Sulfate aerosols

Fix for mass balance of HNO3 and NIT

Becky Alexander (beckya@atmos.washington.edu) wrote:

We need to make a change in sulfate_mod in order to have mass balance for HNO3 and NIT. Duncan Fairlie noticed the bug. There is a simple change:

In routine SEASALT_CHEM in sulfate_mod.f: In order to have mass balance, you need to change:

   !HNO3 lost [eq/timestep] converted back to [v/v/timestep]
   HNO3_ss = TITR_HNO3 * 0.063 * TCVV(IDTHNO3)/AD(I,J,L)

to:

   !HNO3 lost [eq/timestep] converted back to [v/v/timestep]
   HNO3_ss = HNO3_SSC * 0.063 * TCVV(IDTHNO3)/AD(I,J,L)

In my original code where I added isorropia and the new tracers, NITs and SO4s, the line above:

   !HNO3 lost [eq/timestep] converted back to [v/v/timestep]
   HNO3_ss = TITR_HNO3 * 0.063 * TCVV(IDTHNO3)/AD(I,J,L)

is appropriate as long as you also have PNIT (analogous to PNITs). PNIT is in my original code where I did all my mass balance testing. PNIT got dropped when going to the standard version. I don't recall dropping this, but my guess is that I decided it was redundant to have it when isorropia would just repartition HNO3 and NIT anyway according to thermodynamic equilibrium. But when dropping PNIT, you have to change TITR_HNO3 to HNO3_SSC in the above equation in order to achieve mass balance.

NOTE: This fix is slated for inclusion in GEOS-Chem v8-01-02.

--Bob Y. 09:32, 30 July 2008 (EDT)