Calculations of incremental secondary organic aerosol reactivity.

The incremental secondary organic aerosol reactivity (ISOAR) of a species j is defined as the relative incremental change in secondary organic aerosol (SOA) formed per relative incremental change in the amount of species jemitted. The California Institute of Technology three-dimensional air quality model is used in conjunction with the Caltech Atmospheric Chemistry Mechanism (CACM) and the Model to Predict the Multiphase Partitioning of Organics to calculate spatially and temporally averaged ISOAR values for the South Coast Air Basin of California (SoCAB). The base case SOA concentrations are derived for September 9, 1993. The South Coast Air Quality Management District of California provided emission and meteorological data. ISOAR values are calculated for the lumped surrogate compounds considered by CACM: isoprene, low-yield monoterpenes, high-yield monoterpenes, high-yield aromatics, etc. This work presents basin-wide ISOAR values determined through regression analysis. In addition, ISOAR values are reported at individual locations within the SoCAB. Modeled data are compared with ISOAR values calculated using smog chamber data. Results indicate that long-chain alkanes present the highest ISOAR. On the other hand, short-chain organics present the lowest ISOAR.