A Comparison of Two Chemical Mechanisms Using Data from the Southern Oxidant and Aerosol Study

The Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS) is a 1-D column model of the physical and chemical processes occurring from the Earth’s surface to the top of the planetary boundary layer (PBL). In this study, we couple ACCESS with environmental data from the Southern Oxidant and Aerosol Study (SOAS) intensive field measurement campaign to simulate the chemical evolution of biogenic hydrocarbons above a forest canopy over two time periods: a four-day period from June 29-July 2, 2013 and a three-day period from June 21-23, 2013. We quantify the efficacy of the model by calculating R² values between SOAS chemical measurements and simulation results of isoprene, methyl vinyl ketone (MVK), methacrolein (MACR), α-pinene, and limonene. Two kinetic mechanisms, one from Browne et al. (2014) (RACM2+) and another from Schwantes et al. (2015) (CIT), were implemented in ACCESS and used in independent simulations to determine which mechanism better represents the SOAS data through daytime and nighttime periods. The results demonstrate that RACM2+ and CIT perform at comparable levels for simulating the evolution of isoprene, MVK, and MACR, but both differ substantially from measurements of α-pinene and limonene. The mechanisms perform equally well during both daytime and nighttime periods and thus, substantiated by our results, there is no strong justification for implementing one mechanism over the other.