Temporal variation of CO<inf>2</inf> concentrations at a local air quality control region

The present study summarizes the diurnal variations of CO2 concentrations at a local air quality control region in Chennai. The CO 2 concentrations were found to increase with vehicular traffic and the results were comparable with the previous studies 2'4. It was found that average CO2 concentration at the monitoring site was between 391ppm and 666 ppm. The time series data revealed two CO2 peeks corresponding to morning (between 7:00-9:00 AM) and evening peak (at around 8:00 PM) hour traffic flow. The diurnal trends of NO2, NO, and O3 were similar with the results from the literature 3'5'6. The regression analysis between CO 2 and NO2 showed a good correlation (R2=0.78) and showed a moderate correlation between CO2 and NO (R 2=0.31). A similar study, made in Cincinnati, Ohio7, reported correlation coefficients of 0.41 and 0.5 between CO2 and NO2 and between CO2 and NO. The present study R 2 for NO was closely matching with previous studies. However the correlation coefficient values between NO2 and CO2 values at the two sites showed a significant difference which may be due to the complexity of NO2 in formation and the local sources contribution.