Production of highly oxygenated organic molecules (HOMs) from trace contaminants during isoprene oxidation
During nucleation studies from pure isoprene oxidation in the CLOUD chamber at the European Organization for Nuclear Research (CERN) we observed unexpected ion signals at m∕z = 137.133 (C10H17+) and m∕z = 81.070 (C6H9+) with the recently developed proton-transfer-reaction time-of-flight (PTR3-TOF) m...
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Published in | Atmospheric measurement techniques Vol. 11; no. 8; pp. 4763 - 4773 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
14.08.2018
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | During nucleation studies from pure isoprene oxidation in the CLOUD chamber
at the European Organization for Nuclear Research (CERN) we observed
unexpected ion signals at m∕z = 137.133
(C10H17+) and m∕z = 81.070
(C6H9+) with the recently developed
proton-transfer-reaction time-of-flight (PTR3-TOF) mass spectrometer
instrument. The mass-to-charge ratios of these ion signals typically
correspond to protonated monoterpenes and their main fragment. We identified
two origins of these signals: first secondary association reactions of
protonated isoprene with isoprene within the PTR3-TOF reaction chamber and
secondly [4+2] cycloaddition (Diels–Alder) of isoprene inside the gas
bottle which presumably forms the favored monoterpenes limonene and
sylvestrene, as known from literature. Under our PTR3-TOF conditions used in
2016 an amount (relative to isoprene) of 2 % is formed within the
PTR3-TOF reaction chamber and 1 % is already present in the gas bottle.
The presence of unwanted cycloaddition products in the CLOUD chamber impacts
the nucleation studies by creating ozonolysis products as the corresponding
monoterpenes and is responsible for the majority of the observed highly
oxygenated organic molecules (HOMs), which in turn leads to a significant
overestimation of both the nucleation rate and the growth rate. In order to
study new particle formation (NPF) from pure isoprene oxidation under
relevant atmospheric conditions, it is important to improve and assure the
quality and purity of the precursor isoprene. This was successfully achieved
by cryogenically trapping lower-volatility compounds such as monoterpenes
before isoprene was introduced into the CLOUD chamber. |
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ISSN: | 1867-8548 1867-1381 1867-8548 |
DOI: | 10.5194/amt-11-4763-2018 |