Version 4.51 provides the following additional capabilities and features over previous versions:

• The 2005 version of the Carbon Bond gas-phase photochemical mechanism (CB05) has been implemented. CB05 was developed for use in EPA atmospheric modeling studies, and evaluated against smog chamber data from the Universities of North Carolina and California at Riverside. Ideally, you should use emission inventories specifically developed for CB05 speciation, but CB05 will work with existing CB4 inventories. CB05 optionally includes the same aerosol chemistry as CB4 Mechanism 4. CB05 chemistry may be solved with CMC, IEH, and LSODE chemistry solvers.
• The SOA chemistry scheme has been updated and now explicitly includes SOA formation from monoterpenes, sesquiterpenes, isoprene, toluenes, and xylenes. CG/SOA pairs 1 and 2 are formed from anthropogenic VOCs and CG/SOA pairs 3-7 are formed from biogenic VOCs. Polymerization slowly forms organic aerosol polymers called SOPA (anthropogenic) and SOPB (biogenic) which are no longer volatile. Emissions of SOA precursors must be provided separately from the emissions of oxidant precursors. ENVIRON provides an emission pre-processor to perform these conversions.
• Heterogeneous formulation of nitric acid from N2O5 on acid aerosol surfaces has been added when PM chemistry is run.
• Chemical Process Analysis (CPA) has been included for CB05.