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During 2003-2004, SUPARCO, the Pakistan Space and Upper Atmosphere Research Commission has conducted a year long baseline air quality study in country's major urban areas (Karachi, Lahore, Quetta, Rawalpindi, Islamabad and Peshawar). The objective of this study was to establish baseline levels and behavior of airborne pollutants in urban centers with temporal and spatial parameters. This study reveals that the highest concentrations of CO were observed at Quetta (14 ppm) while other pollutants like SO(2) (52.5 ppb), NO(x) (60.75 ppb) and O(3)(50 ppb) were higher at Lahore compared to other urban centers like Karachi, Peshawar etc. The maximum particulate (TSP) and PM10 levels were observed at Lahore (996 ug/m(3) and 368 ug/m(3) respectively), Quetta (778 ug/m(3), 298 ug/m(3)) and in Karachi (410 ug/m(3), 302 ug/m(3)). In all major cities the highest levels were recorded at major intersections and variations were directly correlated with traffic density. These pollutants showed highest levels in summer and spring while lowest were observed in winter and monsoon. A data bank has been generated for future planning and air pollution impact studies.

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Neste trabalho foram estudadas as concentrações das PM 2.5 (partículas com diâmetro aerodinâmico de 2,5 µm ou menos) e das fontes de incremento das PM 2.5 , monitoradas numa área urbana residencial de Lahore, Pasquitão. Amostras de PM 2.5 em aerosol foram coletadas 2 dias por semana, num inetravlo de 12 h por dia, nas estações seca e húmida, usando um filtro de papel Zefluor TM contendo um amostrador de ar ambiente termo-elétrico (Thermo-Electron Corporation Reference Ambient Air Sampler, RAAS ) durante o inverno, os quais aumentam a concentração total de PM 2.5 quando, relativamente, menos dispersão aérea existe. As partículas de sulfato também aumentam a formação de neblina/nevoeiro em condições calmaria e humidade, reduzindo a visbilidade e aumentando a incidência de doenças respiratórias na cidade ao longo do ano.The work reported in this paper was carried out to study the trends of PM 2.5 (particles with an aerodynamic diameter of 2.5 µm or less) concentrations and source apportionment of PM 2.5 monitored at an urban residential site in Lahore, Pakistan. PM 2.5 aerosol samples were collected for 2 days in a week at 12 h interval in a day, both in dry and wet seasons, on Zefluor TM filter papers using Thermo-Electron Corporation Reference Ambient Air Sampler (RAAS). Total 310 samples were collected during the period under study, i.e., from November 2005 to December 2007. High PM 2.5 loads were observed in winter, which were approximately 4 times greater than those observed in the summer, spring, fall and monsoon seasons in the yearlong measurements. Source apportionment was performed on short duration analysis results of November 2005 to March 2006 using Positive Matrix Factorization (PMF) model. The results derived from PMF model indicated that the major contributors to PM 2.5 in Lahore are: soil/road dust, industrial emissions, vehicular emissions and secondary aerosols. It is, therefore, concluded that in addition to local vehicular and industrial emissions, the city is also affected from trans-boundary air pollutants particularly due to secondary aerosols (especially SO 4 2-) during winter which increase PM 2.5 concentrations manifold when relatively less mixing height exists. The sulfate particles also facilitate in haze/fog formation during calm highly humid conditions, thus reduce visibility and increase the incidents of respiratory diseases encountered in the city every year.