# NOTE: For some of the vapour pressure values, you need to perform a boiling point estimation first
# It is therefore wise to do this initially
# 2a) Boiling points [(K)]
boiling_point_dict = collections.defaultdict(lambda: collections.defaultdict())
for smiles in smiles_array:
boiling_point_dict[smiles][
'joback_and_reid'] = boiling_points.joback_and_reid(
Pybel_object_dict[smiles])
boiling_point_dict[smiles][
'stein_and_brown'] = boiling_points.stein_and_brown(
Pybel_object_dict[smiles])
boiling_point_dict[smiles]['nannoolal'] = boiling_points.nannoolal(
Pybel_object_dict[smiles])
# 2b) Vapour pressures [log10 (atm) at a specific temperature]
# For those vapour pressure methods that require a boiling point, we have 3D dictionaries
vapour_pressure_dict_BP = collections.defaultdict(
lambda: collections.defaultdict(lambda: collections.defaultdict()))
vapour_pressure_dict = collections.defaultdict(
lambda: collections.defaultdict())
temperature = 298.15
for smiles in smiles_array:
vapour_pressure_dict_BP[smiles]['VP_Nannoolal'][
'BP_Nannoolal'] = vapour_pressures.nannoolal(
Pybel_object_dict[smiles], temperature,
def Pure_component1(num_species, species_dict, species_dict2array,
Pybel_object_dict, SMILES_dict, temp, vp_method, bp_method,
critical_method, density_method, ignore_vp, vp_cutoff):
""" This function calculates properties that dictate gas-to-particle partitioning
inputs:
• num_species - number of compounds used in the calculations
• species_dict - dict holding names of all compounds
• species_dict2array - dict that mapes compound name to array index
• Pybel_object_dict - dict holding all Pybel objects of each compound [used in UManSysProp]
• SMILES_dict - dict containing all SMILES strings of each compound
• temp - temperature [K]
• vp_method - choice of vapour pressure method [see calling function and/or UManSysProp]
• bp_method - choice of boiling point method [see calling function and/or UManSysProp]
• critical_method - choice of criticl property method [see calling function and/or UManSysProp]
• density_method - choice of density method [see calling function and/or UManSysProp]
• ignore_vp - flag to ignore compounds with vapour pressure above a defined value given by 'vp_cutoff'
• vp_cutoff - log10 value of vapour pressure above which the odel will ignore partitioning
outputs:
• return_dict['y_density_array']=y_density_array - density of each condensing compound
• return_dict['y_mw']=y_mw - molecular weight of each condensing compound
• return_dict['sat_vp']=sat_vp - saturation vapour pressure of each condensing compound
• return_dict['Delta_H']=Delta_H - enthalpy of vapourisation of each condensing compound
• return_dict['Latent_heat_gas']=Latent_heat_gas - latent hear of condensation of each condensing compound
• return_dict['ignore_index']=ignore_index - array that holds information on which compounds to ignore for partitioning
• return_dict['ignore_index_fortran']=ignore_index_fortran - dense array that holds information on which compounds to ignore for partitioning in Fortran functions
• return_dict['include_index']=include_index - array that holds information on which compounds to include for partitioning
"""
y_density_array = [1000.0] * num_species
y_mw = [200.0] * num_species
o_c = [0.0] * num_species
h_c = [0.0] * num_species
sat_vp = [100.0] * num_species
sat_vp_org = dict(
) #Recorded seperately and will not include the extension for water. This is used for any checks with equilibrium partitioning predictions
y_gas = [0.0] * num_species
species_step = 0
ignore_index = [
] #Append to this to identify any compounds that do not have automated calculation of properties. OR are species that will be ignored in partitioning
include_index = []
include_dict = dict()
ignore_index_fortran = numpy.zeros((num_species), )
print("Calculating component properties using UManSysProp")
# Which boiling point method has been chosen
boiling_point = {
'joback_and_reid': boiling_points.joback_and_reid,
'stein_and_brown': boiling_points.stein_and_brown,
'nannoolal': boiling_points.nannoolal,
}[bp_method]
vapour_pressure = {
'nannoolal': vapour_pressures.nannoolal,
'myrdal_and_yalkowsky': vapour_pressures.myrdal_and_yalkowsky,
# Evaporation doesn't use boiling point
'evaporation': lambda c, t, b: vapour_pressures.evaporation(c, t),
}[vp_method]
# Which density method has been chosen
critical_property = {
'nannoolal': critical_properties.nannoolal,
