Custom chemistry reaction rates to support T6 mechanism

[fvitt]

Custom (user defined) reaction rates needed for T6 chemistry mechanism development.

[cacraigucar]

@fvitt, @tilmes, @lkemmons - Are these mods needed for the runs that @cecilehannay will be making? @briandobbins

[fvitt]

@fvitt, @tilmes, @lkemmons - Are these mods needed for the runs that @cecilehannay will be making? @briandobbins

No. This is lower priority.

[jimmielin]

Thanks @fvitt. A minor comment and a suggestion to avoid repetition.

When discussing this PR with @cacraigucar we were not sure if this was intended to go in standalone, or if a T6 mechanism input file was intended be included as well?

[jimmielin]

should this be

Suggested change

	RONO2_yield(:) = scale_a * scale_b * ( fac_Ro(:) / (1 + fac_Ro(:)) )
	RONO2_yield(:) = scale_a * scale_b * ( fac_Ro(:) / (1._r8 + fac_Ro(:)) )

[jimmielin]

Here and below for RONO2_yield there is a lot of duplication, I wonder if something like

pure function rono2_yield( nCON, m, tinv ) result( yield )

    real(r8), intent(in) :: nCON     ! number of C, O and N atoms in R, excluding the peroxy group
    real(r8), intent(in) :: m(:)     ! total atm density (/cm^3)
    real(r8), intent(in) :: tinv(:)  ! 1/T (1/K)
    real(r8) :: yield(size(m))

    real(r8), parameter :: alpha = 2.0e-22_r8  ! low-pressure yield coefficient
    real(r8), parameter :: y_inf = 0.43_r8     ! high-pressure limit yield at 300 K
    real(r8), parameter :: m_inf = 8._r8       ! temperature exponent of the high-pressure limit
    real(r8), parameter :: fac_F = 0.41_r8     ! falloff broadening factor

    real(r8) :: fac_A(size(m)), fac_B(size(m)), fac_z(size(m)), fac_Ro(size(m))

    fac_A(:)  = alpha * exp( nCON ) * m(:)
    fac_B(:)  = y_inf * ( 300._r8 * tinv(:) )**m_inf
    fac_z(:)  = 1._r8 / ( 1._r8 + log10( fac_A(:) / fac_B(:) )**2 )
    fac_Ro(:) = ( fac_A(:) / ( 1._r8 + fac_A(:) / fac_B(:) ) ) * fac_F**fac_z(:)
    yield(:)  = fac_Ro(:) / ( 1._r8 + fac_Ro(:) )

  end function rono2_yield

so the blocks could be simplified as

!-----------------------------------------------------------------
!       ... C2H5O2 + NO, temperature/pressure dependent nitrate yield
!-----------------------------------------------------------------
       if( usr_C2H5O2_NOn_ndx > 0 ) then
          RONO2_yield(:) = rono2_yield( 2._r8, m(:,k), tinv(:) )
          call comp_exp( exp_fac, 365._r8*tinv, ncol )
          rxt(:,k,usr_C2H5O2_NOn_ndx) = 2.6e-12_r8 * exp_fac(:) * RONO2_yield(:)
          rxt(:,k,usr_C2H5O2_NOa_ndx) = 2.6e-12_r8 * exp_fac(:) * ( 1._r8 - RONO2_yield(:) )
       end if

[fvitt]

@lkemmons
Does this need to be part of the CESM3.0 release?