Formation of highly oxygenated organic molecules from chlorine-atom-initiated oxidation of alpha-pinene
Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of alpha-pinene can irreversibly condense to particles and contribute to secondary organic aerosol (SOA) formation. Recently, the formation of nitryl chloride (ClNO2) from heterogeneous reactions, followed by its subsequent photol...
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Veröffentlicht in: | Atmospheric chemistry and physics 2020-04, Vol.20 (8), p.5145-5155 |
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Sprache: | eng |
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Zusammenfassung: | Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of
alpha-pinene can irreversibly condense to particles and contribute to
secondary organic aerosol (SOA) formation. Recently, the formation of nitryl
chloride (ClNO2) from heterogeneous reactions, followed by its
subsequent photolysis, is suggested to be an important source of chlorine
atoms in many parts of the atmosphere. However, the oxidation of
monoterpenes such as alpha-pinene by chlorine atoms has received very little
attention, and the ability of this reaction to form HOMs is completely
unstudied. Here, chamber experiments were conducted with alpha-pinene and
chlorine under low- and high-nitrogen-oxide (NOx, NOx=NO+NO2) conditions. A nitrate-based CI-APi-ToF (chemical
ionization–atmospheric pressure interface–time of flight) mass spectrometer was used to
measure HOM products. Clear distributions of monomers with 9–10 carbon atoms and dimers with 18–20 carbon atoms were observed under low-NOx conditions. With increased concentration of NOx within the chamber, the
formation of dimers was suppressed due to the reactions of peroxy radicals
with NO. We estimated the HOM yields from chlorine-initiated oxidation of
alpha-pinene under low-NOx conditions to be around 1.8 %, though
with a substantial uncertainty range (0.8 %–4 %) due to lack of suitable calibration methods. Corresponding yields at high NOx could not be determined because of concurrent ozonolysis reactions. Our study demonstrates that also the oxidation of alpha-pinene by chlorine atoms
and yield low-volatility organic compounds. |
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ISSN: | 1680-7324 1680-7316 1680-7324 |
DOI: | 10.5194/acp-20-5145-2020 |