'joback_and_reid': critical_properties.joback_and_reid,
}[critical_method]
liquid_density = {
'girolami': lambda c, t, p: liquid_densities.girolami(c),
'schroeder': liquid_densities.schroeder,
'le_bas': liquid_densities.le_bas,
'tyn_and_calus': liquid_densities.tyn_and_calus,
}[density_method]
for compound in species_dict.values():
if compound in SMILES_dict.keys():
# Calculate a boiling point with Nanoolal for density methods
#pdb.set_trace()
b1 = boiling_points.nannoolal(
Pybel_object_dict[SMILES_dict[compound]])
y_density_array[species_dict2array[compound]] = liquid_density(
Pybel_object_dict[SMILES_dict[compound]], temp,
critical_property(Pybel_object_dict[SMILES_dict[compound]],
b1)) * 1.0E3
#y_density_array[species_dict2array[compound]]=(liquid_densities.girolami(Pybel_object_dict[SMILES_dict[compound]])*1.0E3) #Convert from g/cc to kg/m3
#y_density_array.append(1400.0)
y_mw[species_dict2array[compound]] = (
Pybel_object_dict[SMILES_dict[compound]].molwt)
#In the following you will need to select which vapour pressure method you like.
groups_dict = groups.composition(
Pybel_object_dict[SMILES_dict[compound]])
o_c[species_dict2array[
compound]] = groups_dict['O'] / groups_dict['C']
h_c[species_dict2array[
compound]] = groups_dict['H'] / groups_dict['C']
# Calculate boiling point
b = boiling_point(Pybel_object_dict[SMILES_dict[compound]])
sat_vp[species_dict2array[compound]] = vapour_pressure(
Pybel_object_dict[SMILES_dict[compound]], temp, b)
if ignore_vp is True:
if sat_vp[species_dict2array[compound]] > vp_cutoff:
ignore_index.append(species_dict2array[compound])
ignore_index_fortran[species_dict2array[compound]] = 1.0
else:
include_index.append(species_dict2array[compound])
else:
include_index.append(species_dict2array[compound])
#sat_vp[species_dict2array[compound]]=(vapour_pressures.nannoolal(Pybel_object_dict[SMILES_dict[compound]], temp, boiling_points.nannoolal(Pybel_object_dict[SMILES_dict[compound]])))
#sat_vp_org[Pybel_object_dict[SMILES_dict[compound]]]=vapour_pressures.nannoolal(Pybel_object_dict[SMILES_dict[compound]], temp, boiling_points.nannoolal(Pybel_object_dict[SMILES_dict[compound]]))
#y_gas.append(concentration_array[species_step])
else:
ignore_index.append(species_dict2array[compound])
ignore_index_fortran[species_dict2array[compound]] = 1.0
species_step += 1
Delta_H = [
0.0
] * num_species #Dont prescribe an enthalpy of vaporisation. For non-VBS model simulations with varying temperature, we recalculate using GCM
Latent_heat_gas = [
0.0
] * num_species # - Still need to account for any latent heat release [Future work]
return_dict = dict()
return_dict['y_density_array'] = y_density_array
return_dict['y_mw'] = y_mw
return_dict['o_c'] = o_c
return_dict['h_c'] = h_c
return_dict['sat_vp'] = sat_vp
return_dict['Delta_H'] = Delta_H
return_dict['Latent_heat_gas'] = Latent_heat_gas
return_dict['ignore_index'] = ignore_index
return_dict['ignore_index_fortran'] = ignore_index_fortran
return_dict['include_index'] = include_index
return return_dict
from umansysprop import boiling_points from umansysprop import vapour_pressures from umansysprop import liquid_densities NA = si.Avogadro # Avogadro's number (molecules/mol) # vapour pressures of components, excluding water and core at end Psat = np.zeros((1, num_comp-2)) TEMP = 298.15 # temperature (K) for i in range(num_comp-2): # component loop # vapour pressure (log10(atm)) (# eq. 6 of Nannoolal et al. (2008), with dB of # that equation given by eq. 7 of same reference) Psat[0, i] = ((vapour_pressures.nannoolal(Pybel_objects[i], TEMP, boiling_points.nannoolal(Pybel_objects[i])))) # convert from list to array y_mw = np.array((y_mw)) # convert vapour pressures in log10(atm) to saturation concentrations in ug/m3 # using eq. 1 of O'Meara et al. 2014 Psat = 1.e6*y_mw[0:-2].reshape(1, -1)*(10**(Psat))/(8.2057e-5*TEMP) # convert particle-phase concentrations from molecules/cc to ug/m3 to # be comparable with total secondary particulate matter concentration # isolate just particle-phase concentrations (molecules/cc) # note just one size bin in this simulation and want to exclude water # and core SPMi = y[:, num_comp:(num_comp*(num_sb)-2)] # convert to mol/cc
def prop_calc(rel_SMILES, Pybel_objects, TEMP, H2Oi, num_comp, Psat_water,
vol_Comp, volP, testf, corei, pconc, umansysprop_update,
core_dens, spec_namelist, ode_gen_flag, nuci, nuc_comp, num_asb,
dens_comp, dens, seed_name, y_mw):
