CMAQv5.3 ISAM - difference with reference data

Hi Dr. Napelenok et al.,

I enjoyed the 10/8/2019 CMAQv5.3 webinar, Dr. Napelenok mentioned “sum of target species concentrations in ISAM should be very close to the concentration of this species from basic CMAQ output”. I then tested CMAQv5.3 ISAM with benchmark

TAG CLASSES     |SULFATE, OZONE

!!! The following are source definition text blocks in the format:
!!!   TAG NAME        |Three character text string
!!!   REGION(S)       |Keyword EVERYWHERE or variable names from the region file (multiple regions need to be comma delimited)
!!!   FILENAME(S)     |Emissions labels (multiple labels need to be comma delimited)


TAG NAME        |GR1
REGION(S)       |EVERYWHERE
EMIS STREAM(S)  |GRIDDED_EMIS

ENDLIST eof

I then summed up O3_OTHER O3_ICON O3_BCON O3_GR1 and compared the data with O3 from original CMAQv5.3 output. scatter plot and domain average (total_O3_ISAM - O3_orig) look fine
scatter
bar difference

However, I saw some large differences in certain grid-cells
absolute difference (up to 16 ppb in some grids)

percent difference (up to 267%)

Are these large differences normal for CMAQv5.3 ISAM? BTW, I’ve checked my benchmark run with reference data without ISAM, and even in the two-weeks simulation the difference < 0.5%.

Thank you

Joey