CAMP: PD-FiTE Activity

PD-FiTE activity calculates aerosol-phase species activities using Taylor series to describe partial derivatives of mean activity coefficients for ternary solutions, as described in Topping et al. (2009) [Topping2009] . The mean binary activity coefficients for ion pairs are calculated according to eq. 15 in [Topping2009] . The values are then made available to aqueous-phase reactions during solving.

Input data for PDFiTE activity equations have the following format :

{ "camp-data" : [
 {
   "name" : "my PDFiTE activity",
   "type" : "SUB_MODEL_PDFITE",
   "gas-phase water" : "H2O",
   "aerosol-phase water" : "H2O_aq",
   "aerosol phase" : "my aero phase",
   "calculate for" : {
     "H-NO3" : {
       "interactions" : [
         {
           "ion pair" : "H-NO3",
           "min RH" : 0.0,
           "max RH" : 0.1,
           "B" : [ 0.925113 ]
         },
         {
           "ion pair" : "H-NO3",
           "min RH" : 0.1,
           "max RH" : 0.4,
           "B" : [ 0.12091, 13.497, -67.771, 144.01, -117.97 ]
         },
         {
           "ion pair" : "H-NO3",
           "min RH" : 0.4,
           "max RH" : 0.9,
           "B" : [ 1.3424, -0.8197, -0.52983, -0.37335 ]
         },
         {
           "ion pair" : "H-NO3",
           "min RH" : 0.9,
           "max RH" : 1.0,
           "B" : [ -0.3506505 ]
         },
         {
           "ion pair" : "NH4-NO3",
           "min RH" : 0.0,
           "max RH" : 0.1,
           "B" : [ -11.93308 ]
         },
         {
           "ion pair" : "NH4-NO3",
           "min RH" : 0.1,
           "max RH" : 0.99,
           "B" : [ -17.0372, 59.232, -86.312, 44.04 ]
         },
         {
           "ion pair" : "NH4-NO3",
           "min RH" : 0.99,
           "max RH" : 1.0,
           "B" : [ -0.2599432 ]
         }
       ]
     }
     ...
   }
 }
]}

The key-value pair aerosol phase is required to specify the aerosol phase for which to calculate activity coefficients. The key-value pairs gas-phase water and aerosol-phase water must also be present and specify the names for the water species in each phase. The final required key-value pair is calculated for, which should contain a set of ion pairs that activity coefficients will be calculated for.

The key names in this set must correspond to ion pairs that are present in the specified aerosol phase. The values must contain a key-value pair named interactions which includes an array of ion-pair interactions used to calculate equation 15 in [Topping2009] .

Each element in the interactions array must include an ion pair that exists in the specified aerosol phase, a min RH and max RH that specify the bounds for which the fitted curve is valid, and an array of B values that specify the polynomial coefficients B0, B1, B2, ... as in equation 19 in [Topping2009] . At least one polynomial coefficient must be present.

If at least one interaction with an ion pair is included, enough interactions with that ion pair must be included to cover the entire RH range (0.0–1.0). Interactions are assume to cover the range (minRH, maxRH], except for the lowest RH interaction, which covers th range [0.0, maxRH].

When the interacting ion pair is the same as the ion-pair for which the mean binary activity coefficient is being calculated, the interaction parameters are used to calculate \(ln(\gamma_A^0(\mathrm{RH}))\). Otherwise, the parameters are used to calculate \(\frac{d\ln{\gamma_A(\mathrm{RH})}}{d(N_{B,M}N_{B,x})}\).

For the above example, the following input data should be present:

{
  "name" : "H2O",
  "type" : "CHEM_SPEC",
  "phase" : "GAS",
},
{
  "name" : "H2O_aq",
  "type" : "CHEM_SPEC",
  "phase" : "AEROSOL",
},
{
  "name" : "H_p",
  "type" : "CHEM_SPEC",
  "phase" : "AEROSOL",
  "charge" : 1,
  "molecular weight [kg mol-1]" : 1.008
},
{
  "name" : "NH4_p",
  "type" : "CHEM_SPEC",
  "phase" : "AEROSOL",
  "charge" : 1,
  "molecular weight" : 18.04
},
{
  "name" : "NO3_m",
  "type" : "CHEM_SPEC",
  "phase" : "AEROSOL",
  "charge" : -1
  "molecular weight [kg mol-1]" : 62.0049
},
{
  "name" : "NH4-NO3",
  "type" : "CHEM_SPEC",
  "tracer type" : "ION_PAIR",
  "ions" : {
    "NH4_p" : {},
    "NO3_m" : {}
  }
},
{
  "name" : "H-NO3",
  "type" : "CHEM_SPEC",
  "tracer type" : "ION_PAIR",
  "ions" : {
    "H_p" : {},
    "NO3_m" : {}
  }
},
{
  "name" : "my aero phase",
  "type" : "AERO_PHASE",
  "species" : ["H_p", "NO3_m", "NH4_p", "NH4-NO3", "H-NO3", "H2O_aq"]
}