# inputs: ------------------------------------------------------------
# rel_SMILES - array of SMILE strings for components
# (omitting water and core, if present)
# Pybel_objects - list of Pybel objects representing the components in rel_SMILES
# (omitting water and core, if present)
# TEMP - temperature (K) in chamber at time function called
# vol_Comp - names of components (corresponding to those in chemical scheme file)
# that have vapour pressures manually set in volP
# testf - flag for whether in normal mode (0) or testing mode (1)
# corei - index of seed particle component
# pconc - initial number concentration of particles (# particles/cm3 (air))
# umansysprop_update - marker for cloning UManSysProp so that latest version used
# core_dens - density of core material (g/cm3 (liquid/solid density))
# spec_namelist - list of component names in chemical equation file
# ode_gen_flag - whether or not called from middle or ode_gen
# nuci - index of nucleating component
# nuc_comp - name of nucleating component
# num_asb - number of actual size bins (excluding wall)
# dens_comp - chemical scheme names of components with manually assigned
# densities
# dens - manually assigned densities (g/cm3)
# seed_name - chemical scheme name(s) of component(s) comprising seed particles
# y_mw - molar mass of components (g/mol)
# ------------------------------------------------------------
if (testf == 1):
return (0, 0, 0) # return dummies
cwd = os.getcwd() # address of current working directory
# if update required, note this update flag is set when model variables are checked
if (umansysprop_update == 1):
# download latest version of umansysprop
# check if there is an existing umansysprop folder
if os.path.isdir(cwd + '/umansysprop'):
def handleRemoveReadonly(func, path, exc):
excvalue = exc[1]
if not os.access(path, os.W_OK):
# Is the error an access error ?
os.chmod(path, stat.S_IWUSR)
func(path)
else:
raise
# remove existing folder, onerror will change permission of directory if
# needed
shutil.rmtree(cwd + '/umansysprop',
ignore_errors=False,
onerror=handleRemoveReadonly)
git_url = 'https://github.com/loftytopping/UManSysProp_public.git'
Repo.clone_from(git_url, (cwd + '/umansysprop'))
# point to umansysprop folder
sys.path.insert(1, (cwd + '/umansysprop')) # address for updated version
from umansysprop import boiling_points
from umansysprop import vapour_pressures
from umansysprop import liquid_densities
NA = si.Avogadro # Avogadro's number (molecules/mol)
y_dens = np.zeros((num_comp, 1)) # components' liquid density (kg/m3)
# vapour pressures of components, ensures any seed component called
# core has zero vapour pressure
Psat = np.zeros((1, num_comp))
# oxygen:carbon ratio of components
OC = np.zeros((1, num_comp))
if (ode_gen_flag == 0): # estimate densities if called from middle
for i in range(num_comp): # loop through components
# density estimation ---------------------------------------------------------
if (i == H2Oi): # liquid-phase density of water
y_dens[i] = 1. * 1.e3 # (kg/m3 (particle))
continue
# core component properties
if (i == corei[0]): # density of core
y_dens[i] = core_dens * 1.e3 # core density (kg/m3 (particle))
continue
if rel_SMILES[
i] == '[HH]': # omit H2 as unliked by liquid density code
# liquid density code does not like H2, so manually input kg/m3
y_dens[i] = 1.e3
else:
# density (convert from g/cm3 to kg/m3)
y_dens[i] = liquid_densities.girolami(Pybel_objects[i]) * 1.e3
# ----------------------------------------------------------------------------
# account for any manually assigned component densities (kg/m3)
if (len(dens_comp) > 0 and ode_gen_flag == 0):
for i in range(len(dens_comp)):
# index of component in list of components
dens_indx = spec_namelist.index(dens_comp[i])
y_dens[dens_indx] = dens[i]
# for records (e.g. plotting volatility basis set),
# estimate and list the pure component saturation vapour
# pressures (Pa) at standard temperature (298.15 K), though note that
# any manually assigned vapour pressures overwrite these later in
# this module
Psat_Pa_rec = np.zeros((num_comp))
# estimate vapour pressures (log10(atm)) and O:C ratio
# note when the O:C ratio and vapour pressure at 298.15 K are
# combined, one can produce the two-dimensional volatility
# basis set, as shown in Fig. 1 of https://doi.org/10.5194/acp-20-1183-2020
for i in range(num_comp):
if (i == corei[0]): # if this component is 'core'
