Role played by Organic Nitrates in the Production of Secondary Organic Aerosol in a megacity

Secondary Organic Aerosol (SOA) production and chemical composition play a crucial role in the urban air pollution. Here, we used observations from two summer campaigns in Beijing in 2017 and 2023 to show that nighttime production of NOz (NOy - NOx) is particularly enhanced in specific conditions and that can play a significant role for SOA the next day. The observations showed nocturnal peaks of NOz of about 40 ppb, correlated with very high NO and NO2. We employed the Framework for 0-D Atmospheric Modeling (F0AM) model, based on the Master Chemical Mechanism (MCM), running simulations to investigate the organic nitrates (ONs) speciation, and founding that during the night the alkyl nitrates is the most abundant ONs, produced by oxidation of volatile organic compounds (VOCs) by the nitrate radical (NO3). Finally, we used the Framework for 0-D Atmospheric Modeling- Washington Aerosol Module (F0AM-WAM) model, which couple the gas phase chemistry with the SIMPOL representation for the particle phase, to correlate the nocturnal ONs peaks, that we suggested to be mainly in gas phase, to the diurnal particle growth events registered in Beijing.