The AS factor, as well asMI and BR (in PMF2),MI and RD (inME- 2) showed low initial mean contributions (0.14–0.28 mgm3)to PM1 as expected.Nevertheless, to enhance this aspect in PMF2, the Gkey index matrix (with values of 10) was applied to PM1 samples obtaining mean contributions gjk ¼ 0.It was noted that even if Gkey ¼= 5 was able to achieve the objective, several negative contributions were obtained.To avoid this, a stronger pulling (Gkey ¼ 10) was needed (PMF2 User’s Guide).In ME-2, gik (with I relative to PM1 rows and k relative to AS, MI and RD) were ‘‘pulled’’ toward zero by equation (7) with an uncertainty (saux)of 0.02 mgm3 , obtaining mean contributions between 0.07 and 0.27 mgm3