How to modify the rate constant of N2O5 heterogeneous reaction in CMAQ

CMAQ Chemistry and Aerosols
1

Hi All,
I am trying to modify the rate constant of N2O5 heterogeneous reaction in mech.def in CMAQ5.3, but I am confused about its rate constant. In

<HET_N2O5IJ> N2O5 = HNO3 + H2NO3PIJ # 1.0 ~ <HETERO_N2O5IJ> ,

I want to modify its reaction rate constant according to Equation k=(ω1∙γ∙Sa)/4,where ω1 is the average molecular speed of N2O5 (m s-1)，γ is the uptake coefficient of N2O5, and Sa (m2 m-3) is the aerosol surface area concentration, How can I modify the rate constant , where <HETERO_N2O5IJ> is a label or a specific parameter and What does “~” mean.
Can anyone give me some advice?
Thanks!

2

Dear Xue,

The symbol “~” indicates that it is a heterogeneous reaction. All heterogeneous reactions in CMAQ employ k=(ω1∙γ∙Sa)/4 for calculating first order rate constant. For the heterogeneous hydrolysis of N2O5 (<HETERO_N2O5IJ>), k and other related parameters (ω1, γ, Sa) are defined in AEROSOL_CHEMISTRY.F. It contains a function [FUNCTION N2O5_GAMMA( TEMP, RH, GPARAM )] which calculates γ as a function of temperature, relative humidity, and other parameters.

Thanks,
Sarwar

2 Likes
3

Dear Sarwar,

Thank you for your reply, I tried to modify some parameters in GPARAM=4,5 and found no difference in the simulation results. So I want to know how GPARAM is determined or calculated in the pattern and I haven’t found GPARAM in other code. By default, is N2O5_GAMMA calculated with GPARAM = 4 or 5 parameterization? I want to select both GPARAM=4, GPARAM=5 parts to calculate N2O5_GAMMA, how should I set it?

Thanks,
Xue

4

Please change the line
from:
GAMMA = N2O5_GAMMA( AIRTEMP, AIRRH, 0 )

to:
GAMMA = N2O5_GAMMA( AIRTEMP, AIRRH, 4 )

Please recompile and try. It will use GPARAM=4 for fine-mode. It uses GPARAM=5 for coarse-mode by default.