Investigation into relationships among NO, NO2, NOX, O3, and CO at an urban background site in Delhi, India

High resolution concentrations of nitric oxide (NO), nitrogen dioxide (NO₂), oxides of nitrogen (NO_x), and Ozone (O₃) 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, NO_x, O₃ (ppb), and CO (ppm) were observed to be 17.2, 12.5, 29.3, 23.6, and 1.97, respectively. This data was then employed to investigate the relationships between NO, NO₂, and O₃ as a function of NO_x. 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 O3 and NO2, were determined. A study of variation of [OX] and NOx identified two distinct contributions to ambient OX concentrations, i.e., NO_x independent and NO_x dependent. The NO_x-dependent contribution corresponds to the local production of ozone, and the NO_x-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.

Tiwari, S., A. Dahiya, & N. Kumar (2015) Investigation intorelationships among NO, NO₂, NO_X, O₃, and CO at an urban background sitein Delhi, India, ATMOSPHERIC RESEARCH (In Press).