[gradsusr] unit conversion -

[Arlindo da Silva]

On Wed, May 21, 2014 at 6:48 PM, Júlio Barboza Chiquetto
<julio22 at gmail.com>wrote:

> Hello dear users,
> I have a tropospheric ozone time series in micrograms/m3, but I need to
> display it in ppm. I know it's a simple issue, but I don't have much
> experience in writing formulas in GrADS and I was wondering if other users
> might have already needed a script that does this unit conversion when
> displaying a variable.
>

Consult the wikipedia to learn about the part-per notation:

                    http://en.wikipedia.org/wiki/Parts-per_notation

Notice that ppm (parts per million) implies mass mixing ratio (ppmv is used
for volume mixing ratio). All you have to do is to divide your ozone
density time series by the air density which in principle depends on
pressure and temperature:

        rho = p / (RT)

If you express the air density in micrograms/m3 as your ozone density you
will have your mixing ratio in Kg/Kg. Mutiply it by 1,000,000 to have ppm.

    Arlindo

-- 
Arlindo da Silva
*dasilva at alum.mit.edu <dasilva at alum.mit.edu>*
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