Table 2.  Changes Made to the Original Version of the MPMPO During This Worka  		
Change	Adaptations Made	Reasons/Notes
1	general reclassification of lumped surrogate groups	Hydrophobicity and hydrophilicity are no longer used as a means by which to group partitioning compounds.  See Figure 1.
2	replacement of original group 10 with a ring-retaining biogenic category that has a different surrogate species	This adaptation is based on change 1.
3	remove AP7 from original group number 5 and move to the new ring-retaining biogenic group	This adaptation is based on change 2.
4	remove AP8, UR5, and UR6 from original group number 10 and move to the new ring-retaining biogenic group	These adaptations are based on change 2.
5	move UR7 from original group number 10 to the nondissociative biogenic ring-fragmentation product group (group number 5)	This adaptation is based on change 2.
6	move UR8 from original group number 10 to the dissociative biogenic ring-fragmentation product group (group number 4)	This adaptation is based on change 2.
7	move UR26 from the aliphatic anthropogenic hydrophobic group (original group 9) to the dissociative aromatic ring-fragmentation product group (group 2)	This adaptation is based on change 1 and also is made because UR26 is significantly more volatile than the other products in original group 9.
8	remove PAN8, RPR3, and RPR4 from consideration for partitioning	Inclusion of these species caused a temporal peak and subsequent decline in SOA simulations, which was not observed in the chamber experiments being simulated [Odum et al., 1996, 1997a, 1997b; Hoffmann et al., 1997; Griffin et al., 1999].
9	remove UR22 from consideration for partitioning	The vapor pressure of this species was reevaluated using a structure-activity relationship and deemed too high to participate realistically in the partitioning process.
10	adjustment of vapor pressures of surrogate compounds	Vapor pressures were adjusted to avoid underprediction of SOA, to attempt to account for the effects of particle phase chemistry, and to match average vapor pressures estimated from the chamber experiments being simulated [Odum et al., 1996, 1997a, 1997b; Hoffmann et al., 1997; Griffin et al., 1999].
aProduct descriptions and group numbers refer to those presented by Griffin et al. [2002a, 2003], Pun et al. [2002], and Figure 1.