| 1. |
- Baker, Yare, et al.
(författare)
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Impact of HO2/RO2 ratio on highly oxygenated α-pinene photooxidation products and secondary organic aerosol formation potential
- 2024
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Ingår i: ATMOSPHERIC CHEMISTRY AND PHYSICS. - 1680-7316 .- 1680-7324. ; 24:8, s. 4789-4807
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Tidskriftsartikel (refereegranskat)abstract
- Highly oxygenated molecules (HOMs) from the atmospheric oxidation of biogenic volatile organic compounds are important contributors to secondary organic aerosol (SOA). Organic peroxy radicals (RO2) and hydroperoxy radicals (HO2) are key species influencing the HOM product distribution. In laboratory studies, experimental requirements often result in overemphasis on RO2 cross-reactions compared to reactions of RO2 with HO2. We analyzed the photochemical formation of HOMs from alpha-pinene and their potential to contribute to SOA formation under high (approximate to 1/1) and low (approximate to 1/100) conditions. As > 1 is prevalent in the daytime atmosphere, sufficiently high is crucial to mimic atmospheric conditions and to prevent biases by low on the HOM product distribution and thus SOA yield. Experiments were performed under steady-state conditions in the new, continuously stirred tank reactor SAPHIR-STAR at Forschungszentrum J & uuml;lich. The ratio was increased by adding CO while keeping the OH concentration constant. We determined the HOM's SOA formation potential, considering its fraction remaining in the gas phase after seeding with (NH4)(2)SO4 aerosol. An increase in led to a reduction in SOA formation potential, with the main driver being a similar to 60 % reduction in HOM-accretion products. We also observed a shift in HOM-monomer functionalization from carbonyl to hydroperoxide groups. We determined a reduction of the HOM's SOA formation potential by similar to 30 % at approximate to 1/1 compared to approximate to 1/100. Particle-phase observations measured a similar decrease in SOA mass and yield. Our study shows that too low ratios compared to the atmosphere can lead to an overestimation of SOA yields.
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| 2. |
- McFiggans, Gordon, et al.
(författare)
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Secondary organic aerosol reduced by mixture of atmospheric vapours
- 2019
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 565:7741, s. 587-593
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).
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