Electroneutrality in acm_ae7_kmtbr

CMAQ
1

Hi everyone,

Now I am using CB6R3M_AE7_KMTBR gas-phase mechanism and acm_ae7_kmtbr aqueous chemistry routine to simulate the PH value in cloud water. I output the VAR array in aqchem_kmt.F90 to check whether the cloud water satisfies electroneutrality by the equation:

DIFF_ION = HPLUS + NH4 + NA + K + 2.0 * ( CA + MG + Mn) + 3.0 * FE
- 2.0*(CO3 - SO3 - SO4 ) - HCOO
- OH - HCO3 - HSO3 - NO3 - HSO4 - CL - BR
(the unit of ion concentration is mol/kg)
If the DIFF_ION is small enough, the cloud water is considered to satisfy electroneutrality.
But I find that DIFF_ION is up to 1.0D-06 mol/kg. Don’t the cloud water need to consider the electroneutrality in acm_ae7_kmtbr?

Thanks,
Lingyun

2

Hi, Lingyun-

In KMT cloud chemistry, the initial droplet [H+] is calculated when droplets form instantaneously on accumulation and coarse mode particles. This calculation is based on an assumption of electroneutrality at t= 0. After that time, H+ evolves dynamically for the duration of the cloud processing.

For more information, please refer to Fahey et al., 2017: GMD - A framework for expanding aqueous chemistry in the Community Multiscale Air Quality (CMAQ) model version 5.1

Kathleen

3

Hi Kathleen,

Thanks for your help! Your reply is very important for my work!

Best wishes,
Lingyun