Sensitivity of tropospheric ozone to chemical kinetic uncertainties in air masses influenced by anthropogenic and biomass burning emissions

Abstract

We use a Lagrangian chemical transport model with a Monte Carlo approach to determine impacts of kinetic rate uncertainties on simulated concentrations of ozone, NOy and OH in a high‐altitude biomass burning plume and a low‐level industrial pollution plume undergoing long‐range transport. Uncertainties in kinetic rate constants yield 10–12 ppbv (5th to 95th percentile) uncertainty in the ozone concentration, dominated by reactions that cycle NO and NO2, control NOx conversion to NOy reservoir species, and key reactions contributing to O3 loss (O(1D) + H2O, HO2 + O3). Our results imply that better understanding of the peroxyacetylnitrate (PAN) thermal decomposition constant is key to predicting large‐scale O3 production from fire emissions and uncertainty in the reaction of NO + O3 at low temperatures is particularly important for both the anthropogenic and biomass burning plumes. The highlighted reactions serve as a useful template for targeting new laboratory experiments aimed at reducing uncertainties in our understanding of tropospheric O3 photochemistry.

Photochemical box modelling of volcanic SO<sub>2</sub> oxidation: isotopic constraints

“…As a result, the O-MIF of deposited sulfate O-MIF is expected to depend strongly on the amount of SO 2 injected, via the dependency of OH isotopic signature on SO 2 concentration. Since volcanic SO 2 usually reaches ppmv levels during the first stages of volcanic plume (Roberts et al, 2009(Roberts et al, , 2012Oppenheimer et al, 2013;Voigt et al, 2014), our results suggest that volcanic sulfate should carry positive O-MIF anomalies that exceed isotopic measurement uncertainties (≈ 0.1 ‰). This is not supported by atmospheric measurements of volcanic sulfate isotopic composition which mostly lie close to zero within measurement uncertainties.…”

“…During the first stages of plume development concentrations of SO 2 in the range of 10-50 ppmv can be reached right in proximity of volcanic vents (Aiuppa et al, 2005(Aiuppa et al, , 2006aRoberts et al, 2012), while concentrations in the range of 0.1-1 ppmv can be found in aged plumes at longer distances from points of emissions (Delmelle, 2003;Carn et al, 2011). These results are confirmed by modelling simulations which can constrain volcanic emissions by accounting for quick dilution after plume ejection from the vent (Gerlach, 2004;Aiuppa et al, 2007;Roberts et al, 2009). Consequently, based on atmospheric simulations and on in situ measurements, the SO 2 concentration is set to 1.0 ppmv in the standard case, and is varied from 0.1 to 10 ppmv in the sensitivity simulations.…”

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

“…The rate constants J NO2 and k 1 involved in NO‐NO 2 ‐O 3 photochemical cycling have relatively small uncertainties in kinetic assessments, and even then are found to be major sources of uncertainty in model simulations of tropospheric oxidants (Bergin et al, ; Newsome & Evans, ; Ridley et al, ; Vuilleumier et al, ). When the low‐temperature NO + O 3 reaction rate constant (1.4 k 1 ) and NO 2 photolysis frequency ( J NO2 −20%) are adjusted in GEOS‐Chem within these uncertainties to improve the simulation of the NO/NO 2 ratio in the SEAC 4 RS upper tropospheric data, we find that simulated ozone decreases by 7 ppb at 8–12 km altitude.…”

“…On a global scale, NO x increases the concentration of tropospheric oxidants (ozone and OH) with complicated implications for climate forcing (Wild et al, ). NO x in the upper troposphere and the associated cycling between NO and NO 2 are of particular importance for production of tropospheric ozone and OH (Murray et al, ; Newsome & Evans, ; Ridley et al, ). Recent observations from the SEAC 4 RS aircraft campaign over the southeast United States in August–September 2013 show much lower NO/NO 2 ratios in the upper troposphere than expected from models (Travis et al, ).…”

Photochemical box-modelling of volcanic SO<sub>2</sub> oxidation: isotopic constraints

“…Since most isotopic measurements of volcanic sulphate do not indicate the presence of O-MIF, the OH oxidation pathway cannot be the dominant channel for volcanic sulphur. Nonetheless, uncertainties on the rate constant of the isotopic exchange between OH and H 2 O(Dubey et al, 1997) and, more generally, on photochemical modelling are 5 substantial(Ridley et al, 2017). It would be useful for this unexpected model predictions of O-MIF in OH, and hence volcanic sulphate produced in gas phase, to be tested in a controlled environment, ideally laboratory experiments of SO 2 oxidation with a well constrained OH chemical budged, notably the loss processes.…”