# core component not included in Pybel_objects
# assign an assumed O:C ratio of 0.
OC[0, i] = 0.
# continuing
# here means its vapour pressure is 0 Pa, which is fine; if a
# different vapour pressure is specified it is accounted for below
continue
# water vapour pressure already given by Psat_water (log10(atm))
# and water not included in Pybel_objects
if (i == H2Oi):
Psat[0, i] = Psat_water
if (TEMP == 298.15):
Psat_Pa_rec[i] = Psat[0, i]
else:
[_, Psat_Pa_rec[i], _] = water_calc(298.15, 0.5, si.N_A)
OC[0, i] = 0.
continue
if (spec_namelist[i] == 'O3'):
# vapour pressure of ozone from https://doi.org/10.1063/1.1700683
Psat[0, i] = np.log10(
(8.25313 -
(814.941587 / TEMP) - 0.001966943 * TEMP) * 1.31579e-3)
if (TEMP == 298.15):
Psat_Pa_rec[i] = Psat[0, i]
else:
Psat_Pa_rec[i] = np.log10(
(8.25313 - (814.941587 / 298.15) - 0.001966943 * 298.15) *
1.31579e-3)
OC[0, i] = 0.
continue
# use EVAPORATION method for vapour pressure (log10(atm)) of HOMs
if 'api_' in spec_namelist[i] or 'API_' in spec_namelist[i]:
Psat[0, i] = ((vapour_pressures.myrdal_and_yalkowsky(
Pybel_objects[i], TEMP,
boiling_points.nannoolal(Pybel_objects[i]))))
if (TEMP == 298.15):
Psat_Pa_rec[i] = Psat_Pa[0, i]
else:
Psat_Pa_rec[i] = ((vapour_pressures.myrdal_and_yalkowsky(
Pybel_objects[i], 298.15,
boiling_points.nannoolal(Pybel_objects[i]))))
else:
# vapour pressure (log10(atm)) (eq. 6 of Nannoolal et al. (2008), with dB of
# that equation given by eq. 7 of same reference)
Psat[0, i] = ((vapour_pressures.nannoolal(
Pybel_objects[i], TEMP,
boiling_points.nannoolal(Pybel_objects[i]))))
if (TEMP == 298.15):
Psat_Pa_rec[i] = Psat_Pa[0, i]
else:
Psat_Pa_rec[i] = ((vapour_pressures.nannoolal(
Pybel_objects[i], 298.15,
boiling_points.nannoolal(Pybel_objects[i]))))
# O:C ratio determined from SMILES string
if (rel_SMILES[i].count('C') > 0):
OC[0, i] = (rel_SMILES[i].count('O')) / (rel_SMILES[i].count('C'))
else:
OC[0, i] = 0.
ish = (Psat == 0.)
Psat = (10.**Psat) * 101325. # convert to Pa from atm
Psat_Pa_rec = (10.**Psat_Pa_rec) * 101325 # convert to Pa from atm
# retain low volatility where wanted following unit conversion
Psat[ish] = 0.
