SOURCE APPORTIONMENT OF PM2.5 IN LAHORE USING POSITIVE MATRIX FACTORIZATION (PMF)

Abstract

The deteriorating air quality of Lahore is a pressing complication, especially in winter when visibility and public health are compromised. In this study, fine particle (PM2.5) samples were accumulated for two different seasons: summertime (1st to 28th June) and wintertime (1st to 29th December) in Lahore, Pakistan, in 2022. A total of 21 PM2.5 constituents were identified in this work, encompassing Organic carbon (OC), Elemental carbon (EC), water-soluble inorganic ions (Cl-, NO3-, SO42, Na+, NH4+, Ca2+, K+, Mg2+), and trace metals (Fe, Pb, Ti, Ni, V, Cr, As, Ba, Zn, Al, Mn). Positive matrix factorization (PMF) and backward trajectories are applied to effectively source apportion the polluting sectors to improve the city's environment. The monthly averages were found to be 130.16 ± 35.7 μg/m3 and 303.2 ± 95.6 μg/m3 for summertime and wintertime respectively. Over half of the identified PM2.5 comprises carbonaceous species (OC, EC) and secondary inorganic ions (NO3-, SO42-, NH4+) with 63% & 68% representing summertime and wintertime sampling respectively. In the summertime, the sources with percentages are coal combustion and secondary aerosol (31%), total traffic (25%), power plants and industrial emissions (18%), Biomass burning (15%), and crustal matter (11%). Similarly, in the wintertime, industrial emissions and secondary aerosol (28%), biomass burning (26%), total traffic (20%), coal combustion and ammonium sulfate (17%), and crustal matter (9%). The error estimation of “Displacement” is applied to the base run for rotational ambiguity and random errors. All the strong species in specific factors reproduced well, suggesting a ‘well-defined solution’ of factor profiles and concentrations. The backward trajectories of height 2000m, 200m, and 50m are generated from southern, western, and local areas to the receptor site, possibly behind Lahore’s poor air quality