diff --git a/src/acom_music_box/conditions.py b/src/acom_music_box/conditions.py
index 35a709fc..15aec6cf 100644
--- a/src/acom_music_box/conditions.py
+++ b/src/acom_music_box/conditions.py
@@ -1,4 +1,4 @@
-from .utils import convert_time, convert_pressure, convert_temperature, convert_concentration
+from .utils import convert_pressure, convert_temperature, convert_concentration
 from .species_concentration import SpeciesConcentration
 from .species import Species
 from .reaction_rate import ReactionRate
@@ -9,7 +9,6 @@
 from .reaction_rate import ReactionRate
 from .species import Species
 from .species_concentration import SpeciesConcentration
-from .utils import convert_time, convert_pressure, convert_temperature, convert_concentration
 
 import logging
 logger = logging.getLogger(__name__)
@@ -54,7 +53,7 @@ def __str__(self):
         return f"Pressure: {self.pressure}, Temperature: {self.temperature}, Species Concentrations: {self.species_concentrations}, Reaction Rates: {self.reaction_rates}"
 
     @classmethod
-    def from_UI_JSON(cls, UI_JSON, species_list, reaction_list):
+    def from_UI_JSON(self, UI_JSON, species_list, reaction_list):
         """
         Creates an instance of the class from a UI JSON object.
 
@@ -108,7 +107,7 @@ def from_UI_JSON(cls, UI_JSON, species_list, reaction_list):
 
             reaction_rates.append(ReactionRate(reaction_from_list, rate))
 
-        return cls(
+        return self(
             pressure,
             temperature,
             species_concentrations,
@@ -116,7 +115,7 @@ def from_UI_JSON(cls, UI_JSON, species_list, reaction_list):
 
     @classmethod
     def from_config_JSON(
-            cls,
+            self,
             path_to_json,
             config_JSON,
             species_list,
@@ -164,7 +163,7 @@ def from_config_JSON(
             for chem_spec in config_JSON['chemical species']:
                 species = Species(name=chem_spec)
                 concentration = convert_concentration(
-                    config_JSON['chemical species'][chem_spec], 'initial value')
+                    config_JSON['chemical species'][chem_spec], 'initial value', temperature, pressure)
 
                 species_concentrations.append(
                     SpeciesConcentration(
@@ -190,14 +189,14 @@ def from_config_JSON(
             if not reaction_exists:
                 reaction_rates.append(ReactionRate(reaction, 0))
 
-        return cls(
+        return self(
             pressure,
             temperature,
             species_concentrations,
             reaction_rates)
 
     @classmethod
-    def read_initial_rates_from_file(cls, file_path, reaction_list):
+    def read_initial_rates_from_file(self, file_path, reaction_list):
         """
         Reads initial reaction rates from a file.
 
diff --git a/src/acom_music_box/constants.py b/src/acom_music_box/constants.py
index 48b450d9..c3e561b9 100644
--- a/src/acom_music_box/constants.py
+++ b/src/acom_music_box/constants.py
@@ -1,3 +1,3 @@
-BOLTZMANN_CONSTANT = 1.380649e-23
-AVOGADRO_CONSTANT = 6.02214076e23
-GAS_CONSTANT = BOLTZMANN_CONSTANT * AVOGADRO_CONSTANT
+BOLTZMANN_CONSTANT = 1.380649e-23       # joules / Kelvin
+AVOGADRO_CONSTANT = 6.02214076e23       # / mole
+GAS_CONSTANT = BOLTZMANN_CONSTANT * AVOGADRO_CONSTANT   # joules / Kelvin-mole
\ No newline at end of file
diff --git a/src/acom_music_box/examples/configs/analytical/evolving_conditions.csv b/src/acom_music_box/examples/configs/analytical/evolving_conditions.csv
deleted file mode 100644
index 5c133edf..00000000
--- a/src/acom_music_box/examples/configs/analytical/evolving_conditions.csv
+++ /dev/null
@@ -1,2 +0,0 @@
-time.s
-0
diff --git a/src/acom_music_box/examples/configs/analytical/my_config.json b/src/acom_music_box/examples/configs/analytical/my_config.json
index dc10326f..16d330db 100644
--- a/src/acom_music_box/examples/configs/analytical/my_config.json
+++ b/src/acom_music_box/examples/configs/analytical/my_config.json
@@ -26,7 +26,6 @@
     }
   },
   "evolving conditions": {
-    "evolving_conditions.csv": {}
   },
   "initial conditions": {},
   "model components": [
diff --git a/src/acom_music_box/music_box.py b/src/acom_music_box/music_box.py
index d8cb9f38..b2c15bda 100644
--- a/src/acom_music_box/music_box.py
+++ b/src/acom_music_box/music_box.py
@@ -10,7 +10,6 @@
 import pandas as pd
 