# list to remember which components have vapour pressures specified
vi_rec = []
# manually assigned vapour pressures (Pa)
if (len(vol_Comp) > 0 and ode_gen_flag == 0):
for i in range(len(vol_Comp)):
# index of component in list of components
vol_indx = spec_namelist.index(vol_Comp[i])
Psat[0, vol_indx] = volP[i]
Psat_Pa_rec[vol_indx] = volP[i]
vi_rec.append(vol_indx)
# ensure if nucleating component is core that it is involatile
if (nuc_comp == 'core'):
Psat[0, nuci] = 0.
Psat_Pa = np.zeros(
(1, num_comp)) # for storing vapour pressures in Pa (Pa)
Psat_Pa[0, :] = Psat[0, :]
# convert saturation vapour pressures from Pa to # molecules/cm3 (air) using ideal
# gas law, R has units cc.Pa/K.mol
Psat = Psat * (NA / ((si.R * 1.e6) * TEMP))
# now, in preparation for ode solver, repeat over number of size bins
if (num_asb > 0):
Psat = np.repeat(Psat, num_asb, axis=0)
return (Psat, y_dens, Psat_Pa, Psat_Pa_rec, OC)
def volat_calc(spec_list, Pybel_objects, TEMP, H2Oi, num_speci, Psat_water, vol_Comp,
volP, testf, corei, seed_name, pconc, umansysprop_update, core_dens, spec_namelist,
ode_gen_flag, nuci, nuc_comp):
# inputs: ------------------------------------------------------------
# spec_list - array of SMILE strings for components
# (omitting water and core, if present)
# Pybel_objects - list of Pybel objects representing the species in spec_list
# (omitting water and core, if present)
# TEMP - temperature (K) in chamber at time function called
# vol_Comp - names of components (corresponding to those in chemical scheme file)
# that have vapour pressures manually set in volP
# testf - flag for whether in normal mode (0) or testing mode (1)
# corei - index of seed particle component
# seed_name - name(s) of components(s) comprising seed particles
# pconc - initial number concentration of particles (#/cc (air))
# umansysprop_update - marker for cloning UManSysProp so that latest version used
# core_dens - density of core material (g/cc (liquid/solid density))
# spec_namelist - list of components' names in chemical equation file
# ode_gen_flag - whether or not called from front or ode_gen
# nuci - index of nucleating component
# nuc_comp - name of nucleating component
# ------------------------------------------------------------
if testf==1:
return(0,0,0) # return dummies
cwd = os.getcwd() # address of current working directory
if umansysprop_update == 1:
print('Cloning latest version of UManSysProp in volat_calc module')
# download latest version of umansysprop
# check if there is an existing umansysprop folder
if os.path.isdir(cwd + '/umansysprop'):
def handleRemoveReadonly(func, path, exc):
excvalue = exc[1]
if not os.access(path, os.W_OK):
# Is the error an access error ?
os.chmod(path, stat.S_IWUSR)
func(path)
else:
raise
# remove existing folder, onerror will change permission of directory if
# needed
shutil.rmtree(cwd + '/umansysprop', ignore_errors=False, onerror=handleRemoveReadonly)
git_url = 'https://github.com/loftytopping/UManSysProp_public.git'
Repo.clone_from(git_url, (cwd + '/umansysprop'))
# point to umansysprop folder
sys.path.insert(1, (cwd + '/umansysprop')) # address for updated version
from umansysprop import boiling_points
from umansysprop import vapour_pressures
from umansysprop import liquid_densities
NA = si.Avogadro # Avogadro's number (molecules/mol)
y_dens = np.zeros((num_speci, 1)) # components' liquid density (kg/m3)
Psat = np.zeros((num_speci, 1)) # species' vapour pressure
if ode_gen_flag == 0: # estimate densities
for i in range (num_speci):
# density estimation ---------------------------------------------------------
if i == H2Oi:
y_dens[i] = 1.0*1.0E3 # (kg/m3 (particle))
continue
# core properties
if (i == corei[0]):
y_dens[i] = core_dens*1.e3 # core density (kg/m3 (particle))
continue
# nucleating component density, if component is core (kg/m3 (particle))
if i == nuci and nuc_comp[0] == 'core':
y_dens[i] = 1.0*1.0E3
continue
