Effect of temperature on the formation of highly oxygenated organic molecules (HOMs) from alpha-pinene ozonolysis

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Quéléver , L L J , Kristensen , K , Jensen , L N , Rosati , B , Teiwes , R , Dällenbach , K , Peräkylä , O , Roldin , P , Bossi , R , Pedersen , H B , Glasius , M , Bilde , M & Ehn , M 2019 , ' Effect of temperature on the formation of highly oxygenated organic molecules (HOMs) from alpha-pinene ozonolysis ' , Atmospheric Chemistry and Physics , vol. 19 , no. 11 , pp. 7609-7625 . https://doi.org/10.5194/acp-19-7609-2019

Title: Effect of temperature on the formation of highly oxygenated organic molecules (HOMs) from alpha-pinene ozonolysis
Author: Quéléver, Lauriane L. J.; Kristensen, Kasper; Jensen, Louise Normann; Rosati, Bernadette; Teiwes, Ricky; Dällenbach, Kaspar; Peräkylä, Otso; Roldin, Pontus; Bossi, Rossana; Pedersen, Henrik B.; Glasius, Marianne; Bilde, Merete; Ehn, Mikael
Contributor: University of Helsinki, INAR Physics
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, INAR Physics
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
Date: 2019-06-07
Language: eng
Number of pages: 17
Belongs to series: Atmospheric Chemistry and Physics
ISSN: 1680-7316
URI: http://hdl.handle.net/10138/303519
Abstract: Highly oxygenated organic molecules (HOMs) are important contributors to secondary organic aerosol (SOA) and new-particle formation (NPF) in the boreal atmosphere. This newly discovered class of molecules is efficiently formed from atmospheric oxidation of biogenic volatile organic compounds (VOCs), such as monoterpenes, through a process called autoxidation. This process, in which peroxy-radical intermediates isomerize to allow addition of molecular oxygen, is expected to be highly temperature-dependent. Here, we studied the dynamics of HOM formation during a -pinene ozonolysis experiments performed at three different temperatures, 20, 0 and - 15 degrees C, in the Aarhus University Research on Aerosol (AURA) chamber. We found that the HOM formation, under our experimental conditions (50 ppb alpha-pinene and 100 ppb ozone), decreased considerably at lower temperature, with molar yields dropping by around a factor of 50 when experiments were performed at 0 degrees C, compared to 20 degrees C. At -15 degrees C, the HOM signals were already close to the detection limit of the nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer used for measuring gas-phase HOMs. Surprisingly, comparing spectra measured at 0 and 20 degrees C, ratios between HOMs of different oxidation levels, e.g., the typical HOM products C10H14O7, C10H14O9, and C10H14O11, changed considerably less than the total HOM yields. More oxidized species have undergone more isomerization steps; yet, at lower temperature, they did not decrease more than the less oxidized species. One possible explanation is that the primary rate-limiting steps forming these HOMs occur before the products become oxygenated enough to be detected by our CI-APi-TOF (i.e., typically seven or more oxygen atoms). The strong temperature dependence of HOM formation was observed under temperatures highly relevant to the boreal forest, but the exact magnitude of this effect in the atmosphere will be much more complex: the fate of peroxy radicals is a competition between autoxidation (influenced by temperature and VOC type) and bimolecular termination pathways (influenced mainly by concentration of reaction partners). While the temperature influence is likely smaller in the boreal atmosphere than in our chamber, both the magnitude and complexity of this effect clearly deserve more consideration in future studies in order to estimate the ultimate role of HOMs on SOA and NPF under different atmospheric conditions.
Subject: OXIDIZED RO2 RADICALS
MASS-SPECTROMETER
TROPOSPHERIC DEGRADATION
AEROSOL
PRODUCTS
AUTOXIDATION
GROWTH
SIZE
MECHANISM
PROTOCOL
114 Physical sciences
116 Chemical sciences
1172 Environmental sciences
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