On The Understanding Of Surface Ozone Variability, Its Precursors And Their Associations With Atmospheric Conditions Over The Delhi Region

The present study investigates the variability of surface ozone (O-3) and its precursors (NOX, CO) at different time scales for 3-year period (2016-2018) using continuous ground-based observations from 25 stations located within the Indian Capital Delhi (28.83. N, 77.81 degrees E). Observations indicate that there is a clear spatial heterogeneity and seasonality in surface O-3 where larger magnitudes (40-60 ppb) are observed during pre-monsoon season, and 10-20 ppb in other seasons. The frequency distribution exhibits that 70% of O-3 concentrations are in the range of 10-50 ppb, while 10% lies larger than 50 ppb and the remaining 20% is mostly confined within 50-80 ppb. Further, a detailed analysis on the diurnal cycle of surface ozone and its precursors performed over IMD Lodhi Road location. Analysis of diurnal cycles show maximum and minimum O-3 concentrations during the morning and nocturnal hours, with a rate of change 4.8 +/- 1.96 and 7.4 +/- 0.95 ppb h(-1), respectively. On the other hand, the rate of change of O-3 during high ozone days (HOD) is found to be 5.61 +/- 2.6 ppb h(-1) in the morning and 8.04 +/- 3.4 ppb h(-1) in the evening hours, respectively. It is also noted that the increase in precursor concentrations and associated titration effects appear to play a considerable role in surface O-3 depletion during the evening hours. It is also noted from the composites of HODs that there is an enhanced diurnal O-3 (80-90 ppb) concentrations compared to 3-year average (40-60 ppb). Further evaluation of associations between surface O-3 changes and meteorological parameters shows that observed surface O-3 (Copernicus Atmosphere Monitoring Service-CAMS modelled O-3) show positive correlations of R-2 = 0.3 (0.42) with temperature, of R-2 = 0.47 (0.60) with Solar Radiation (SR), of R-2 = 0.39 (0.59) with boundary layer height. An overall assessment shows CAMS modelled three year daily averaged ozone values are generally in good agreement with surface ozone observations with a CC value of about R-2 = 0.65.