AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Modeling of High-NO Chemistry in Oxidation Flow Reactors
ZHE PENG, Brett Palm, Ranajit Talukdar, Weiwei Hu, Andrew Lambe, William Brune, Jose-Luis Jimenez, CIRES, University of Colorado
Abstract Number: 48 Working Group: Aerosol Chemistry
Abstract Oxidation flow reactors (OFRs) using OH produced from low-pressure Hg lamps at 254 nm (OFR254) or both 185 and 254 nm (OFR185) are commonly used in atmospheric chemistry. We perform a comprehensive modeling study of OFR chemistry and find that high-NO (NO-dominated RO2 radical fate) OFR experiments are very difficult to conduct by initial NO injection (OFR-iNO) due to its rapid oxidation to NO2. Combustion sources used in OFR studies often contain very high VOC and NO, which should be diluted by >x100 to avoid non-tropospheric VOC photolysis at 185 and 254 nm. It needs to be realized, however, that strong dilution almost certainly results in low-NO conditions. We thus examine new experimentally-evaluated techniques maintaining high NO, i.e., injection of percent-level N2O in both OFR185 (OFR185-iN2O) and OFR254 (OFR254-iN2O), and also a technique proposed based on model calculations: continuous NO injection along the flow in OFR185 (OFR185-cNO). OFR185-iN2O represents the best compromise between performance and experimental complexity. Lowering O2 or using lamps with higher 185-nm–to–254-nm emission ratio may improve the performance of OFR185-iN2O experiments with certain precursors. In the case of precursors highly reactive toward NO3 (e.g., dihydrofurans, α-terpinene, and terpinolene), OFR185-cNO may be needed to avoid significant NO3 addition pending experimental validation. To obtain high-NO chemistry and avoid various experimental artifacts (including non-tropospheric photolysis, RO2 suppression by NO2, and VOC oxidation by NO3), high relative humidity, modest UV lamp setting, low VOC concentration, and substantial (but not too high) NOx precursor injection are preferable.