Study of meteorological impact on air quality in a humid tropical urban area

Abstract

Urban air quality is highly dynamic and influenced by micrometeorological conditions. In this paper, meteorological impact on criteria air pollutants namely sulphur dioxide (\(\hbox {SO}_{2})\), nitrogen dioxide (\(\hbox {NO}_{2})\) and particulate matter (\(\hbox {PM}_{10})\) were studied using correlation analysis at contrasting locations in the urban environment of Chennai city. Daily average air quality data from five monitoring stations during 2009–2012 were analysed. Out of the five monitoring locations, three locations (Kathivakkam, Thiruvottiyur and Manali) were categorised as industrial locations, General Hospital as a traffic intersection and Taramani as a residential location. The frequency distribution of industrial sites showed higher concentration compared to residential and traffic intersection sites (TS). The increase in annual average concentration of 15–38%, 4–52% and 5–58% was observed for \(\hbox {SO}_{2}\), \(\hbox {NO}_{2}\) and \(\hbox {PM}_{10}\) over the study period, respectively, attributed to vehicular and industrial emissions. \(\hbox {SO}_{2 }\) showed high correlation with humidity (\(R = -0.57\)) and cloud cover (\(R = 0.63\)) during summer. \(\hbox {NO}_{2}\) showed a higher correlation with temperature (\(R = 0.72\)) during monsoon, and with humidity (\(R = 0.7\)) and cloud cover (\(R = 0.75\)) during winter. \(\hbox {PM}_{10 }\) showed moderate correlation with temperature (\(R = -0.55\)) and wind speed (\(R = -0.51\)) during summer. Non-parametric tests and Q–Q plot showed the distribution of \(\hbox {SO}_{2}\) and \(\hbox {NO}_{2}\) as Weibull and lognormal for \(\hbox {PM}_{10}\). The wind rose plots depicted predominant wind direction in the south and south-west directions with most observations having a wind speed of \(\ge 5\hbox { m/s}\). The estimated national ambient air quality index was good for traffic and residential sites. Industrial sites were moderately polluted during the winter season due to high \(\hbox {PM}_{10}\) concentration. No exceedances were observed for daily concentration of \(\hbox {SO}_{2}\) and \(\hbox {NO}_{2}\). Daily average \(\hbox {PM}_{10}\) concentration showed exceedances at industrial locations Kathivakkam, Manali and Thiruvottiyur for 305 (92%), 84 (68%) and 164 (53.4%) days, respectively. At TS (General Hospital) and residential site (RS) (Taramani), lower number of exceedances was observed at 25 (13.2%) days and 11 (5.8%) days, respectively.