Dear Prasanta,
I relay the response from Simon, who is quoting another colleague at the Met Office:
Quote:
Given what the observational data are, it looks like STASH code 00-101 ("SO2 MASS MIXING RATIO AFTER TSTEP") from the lowest model layer would be the obvious thing to compare against.
Notes:
(1) As the name says, this is mass mixing ratio, so would need to be multiplied by air density to convert to kg/m3 (and then to mg/m3).
(2) As with all sulphur-cycle variables, this one is mass mixing ratio of S-in-SO2, i.e. only the mass of the sulphur atom is considered. If the observations are of the mass of SO2 (which is likely), then as well as multiplying by air density, 00-101 will need to be multplied by the ratio of the atomic weights of SO2 and S (which, conveniently enough, in this case is just a multiplication by 2: S=32, O=16, so SO2/S = (32+16+16)/32 = 2)
Thank you,
David on behalf of Simon T and the PRECIS team