 from tqdm import tqdm
-from tqdm.contrib.logging import logging_redirect_tqdm
 
 import logging
 logger = logging.getLogger(__name__)
@@ -55,7 +54,6 @@ def __init__(
         self.evolving_conditions = evolving_conditions if evolving_conditions is not None else EvolvingConditions([
         ], [])
         self.config_file = config_file if config_file is not None else "camp_data/config.json"
-
         self.solver = None
 
     def add_evolving_condition(self, time_point, conditions):
@@ -70,26 +68,6 @@ def add_evolving_condition(self, time_point, conditions):
             time=[time_point], conditions=[conditions])
         self.evolvingConditions.append(evolving_condition)
 
-    def create_solver(
-            self,
-            path_to_config,
-            solver_type=musica.micmsolver.rosenbrock,
-            number_of_grid_cells=1):
-        """
-        Creates a micm solver object using the CAMP configuration files.
-
-        Args:
-            path_to_config (str): The path to CAMP configuration directory.
-
-        Returns:
-            None
-        """
-        # Create a solver object using the configuration file
-        self.solver = musica.create_solver(
-            path_to_config,
-            solver_type,
-            number_of_grid_cells)
-
     def check_config(self, boxConfigPath):
         """
         Verifies correct configuration of the MusicBox object.
@@ -106,7 +84,17 @@ def check_config(self, boxConfigPath):
             Throws error for the first check failed.
         """
 
-        # look for duplicate reaction names
+        # Check for duplicate reactions in the reaction list
+        if self.reaction_list:
+            reaction_names = [reaction.name for reaction in self.reaction_list.reactions]
+            reaction_names = [name for name in reaction_names if name is not None]
+            dup_names = [name for name in reaction_names if reaction_names.count(name) > 1]
+
+            if dup_names:
+                raise Exception(f"Error: Duplicate reaction names specified within {boxConfigPath}: {dup_names}. "
+                        "Please remove or rename the duplicates.")
+
+        # look for duplicate reaction names in the initial conditions
         if (self.initial_conditions):
             if (self.initial_conditions.reaction_rates):
                 reactionNames = []
@@ -301,6 +289,7 @@ def loadJson(self, path_to_json):
 
         with open(path_to_json, 'r') as json_file:
             data = json.load(json_file)
+            self.config_file = data['model components'][0]['configuration file']
             # Set box model options
             self.box_model_options = BoxModelOptions.from_config_JSON(data)
 
diff --git a/src/acom_music_box/reaction_list.py b/src/acom_music_box/reaction_list.py
index a7592caf..f07d0b83 100644
--- a/src/acom_music_box/reaction_list.py
+++ b/src/acom_music_box/reaction_list.py
@@ -81,8 +81,7 @@ def from_config_JSON(cls, path_to_json, config_JSON, species_list):
 
             # assumes reactions file is second in the list
             if (len(config['camp-files']) > 1):
-                reaction_file_path = os.path.dirname(
-                    config_file_path) + "/" + config['camp-files'][1]
+                reaction_file_path = os.path.join(os.path.dirname(config_file_path), config['camp-files'][1])
                 with open(reaction_file_path, 'r') as reaction_file:
                     reaction_data = json.load(reaction_file)
 
diff --git a/src/acom_music_box/species_list.py b/src/acom_music_box/species_list.py
index 4d815d53..db3311a6 100644
--- a/src/acom_music_box/species_list.py
+++ b/src/acom_music_box/species_list.py
@@ -80,8 +80,7 @@ def from_config_JSON(cls, path_to_json, config_JSON):
 
