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Title: Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

Abstract

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions inmore » both OFR and troposphere. We define “riskier OFR conditions” as those with either low H2O (< 0.1 %) or high OHRext ( ≥  100 s−1 in OFR185 and > 200 s−1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm−2 s−1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Univ. of Colorado, Denver, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1245673
Alternate Identifier(s):
OSTI ID: 1258747
Grant/Contract Number:  
SC0011105
Resource Type:
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 16; Journal Issue: 7; Journal ID: ISSN 1680-7324
Publisher:
Copernicus GmbH
Country of Publication:
Germany
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Peng, Zhe, Day, Douglas A., Ortega, Amber M., Palm, Brett B., Hu, Weiwei, Stark, Harald, Li, Rui, Tsigaridis, Kostas, Brune, William H., and Jimenez, Jose L. Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling. Germany: N. p., 2016. Web. doi:10.5194/acp-16-4283-2016.
Peng, Zhe, Day, Douglas A., Ortega, Amber M., Palm, Brett B., Hu, Weiwei, Stark, Harald, Li, Rui, Tsigaridis, Kostas, Brune, William H., & Jimenez, Jose L. Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling. Germany. doi:10.5194/acp-16-4283-2016.
Peng, Zhe, Day, Douglas A., Ortega, Amber M., Palm, Brett B., Hu, Weiwei, Stark, Harald, Li, Rui, Tsigaridis, Kostas, Brune, William H., and Jimenez, Jose L. Wed . "Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling". Germany. doi:10.5194/acp-16-4283-2016.
@article{osti_1245673,
title = {Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling},
author = {Peng, Zhe and Day, Douglas A. and Ortega, Amber M. and Palm, Brett B. and Hu, Weiwei and Stark, Harald and Li, Rui and Tsigaridis, Kostas and Brune, William H. and Jimenez, Jose L.},
abstractNote = {Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H2O (< 0.1 %) or high OHRext ( ≥  100 s−1 in OFR185 and > 200 s−1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm−2 s−1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.},
doi = {10.5194/acp-16-4283-2016},
journal = {Atmospheric Chemistry and Physics (Online)},
number = 7,
volume = 16,
place = {Germany},
year = {2016},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.5194/acp-16-4283-2016

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Cited by: 19 works
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