TY - JOUR
T1 - Model Evaluation of New Techniques for Maintaining High-NO Conditions in Oxidation Flow Reactors for the Study of OH-Initiated Atmospheric Chemistry
AU - Peng, Zhe
AU - Palm, Brett B.
AU - Day, Douglas A.
AU - Talukdar, Ranajit K.
AU - Hu, Weiwei
AU - Lambe, Andrew T.
AU - Brune, William H.
AU - Jimenez, Jose L.
N1 - Funding Information:
This work was partially supported by DOE (BER/ASR) DE-SC0011105 and DE-SC0016559, EPA STAR 83587701-0, and NSF AGS-1360834. A.T.L. acknowledges support from NSF AGS-1536939 and AGS-1537446 and DoE (BER/ASR) DE-SC0006980 and DE-SC0011935. B.B.P. thanks support from a CIRES Graduate Student Research Fellowship and a U.S. EPA STAR Graduate Fellowship (FP-91761701-0). EPA has not reviewed this manuscript and thus no endorsement should be inferred.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2018/2/15
Y1 - 2018/2/15
N2 - Oxidation flow reactors (OFRs) efficiently produce OH radicals using low-pressure Hg-lamp emissions at λ = 254 nm (OFR254) or both λ = 185 and 254 nm (OFR185). OFRs under most conditions are limited to studying low-NO chemistry (where RO2 + HO2 dominates RO2 fate), even though substantial amounts of initial NO may be injected. This is due to very fast NO oxidation by high concentrations of OH, HO2, and O3. In this study, we model new techniques for maintaining high-NO conditions in OFRs, that is, continuous NO addition along the length of the reactor in OFR185 (OFR185-cNO), recently proposed injection of N2O at the entrance of the reactor in OFR254 (OFR254-iN2O), and an extension of that idea to OFR185 (OFR185-iN2O). For these techniques, we evaluate (1) fraction of conditions dominated by RO2 + NO while avoiding significant nontropospheric photolysis and (2) fraction of conditions where reactions of precursors with OH dominate over unwanted reactions with NO3. OFR185-iN2O is the most practical for general high-NO experiments because it represents the best compromise between experimental complexity and performance upon proper usage. Short lamp distances are recommended for OFR185-iN2O to ensure a relatively uniform radiation field. OFR185-iN2O with low O2 or using Hg lamps with higher 185 nm-to-254 nm ratio can improve performance. OFR185-iN2O experiments should generally be conducted at higher relative humidity, higher UV, lower concentration of non-NOy external OH reactants, and percent-level N2O. OFR185-cNO and OFR185-iN2O at optimal NO precursor injection rate (∼2 ppb/s) or concentration (∼3%) would have satisfactory performance in typical field studies where ambient air is oxidized. Exposure estimation equations are provided to aid experimental planning. This work enables improved high-NO OFR experimental design and interpretation.
AB - Oxidation flow reactors (OFRs) efficiently produce OH radicals using low-pressure Hg-lamp emissions at λ = 254 nm (OFR254) or both λ = 185 and 254 nm (OFR185). OFRs under most conditions are limited to studying low-NO chemistry (where RO2 + HO2 dominates RO2 fate), even though substantial amounts of initial NO may be injected. This is due to very fast NO oxidation by high concentrations of OH, HO2, and O3. In this study, we model new techniques for maintaining high-NO conditions in OFRs, that is, continuous NO addition along the length of the reactor in OFR185 (OFR185-cNO), recently proposed injection of N2O at the entrance of the reactor in OFR254 (OFR254-iN2O), and an extension of that idea to OFR185 (OFR185-iN2O). For these techniques, we evaluate (1) fraction of conditions dominated by RO2 + NO while avoiding significant nontropospheric photolysis and (2) fraction of conditions where reactions of precursors with OH dominate over unwanted reactions with NO3. OFR185-iN2O is the most practical for general high-NO experiments because it represents the best compromise between experimental complexity and performance upon proper usage. Short lamp distances are recommended for OFR185-iN2O to ensure a relatively uniform radiation field. OFR185-iN2O with low O2 or using Hg lamps with higher 185 nm-to-254 nm ratio can improve performance. OFR185-iN2O experiments should generally be conducted at higher relative humidity, higher UV, lower concentration of non-NOy external OH reactants, and percent-level N2O. OFR185-cNO and OFR185-iN2O at optimal NO precursor injection rate (∼2 ppb/s) or concentration (∼3%) would have satisfactory performance in typical field studies where ambient air is oxidized. Exposure estimation equations are provided to aid experimental planning. This work enables improved high-NO OFR experimental design and interpretation.
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U2 - 10.1021/acsearthspacechem.7b00070
DO - 10.1021/acsearthspacechem.7b00070
M3 - Article
AN - SCOPUS:85043360498
SN - 2472-3452
VL - 2
SP - 72
EP - 86
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 2
ER -