             # assumes species file is first in the list
             if (len(config['camp-files']) > 0):
-                species_file_path = os.path.dirname(
-                    config_file_path) + "/" + config['camp-files'][0]
+                species_file_path = os.path.join( os.path.dirname(config_file_path), config['camp-files'][0])
                 with open(species_file_path, 'r') as species_file:
                     species_data = json.load(species_file)
                     # loads species by names from camp files
diff --git a/src/acom_music_box/tools/waccmToMusicBox.py b/src/acom_music_box/tools/waccmToMusicBox.py
index 53293eaf..8b438792 100644
--- a/src/acom_music_box/tools/waccmToMusicBox.py
+++ b/src/acom_music_box/tools/waccmToMusicBox.py
@@ -17,6 +17,7 @@
 import tempfile
 import zipfile
 from acom_music_box import Examples
+from acom_music_box.utils import calculate_air_density
 
 import logging
 logger = logging.getLogger(__name__)
@@ -219,19 +220,6 @@ def readWACCM(waccmMusicaDict, latitude, longitude,
     return (musicaDict)
 
 
-# Calculate air density from the ideal gas law.
-# tempK = temperature in degrees Kelvin
-# pressPa = pressure in Pascals
-# return density of air in moles / cubic meter
-def calcAirDensity(tempK, pressPa):
-    BOLTZMANN_CONSTANT = 1.380649e-23       # joules / Kelvin
-    AVOGADRO_CONSTANT = 6.02214076e23       # / mole
-    GAS_CONSTANT = BOLTZMANN_CONSTANT * AVOGADRO_CONSTANT   # joules / Kelvin-mole
-    airDensity = pressPa / (GAS_CONSTANT * tempK)           # moles / m3
-
-    return airDensity
-
-
 # set up indexes for the tuple
 musicaIndex = 0
 valueIndex = 1
@@ -252,7 +240,7 @@ def convertWaccm(varDict):
     temperature = varDict["temperature"][valueIndex]
     pressure = varDict["pressure"][valueIndex]
     logger.info(f"temperature = {temperature} K   pressure = {pressure} Pa")
-    air_density = calcAirDensity(temperature, pressure)
+    air_density = calculate_air_density(temperature, pressure)
     logger.info(f"air density = {air_density} mol m-3")
 
     for key, vTuple in varDict.items():
diff --git a/src/acom_music_box/utils.py b/src/acom_music_box/utils.py
index 072179b9..639bc5e8 100644
--- a/src/acom_music_box/utils.py
+++ b/src/acom_music_box/utils.py
@@ -1,3 +1,15 @@
+import re
+from .constants import GAS_CONSTANT, AVOGADRO_CONSTANT
+
+def extract_unit(data, key):
+    """Extract the value and unit from the key in data."""
+    pattern = re.compile(rf'{key} \[(.+)\]')
+    for k, v in data.items():
+        match = pattern.match(k)
+        if match:
+            return float(v), match.group(1)
+    return None, None
+
 def convert_time(data, key):
     """
     Convert the time from the input data to seconds.
@@ -5,26 +17,21 @@ def convert_time(data, key):
     Args:
         data (dict): The input data.
         key (str): The key for the time in the input data.
-
     Returns:
         float: The time in seconds.
     """
-    time = None
-
-    for unit in ['sec', 'min', 'hour', 'hr', 'day']:
-        if f'{key} [{unit}]' in data:
-            time_value = float(data[f'{key} [{unit}]'])
-            if unit == 'sec':
-                time = time_value
-            elif unit == 'min':
-                time = time_value * 60
-            elif unit == 'hour' or unit == 'hr':
-                time = time_value * 3600
-            elif unit == 'day':
-                time = time_value * 86400
-            break
-    return time
-
+    time_value, unit = extract_unit(data, key)
+    
+    if unit == 'sec':
+        return time_value
+    elif unit == 'min':
+        return time_value * 60
+    elif unit in ['hour', 'hr']:
+        return time_value * 3600
+    elif unit == 'day':
+        return time_value * 86400
+    else:
+        raise ValueError(f"Unsupported time unit: {unit}")
 
