Atmospheric Chemistry Program Seminar

Variability and diel dependence of O 3 – NO x – VOC chemistry in western wildfire plumes: Results from the NOAA Twin Otter during FIREX-AQ
Michael Robinson, ANYL 1st year
"The variability in photochemical ozone production from western wildfire plumes is important to the accurate prediction of their influence on North American air quality. A set of photochemical measurements including ozone, nitrogen oxides, photolysis rates and a suite of volatile organic compounds (VOCs), were made from the NOAA Twin Otter research aircraft as a part of the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) experiment. This research aircraft sampled nine unique fire complexes in five western states. Typical research flight days included flights during the afternoon, evening and night. In general, observed ozone production in the sampled plumes is rapid, reaching maximum ozone within 30 minutes downwind. A 0-D box modeling tool was developed to further probe the chemistry driving ozone production in these plumes. This tool was used to calculate afternoon and evening ozone isopleths which allows for a comparison of each individual fire complex in a common framework. The analysis shows the sensitivity of ozone production to initial NOx and VOC emissions. However ozone isopleths are not capable of describing the temporal transition of NO x and VOC sensitive chemical regimes. A radical budget approach is used for probing the temporal evolution of the chemistry. Afternoon photochemical plumes display a rapid transition from VOC sensitive chemistry to NO x sensitive chemistry, mainly driven by radical production from photolysis of HCHO and HONO emitted directly from the fire. Evening photochemical plumes exhibit a slower transition from NO x sensitive chemistry to VOC sensitive chemistry, with a larger portion radical production from alkene ozonolysis."
Michael A. Robinson, Zachary C.J. Decker, Kelley C. Barasanti, Matthew M. Coggon, Frank M. Flocke, Carley D. Fredrickson, Georgios I. Gkatzelis, Christopher D. Holmes, Denise D. Montzka, Brett B. Palm, R. Bradley Pierce, Rebecca H. Schwantes, Geoffrey S. Tyndall, Joel A. Thornton, Paul Van Rooy, Andrew J. Weinheimer, and Steven S. Brown.
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Model Inter-comparisons of Inorganic Nitrate Formation During KORUS-AQ Campaign
Seonsik Yun, ANYL 1st year
"Nitrogen oxides play an important role in global tropospheric chemistry. The lifetime of nitrogen oxides is controlled by organic and inorganic nitrate formation. GEOS-Chem, a global 3-D chemical transport model, has historically had an over-estimation problem of inorganic nitrates relative to surface observation networks. This study investigated this problem by using model inter-comparisons with six different chemical transport model simulations during the KORUS-AQ field campaign period. N2O5 hydrolysis reaction, a primary nocturnal inorganic nitrate formation, was investigated to compare differences in calculations of inorganic nitrate formation between the model simulations. Differences in heterogeneous loss of N2O5 between the models were analyzed with the uptake coefficient, aerosol surface area density, and N2O5 concentration. Results show that high N2O5 concentrations at nighttime in GEOS-Chem could be attributed to the high O3 concentrations at nighttime compared to the Ensemble model, which can contribute to the over-estimation of inorganic nitrates in GEOS-Chem."
 
Please note: seminar starts at 12:40 PM. Contact anne.handschy@colorado.edu for Zoom link.