c$Author: fredfox $
c$Date: 2001-07-09 23:02:37 $
c$Revision: 1.1.2.2 $
c$Source: /weru/cvs/weps/weps.src/hydro/vaporden.for,v $
      real*4 function vaporden( airtemp, relhum )

c     returns the water vapor density in air (kg/m^3)
c     calculated directly from PV = nRT

c*** Argument declarations ***
      real*4 airtemp, relhum
c     airtemp - the temperature of the air (C)
c     relhum - relative humidity of the air (fraction)

c*** function declarations ***
      real*4 satvappres
c     satvappres - function to find the saturated vapor pressure (Pascals)

c*** Local declarations ***
      real*4 actvappres
c     actvappres - actual vapor pressure (kPa)

      actvappres =  relhum * satvappres(airtemp)

c      if(actvappres.lt.1.0e-34) write(*,*) 'vaporden:',relhum,airtemp
      vaporden = 2.166 * actvappres / (airtemp + 273.15)

      return
      end