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Ozone and OH-induced oxidation of monoterpenes: Changes in the thermal properties of secondary organic aerosol (SOA)

Artikel i vetenskaplig tidskrift
Författare Ågot Watne
Jonathan Westerlund
Å M. Hallquist
W. H. Brune
Mattias Hallquist
Publicerad i Journal of Aerosol Science
Volym 114
Sidor 31-41
ISSN 0021-8502
Publiceringsår 2017
Publicerad vid Institutionen för kemi och molekylärbiologi
Sidor 31-41
Språk en
Länkar dx.doi.org/10.1016/j.jaerosci.2017....
Ämnesord ELVOC, Flow reactor, Oxidative ageing, PAM, Terpenes, Volatility, Aerosols, Atmospheric movements, Ozone, Pulse amplitude modulation, Thermodynamic properties, Flow reactors, Induced oxidations, Secondary organic aerosols, Temporal evolution, Volatility distribution, Monoterpenes
Ämneskategorier Meteorologi och atmosfärforskning, Kemi, Fysikalisk kemi, Organisk kemi, Klimatforskning, Miljökemi

Sammanfattning

The behaviour of secondary organic aerosols (SOA) in the atmosphere is highly dependent on their thermal properties. Here we investigate the volatility of SOA formed from α-pinene, β-pinene and limonene upon ozone- and OH-induced oxidation, and the effect of OH-induced ageing on the initially produced SOA. For all three terpenes, the ozone-induced SOA was less volatile than the OH-induced SOA. The thermal properties of the SOA were described using three parameters extracted from the volatility measurements: the temperature at which 50% of the volume has evaporated (TVFR0.5), which is used as a general volatility indicator; a slope factor (SVFR), which describes the volatility distribution; and TVFR0.1, which measures the volatility of the least volatile particle fraction. Limonene-derived SOA generally had higher TVFR0.5 values and shallower slopes than SOA derived from α- and β-pinene. This was especially true for the ozone-induced SOA, partially because the ozonolysis of limonene has a strong tendency to cause SOA formation and to produce extremely low volatility VOCs (ELVOCs). Ageing by OH exposure did not reduce TVFR0.5 for any of the studied terpenes but did increase the breadth of the volatility distribution by increasing the aerosols’ heterogeneity and contents of substances with different vapour pressures, also leading to increases in TVFR0.1. This stands in contrast to previously reported results from smog chamber experiments, in which TVFR0.5 always increased with ageing. These results demonstrate that there are two opposing processes that influence the evolution of SOAs’ thermal properties as they age, and that results from both flow reactors and static chambers are needed to fully understand the temporal evolution of atmospheric SOA’ thermal properties. © 2017 The Authors

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