Abstract:
The present study depicts a comparison of ozone (O3) concentrations over a decade time (1993-94 to 2006) using plant biomonitoring and continuous ozone monitors techniques in Lahore city of Pakistan. The variations in O3 levels were assessed at city centre, suburbs and semi-rural/rural locations in and around the city of Lahore by using American O3- sensitive tobacco biomonitor plant (Nicotiana tabaccum L. cv. Bel-W3) for the first time in Pakistan during 1993 and 1994 seasons through weekly assessment of visible damage to leaves. Results for both 1993 and 1994 seasons indicated significant differences between sites in the mean 6-h O3 concentrations with a range of over 20 ppb and 15 ppb across the sites in 1993 and 1994, respectively. An inverse relationship between the levels of NO2 and O3 was found during investigation. The highest O3 levels of 75-80 ppb were found at rural areas and the lowest at city centre sites. The extent of O3 injury on the tobacco cv. Bel-W3 leaves reflected the trends seen in O3 concentrations. The highest and lowest leaf injury
indices of 18-27% and 5-7% occurred at the rural and city centre sites, respectively. Results for 2006 season indicated the highest seasonal mean O3 concentration of 100 ppb in semi-rural areas compared with city centre sites (68 ppb). The highest 26% and 20% increase in O3 levels was observed at rural/semi-rural and city centre sites, respectively when compared with 1993 O3 survey. Application of O3 biomonitoring technique proved very cost-effective and feasible for the estimation of atmospheric O3 levels in South East Asian regions like Pakistan where shortage of electric supply, trained man power and poverty is already playing havoc.
