Preprints
https://doi.org/10.5194/amt-2021-128
https://doi.org/10.5194/amt-2021-128

  07 May 2021

07 May 2021

Review status: this preprint is currently under review for the journal AMT.

Impact of ozone and inlet design on the detection of isoprene-derived organic nitrates by thermal dissociation cavity ring-down spectroscopy (TD-CRDS)

Patrick Dewald, Raphael Dörich, Jan Schuladen, Jos Lelieveld, and John N. Crowley Patrick Dewald et al.
  • Atmospheric Chemistry Department, Max-Planck-Institut für Chemie, 55128 Mainz, Germany

Abstract. We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO3) in a 1 m3 Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO2), which is monitored by cavity ring-down spectroscopy (TD-CRDS). Using thermal dissociation inlets (TDIs) made of quartz, the temperature-dependent dissociation profiles (thermograms) of ISOP-NITs measured in the presence of ozone (O3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for e.g. isopropyl nitrate (iPN) or peroxy acetyl nitrate (PAN) under the same conditions. The shape of the thermograms varied with the TDI’s surface to volume ratio and with material of the inlet walls, providing clear evidence that ozone and quartz surfaces catalyse the dissociation of unsaturated organic nitrates leading to formation of NO2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). We present a simple, viable solution to this problem and discuss the potential for interference by the thermolysis of nitric acid (HNO3), nitrous acid (HONO) and O3.

Patrick Dewald et al.

Status: open (until 14 Jul 2021)

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Patrick Dewald et al.

Patrick Dewald et al.

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Short summary
Organic nitrates generated from the reaction between isoprene and the nitrate radical (ISOP-NITs) were detected via their thermal disscoiation in heated quartz inlets to nitrogen dioxide monitored by cavity ring-down spectroscopy. The temperature-dependent dissociation profiles of ISOP-NITs in the presence of ozone (O3) are broad in contrast to narrow profiles of common reference compounds. We demonstrate that this broadening is caused by O3-assisted reactions of ISOP-NITs on quartz surfaces.