Methodology: The ground-level ozone formation was analysed using outlier detection via thresholding. Indian regulations define 180 µg/m3 of ozone concentration as the hourly safe-standard, which was used as the threshold to establish instances of unacceptable pollution level. Internationally, 8 hourly mean concentration is used to determine safe standard (WHO standard = 100 µg/m3) but due to missing data entries it was not possible to carry out rolling mean analysis based on the international standard, which could have given results that can be compared with other international studies. 

Periodicity of peaking of ozone concentration was established using the Fourier analysis (See Figure 4). Further, the peaks of each individual variable was visually assessed if  they correlated in their distributed in time. Correlation of ozone concentration with NOx, PM2.5, temperature, solar radiation, wind speed and relative humidity was assessed via linear regression analysis, which was done for the full sample and then repeated for three seasons (summer, winter and monsoon) with a smaller sample size of 30 days each.