Exploring the complex chemistry of biomass burning emissions Rhianna L. Evans 1 , Rubén Soler 2 , Teresa Vera 2 , Mila Ródenas 2 , Esther Borrás 2 , Tatiana Gómez 2 , Amalia Muñoz 2 , Andrew R. Rickard 1,3 1 Department of Chemistry, University of York, UK, 2 Instituto Universitario Centro de Estudios Ambientales del Mediterráneo (CEAM-UMH), Valencia, Spain, 3 National Centre for Atmospheric Science, University of York, UK The World Health Organisation (WHO) estimates 99% of the global population breathes air which exceeds air quality guidelines. Biomass burning, which encompasses wildfires, agricultural burning, and domestic combustion, releases large quantities of organic carbon to the atmosphere. Once emitted, the photochemical oxidation of biomass burning volatile organic compounds (BBVOCs) produces harmful secondary pollutants such as ozone (O 3 ) and secondary organic aerosol (SOA). With rapidly increasing global temperatures, the frequency of wildfires is predicted to be exacerbated by climate change resulting in poorer air quality. Some of the most reactive BBVOCs are oxygenated aromatic compounds such as phenolic and furanic species, previously identified as important precursors to SOA. Atmospheric chamber experiments can be used to study how these compounds react in the atmosphere. Many previous chamber studies have examined the chemistry of individual BBVOCs in dark or light conditions, equivalent to nighttime and daytime reactivity respectively, but few have observed the transition of chemical regime between day and night. A series of outdoor simulation chamber experiments were conducted at the EUropean PHOtoREactor (EUPHORE) in Valencia, Spain during May 2023 to replicate the night-to-day reactivity transitions of 4 BBVOCs: guaiacol, catechol, 2-methylfuran and furfural. This work aimed to understand the atmospheric chemical mechanisms of BBVOCs and observe any compositional changes between daytime and nighttime SOA which could thereby impact on toxicity. Analysis of the guaiacol experiments showed it reacted with nitrate radicals to form nitro-guaiacol during the night which subsequently decayed photochemically in the day. This indicates nitro-guaiacol chemistry is therefore important for daytime SOA and O 3 production. Concentrations of products, such as nitro-catechol and 2-methoxy- p-benzoquinone increased more rapidly in the day compared to the night suggesting reactions with daytime oxidants as major formation pathways. Overall, this work provides important mechanistic updates to BBVOC atmospheric chemistry for inclusion into air quality and climate models.
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© The Author(s), 2023
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