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.

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.

Robust knowledge on the occurrence and distribution of persistent organic pollutants (POPs) in the atmosphere of low-latitude regions is inevitable to forecast their transportation to pristine ecosystem and assess toxicological impacts upon local biota. Despite the earlier revelation of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in soils/sediments and water bodies in Pakistan, knowledge about atmospheric levels and sources of these POPs remains limited. For the first time, a network of XAD resin-based passive air samplers (PAS) was established across megacities of Pakistan, i.e., Karachi, the coastal city, and Lahore, lying in an agricultural region. Typical geographical locations of the two cities allowed assessing the influence of source regions on the occurrence and distribution patterns of selected POPs. Average concentrations (ng/PAS) in both cities ranged as endosulfan 39-101, DDTs 63-92, HCHs 33-65, heptachlor 10-26, and PCBs 48-61. High concentrations of endosulfan and lindane as observed throughout Lahore were certainly due to their ongoing applications in surrounding agricultural fields. Lower proportions of parental DDTs as compared to their metabolites were observed in both cities, suggesting inputs of DDTs from older or secondary sources. Owing to ultimate discharge of country's agricultural/industrial waste through river streams in to Arabian Sea, the coastal region of Karachi was found potential source of weathered POPs that could be dissipated at regional/global scales by maritime advections. The study contributes to the pool of information on fate and geographical distribution of POPs in subtropical developing countries.

Air pollution has become a serious challenge for developing countries like Pakistan. Very scarce information is available regarding pollution levels in this geographic region. This study presents the first modelling work to simulate the spatial distribution and temporal variation of aerosol concentrations over Pakistan by using the Weather Research and Forecasting Model coupled with chemistry (WRF-Chem). Simulated aerosols species include sulfate, nitrate, ammonium, organic carbon, black carbon, and PM 2.5 (particles with a diameter of 2.5 μm or less), which are evaluated against groundbased observations and satellite measurements. In year 2006, simulated PM 2.5 concentrations averaged over northeastern Pakistan (71-74.5°E, 28-34°N) are 55, 48.5, 31.5, and 98 µg/m 3 in January, April, July, and October, respectively. The simulated highest PM 2.5 concentration in October results from the relatively low temperatures that favor nitrate formation as well as the lowest precipitation that leads to the smallest wet deposition of all aerosol species. The simulated lowest concentration of PM 2.5 in July can be attributed to the largest precipitation associated with the South Asian summer monsoon. Sensitivity studies show that transboundary transport contributes to PM 2.5 aerosol levels in northeastern Pakistan by 10-20% in January and April and by 10-40% in July and October of year 2006. Wind over India and Pakistan is found to be the major meteorological parameter that determines the transboundary aerosol transport.

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