Gaseous and Aerosols Pollutants in Urban Air – Pakistan
Abstract
The levels of air pollution in these cities were estimated to be 20 times higher than the standards set by World Health Organization (24 hr-average ambient concentration: TSP particulate, 150-230 µg/m3; SO2, 90 µg/m3) [WHO report, 1992]. With its many low-tech-industries and poorly controlled combustion, huge quantities of pollutants are exhausted into air. Emissions from vehicles, vegetation burnings and industrial processes (steel production, thermal power generation, coal burning, glass, ceramic, and brick manufacture) are considered to be major sources of pollutants like PM2.5, SO2, and NOx as well as K+, NH4+ and (COOH)2. An annular denuder system was used to measure acidic gases, ammonia (NH3), and PM2.5 aerosols (particles of <2.5 m aerodynamic diameter) from December 2005 to February 2006 in Lahore, Pakistan. The denuders yielded average concentrations (g m-3) as follows: nitrous acid, 19.6; sulfur dioxide, 19.4; hydrochloric acid, 1.16; nitric acid, 1.00; oxalic acid, 0.6; and ammonia, 50. The filters yielded average concentrations (g m-3): PM2.5, 209; sulfate, 19.2; nitrate, 18.9; chloride, 7.43; fluoride, 0.1; oxalate, 0.97; ammonium, 16.1; potassium, 3.49; calcium, 0.89; sodium, 0.76; and magnesium, 0.08.
The results from measurement of EC and BC from two major cities Lahore (31.6oN, and 74.3oE) and Karachi (24.5oN, and 67.0oE) are being reported here. In Lahore, BC concentrations were very high, ranging from about 5 to 110 g m-3 . The daily mean BC concentration in Lahore was 21.7 g m-3, however; there was a strong diurnal pattern and concentrations greater than 60 g m-3 were common during November 2005 to January 2006. Total carbonaceous aerosols averaged 96g m-3 of carbon and these contributed around 69% of the PM2.5 mass in Lahore. Further a yearlong monitoring of BC at 5-minute intervals (2006-07) at Karachi reveals that BC concentrations varied from about 1 to 15 µgm-3; however, short term spikes > 40 µg m-3 were common but primarily during the morning and evening rush-hours. BC concentration was highest during November through February and lowest during June through September.
Key words: PM2.5; Pakistan; Acidic gases; denuder; carbonaceous aerosols; black carbon; elemental carbon; urban air
