Photochemistry in biomass burning plumes and implications for tropospheric ozone over the tropical South Atlantic

Abstract

Abstract. Photochemistry occuring in biomass burning plumes over the tropical south Atlantic is analyzed using data collected during the Transport and Atmospheric Chemistry Near the Equator-Atlantic aircraft expedition conducted during the tropical dry season in September 1992 and a photochemical point model. Enhancement ratios (AY/AX, where A indicates the enhancement of a compound in the plume above the local background mixing ratio, Y are individual hydrocarbons, CO, 03, N20, HNO3, peroxyacetyl nitrate (PAN), CH20, acetone, H202, CH3OOH, HCOOH, CH3COOH or aerosols and X is CO or CO2) are reported as a function of plume age inferred from the progression of Anon-methane hydrocarbons/ACO enhancement ratios. Emission, formation, and loss of species in plumes can be diagnosed from progression of enhancement ratios from fresh to old plumes. 03 is produced in plumes over at least a 1 week period with mean AO3/ACO = 0.7 in old plumes. However, enhancement ratios in plumes can be influenced by changing background mixing ratios and by photochemical loss of CO. We estimate a downward correction of-20% in enhancement ratios in old plumes relative to ACO to correct for CO loss. In a case study of a large persistent biomass burning plume at 4 -km we found elevated concentrations of PAN in the fresh plume. The degradation of PAN helped maintain NOxmixing ratios in the plume where, over the course of a week, PAN was converted to HNO 3. Ozone production in the plume was limited by the availability of NOx, and because of the short lifetime of 03 at 4 -km, net ozone production in the plume was negligible. Within the region, the majority of 03 production takes place in air above median CO concentration, indicating that most 03 production occurs in plumes. Scaling up from the mean observed AO3/ACO in old plumes, we estimate a minimum regional 03 production of 17 x 101ømolecules 03 cm-2s -1. This 03 production rate is sufficient to fully explain the observed enhancement in tropospheric 03 over the tropical South Atlantic during the dry season.

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…Model studies have also found that limiting fire emissions to the boundary layer underestimates their influence in downwind regions (Cook et al, 2007;Freitas et al, 2007;Brioude et al, 2009;Chen et al, 2009;Jian and Fu, 2014). More effort is needed to evaluate model simulation of ozone production from biomass burning emissions, in particular during the evolution of fire plumes and over regions that are dominated by biomass burning emissions (e.g., Mauzerall et al, 1998;Alvardo et al, 2010;Singh et al, 2010;Arnold et al, 2015).…”

Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006

“…This enhancement ratio is in the range of that calculated in Pfister et al (2006), of approximately 0.26 ppbv/ppbv downwind of the 2004 fires. Mauzerall et al (1998) reported different O 3 / CO ratios depending on the age of the air mass ranging from 0.15 to 0.74 for fresh to aged plumes during the TRACE-A experiment. While CO is emitted from fires, O 3 is produced from the fire-emitted precursors as the air mass moves downstream.…”

Trace gas emissions from biomass burning inferred from aerosol optical depth

“…Another limitation is that the technique cannot be used if cloud cover inhibits the satellite AOD measurements. Also the smoke must dissipate out of the defined active region (where the fires are burning) before the trace-gas-to-AOD ratios change significantly as a result of the different atmospheric lifetimes of the various components: (hours for NH 3 and H 2 CO; days for the particulate matter that causes elevated AOD; 1 -2 months for CO and approximately 3 months for HCN) [Li et al, 2000;Mauzerall et al, 1998]. …”