Dear all,
I am looking at organic carbon after run COMBINE and I have few questions:
PM25_OC = AOCI * PM25AT + AOCJ * PM25AC
and
AOCI = APOCI + ASOCI
AOCJ = APOCJ + ASOCJ
and
ASOCIJ = ASOCI + ASOCJ
AOCIJ = APOCIJ + ASOCIJ
When I plot the diurnal cycle (average of the hours of a month simulation) of PM25_OC and ASOCIJ, sometimes the ASOCIJ is higher than PM25_OC.
So I am a little confused with these results since PM25_OC is the sum of primary and secondary organic carbon in I and J mode, it should have higher mass than ASOCIJ.
What am I missing?
Should I use PM25_OC as Organic carbon, or should I use the sum of AOCI + AOCJ (AOCIJ)?
Another question is about the values that aerosol species are being divided by, for example:
APOCI ,ugC m-3 ,ALVPO1I[1]/1.39 + ASVPO1I[1]/1.32 + ASVPO2I[1]/1.26 +APOCI[1]
What are these values 1.39, 1.32, 1.26?
Can the community help me understand it?
@Ben_Murphy @hogrefe.christian @wyat.appel
Thank you so much for your attention
Regards
Rizzieri
Hi Rizzieri,
could you please specify which CMAQ version and associated species definition file you are using as input to combine?
In general, the species starting with “PM25” have the size cutoffs from the aerosol diagnostic file applied to the Aitken (I) and accumulation (J) mode species to provide a model-based estimate of these species that is comparable to a measurement with an instrument that has an inlet to restrict sampling to particles with a diameter less than 2.5 um. These size cutoffs (PM25AT and PM25AC) provide the fraction of CMAQ I and J mode aerosols that have a diameter less than 2.5 um.
Since AOCI and AOCJ had these fractions applied for the calculation of PM25_OC but not ASOCIJ, there might indeed be cases where these ASOCIJ estimates are greater than PM25_OC, i.e. cases where there is more mass associated with secondary OC particles >2.5 um than there is with primary OC particles <= 2.5 um. To do an apples-to-apples comparison, you would want to apply the size cutoffs to either all or none of your calculations.
In my recollection, the fractions in the POCI calculations (as well as other OC calculations) represent the OM/OC ratios assumed by CMAQ for each of these species.
@Ben_Murphy, please add anything I may have missed or correct anything I got wrong.
1 Like
Dear @hogrefe.christian,
thank you so much for your explanation.
Regards
Rizzieri