Hyperlocal air quality monitoring and source apportionment of non-refractory PM_2.5 at three urban sites using stationary van-based measurements: A Lucknow case study

Abstract. The present study addresses a key gap in characterizing hyperlocal air quality across three contrasting land-use settings during the peak pollution season in a central city in the Indo-Gangetic Plain (CIGP). We conducted ~744 hours of hyperlocal measurements in Lucknow city, spanning the post-monsoon to winter season over 31 days, using a mobile ambient air quality monitoring platform (MAAQMP). Measurements were conducted at three contrasting land-use settings—a background Site (“Site 1”), a traffic corridor (“Site 2”), and a major industrial cluster (“Site 3”). High-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) organic and inorganic mass spectra were subjected to Multilinear Engine-2, Positive Matrix Factorization (ME-2 PMF) source apportionment using a unified organic-inorganic aerosol (OA–IA) matrix. Across sites, NR-PM_2.5 was dominated by secondary organic aerosols (SOA), with biomass burning, traffic, and inorganic-associated organic factors (sulphate, nitrate-rich OA). Unlike Sites 1–2 (sulphate/low-volatility oxygenated organic aerosol (OOA)-dominant), Site 3 showed heterogeneous OA from biomass burning, semi-volatile/nitrate OOA, solid fuel, and traffic. Particle growth events (PGEs) were predominantly nocturnal, occurring under stable boundary-layer and inversion conditions. Site 3 exhibited ~5 times more nocturnal PGEs than the background, which was attributed to a higher condensation sink (CS). Stack vapors drive these PGEs (5–15 nm/h), enhancing the growth of oxidized biomass-burning organic aerosols (O-BBOA) and low-volatility OOA under inversions (r = 0.24). These results highlight the potential of near-source stationary van-based measurements for resolving hyperlocal aerosol growth processes and source influences.