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Carboxylic acids from limonene oxidation by ozone and hydroxyl radicals: insights into mechanisms derived using a FIGAERO-CIMS

Journal article
Authors Julia Hammes
Anna Lutz
Thomas Mentel
Cameron Faxon
Mattias Hallquist
Published in Atmospheric Chemistry and Physics
Volume 19
Issue 20
Pages 13037-13052
ISSN 1680-7316
Publication year 2019
Published at Department of Chemistry and Molecular Biology
Pages 13037-13052
Language en
Links dx.doi.org/10.5194/acp-19-13037-201...
Keywords secondary organic aerosol, alpha-pinene, initiated oxidation, kinetic, mechanism, oh scavenger, beta-pinene, indoor air, ozonolysis, gas, soa, Environmental Sciences & Ecology, Meteorology & Atmospheric Sciences
Subject categories Earth and Related Environmental Sciences, Chemical Sciences, Environmental chemistry, Environmental Sciences, Meteorology and Atmospheric Sciences, Climate Research, Organic Chemistry, Analytical Chemistry

Abstract

This work presents the results from a flow reactor study on the formation of carboxylic acids from limonene oxidation in the presence of ozone under NOx-free conditions in the dark. A High-Resolution Time-of-Flight acetate Chemical Ionisation Mass Spectrometer (HR-ToF-CIMS) was used in combination with a Filter Inlet for Gases and AEROsols (FIGAERO) to measure the carboxylic acids in the gas and particle phases. The results revealed that limonene oxidation produced large amounts of carboxylic acids which are important contributors to secondary organic aerosol (SOA) formation. The highest 10 acids contributed 56 %-91 % to the total gas-phase signal, and the dominant gas-phase species in most experiments were C8H12O4, C9H14O4, C7H10O4 and C10H16O3. The particle-phase composition was generally more complex than the gas-phase composition, and the highest 10 acids contributed 47 %-92 % to the total signal. The dominant species in the particle phase were C8H12O5, C9H14O5, C9H12O5 and C10H16O4. The measured concentration of dimers bearing at least one carboxylic acid function in the particle phase was very low, indicating that acidic dimers play a minor role in SOA formation via ozone (O-3)/hydroxyl (OH) oxidation of limonene. Based on the various experimental conditions, the acidic compositions for all experiments were modelled using descriptions from the Master Chemical Mechanism (MCM). The experiment and model provided a yield of large (C-7-C-10) carboxylic acid of the order of 10 % (2 %-23 % and 10 %-15 %, respectively). Significant concentrations of 11 acids, from a total of 16 acids, included in the MCM were measured with the CIMS. However, the model predictions were, in some cases, inconsistent with the measurement results, especially regarding the OH dependence. Reaction mechanisms are suggested to fill-in the knowledge gaps. Using the additional mechanisms proposed in this work, nearly 75 % of the observed gas-phase signal in our lowest concentration experiment (8.4 ppb converted, ca. 23 % acid yield) carried out under humid conditions can be understood.

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