Dispersion of pollutants in convective low wind: a case study of Delhi

The transport and dispersion of pollutants becomes weak under low wind conditions resulting in large ground level concentrations (g.l.c.ʹs). Largest mean g.l.c.ʹs due to elevated sources are typically found under daytime convective conditions with moderate to weak winds in the earlier studies. Similar cases have been studied here by using three different dispersion models, i.e. Gaussian plume model (GPM) and two low wind models (LWM1 and LWM2) at few vulnerable places in Delhi. The models compute the hourly g.l.c.ʹs of SO2 due to industrial and power plant sources. The performance of these models has been compared against observed data to identify one of the model, appropriate for dispersion of pollutants in low wind convective conditions, which are frequently occurring meteorological conditions in Delhi and also in urban cities of India. This evaluation has been performed at four receptors by using three different methods: (i) comparison of hourly concentrations of the models against observed data, (ii) Q–Q-plots (Quantile–Quantile) and (iii) statistical measures. On the basis of the results and discussion of above methods, it has been concluded that GPM is always overpredicting and LWM2 is consistently underpredicting the concentrations, whereas, LWM1 is performing better than GPM and LWM2. Thus LWM1 may be recommended for studying dispersion of pollutants from elevated point sources in low wind convective conditions.