How to add photolysis frequency

[morshedahmed17]

Hello,

I need to add the photolysis frequency of some nitrophenol compounds which are not included in the MCM. And I am not sure how and where in the mechanism file to add that. Can you please help me with that?

[rs028]

Hi @morshedahmed17 the MCM uses a parametrization to calculate photolysis rates. This is explained in the MCM protocol (and in the AtChem2 manual). There are 61 j-values (see http://mcm.york.ac.uk/parameters/photolysis_param.htt) but not all of them are used in the full MCM, so you can repurpose one of the unused j-values for your objectives. You can do it in two ways: you scale with JFAC paramater the calculated value of the j-value you are repurposing or you change the l, m, n parameters of that j-value to fit your photolysis rate. The first method is easy but not very accurate, the second takes a bit more time but should give you better results. Hope this helps.

[morshedahmed17]

Hello @rs028, Thanks for your email. I think I understand what you said but not sure how to execute it. I am providing you with an example. "The photolysis of NP (and other nitrated phenols) is not included in the MCM v3.2. We added the photolysis frequency of NP (1.4% of photolysis frequency of NO2) into the MCM v3.2." (Yuan et al., 2016) Can you please let me know exactly where (photolysisConstant.config?) and what format should I write to add the above photolysis frequency? Note: My photolysisConstant.Config and photolysisConstrained.config files are empty.

[rs028]

@morshedahmed17 If I understand correctly what you are trying to do, the easiest implementation would be something like this. In the mechanism file (the .fac file):

% J<4>*0.014  :  NP = A + B ;

where A and B are the products of NP's photolysis.

The files photolysisConstant.config and photolysisConstrained.config should remain empty if your photolysis rates are calculated. You need them only if your photolysis rates are constant or constrained to measured values, respectively. See section 3.5 of the manual and figure 3.1 to understand how this works.

[morshedahmed17]

@rs028 Thanks for your reply. It worked.

Currently, I am stuck on a different issue. How can I add physical loss rate data to AtChem2?

[rs028]

The easiest way would be to represent them as "chemical reactions". See the manual section 3.1.1 for a quick explanation.

[rs028]

@morshedahmed17 have you solved this problem?

[morshedahmed17]

@rs028 the issue is solved. However, I recently encountered another issue related to the photolysis frequency of J(NO2). I want to constrain the measured J(NO2). During the night the J(NO2) values are zero but the model does not accept zero values. Any idea how to resolve this issue?

[rs028]

Great, then I am going to close this issue.

The easiest way for this new problem is to set the nocturnal values in the constraint file to a very small number, such as 1e-100 or something like that. I would then check the output of J4 (in photolysisRates.output) to make sure that it is okay.