Aerosol size distribution and mass concentration measurements in various cities of Pakistan

Abstract

During March and April 2010 aerosol inventories from four large cities in Pakistan were assessed in terms of particle size distributions (N), mass (M) concentrations, and particulate matter (PM) concentrations. These M and PM concentrations were obtained for Karachi, Lahore, Rawalpindi, and Peshawar from N concentrations using a native algorithm based on the Grimm model 1.109 dust monitor. The results have confirmed high N, M and PM concentrations in all four cities. They also revealed major contributions to the aerosol concentrations from the re-suspension of road dust, from sea salt aerosols, and from vehicular and industrial emissions. During the study period the 24 hour average PM10 concentrations for three sites in Karachi were found to be 461 mg/m^3, 270 mg/m^3, and 88 mg/m^3, while the average values for Lahore, Rawalpindi and Peshawar were 198 mg/m^3, 448 mg/m^3, and 540 mg/m^3, respectively. The corresponding 24 hour average PM2.5 concentrations were 185 mg/m^3, 151 mg/m^3, and 60 mg/m^3 for the three sites in Karachi, and 91 mg/m^3, 140 mg/m^3, and 160 mg/m^3 for Lahore, Rawalpindi and Peshawar, respectively. The low PM2.5/PM10 ratios revealed a high proportion of coarser particles, which are likely to have originated from (a) traffic, (b) other combustion sources, and (c) the re-suspension of road dust. Our calculated 24 hour averaged PM10 and PM2.5 concentrations at all sampling points were between 2 and 10 times higher than the maximum PM concentrations recommended by the WHO guidelines. The aerosol samples collected were analyzed for crustal elements (Al, Fe, Si, Mg, Ca) and trace elements (B, Ba, Cr, Cu, K, Na, Mn, Ni, P, Pb, S, Sr, Cd, Ti, Zn and Zr). The averaged concentrations for crustal elements ranged from 1.02 +/- 0.76 mg m^3 for Si at the Sea View location in Karachi to 74.96 +/- 7.39 mg/m^3 for Ca in Rawalpindi, and averaged concentrations for trace elements varied from 7.0 +/- 0.75 ng /m^3 for B from the SUPARCO location in Karachi to 17.84 +/- 0.30 mg/m^3 for Na at the M. A. Jinnah Road location, also in Karachi.