Tab::Chemistry
Photochemistry
The photochemistry is calculated from the actinic flux (short wave radiation), quantum yields and the cross sections of the reactions. The model needs the spectral irradiance, but most often just a total sum over a wavelength range is available. The model has a couple of spectra, which are used to calculate the irradiance at 5 nm intervals. The default spectrum (also used if no spectrum is defined), is based on a model estimation of the clear sky spectrum at sea level. This spectrum ranges from 280 nm to 5 µm, and has approximately 28% of the energy at the range of 280-580 nm. The spectrum is normalized so that the integral between 300-4800 nm equals 1, as this is the typical range of the pyranometers used to measure the global shortwave radiation. If the instrument has a different range, it can be specified in the Input shortwave measurement range (only available when glob_swr_distr.txt is used, or no spectral file is defined).
The format of the spectral file
the Spectral file is typically just one line containing space-separated weights of the spectrum, in 5 nm intervals. The total integral of the spectrum in the range of the SW_RADIATION should be 1 (meaning that sum(si)×5 ~ 1). If time-dependent spectral data is available, this can be given in a format where each line is the spectrum in time t, (where time is in the 1st column, expressed in same units as in the ENV and MCM files). The first row can be (and should be) a comment, starting with the "hash" symbol:
#0 280 285 290 295 ... 695 0.0 1.418e-10 1.418e-10 5.557e-09 6.845e-07 ... 1.187e-03 0.1 1.418e-09 1.418e-10 6.557e-09 7.845e-07 ... 1.146e-03 0.2 1.418e-08 1.918e-10 7.557e-09 8.845e-07 ... 1.258e-03
Note that the file is always assumed to contain the values for 280-695 nm, leading to integral of 280-700 nm. Any exceeding columns are ignored. The comments are not used to parse the wavelength information, they are just for the modeller's benefit.
SW_RADIATION is Actinic Flux
If this option is on, the parametric calculation of actinic flux is omitted and the product of the spectrum and SW_RADIATION is used directly as actinic flux [W/m² nm]. The figure below illustrates how short wave radiation is handled.
Location settings
Surface albedoThis value is used to calculate the radion that gets reflected from the surface, and affects the available actinic flux. The effect of albedo and solar angle to the actinic flux becomes evident from the figure below, which shows the factor used to multiply irradiation (obtained earlier with the spectral data and SW_RADIATION) to calculate actinic flux:
Latitude
Latitude of the simulation location. Affects the calculation of Solar Zenith Angle if the case identifier is using Date. With Index this option has no effect and they are not available. Positive values = North.
Longitude
Longitude of the simulation location. Currently is not used but this information is saved for consistency. Positive values=West.
Switch chemistry
Switch chemistry schemes is explained here.
Chemistry tools
Create KPP definitions is explained here.
Create Vapour file is explained here.
Miscellanious options
Replace any H2SO4 input with modelled
By default H2SO4 which could be used in ACDC is not coming from the chemistry scheme, but from the input variables. If the chemistry can simulate H2SO4 production, checking this option will use that value.
Custom functions
Warning, this is an advanced option. If you know your way around Fortran, here you can add your own functions (recompile after editing). The functions will be run after the chemistry module is finished, provided you have the check box Use custom function selected. You can operate with the CH_GAS vector (and all the global variables of the model, defined in constants.f90 and input.f90) that contains all the gas concentrations from the chemistry module. You might have to save the output on a separate output file as there are limited possibilities to inject any new data back to the model.