pro nap_equilib,q_hno3,q_h2o,p,t,t_nap,p_hno3_eq,v_nap ;------------------------------------------------------------------ ; Routine calculates the: ; a) equilibrium temperature of nitric acid pentahydrate (NAP) ; which is: HNO3 / 5H2O ; b) equilibrium vapor pressure of hno3 over NAP ; c) volume of condensed NAP ; ; The equilibrium over NAP is from Koop et al., 1997, ; GRL, page 2199, from Table 1: Kn = exp(156.13 - 40870/T) ; ; parameters: ; ; input: ; q_hno3.......hno3 vapor mixing ratio (ppbv) ; q_h2o........water vapor mixing ratio (ppmv) ; p............pressure (mb) ; t............temperature (K) ; ; output: ; t_nap........NAP equilibrium temperature (K) ; p_hno3_eq....equilibrium hno3 vapor presure (mb) ; v_nap........volume of condensed NAP (um3/cm3) ; ; source: Mark Hervig ;------------------------------------------------------------------- p_hno3 = 0.0 p_h2o = 0.0 v_nap = 0.0 t_nap = 0.0 p_hno3_eq = 0.0 if (q_hno3 le 0.0) then return ;---- some constants torr_mb = 1.333224 ; pressure, torr to mb R = 8.314 ; J/mol/K Mwp = 153.0 ; molec wt. NAP, g/mol Mwn = 63.0 ; molec wt. hno3, g/mol dp = 1.5 ; density of NAP, g/cm3, this number should be checked !! wfn = Mwn/Mwp ; wt. fraction hno3 in NAP a = 156.13 ; constants describing Kn b = -40870.0 ;---- the h2o and hno3 partial pressures p_torr = p / torr_mb p_hno3 = p_torr * q_hno3 * 1.0e-9 p_h2o = p_torr * q_h2o * 1.e-6 ;---- solve for equilibrium NAP temperature t_nap = b / (alog(p_hno3 * p_h2o^5) -a) ; K ;---- solve for equilibrium pressure of hno3 over NAP Kn = exp( a + b /T) ; torr^6 p_hno3_eq = torr_mb * Kn * p_h2o ^(-5) ; equilib p, mb q_hno3_eq = p_hno3_eq / (p *1.e-9) ; equilib mix, ppbv ;---- for T < t_nap, compute NAP volume if (t le t_nap) then begin q_hno3_xs = q_hno3 - q_hno3_eq ; excess hno3 nn = p*100.0 *q_hno3_xs*1.e-9/(R*T) ; mols condensed hno3 per m3 air v_nap = 1.0e6 * (nn * Mwn) / (wfn * dp) ; NAP volume, um3/cm3 endif return end