Low-NO atmospheric oxidation pathways in a polluted megacity

Abstract. The impact of emissions volatile organic compounds (VOCs) to the atmosphere on production secondary pollutants, such as ozone and aerosol (SOA), is mediated by concentration nitric oxide (NO). Polluted urban atmospheres are typically considered be “high-NO” environments, while remote regions rainforests, with minimal anthropogenic influences, “low NO”. However, our observations from central Beijing show that this simplistic separation regimes flawed. Despite being in one largest megacities world, we observe formation gas- aerosol-phase oxidation products usually associated low-NO “rainforest-like” atmospheric pathways during afternoon, caused extreme suppression NO concentrations at time. Box model calculations suggest morning high-NO chemistry predominates (95 %) but afternoon plays a greater role (30 %). Current inventories applied GEOS-Chem which shows models, when run regional scale, fail accurately predict an diurnal cycle concentration. With increasing global emphasis reducing air pollution, it crucial for modelling tools used develop quality policy able represent variations pollutants SOA ozone.