Photochemical environment over Southeast Asia primed for hazardous ozone levels with influx of nitrogen oxides from seasonal biomass burning

Abstract. Mainland and maritime Southeast Asia is home to more than 655 million people, representing nearly 10 % of the global population. The dry season in this region typically associated with intense biomass burning activity, which leads a significant increase surface air pollutants that are harmful human health, including ozone (O3). Latitude-based differences land use distinguish two regional regimes: (1) on peninsular mainland peaking March (2) across Indonesia September. type amount material burned each regime impact emissions nitrogen oxides (NOx = NO + NO2) volatile organic compounds (VOCs), combine produce ozone. Here, we nested GEOS-Chem atmospheric chemistry transport model (horizontal resolution 0.25? × 0.3125?), combination satellite observations from Ozone Monitoring Instrument (OMI) ground-based Malaysia, investigate photochemistry over 2014. Seasonal cycles tropospheric columns OMI peak emissions. Compared OMI, has mean annual bias ?11 but tends overestimate near areas seasonal fire activity. We find outside these areas, underlying photochemical environment generally NOx-limited dominated by anthropogenic NOx biogenic non-methane VOC Pyrogenic play key role photochemistry, shifting towards VOC-limited production contributing about 30 formation potential during both seasons. Using model, activity coincides widespread exposure at levels exceed world public health guidelines, resulting 260 premature deaths 2014 another 160 Despite positive bias, hazardous confirmed