 def convert_pressure(data, key):
     """
@@ -33,27 +40,23 @@ def convert_pressure(data, key):
     Args:
         data (dict): The input data.
         key (str): The key for the pressure in the input data.
-
     Returns:
         float: The pressure in Pascals.
     """
-    pressure = None
-    for unit in ['Pa', 'atm', 'bar', 'kPa', 'hPa', 'mbar']:
-        if f'{key} [{unit}]' in data:
-            pressure_value = float(data[f'{key} [{unit}]'])
-            if unit == 'Pa':
-                pressure = pressure_value
-            elif unit == 'atm':
-                pressure = pressure_value * 101325
-            elif unit == 'bar':
-                pressure = pressure_value * 100000
-            elif unit == 'kPa':
-                pressure = pressure_value * 1000
-            elif unit == 'hPa' or unit == 'mbar':
-                pressure = pressure_value * 100
-            break
-    return pressure
-
+    pressure_value, unit = extract_unit(data, key)
+    
+    if unit == 'Pa':
+        return pressure_value
+    elif unit == 'atm':
+        return pressure_value * 101325
+    elif unit == 'bar':
+        return pressure_value * 100000
+    elif unit == 'kPa':
+        return pressure_value * 1000
+    elif unit in ['hPa', 'mbar']:
+        return pressure_value * 100
+    else:
+        raise ValueError(f"Unsupported pressure unit: {unit}")
 
 def convert_temperature(data, key):
     """
@@ -62,46 +65,62 @@ def convert_temperature(data, key):
     Args:
         data (dict): The input data.
         key (str): The key for the temperature in the input data.
-
     Returns:
         float: The temperature in Kelvin.
     """
-    temperature = None
-    for unit in ['K', 'C', 'F']:
-        if f'{key} [{unit}]' in data:
-            temperature_value = float(data[f'{key} [{unit}]'])
-            if unit == 'K':
-                temperature = temperature_value
-            elif unit == 'C':
-                temperature = temperature_value + 273.15
-            elif unit == 'F':
-                temperature = (temperature_value - 32) * 5 / 9 + 273.15
-            break
-    return temperature
-
+    temperature_value, unit = extract_unit(data, key)
+    
+    if unit == 'K':
+        return temperature_value
+    elif unit == 'C':
+        return temperature_value + 273.15
+    elif unit == 'F':
+        return (temperature_value - 32) * 5 / 9 + 273.15
+    else:
+        raise ValueError(f"Unsupported temperature unit: {unit}")
 
-def convert_concentration(data, key):
+def convert_concentration(data, key, temperature, pressure):
     """
     Convert the concentration from the input data to molecules per cubic meter.
 
