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Title: Model Evaluation of New Techniques for Maintaining High-NO Conditions in Oxidation Flow Reactors for the Study of OH-Initiated Atmospheric Chemistry

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. Here, we model new techniques for maintaining high-NO conditions in OFRs, i.e., 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 non-tropospheric 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 since 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 shouldmore » 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. Finally, we provide exposure estimation equations to aid experimental planning. This work enables improved high-NO OFR experimental design and interpretation.« less
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [1]
  1. Univ. of Colorado, Boulder, CO (United States). Cooperative Inst. for Research in Environmental Sciences, Dept. of Chemistry
  2. Boston College, Chestnut Hill, MA (United States). Chemistry Dept.; Aerodyne Research Inc., Billerica, MA (United States)
  3. Pennsylvania State Univ., University Park, PA (United States). Dept. of Meterology
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 2; Journal Issue: 2; Journal ID: ISSN 2472-3452
American Chemical Society
Research Org:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; oxidation flow reactor; high-NO chemistry; kinetic modeling; non-tropospheric organic photolysis; VOC oxidation by NO3; experimental design
OSTI Identifier: