SUBROUTINE aeropt(pplay, paprs, t_seri, msulfate, RHcl,
     .            tau_ae, piz_ae, cg_ae, ai        )
c
      IMPLICIT none
c
c
c     
#include "dimensions.h"
#include "dimphy.h"
#include "YOMCST.h"
c
c Arguments:
c
      REAL paprs(klon,klev+1)
      REAL pplay(klon,klev), t_seri(klon,klev)
      REAL msulfate(klon,klev) ! masse sulfate ug SO4/m3  [ug/m^3]
      REAL RHcl(klon,klev)     ! humidite relative ciel clair
      REAL tau_ae(klon,klev,2) ! epaisseur optique aerosol
      REAL piz_ae(klon,klev,2) ! single scattering albedo aerosol
      REAL cg_ae(klon,klev,2)  ! asymmetry parameter aerosol
      REAL ai(klon)            ! POLDER aerosol index 
c
c Local
c
      INTEGER i, k, inu
      INTEGER RH_num, nbre_RH
      PARAMETER (nbre_RH=12)
      REAL RH_tab(nbre_RH)
      REAL RH_MAX, DELTA, rh 
      PARAMETER (RH_MAX=95.)
      DATA RH_tab/0.,10.,20.,30.,40.,50.,60.,70.,80.,85.,90.,95./
      REAL zrho, zdz
      REAL taue670(klon)       ! epaisseur optique aerosol absorption 550 nm
      REAL taue865(klon)       ! epaisseur optique aerosol extinction 865 nm
      REAL alpha_aer_sulfate(nbre_RH,5)   !--unit m2/g SO4
      REAL alphasulfate      
c
c Proprietes optiques
c
      REAL alpha_aer(nbre_RH,2)   !--unit m2/g SO4
      REAL cg_aer(nbre_RH,2)
      DATA alpha_aer/.500130E+01,  .500130E+01,  .500130E+01,  
     .               .500130E+01,  .500130E+01,  .616710E+01,  
     .               .826850E+01,  .107687E+02,  .136976E+02,  
     .               .162972E+02,  .211690E+02,  .354833E+02,  
     .               .139460E+01,  .139460E+01,  .139460E+01,  
     .               .139460E+01,  .139460E+01,  .173910E+01,  
     .               .244380E+01,  .332320E+01,  .440120E+01,  
     .               .539570E+01,  .734580E+01,  .136038E+02 / 
      DATA cg_aer/.619800E+00,  .619800E+00,  .619800E+00,  
     .            .619800E+00,  .619800E+00,  .662700E+00,  
     .            .682100E+00,  .698500E+00,  .712500E+00,  
     .            .721800E+00,  .734600E+00,  .755800E+00,  
     .            .545600E+00,  .545600E+00,  .545600E+00,  
     .            .545600E+00,  .545600E+00,  .583700E+00,  
     .            .607100E+00,  .627700E+00,  .645800E+00,  
     .            .658400E+00,  .676500E+00,  .708500E+00 / 
      DATA alpha_aer_sulfate/
     . 4.910,4.910,4.910,4.910,6.547,7.373,
     . 8.373,9.788,12.167,14.256,17.924,28.433,
     . 1.453,1.453,1.453,1.453,2.003,2.321,
     . 2.711,3.282,4.287,5.210,6.914,12.305,
     . 4.308,4.308,4.308,4.308,5.753,6.521,
     . 7.449,8.772,11.014,12.999,16.518,26.772,
     . 3.265,3.265,3.265,3.265,4.388,5.016,
     . 5.775,6.868,8.745,10.429,13.457,22.538,
     . 2.116,2.116,2.116,2.116,2.882,3.330,
     . 3.876,4.670,6.059,7.327,9.650,16.883/
c
      DO i=1, klon
         taue670(i)=0.0
         taue865(i)=0.0
      ENDDO
c      
      DO k=1, klev
      DO i=1, klon
         if (t_seri(i,k).eq.0) write (*,*) 'aeropt T ',i,k,t_seri(i,k)
         if (pplay(i,k).eq.0) write (*,*) 'aeropt p ',i,k,pplay(i,k)         
        zrho=pplay(i,k)/t_seri(i,k)/RD                  ! kg/m3
        zdz=(paprs(i,k)-paprs(i,k+1))/zrho/RG           ! m
        rh=MIN(RHcl(i,k)*100.,RH_MAX)
        RH_num = INT( rh/10. + 1.)
        IF (rh.LT.0.) STOP 'aeropt: RH < 0 not possible'
        IF (rh.gt.85.) RH_num=10
        IF (rh.gt.90.) RH_num=11
        DELTA=(rh-RH_tab(RH_num))/(RH_tab(RH_num+1)-RH_tab(RH_num))
c                
        inu=1
        tau_ae(i,k,inu)=alpha_aer(RH_num,inu) +
     .             DELTA*(alpha_aer(RH_num+1,inu)-alpha_aer(RH_num,inu))
        tau_ae(i,k,inu)=tau_ae(i,k,inu)*msulfate(i,k)*zdz*1.e-6
        piz_ae(i,k,inu)=1.0
        cg_ae(i,k,inu)=cg_aer(RH_num,inu) +
     .                 DELTA*(cg_aer(RH_num+1,inu)-cg_aer(RH_num,inu))
c
        inu=2
        tau_ae(i,k,inu)=alpha_aer(RH_num,inu) +
     .             DELTA*(alpha_aer(RH_num+1,inu)-alpha_aer(RH_num,inu))
        tau_ae(i,k,inu)=tau_ae(i,k,inu)*msulfate(i,k)*zdz*1.e-6
        piz_ae(i,k,inu)=1.0
        cg_ae(i,k,inu)=cg_aer(RH_num,inu) +
     .                 DELTA*(cg_aer(RH_num+1,inu)-cg_aer(RH_num,inu))
cjq
cjq for aerosol index
c
        alphasulfate=alpha_aer_sulfate(RH_num,4) +
     .       DELTA*(alpha_aer_sulfate(RH_num+1,4)-
     .       alpha_aer_sulfate(RH_num,4)) !--m2/g 
c     
        taue670(i)=taue670(i)+
     .       alphasulfate*msulfate(i,k)*zdz*1.e-6
c
        alphasulfate=alpha_aer_sulfate(RH_num,5) +
     .       DELTA*(alpha_aer_sulfate(RH_num+1,5)-
     .       alpha_aer_sulfate(RH_num,5)) !--m2/g 
c
        taue865(i)=taue865(i)+
     .         alphasulfate*msulfate(i,k)*zdz*1.e-6
        
      ENDDO
      ENDDO
c      
      DO i=1, klon
        ai(i)=(-log(MAX(taue670(i),0.0001)/
     .                MAX(taue865(i),0.0001))/log(670./865.)) * 
     .        taue865(i)
      ENDDO     
c
      RETURN
      END