     Args:
         data (dict): The input data.
         key (str): The key for the concentration in the input data.
-
+        temperature (float): The temperature in Kelvin.
+        pressure (float): The pressure in Pascals.
     Returns:
         float: The concentration in molecules per cubic meter.
     """
-    concentration = None
-    for unit in ['mol m-3', 'mol cm-3', 'molec m-3', 'molec cm-3']:
-        if f'{key} [{unit}]' in data:
-            concentration_value = float(data[f'{key} [{unit}]'])
-            if unit == 'mol m-3':
-                concentration = concentration_value
-            elif unit == 'mol cm-3':
-                concentration = concentration_value * 1e3
-            elif unit == 'molec m-3':
-                concentration = concentration_value / 6.02214076e23
-            elif unit == 'molec cm-3':
-                concentration = concentration_value * 1e3 / 6.02214076e23
-            break
-    return concentration
+    concentration_value, unit = extract_unit(data, key)
+    air_density = calculate_air_density(temperature, pressure)
+
+    unit_conversions = {
+        'mol m-3': 1,
+        'mol cm-3': 1e3,
+        'molec m-3': 1 / AVOGADRO_CONSTANT,
+        'molecule m-3': 1 / AVOGADRO_CONSTANT,
+        'molec cm-3': 1e3 / AVOGADRO_CONSTANT,
+        'molecule cm-3': 1e3 / AVOGADRO_CONSTANT,
+        'ppth': 1e-3 * air_density,
+        'ppm': 1e-6 * air_density,
+        'ppb': 1e-9 * air_density,
+        'ppt': 1e-12 * air_density,
+        'mol mol-1': 1 * air_density
+    }
+
+    if unit in unit_conversions:
+        return concentration_value * unit_conversions[unit]
+    else:
+        raise ValueError(f"Unsupported concentration unit: {unit}")
+
+def calculate_air_density(temperature, pressure):
+    """
+    Calculate the air density in moles/m^3.
+
+    Args:
+        temperature (float): The temperature in Kelvin.
+        pressure (float): The pressure in Pascals.
+    Returns:
+        float: The air density in moles/m^3.
+    """
+    return pressure / (GAS_CONSTANT * temperature)
diff --git a/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/config.json b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/config.json
new file mode 100644
index 00000000..03622f15
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/config.json	
@@ -0,0 +1 @@
+{"camp-files": ["species.json", "reactions.json"]}
\ No newline at end of file
diff --git a/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/reactions.json b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/reactions.json
new file mode 100644
index 00000000..bcd7de3e
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/reactions.json	
@@ -0,0 +1,49 @@
+{
+    "camp-data": [
+        {
+            "type": "MECHANISM",
+            "name": "music box interactive configuration",
+            "reactions": [
+                {
+                    "type": "ARRHENIUS",
+                    "A": 0.00012,
+                    "B": 7,
+                    "C": 75,
+                    "D": 50,
+                    "E": 0.5,
+                    "reactants": {
+                        "B": {
+                            "qty": 1
+                        }
+                    },
+                    "products": {
+                        "C": {
+                            "yield": 1
+                        },
+                        "irr__089f1f45-4cd8-4278-83d5-d638e98e4315": {
+                            "yield": 1
+                        }
+                    }
+                },
+                {
+                    "type": "ARRHENIUS",
+                    "A": 0.004,
+                    "C": 50,
+                    "reactants": {
+                        "A": {
+                            "qty": 1
+                        }
+                    },
+                    "products": {
+                        "B": {
+                            "yield": 1
+                        },
+                        "irr__2a109b21-bb24-41ae-8f06-7485fd36f1a7": {
+                            "yield": 1
+                        }
+                    }
+                }
+            ]
+        }
+    ]
+}
\ No newline at end of file
diff --git a/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/species.json b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/species.json
new file mode 100644
index 00000000..0a3282b3
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/mol mol-1/camp_data/species.json	
@@ -0,0 +1,24 @@
+{
+    "camp-data": [
+        {
+            "name": "A",
+            "type": "CHEM_SPEC"
+        },
+        {
+            "name": "B",
+            "type": "CHEM_SPEC"
+        },
+        {
+            "name": "C",
+            "type": "CHEM_SPEC"
