Fig. 1 (a) The traditional van Krevelen diagram; (b) The modified van
Krevelen diagram; (c) The modified van Krevelen diagram associated with
NOSC; (d) The modified van Krevelen diagram associated with NOSC’. (In
(a) and (b), the red dots symbol the compounds with H/C<1.5,
the green dots are the compounds with 1.5≤H/C<2.0, and the
blue dots are the compounds with H/C≥2.0; NOSC: the nominal oxidation
state of carbon; NOSC’: the adjusted nominal oxidation state of carbon)
Fig. 1(c) and (d) demonstrate the modified van Krevelen diagrams
associated with NOSC and NOSC’, respectively. It can be seen that the
compounds with NOSC’>0 are slightly higher than those with
NOSC>0. Among the 2235 organics in the database,
approximately 21.3% with NOSC<0 in Fig. 1(c) change into that
with NOSC’≥0 in Fig. 1(d).
Generally, compounds with NOSC>0 are more oxidized and less
degradable, while those with NOSC<0 are more likely degraded.
When the impact of halogen is not considered, the oxidation state of
organic carbon is underestimated, and the degradation potential of
organic matter is overestimated.
Aromatic indexes
Three methods were used for calculating the aromaticity index, including
AI, AImod 4 and Xc.5 Of them, AI was
suggested for compounds in which oxygen was mainly present as carbonyl
functional groups; AImod was adjusted on the basis of AI when oxygen
could also be bound with π-bonds in carboxyl groups;12and Xc was aimed at aromatic compounds with long alkylation.5 Considering the contribution of halogen elements to
the saturation of organic matter, we adjusted these three indexes based
on the original equations and put forward them as AI’, AImod’ and Xc’,
respectively. The equations used to calculate the tree adjusted indexes
are as follows:
AI’ = (1+C-O-S-0.5(N+P+H+X))/(C-O-N-S-P)
AImod’ = (1+C-0.5O-S-0.5(N+P+H+X)/(C-0.5O-N-S-P)
Xc’ =
[3((1+C-0.5(H+X)+0.5(N+P)-(O+S))-2]/(1+C-0.5(H+X)+0.5(N+P)-(O+S))