Abstract
Abstract. The effect of reaction temperature and how water vapour influences the formation of secondary organic aerosol (SOA) in ozonolysis of limonene, Δ3-carene and α-pinene, both regarding number and mass of particles, has been investigated by using a laminar flow reactor (G-FROST). Experiments with cyclohexane and 2-butanol as OH scavengers were compared to experiments without any scavenger. The reactions were conducted in the temperature range between 298 and 243 K, and at relative humidities between <10 and 80%. Results showed that there is still a scavenger effect on number and mass concentrations at low temperatures between experiments with and without an addition of an OH scavenger. This shows that the OH chemistry is influencing the SOA formation also at these temperatures. The overall temperature dependence on SOA formation is not as strong as expected from partitioning theory. In some cases there is even a positive temperature dependence that must be related to changes in the chemical mechanism and/or reduced rates of secondary chemistry at low temperatures. The precursor's α-pinene and Δ3-carene exhibit a similar temperature dependence regarding both number and mass of particles formed, whereas limonene shows a different dependence. The water effect at low temperature could be explained by physical uptake and cluster stabilisation. At higher temperatures, only a physical explanation is not sufficient and the observations are in line with water changing the chemical mechanism or reaction rates. The data presented adds to the understanding of SOA contribution to new particle formation and atmospheric degradation mechanisms.
Highlights
Vegetation emits a vast number of biogenic volatile organic compounds (BVOC), where isoprene and the monoterpenes are the non methane BVOC that dominate on the global scale (Guenther, 2002)
This paper extends earlier investigations on the ozonolysis of α-pinene, 3-carene and limonene
The water effect at low temperatures may be explained by physical uptake and cluster stabilisation, while at higher temperatures a physical explanation can not account for the observations
Summary
Vegetation emits a vast number of biogenic volatile organic compounds (BVOC), where isoprene and the monoterpenes are the non methane BVOC that dominate on the global scale (Guenther, 2002). In the atmosphere they undergo oxidation, forming compounds with low volatility that can end up in the condensed phase by gas-to-particle conversion (Griffin et al, 1999; Yokouchi and Ambe, 1985). It has been shown that the use of OH scavengers and which scavengers used can influence the SOA formation
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