Observed NO/NO₂ Ratios in the Upper Troposphere Imply Errors in NO‐NO₂‐O₃ Cycling Kinetics or an Unaccounted NO_x Reservoir

Abstract

Observations from the SEAC 4 RS aircraft campaign over the southeast United States in August-September 2013 show NO/NO 2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NO x reservoir species, presumably organic, decomposing thermally to NO 2 in the instrument. The NO 2 instrument corrects for this artifact from known labile HNO 4 and CH 3 O 2 NO 2 NO x reservoirs. To bridge the gap between measured and simulated NO 2 , additional unaccounted labile NO x reservoir species would have to be present at a mean concentration of 40 ppt for the SEAC 4 RS conditions (compared with 197 ppt for NO x ). An alternative explanation is error in the low-temperature rate constant for the NO + O 3 reaction (30% 1-σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO 2 photolysis (20% 1-σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO 2 columns.Plain Language Summary We identify large discrepancies between observed NO/NO 2 ratios and models representing our best understanding of the chemistry controlling NO and NO 2 in the upper troposphere over the southeast United States during August-September 2013. We suggest that either unrecognized chemistry or errors in modeled cycling between NO, NO 2 , and O 3 could explain this discrepancy. Either explanation will have important implications for global tropospheric chemistry and for the interpretation of satellite observations of NO 2 .

Estimates of lightning NO<sub><i>x</i></sub> production based on high-resolution OMI NO<sub>2</sub> retrievals over the continental US

“…LNO x (p) is the LNO x vertical profile calculated by the difference of vertical profiles between WRF-Chem simulations with and without lightning. Please note that the CP is a reflectance-weighted pressure retrieved by the collision-induced O 2 -O 2 absorption band near 477 nm (Acarreta et al, 2004;Sneep et al, 2008;Stammes et al, 2008). For a deep convective cloud with lightning, the CP lies below the geometrical cloud top, which is much closer to that detected by thermal infrared sensors, such as CloudSat and the Aqua Moderate Resolution Imaging Spectrometer (MODIS) (Vasilkov et al, 2008;Joiner et al, 2012).…”

“…Recent studies revealed that the modeled NO/NO 2 ratio departs from the data in the SEAC 4 RS aircraft campaign (Travis et al, 2016;Silvern et al, 2018). Silvern et al (2018) attributed this to the positive interference on the NO 2 measurements or errors in the cold-temperature NO−NO 2 −O 3 photochemical reaction rate.…”

“…Recent studies revealed that the modeled NO/NO 2 ratio departs from the data in the SEAC 4 RS aircraft campaign (Travis et al, 2016;Silvern et al, 2018). Silvern et al (2018) attributed this to the positive interference on the NO 2 measurements or errors in the cold-temperature NO−NO 2 −O 3 photochemical reaction rate. We assign a 20 % bias with ±15 % uncertainty to this error considering the possible positive NO 2 measurement interferences (Allen et al, 2019;Bucsela et al, 2019) and estimate the uncertainty to be 15 % for LNO x PE.…”

Midlatitude Lightning NOx Production Efficiency Inferred From OMI and WWLLN Data

“…The partitioning of NO x into NO and NO 2 in GMI/GEOS‐Chem, which affects the AMF, has been re‐examined recently by Travis et al () and Silvern et al (). They found GEOS‐Chem NO/NO 2 ratios near and above 10 km to be approximately a factor of 2 larger than those of in situ measurements from the SEAC 4 RS campaign.…”

Single-photon laser-induced fluorescence detection of nitric oxide at sub-parts per trillion mixing ratios

“…Autooxidation of organic compounds in low-NO environments is increasingly recognized as a key source of highly-oxidized/low-volatility organic compounds in the atmosphere (Crounse et al, 2013). Measurements of the ratio of NO to nitrogen dioxide (NO 2 ) in the upper troposphere (UT) frequently cannot be reconciled with models (Cohen et al, 2000;Silvern et al, 2018). Zhao et al (2019) show that differences in background NO at the single pptv level are responsible for differences in global modeled OH on the order of 50%.…”