diff --git a/photochem/cython/PhotochemVars.pyx b/photochem/cython/PhotochemVars.pyx
index 72056fa..c378681 100644
--- a/photochem/cython/PhotochemVars.pyx
+++ b/photochem/cython/PhotochemVars.pyx
@@ -59,6 +59,15 @@ cdef class PhotochemVars:
         raise PhotoException("Input array is the wrong size.")
       var_pxd.photochemvars_particle_radius_set(self._ptr, &dim1, &dim2, <double *>arr_.data)
 
+  property diurnal_fac:
+    "double. Default is 0.5, to account for half planet facing the sun."
+    def __get__(self):
+      cdef double val
+      var_pxd.photochemvars_diurnal_fac_get(self._ptr, &val)
+      return val
+    def __set__(self, double val):
+      var_pxd.photochemvars_diurnal_fac_set(self._ptr, &val)
+
   property trop_alt:
     "double. Tropopause altitude."
     def __get__(self):
diff --git a/photochem/cython/PhotochemVars_pxd.pxd b/photochem/cython/PhotochemVars_pxd.pxd
index 4c6a337..18b3a28 100644
--- a/photochem/cython/PhotochemVars_pxd.pxd
+++ b/photochem/cython/PhotochemVars_pxd.pxd
@@ -26,6 +26,9 @@ cdef extern void photochemvars_particle_radius_get_size(PhotochemVars *ptr, int
 cdef extern void photochemvars_particle_radius_get(PhotochemVars *ptr, int *dim1, int *dim2, double *arr)
 cdef extern void photochemvars_particle_radius_set(PhotochemVars *ptr, int *dim1, int *dim2, double *arr)
 
+cdef extern void photochemvars_diurnal_fac_get(PhotochemVars *ptr, double *val)
+cdef extern void photochemvars_diurnal_fac_set(PhotochemVars *ptr, double *val)
+
 cdef extern void photochemvars_trop_alt_get(PhotochemVars *ptr, double *val)
 
 cdef extern void photochemvars_trop_ind_get(PhotochemVars *ptr, int *val)
diff --git a/photochem/fortran/PhotochemVars_wrapper.f90 b/photochem/fortran/PhotochemVars_wrapper.f90
index 12f6af9..2103fd1 100644
--- a/photochem/fortran/PhotochemVars_wrapper.f90
+++ b/photochem/fortran/PhotochemVars_wrapper.f90
@@ -80,6 +80,22 @@ subroutine photochemvars_particle_radius_set(ptr, dim1, dim2, arr) bind(c)
     var%particle_radius = arr
   end subroutine
 
+  subroutine photochemvars_diurnal_fac_get(ptr, val) bind(c)
+    type(c_ptr), value, intent(in) :: ptr
+    real(c_double), intent(out) :: val
+    type(PhotochemVars), pointer :: var
+    call c_f_pointer(ptr, var)
+    val = var%diurnal_fac
+  end subroutine
+  
+  subroutine photochemvars_diurnal_fac_set(ptr, val) bind(c)
+    type(c_ptr), value, intent(in) :: ptr
+    real(c_double), intent(in) :: val
+    type(PhotochemVars), pointer :: var
+    call c_f_pointer(ptr, var)
+    var%diurnal_fac = val
+  end subroutine
+
   subroutine photochemvars_trop_alt_get(ptr, val) bind(c)
     type(c_ptr), value, intent(in) :: ptr
     real(c_double), intent(out) :: val