diff --git a/src/gas_state.F90 b/src/gas_state.F90
index 5d501500..79c32a8d 100644
--- a/src/gas_state.F90
+++ b/src/gas_state.F90
@@ -93,4 +93,56 @@ subroutine f_gas_state_set_size(ptr_c, gas_data_ptr_c) bind(C)
     call gas_state_set_size(ptr_f, gas_data_n_spec(gas_data_ptr_f))
 
   end subroutine
+
+  subroutine f_gas_state_molar_conc_to_ppb(ptr_c, env_state_ptr_c) bind(C)
+    type(c_ptr), intent(inout) :: ptr_c
+    type(c_ptr), intent(in) :: env_state_ptr_c
+    type(gas_state_t), pointer :: ptr_f => null()
+    type(env_state_t), pointer :: env_state_ptr_f => null()
+
+    call c_f_pointer(ptr_c, ptr_f)
+    call c_f_pointer(env_state_ptr_c, env_state_ptr_f)
+
+    call gas_state_molar_conc_to_ppb(ptr_f, env_state_ptr_f)
+
+  end subroutine
+
+  subroutine f_gas_state_scale(ptr_c, alpha) bind(C)
+    type(c_ptr), intent(inout) :: ptr_c
+    type(gas_state_t), pointer :: ptr_f => null()
+    real(kind=c_double), intent(in) :: alpha
+
+    call c_f_pointer(ptr_c, ptr_f)
+
+    call gas_state_scale(ptr_f, alpha)
+
+  end subroutine
+
+  subroutine f_gas_state_add(ptr_c, delta_gas_state_ptr_c) bind(C)
+    type(c_ptr), intent(inout) :: ptr_c
+    type(c_ptr), intent(in) :: delta_gas_state_ptr_c
+    type(gas_state_t), pointer :: ptr_f => null()
+    type(gas_state_t), pointer :: delta_gas_state_ptr_f => null()
+
+    call c_f_pointer(ptr_c, ptr_f)
+    call c_f_pointer(delta_gas_state_ptr_c, delta_gas_state_ptr_f)
+
+    call gas_state_add(ptr_f, delta_gas_state_ptr_f)
+
+  end subroutine
+
+  subroutine f_gas_state_add_scaled(ptr_c, delta_gas_state_ptr_c, alpha) bind(C)
+    type(c_ptr), intent(inout) :: ptr_c
+    type(c_ptr), intent(in) :: delta_gas_state_ptr_c
+    type(gas_state_t), pointer :: ptr_f => null()
+    type(gas_state_t), pointer :: delta_gas_state_ptr_f => null()
+    real(kind=c_double), intent(in) :: alpha
+
+    call c_f_pointer(ptr_c, ptr_f)
+    call c_f_pointer(delta_gas_state_ptr_c, delta_gas_state_ptr_f)
+
+    call gas_state_add_scaled(ptr_f, delta_gas_state_ptr_f, alpha)
+
+  end subroutine
+
 end module
diff --git a/src/gas_state.hpp b/src/gas_state.hpp
index 6b1ad688..68f5eb2c 100644
--- a/src/gas_state.hpp
+++ b/src/gas_state.hpp
@@ -10,6 +10,7 @@
 #include "json_resource.hpp"
 #include "pmc_resource.hpp"
 #include "gas_data.hpp"
+#include "env_state.hpp"
 
 extern "C" void f_gas_state_ctor(void *ptr) noexcept;
 extern "C" void f_gas_state_dtor(void *ptr) noexcept;
@@ -19,7 +20,15 @@ extern "C" void f_gas_state_len(const void *ptr, int *len) noexcept;
 extern "C" void f_gas_state_to_json(const void *ptr) noexcept;
 extern "C" void f_gas_state_from_json(const void *ptr, const void *gasdata_ptr) noexcept;
 extern "C" void f_gas_state_set_size(const void *ptr, const void *gasdata_ptr) noexcept;
-extern "C" void f_gas_state_mix_rats(const void *ptr, const double *data, const int *len);
+extern "C" void f_gas_state_mix_rats(const void *ptr, const double *data, const int *len) noexcept;
+extern "C" void f_gas_state_molar_conc_to_ppb(const void *ptr, const void *envstate_ptr) noexcept;
+extern "C" void f_gas_state_scale(const void *ptr_c, const double *alpha) noexcept;
+extern "C" void f_gas_state_add(const void *ptr_c, const void *delta_ptr) noexcept;
+extern "C" void f_gas_state_add_scaled(
+    const void *ptr_c,
+    const void *delta_ptr,
+    const double *alpha
+) noexcept;
 
