Retrieval of SO2 column densities during extreme weather conditions by using CAR MAX-DOAS in the cities of Faisalabad and Lahore.

Abstract

Deteriorating air quality is one of the global environmental issues, which is increasing with increase in the urban population and industrial development. Air is a blend of numerous gas particles, tiny liquid and solid particles, originating from both natural and anthropogenic actions such as industrial activities, vehicular emissions, domestic activities and several others. These become notorious when they breach their threshold limits and inflict harm or distress to ecosystem disturbing the chain linking biotic and abiotic elements. Beside other trace gases Sulfur Dioxide SO2 is one of the main criteria pollutants. Increasing concentrations of SO2 is a major threat and is now widely included in health risk assessment studies. Faisalabad and particularly Lahore is densely populated and one of the important economic zones in Pakistan. In this study widely used remote sensing technique DOAS is used. Car based MAX-DOAS measurements were retrieved using mini MAX-DOAS in both the cities, and stationary monitoring in Lahore, at Lahore University of Management Sciences (LUMS) as well. These two cities were selected to observe SO2 concentrations during extreme weather conditions like winter fog. This paper presents the technical information and characteristics of the instrument, way of retrieval of SO2 concentrations and results of vertical column densities (VCD) of SO2, and most importantly the comparison of different settings and fitting intervals as well. Average diurnal variation of tropospheric SO2 in winter season over the research area yielded minimum values in late morning i.e. 8am-9am and noon i.e. 12pm-1pm with the concentration of 2.8E16 molecules/cm2 and 2.9E16 molecules/cm2 respectively. Whereas tropospheric SO2 reached the maximum value in the early evening i.e. 5pm-6pm with the concentration of 6.6E16 molecules/cm2. Slight and gradual reduction in the SO2 concentration occurred on the weekends because of reduction in the pollutants and emissions particularly from vehicles over the weekends. Tropospheric VCDs were compared for both field campaigns and stationary monitoring to with those from Ozone Monitoring Instrument (OMI) satellite observations, resulting in R2 of 0.499 with the Pearson value of .70 for Filed campaigns and for the stationary monitoring at Lahore University of Management Sciences (LUMS) R2 of 0.68 and Pearson value of 0.82.