Title: Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

Abstract

Oxidation flow reactors (OFRs) are a promising complement to environmental chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals (RO₂), which play a central role in atmospheric organic chemistry, in OFRs and environmental chambers by chemical kinetic modeling and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO₂, their bimolecular fates in OFRs are mainly RO₂+HO₂ and RO₂+NO, similar to chambers and atmospheric studies. For substituted primary RO₂ and acyl RO₂, RO₂+RO₂ can make a significant contribution to the fate of RO₂ in OFRs, chambers and the atmosphere, but RO₂+RO₂ in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO₂+NO dominates RO₂ fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, RO₂+OH can be a major RO₂ fate and RO₂ isomerization can be negligible for common multifunctional RO₂, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added O₃), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO₂ lifetimes long enough (~10 s) to allow atmospherically relevant RO₂ isomerization. In the OFR185 mode (for which OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recommended for the atmospherically relevant gas-phase chemistry of both stable species and RO₂. These conditions ensure minor or negligible RO₂+OH and a relative importance of RO₂ isomerization in RO₂ fate in OFRs within $~\times 2$ of that in the atmosphere. Under these conditions, the photochemical age within OFR185 systems can reach a few equivalent days at most, encompassing the typical ages for maximum secondary organic aerosol (SOA) production. A small increase in OFR temperature may allow the relative importance of RO₂ isomerization to approach the ambient values. To study the heterogeneous oxidation of SOA formed under atmospherically relevant OFR conditions, a different UV source with higher intensity is needed after the SOA formation stage, which can be done with another reactor in series. Finally, we recommend evaluating the atmospheric relevance of RO₂ chemistry by always reporting measured and/or estimated OH, HO₂, NO, NO₂ and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use RO₂ fate estimator program is included with this paper to facilitate the investigation of this topic in future studies.

Authors:

Peng, Zhe ;

• Search DOE PAGES for author "Peng, Zhe"
• Search DOE PAGES for ORCID "0000-0002-6823-452X"

Lee-Taylor, Julia; Orlando, John J.; Tyndall, Geoffrey S. ;

• Search DOE PAGES for author "Tyndall, Geoffrey S."
• Search DOE PAGES for ORCID "0000-0002-0695-5241"

Jimenez, Jose L.

• Search DOE PAGES for author "Jimenez, Jose L."
• Search DOE PAGES for ORCID "0000-0001-6203-1847"

Publication Date:

Tue Jan 22 00:00:00 EST 2019

Research Org.:

Univ. of Colorado, Boulder, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1491606

Alternate Identifier(s):

OSTI ID: 1612638

Grant/Contract Number:  

SC0016559

Resource Type:

Published Article

Journal Name:

Atmospheric Chemistry and Physics (Online)

Additional Journal Information:

Journal Name: Atmospheric Chemistry and Physics (Online) Journal Volume: 19 Journal Issue: 2; Journal ID: ISSN 1680-7324

Publisher:

Copernicus Publications, EGU

Country of Publication:

Germany

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Environmental Sciences & Ecology; Meteorology & Atmospheric Sciences