# Reaction Coefficients in Aging with Func. and Frag

Hello all,

I am learning about aging POA with func. and Frag. I read paper Murphy et al. (2017), but still cannot understand well how to calculate the coefficients in reaction equations in CMAQ5.2:
! Aging with Func. and Frag. (Donahue et al. 2012)
<POA_AGE1> VLVPO1 + OH = OH
+ 0.4857 * VLVPO1 + 0.0062 * VSVPO1
+ 0.0025 * VSVPO2 + 0.0026 * VSVPO3
+ 0.0023 * VIVPO1 + 0.2944 * VLVOO1
+ 0.2021 * VLVOO2 + 0.0019 * VSVOO2
+ 0.0023 * VSVOO3 #4.0e-11;
<POA_AGE2> VSVPO1 + OH = OH
+ 0.3003 * VLVPO1 + 0.2862 * VSVPO1
+ 0.0041 * VSVPO2 + 0.0035 * VSVPO3
+ 0.2239 * VLVOO1 + 0.1820 * VLVOO2 #4.0e-11;
<POA_AGE3> VSVPO2 + OH = OH
+ 0.3856 * VLVPO1 + 0.0950 * VSVPO1
+ 0.1373 * VSVPO2 + 0.0005 * VSVPO3
+ 0.2051 * VLVOO1 + 0.1764 * VLVOO2 #4.0e-11;
<POA_AGE4> VSVPO3 + OH = OH
+ 0.2181 * VLVPO1 + 0.3063 * VSVPO1
+ 0.0153 * VSVPO2 + 0.1043 * VSVPO3
+ 0.1893 * VLVOO1 + 0.1668 * VLVOO2 #4.0e-11;
<POA_AGE5> VIVPO1 + OH = OH
+ 0.2412 * VLVPO1 + 0.2089 * VSVPO1
+ 0.3000 * VSVPO2 + 0.2028 * VLVOO1
+ 0.0471 * VLVOO2 #4.0e-11;
<POA_AGE6> VLVOO1 + OH = OH
+ 0.6664 * VLVOO1 + 0.0143 * VLVOO2
+ 0.0123 * VSVOO1 + 0.1239 * VSVOO2
+ 0.1831 * VSVOO3 #4.0e-11;
<POA_AGE7> VLVOO2 + OH = OH
+ 0.2858 * VLVOO1 + 0.3931 * VLVOO2
+ 0.0139 * VSVOO1 + 0.1027 * VSVOO2
+ 0.2045 * VSVOO3 #4.0e-11;
<POA_AGE8> VSVOO1 + OH = OH
+ 0.3303 * VLVOO1 + 0.2272 * VLVOO2
+ 0.2607 * VSVOO1 + 0.0702 * VSVOO2
+ 0.1116 * VSVOO3 #4.0e-11;
<POA_AGE9> VSVOO2 + OH = OH
+ 0.3444 * VLVOO1 + 0.2749 * VLVOO2
+ 0.0491 * VSVOO1 + 0.2577 * VSVOO2
+ 0.0739 * VSVOO3 #4.0e-11;
<POA_AGE10> VSVOO3 + OH = OH
+ 0.3886 * VLVOO1 + 0.2421 * VLVOO2
+ 0.0640 * VSVOO1 + 0.0385 * VSVOO2
+ 0.2667 * VSVOO3 #4.0e-11;

Hello,

The calculation of these stoichiometric coefficients is quite complicated and dependent on a number of factors including the chemical properties of the model species (i.e. where they fall in the C* vs. O:C space) and what assumptions are made about the aging process, such as the fragmentation branching ratio formulation, the probability of the number of oxygens added, and the probability of the reduction in C* for every oxidation step. These last two aspects are summed up in the ‘aging kernel’, which is described in the series of papers by Donahue and co-authors (references below).

A second layer of modification is needed for this particular implementation (in CMAQv5.2). The products that are created by the aging kernel need to be represented in terms of linear combinations of existing model species to conserve carbon mass. This is done with a inverse distance weighting approach that was optimized to give performance similar to other existing aging models like Koo et al. (2014).

The third layer of calculation involves converting all coefficients from a carbon number basis, which is how they are derived in the steps above, to a molar basis using the carbon number of each model species.

If you’re interested in algorithms for calculating 2D-VBS coefficients, there is code published with Chuang et al. (2016) in the supplement.

Best regards,
Ben

References:
Donahue et al. (2011): ACP - A two-dimensional volatility basis set: 1. organic-aerosol mixing thermodynamics
Donahue et al. (2012): ACP - A two-dimensional volatility basis set – Part 2: Diagnostics of organic-aerosol evolution
Chuang et al. (2016): ACP - A two-dimensional volatility basis set – Part 3: Prognostic modeling and NOx dependence

1 Like

Hi Ben,

Thank you very much for this detailed and helpful information!

Best