diff --git a/src/gas_state.F90 b/src/gas_state.F90
index d90490d8d..3ce7eb465 100644
--- a/src/gas_state.F90
+++ b/src/gas_state.F90
@@ -188,20 +188,6 @@ subroutine gas_state_molar_conc_to_ppb(gas_state, env_state)
 
   end subroutine gas_state_molar_conc_to_ppb
 
-!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-
-  !> Convert (ppb) to (mol m^{-3}).
-  subroutine gas_state_ppb_to_molar_conc(gas_state, env_state)
-
-    !> Gas state.
-    type(gas_state_t), intent(inout) :: gas_state
-    !> Environment state.
-    type(env_state_t), intent(in) :: env_state
-
-    call gas_state_scale(gas_state, env_state_air_molar_den(env_state) / 1e9)
-
-  end subroutine gas_state_ppb_to_molar_conc
-
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 #ifdef PMC_USE_CAMP