if spec_list[i] == '[HH]': # omit H2 as unliked by liquid density code
# liquid density code does not like H2, so manually input kg/m3
y_dens[i] = 1.0e3
else:
# density (convert from g/cc to kg/m3)
y_dens[i] = liquid_densities.girolami(Pybel_objects[i])*1.0E3
# ----------------------------------------------------------------------------
# estimate vapour pressures (log10(atm))
for i in range (num_speci):
if (i == corei[0]): # if this core component
continue # core component not included in Pybel_objects
if i == nuci and nuc_comp[0] == 'core':
continue # core component not included in Pybel_objects
# water vapour pressure already given by Psat_water (log10(atm))
if i == H2Oi:
Psat[i] = Psat_water
continue # water not included in Pybel_objects
# vapour pressure (log10 atm) (# eq. 6 of Nannoolal et al. (2008), with dB of
# that equation given by eq. 7 of same reference)
Psat[i] = ((vapour_pressures.nannoolal(Pybel_objects[i], TEMP,
boiling_points.nannoolal(Pybel_objects[i]))))
ish = Psat==0.0
Psat = (np.power(10.0, Psat)*101325.0) # convert to Pa from atm
# retain low volatility where wanted
Psat[ish] = 0.0
# manually assigned vapour pressures (Pa)
if len(vol_Comp)>0 and ode_gen_flag==0:
for i in range (len(vol_Comp)):
# index of component in list of components
vol_indx = spec_namelist.index(vol_Comp[i])
Psat[vol_indx, 0] = volP[i]
# ensure if nucleating component is core that it is involatile
if nuc_comp == 'core':
Psat[nuci, 0] = 0.0
Psat_Pa = np.zeros((len(Psat), 1)) # for storing vapour pressures in Pa (Pa)
Psat_Pa[:, 0] = Psat[:, 0]
# convert saturation vapour pressures from Pa to molecules/cc (air) using ideal
# gas law, R has units cc.Pa/K.mol
Psat = Psat*(NA/((si.R*1.e6)*TEMP))
return Psat, y_dens, Psat_Pa
def volat_calc(spec_list, Pybel_objects, TEMP, H2Oi, num_speci, Psat_water,
voli, volP, testf, corei):
# ------------------------------------------------------------
# inputs:
# spec_list - array of SMILE strings for components
# (omitting water and core, if present)
# Pybel_objects - list of Pybel objects representing the species in spec_list
# (omitting water and core, if present)
# testf - flag for whether in normal mode (0) or testing mode (1)
# corei - index of seed particle component
# ------------------------------------------------------------
if testf == 1:
return (0, 0, 0) # return dummies
# if voli is in relative index (-n), change to absolute
for i in range(len(voli)):
if voli[i] < 0:
voli[i] = num_speci + voli[i]
NA = si.Avogadro # Avogadro's number (molecules/mol)
y_dens = np.zeros((num_speci, 1)) # components' liquid density (kg/m3)
Psat = np.zeros((num_speci, 1)) # species' vapour pressure
for i in range(num_speci):
# omit estimation for water as it's value is already given in Psat_water
# (log10(atm))
if i == H2Oi:
Psat[i] = Psat_water
y_dens[i] = 1.0 * 1.0E3 # (kg/m3 (particle))
continue
if i == corei: # core properties (only used if seed particles present)
y_dens[i] = 1.77 * 1.0E3 # core density (kg/m3 (particle))
continue
if spec_list[i] == '[HH]': # omit H2 as unliked by liquid density code
# liquid density code does not like H2, so manually input kg/m3
y_dens[i] = 1.0e3
else:
# density (convert from g/cc to kg/m3)
y_dens[i] = liquid_densities.girolami(Pybel_objects[i]) * 1.0E3
# vapour pressure (log10 atm) (# eqn. 6 of Nannoolal et al. (2008), with dB of
# that equation given by eq. 7)
Psat[i] = ((vapour_pressures.nannoolal(
Pybel_objects[i], TEMP,
boiling_points.nannoolal(Pybel_objects[i]))))
Psat = (np.power(10.0, Psat) * 101325.0) # convert to Pa
# manually assigned vapour pressures (Pa) (including seed component (if applicable))
if len(voli) > 0:
Psat[voli, 0] = volP
Psat_Pa = np.zeros(
(len(Psat), 1)) # for storing vapour pressures in Pa (Pa)
Psat_Pa[:, 0] = Psat[:, 0]
# convert saturation vapour pressures from Pa to molecules/cc (air) using ideal
# gas law, R has units cc.Pa/K.mol
Psat = Psat * (NA / (8.3144598e6 * TEMP))
return Psat, y_dens, Psat_Pa
