Cloud and Biomass Burning Effects on the Abundance of Ozone and Its Precursors over the Amazon Basin and Central and Southeast U.S.

Megan M. Bela, University of Colorado at Boulder


Gaseous precursors to ozone (O3) are emitted from biomass burning, anthropogenic, and biogenic sources, and transported to the upper troposphere (UT) by deep convection. O3 in the UT affects radiative forcing and at the surface negatively impacts human and ecosystem health. First, we analyze and simulate the first Amazon Basin-wide aircraft measurements of O3 during both the dry-to-wet and wet-to-dry transition seasons. Extremely low background values were observed in remote regions in both seasons and in all regions during the wet-to-dry transition, while elevated O3 was seen during the dry-to-wet transition to the east and south of Manaus, where biomass burning emissions of O3 precursors were present. WRF-Chem simulations represent observed O3 profiles in polluted conditions, but overestimate O3 in clean conditions, despite lacking the predominant NO source from soil. The model O3 production is very sensitive to both the O3 deposition velocities and the NOx emissions. Next, we compare scavenging efficiencies calculated from 2012 aircraft observations of inflow and outflow of storms that formed in Oklahoma, Alabama, and Colorado, and conduct high-resolution (dx <= 1 km) WRF-Chem simulations of the Oklahoma storm. We simulate the scavenging efficiencies (SEs) of several soluble gases within the error bars of the aircraft observations by assuming zero ice retention for CH2O and H2O2 and complete retention for CH3OOH and SO2. More scavenging of HNO3 and less removal of CH3OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Finally, we perform high-resolution WRF-Chem simulations of the Alabama storm and a mesoscale convective system over Arkansas/Missouri/Illinois/Mississippi. More removal of CH3OOH than CH2O is observed despite the lower solubility of CH3OOH, and higher ice retention fractions are required for CH3OOH (rf = 0.5-1) than CH2O and H2O2 (rf = 0-0.25) to simulate the higher observed SEs of CH3OOH.