Simulation of ozone and its precursors over the southeast US with a high-resolution chemistry-climate model

We implemented a new isoprene oxidation mechanism [Mao et al., 2013] in a global chemistry-climate atmosphere model (GFDL AM3). This new mechanism includes recent updates on isoprene nitrates, isoprene epoxides, isomerization of peroxy radicals, and nighttime oxidation. The model simulations are conducted at high resolution (50 km x 50 km) with horizontal winds nudged to NCEP GFS data. The model is evaluated against the observations from the NOAA SENEX aircraft campaign (June 1st to July 15th 2013), and surface ozone measurements from the CASTNET network over the Southeast US. Preliminary results show significant improvement on the simulation of ozone and it precursors, compared to the standard version of AM3. In particular, regional mean bias of surface ozone relative to CASTNET observations has been reduced from + 12.9 ppbv to +3.3 ppbv over the Southeast US during 2000-2005. This improvement has been largely attributed to the new treatment of more specific isoprene nitrates (yield, reactivity and NOx recycling) and heterogeneous chemistry on HO2. Additional model evaluation will focus on the comparison of nighttime oxidants (including NO3 and N2O5 etc.) and SOA precursors (including glyoxal and organic acids etc.), measured from the NOAA P-3 aircraft during SENEX. We will further investigate the role of organic nitrates as a pathway for NOy export, particularly those formed from both daytime and nighttime isoprene oxidation. Reference Mao et al., Ozone and organic nitrates over the eastern United States: sensitivity to isoprene chemistry, submitted to J. Geophys. Res., 2013.