) in New Delhi, India for a period of two years from September 2010 to August 2012. During the study period, the mean concentrations of NO, NO2, NOx, O-3 (PPb), and CO (ppm) were observed to be 172, 12.5, 29.3, 23.6, and 1.97, respectively. This data was then employed to investigate the relationships between NO, NO2, and O-3 as a function of NOx. The highest mean concentrations of NO were observed from midnight 00:00 to 05:00 h local time (LT) in the morning as a result of an increase in traffic emissions and a reduction in boundary layer height during the night. The total levels of oxidant [OX], which are considered to be the sum of O-3 and NO2, were determined. A study of variation of [OX] and NOx identified two distinct contributions to ambient OX concentrations, i.e., NOx independent and NOx dependent. The NOx-dependent contribution corresponds to the local production of ozone, and the NOx-independent contribution corresponds to. regional concentrations, which at this site is the background level of ozone. The monthly and diurnal variations of [OX] are discussed. Wind directions were used to identify possible regional sources of [OX]. The analysis suggests that [OX] concentrations were about six times higher with winds originating from the Northwest direction (NW) compared to those from the East. (C) 2015 Elsevier B.V. All rights reserved.