 struct GasState {
     PMCResource ptr;
@@ -126,4 +135,26 @@ struct GasState {
         );
         guard.check_parameters();
     }
+
+    static void molar_conc_to_ppb(const GasState &self, const EnvState &env_state) {
+
+        f_gas_state_molar_conc_to_ppb(self.ptr.f_arg(), env_state.ptr.f_arg());
+    }
+
+    static void scale(const GasState &self, const double &alpha) {
+
+        f_gas_state_scale(self.ptr.f_arg(), &alpha);
+    }
+
+    static void add(const GasState &self, const GasState &delta_gas_state) {
+
+        f_gas_state_add(self.ptr.f_arg(), delta_gas_state.ptr.f_arg());
+    }
+
+    static void add_scaled(const GasState &self, const GasState &delta_gas_state,
+        const double &alpha) {
+
+        f_gas_state_add_scaled(self.ptr.f_arg(), delta_gas_state.ptr.f_arg(), &alpha);
+    }
+
 };
diff --git a/src/pypartmc.cpp b/src/pypartmc.cpp
index 621f8772..4aa26309 100644
--- a/src/pypartmc.cpp
+++ b/src/pypartmc.cpp
@@ -524,6 +524,12 @@ NB_MODULE(_PyPartMC, m) {
             "Return the mixing ratio of a gas species.")
         .def_prop_rw("mix_rats", &GasState::mix_rats, &GasState::set_mix_rats,
             "Provide access (read or write) to the array of mixing ratios.")
+        .def("molar_conc_to_ppb", &GasState::molar_conc_to_ppb,
+            "Convert (mol m^{-3}) to (ppb).")
+        .def("scale", &GasState::scale, "Scale a gas state.")
+        .def("add", &GasState::add, "Adds the given gas_state_delta.")
+        .def("add_scaled", &GasState::add_scaled,
+            "Adds the given gas_state_delta scaled by alpha to an existing gas_state.")
     ;
 
     nb::class_<RunPartOpt>(m,
diff --git a/tests/test_gas_state.py b/tests/test_gas_state.py
index 3ab4b495..63e6fede 100644
--- a/tests/test_gas_state.py
+++ b/tests/test_gas_state.py
@@ -7,11 +7,15 @@
 import gc
 import platform
 
+import numpy as np
 import pytest
 
 import PyPartMC as ppmc
 
+from .common import ENV_STATE_CTOR_ARG_MINIMAL
+from .test_aero_data import AERO_DATA_CTOR_ARG_MINIMAL
 from .test_gas_data import GAS_DATA_CTOR_ARG_MINIMAL
+from .test_scenario import SCENARIO_CTOR_ARG_MINIMAL
 
 GAS_DATA_MINIMAL = ppmc.GasData(GAS_DATA_CTOR_ARG_MINIMAL)
 
@@ -103,6 +107,77 @@ def test_get_mix_rats():
         # assert
         assert len(sut.mix_rats) == len(sut)
 
+    @staticmethod
+    def test_scale():
+        # arrange
+        gas_data = ppmc.GasData(
+            (
+                "SO2",
+                "CO",
+            )
+        )
+        sut = ppmc.GasState(gas_data)
+        gas_state_init_values = ({"SO2": [0.1]}, {"CO": [0.5]})
+        sut.mix_rats = gas_state_init_values
+
+        # act
+        alpha = 5.0
+        sut.scale(alpha)
+
+        # assert
+        idx_set = []
+        for item in gas_state_init_values:
+            keys = item.keys()
+            assert len(keys) == 1
+            key = tuple(keys)[0]
+            val = tuple(item.values())[0][0]
+            idx_set.append(gas_data.spec_by_name(key))
+            assert sut[gas_data.spec_by_name(key)] == val * alpha
+
+    @staticmethod
+    def test_molar_conc_to_ppb():
+        # arrange
+        gas_data = GAS_DATA_MINIMAL
+        aero_data = ppmc.AeroData(AERO_DATA_CTOR_ARG_MINIMAL)
+        scenario = ppmc.Scenario(gas_data, aero_data, SCENARIO_CTOR_ARG_MINIMAL)
+        env_state = ppmc.EnvState(ENV_STATE_CTOR_ARG_MINIMAL)
+        scenario.init_env_state(env_state, 0.0)
+        sut = ppmc.GasState(GAS_DATA_MINIMAL)
+        sut.mix_rats = GAS_STATE_MINIMAL
+
+        # act
+        sut.molar_conc_to_ppb(env_state)
+
+        # assert
+        assert sut.mix_rats[0] > GAS_STATE_MINIMAL[0][list(gas_data.species)[0]][0]
+
+    @staticmethod
+    def test_add():
+        sut = ppmc.GasState(GAS_DATA_MINIMAL)
+        sut.mix_rats = GAS_STATE_MINIMAL
+        gas_state_delta = ppmc.GasState(GAS_DATA_MINIMAL)
+        gas_state_delta.mix_rats = GAS_STATE_MINIMAL
+        tot_mix_rats = np.add(sut.mix_rats, gas_state_delta.mix_rats)
+
+        # act
+        sut.add(gas_state_delta)
+
+        assert sut.mix_rats == tot_mix_rats
+
+    @staticmethod
+    def test_add_scaled():
+        sut = ppmc.GasState(GAS_DATA_MINIMAL)
+        sut.mix_rats = GAS_STATE_MINIMAL
+        gas_state_delta = ppmc.GasState(GAS_DATA_MINIMAL)
+        gas_state_delta.mix_rats = GAS_STATE_MINIMAL
+        alpha = 2.5
+        tot_mix_rats = np.add(sut.mix_rats, np.array(gas_state_delta.mix_rats) * alpha)
+
+        # act
+        sut.add_scaled(gas_state_delta, alpha)
+
+        assert sut.mix_rats == tot_mix_rats
+
     @staticmethod
     def test_set_mix_rats_from_json():
         # arrange