Revisiting the Simulation of Intermediate Volatility Compounds (IVOCs) in Chemical Transport Models
STELLA EFTYCHIA MANAVI, Spyros Pandis,
University of Patras, FORTH Abstract Number: 272
Working Group: Aerosol Chemistry
AbstractIntermediate volatility organic compounds (IVOCs) are compounds with an effective saturation concentration (C
*) at 298 K between 10
3 and 10
6 μg m
-3 and they can be an important class of secondary organic aerosol (SOA) precursors. The first implementations of SOA formation from IVOCs (SOA-iv) in chemical transport models (CTMs) were done by using the volatility basis set (VBS), a highly parametrized scheme that oversimplifies the corresponding chemistry. In this study we develop a more detailed approach for simulating both IVOC chemistry and SOA-iv formation in CTMs, by treating IVOCs as lumped species that retain their chemical characteristics.
The new approach includes seven new lumped IVOC species; four representing larger alkanes, two representing polycyclic aromatic compounds (PAHs) and one representing intermediate-length aromatics. The simulation of their gas-phase chemistry was assumed to be equivalent to that of larger alkanes and aromatics but with appropriate parameters. Recent smog chamber experimental data were used to estimate the SOA yields of the additional IVOCs under both high and low-NO
x conditions. As most emissions inventories do not include IVOCs, we estimated their emissions starting from on-road transport using existing non-methane hydrocarbons emissions and source specific emissions factors of individual IVOCs.
The new emissions and the extended mechanism were introduced to PMCAMx, a three-dimensional CTM, and used to simulate the EUCAARI intensive period. Over the European domain, for the simulated month of May 2008, estimated IVOC emissions from on-road transport were 8 times higher than emissions used in previous VBS-applications. Moreover, the predicted averaged SOA-iv concentrations increased by 58% compared to those predicted by the VBS approach. The overall role and contributions of the various IVOCs to SOA formation were also explored. Unspeciated cyclic compounds were identified as the most important precursors contributing of 78% of the total SOA-iv mass. The major remaining uncertainties are summarized.