SIMPOL.1

[Aariq]

I'm trying to understand exactly how the SIMPOL.1 formula is implemented in volcalc and wondering if someone can help confirm what I've figured out so far.

This bit of code is the $\sum_k\nu_{k,i}b_k(T)$ part in Eq. 4 of Pankow & Asher:

volcalc/R/calc_vol.R

Lines 69 to 100 in e1d2046

	log_Sum =
	(-0.438 * carbons) %+%
	(-0.935 * ketones) %+%
	(-1.35 * aldehydes) %+%
	(-2.23 * hydroxyl_groups) %+%
	(-3.58 * carbox_acids) %+%
	(-0.368 * peroxide) %+%
	(-2.48 * hydroperoxide) %+%
	(-2.23 * nitrate) %+%
	(-2.15 * nitro) %+%
	(-0.105 * carbon_dbl_bonds) %+%
	(-0.0104 * rings) %+%
	(-0.675 * rings_aromatic) %+%
	(-2.14 * phenol) %+%
	(0.0432 * nitrophenol) %+%
	(-2.67 * nitroester) %+%
	(-1.20 * ester) %+%
	(-0.718 * ether) %+%
	(-0.683 * ether_alicyclic) %+%
	(-1.03 * ether_aromatic) %+%
	(-1.03 * amine_primary) %+%
	(-0.849 * amine_secondary) %+%
	(-0.608 * amine_tertiary) %+%
	(-1.61 * amine_aromatic) %+%
	(-2.23 * amines) %+%
	(-2.23 * amides) %+%
	(-2.23 * phosphoric_acid) %+%
	(-2.23 * phosphoric_ester) %+%
	(-2.23 * sulfate) %+%
	(-2.23 * sulfonate) %+%
	(-2.23 * thiol) %+%
	(-1.20 * carbothioester),

The constant 1.79 is the $b_0(T)$ in Eq 4.

Adding the constant and the log_Sum variable gives $\textrm{log}{10} P_{\textrm{L},i}^\circ(T)$ in Pankown & Asher 2008, I think.

But I'm not sure I understand where the log_alpha variable relates to the equations in the Pankow & Asher paper and why volatility is volatility = log_alpha + constant + log_Sum

[Aariq]

Ok, got it now thanks to the very readable draft manuscript. Based on what I understand, SIMPOL.1 calculates $\mathrm{log_{10}} P_{\mathrm{L},i}^\circ(T) = \sum_k\nu_{k,i}b_k(T)$ which is the estimated liquid vapor pressure of the compound (constant + log_Sum in original volcalc code). Meredith et al. add to that by calculating a measure of relative volatility, $\textrm{RVI} = \mathrm{log_{10}}C^* = \mathrm{log_{10}}(PM/RT)$ which can also be written $\mathrm{log_{10}}P + \mathrm{log_{10}}(M/RT)$ which is what is happening here: https://github.com/Meredith-Lab/volcalc/blob/9e7250a9462224659766546efc1937236c07908b/R/calc_vol.R#L101C12-L101C12