Real-time measurements of NMVOCs in the central IGB, Lucknow, India: Source characterization and their role in O₃ and SOA formation

Abstract

Abstract. Lucknow is the capital of India’s largest state, Uttar Pradesh, one of South Asia’s most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time of flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real-time from Dec-2020–May 2021. The campaign mean concentrations of the NMVOCs were 125.5 ±37.5 ppbv. The average concentrations of NMVOCs are relatively high during winter. An advanced multi-linear engine (ME-2) model was used to perform the NMVOCs source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic, two solid fuel combustion factors, secondary volatile organic compounds and volatile chemical products. Biomass burning contributes most to the NMVOCs and SOA formation, while interestingly, traffic sources most influence ozone formation. Significant differences in the composition of the two solid fuel combustion indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs.