Statistical interpretation of weekday/weekend differences of ambient gaseous pollutants, vehicular traffic and meteorological parameters in urban region of Kolkata.

An air quality sampling program has been designed and implemented to collect the concentrations of gaseous pollutants (SO2, NO2 and NH3) at weekdays and weekends from a network of three monitoring stations during November 2003 to May 2004 along a populated urban region of Kolkata. Monitoring of ambient SO2 (sulphur dioxide), NO2 (nitrogen dioxide) and NH3 (ammonia) was done once in a week for 24 h at the residential (Kasba) and industrial (Cossipore) sites while 8 h at the commercial (Lalbazar) site. Average ratio of the weekday/ weekend concentrations of SO2, NO2 and NH3 were 1.41, 1.01 and 0.99 at Kasba; 1.33, 1.13 and 1.10 at Cossipore and 1.09, 1.17 and 1.10 at Lalbazar, respectively. Linear regression analysis between SO2 and NO2 showed good (R2 > 0.70) relationship at weekdays in residential and industrial sites. It also showed moderate (R2 > 0.50) relationship in residential site and good (R2 > 0.70) relationship in industrial sites at weekends. In the commercial site, a strong (R2 > 0.90) linear association has been observed between SO2 and NO2 at weekdays and weekends. Daily average vehicular traffic at weekdays was higher than those on weekends. The spearman rank correlation coefficient showed that measured gaseous pollutants have inverse correlation with meteorological parameters (temperature, relative humidity and wind speed) at all the sites, both on weekdays and weekends.