AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Constraining Ambient Organic Aerosol Chemical Aging Rates Using the Pegasos Campaign Measurements
ELENI KARNEZI, Benjamin Murphy, Spyros Pandis, Carnegie Mellon University
Abstract Number: 235 Working Group: Aerosol Chemistry
Abstract The effects of parameterization of chemical aging processes of atmospheric organic compounds on organic aerosol (OA) concentration and chemical composition are investigated by using the two-dimensional Volatility Basis Set (2D-VBS). The OA module simulates the primary and secondary OA mass as a function of volatility and oxygen to carbon ratio (O:C). The model is applied in the two different environments of the PEGASOS field campaigns during the summers of 2012 and 2013: the polluted Po Valley in Italy and the cleaner environment of Finland. The model predictions are compared with measurements both at the ground and aloft using a Zeppelin airship.
Different aging mechanisms were examined, taking into account various functionalization and fragmentation paths for biogenic and anthropogenic species. For the polluted Po Valley atmosphere in Italy, model predictions and measurements, both at the ground and aloft, suggested a relatively oxidized OA with little average diurnal variation. Simple functionalization schemes, more rigorous functionalization schemes accompanied with fragmentation varying in branching ratios, resulted in very different fractional attribution for OA to anthropogenic and biogenic sources. Total OA concentration and O:C were predicted within experimental error by a number of chemical aging schemes. In the Po Valley, anthropogenic SOA sources contributed between 15-25% of the total OA, while SOA from intermediate volatility compounds oxidation contributed between 20-35%. Biogenic SOA contributions varied from 15 to 45% depending on the modeling scheme. Other measurements were then used to further constrain the model.
The sensitivity of the model to the assumed vaporization enthalpy was also examined. The average OA and O:C diurnal variation and their vertical profiles showed a surprisingly low to modest sensitivity to this parameter independently for all aging schemes. This can be explained by the intricate interplay between the changes in partitioning of the semivolatile compounds and their gas-phase chemical aging reactions.