AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Constraining IEPOX and IEPOX-derived SOA Formation in CMAQ with the Use of SOAS Observations
PETROS VASILAKOS, Havala Pye, Yongtao Hu, Lu Xu, Hongyu Guo, Aikaterini Bougiatioti, Kate Cerully, Lindsay Yee, Allen H. Goldstein, Nga Lee Ng, Rodney J. Weber, Matthieu Riva, Jason Surratt, Abigail Koss, Alex Guenther, Joost de Gouw, Kevin Olson, Armistead G. Russell, Athanasios Nenes, Georgia Institute of Technology
Abstract Number: 495 Working Group: Aerosol Chemistry
Abstract Biogenic aerosol has important impacts on climate and air quality. There are large uncertainties, however, on the magnitude of their impacts, largely because of the incomplete understanding of their production mechanisms and interactions with health and climate.
The 2013 Southern Oxidant Aerosol Study (SOAS) campaign was aimed towards addressing major uncertainties around the formation of biogenic secondary organic aerosol (SOA) production and the synergistic role of anthropogenic pollutants. A major focus of SOAS was the SOA forming from IEPOX through acid-mediated reactions in the aerosol aqueous phase.
In this study, we utilize the rich SOAS dataset collected at the Centerville, Alabama site to evaluate and constrain the mechanisms of IEPOX-mediated SOA (Pye et al., 2013) implemented in the Community Multi-scale Air Quality (CMAQ) model. For this, forecasted meteorology from the Weather Research and Forecasting (WRF) model specific for the SOAS period was used to drive WRF. Biogenic emissions and land use were provided from the Biogenic Emissions Inventory System version 3 (BEIS3), adjusted to match the observations of isoprene collected during the SOAS period. Both ground and aloft measurements were used for comparison.
A wide range of sensitivity studies were carried out to understand the main sources of uncertainty in all the steps of conversion of isoprene, through the pathway of isoprene epoxydiols (IEPOX) to SOA. Using the available observations of key intermediate species observed (isoprene, IEPOX, ISOPOOH, MVK, MACR, methyltetrols, organosulfates and others), adjustments were made in many of the highly uncertain reaction rate constants, partitioning coefficients and deposition coefficients of the relevant species. The Henry’s law coefficient for IEPOX in water was found to be one of the most important of parameters that control aqueous isoprene OA products SOA, while the simulations reproduce the diurnal trends of all measured species available for evaluation.
Finally, the simulations suggest a strong correlation of isoprene OA with sulfate, and almost no correlation with acidity or liquid water content, consistent with correlations derived from the SOAS data set. The underlying reasons for this behavior are identified and the implications are discussed for the SE US.