+        },
+        {
+            "name": "irr__089f1f45-4cd8-4278-83d5-d638e98e4315",
+            "type": "CHEM_SPEC"
+        },
+        {
+            "name": "irr__2a109b21-bb24-41ae-8f06-7485fd36f1a7",
+            "type": "CHEM_SPEC"
+        }
+    ]
+}
\ No newline at end of file
diff --git a/tests/integration/configs/mixing_ratio/mol mol-1/my_config.json b/tests/integration/configs/mixing_ratio/mol mol-1/my_config.json
new file mode 100644
index 00000000..c529ac53
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/mol mol-1/my_config.json	
@@ -0,0 +1,45 @@
+
+{
+  "box model options": {
+    "grid": "box",
+    "chemistry time step [sec]": 1,
+    "output time step [sec]": 1,
+    "simulation length [sec]": 100
+  },
+  "chemical species": {
+    "A": {
+      "initial value [mol mol-1]": 0.02237646638131061
+    },
+    "B": {
+      "initial value [mol m-3]": 0
+    },
+    "C": {
+      "initial value [mol m-3]": 0
+    }
+  },
+  "environmental conditions": {
+    "pressure": {
+      "initial value [Pa]": 101253.3
+    },
+    "temperature": {
+      "initial value [K]": 272.5
+    }
+  },
+  "evolving conditions": {
+  },
+  "initial conditions": {},
+  "model components": [
+    {
+      "type": "CAMP",
+      "configuration file": "camp_data/config.json",
+      "override species": {
+        "M": {
+          "mixing ratio mol mol-1": 1
+        }
+      },
+      "suppress output": {
+        "M": {}
+      }
+    }
+  ]
+}
diff --git a/tests/integration/configs/mixing_ratio/ppb/my_config.json b/tests/integration/configs/mixing_ratio/ppb/my_config.json
new file mode 100644
index 00000000..21ec7d13
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/ppb/my_config.json
@@ -0,0 +1,44 @@
+
+{
+  "box model options": {
+    "grid": "box",
+    "chemistry time step [sec]": 1,
+    "output time step [sec]": 1,
+    "simulation length [sec]": 100
+  },
+  "chemical species": {
+    "A": {
+      "initial value [ppb]": 22376466.38131061
+    },
+    "B": {
+      "initial value [mol m-3]": 0
+    },
+    "C": {
+      "initial value [mol m-3]": 0
+    }
+  },
+  "environmental conditions": {
+    "pressure": {
+      "initial value [Pa]": 101253.3
+    },
+    "temperature": {
+      "initial value [K]": 272.5
+    }
+  },
+  "evolving conditions": {},
+  "initial conditions": {},
+  "model components": [
+    {
+      "type": "CAMP",
+      "configuration file": "../mol mol-1/camp_data/config.json",
+      "override species": {
+        "M": {
+          "mixing ratio mol mol-1": 1
+        }
+      },
+      "suppress output": {
+        "M": {}
+      }
+    }
+  ]
+}
diff --git a/tests/integration/configs/mixing_ratio/ppm/my_config.json b/tests/integration/configs/mixing_ratio/ppm/my_config.json
new file mode 100644
index 00000000..1a072ef0
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/ppm/my_config.json
@@ -0,0 +1,45 @@
+
+{
+  "box model options": {
+    "grid": "box",
+    "chemistry time step [sec]": 1,
+    "output time step [sec]": 1,
+    "simulation length [sec]": 100
+  },
+  "chemical species": {
+    "A": {
+      "initial value [ppm]": 22376.46638131061
+    },
+    "B": {
+      "initial value [mol m-3]": 0
+    },
+    "C": {
+      "initial value [mol m-3]": 0
+    }
+  },
+  "environmental conditions": {
+    "pressure": {
+      "initial value [Pa]": 101253.3
+    },
+    "temperature": {
+      "initial value [K]": 272.5
+    }
+  },
+  "evolving conditions": {
+  },
+  "initial conditions": {},
+  "model components": [
+    {
+      "type": "CAMP",
+      "configuration file": "../mol mol-1/camp_data/config.json",
+      "override species": {
+        "M": {
+          "mixing ratio mol mol-1": 1
+        }
+      },
+      "suppress output": {
+        "M": {}
+      }
+    }
+  ]
+}
diff --git a/tests/integration/configs/mixing_ratio/ppt/my_config.json b/tests/integration/configs/mixing_ratio/ppt/my_config.json
new file mode 100644
index 00000000..4dc0b372
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/ppt/my_config.json
@@ -0,0 +1,45 @@
+
+{
+  "box model options": {
+    "grid": "box",
+    "chemistry time step [sec]": 1,
+    "output time step [sec]": 1,
+    "simulation length [sec]": 100
+  },
+  "chemical species": {
+    "A": {
+      "initial value [ppt]": 22376466381.310608
+    },
+    "B": {
+      "initial value [mol m-3]": 0
+    },
+    "C": {
+      "initial value [mol m-3]": 0
+    }
+  },
+  "environmental conditions": {
+    "pressure": {
+      "initial value [Pa]": 101253.3
+    },
+    "temperature": {
+      "initial value [K]": 272.5
+    }
+  },
+  "evolving conditions": {
+  },
+  "initial conditions": {},
+  "model components": [
+    {
+      "type": "CAMP",
+      "configuration file": "../mol mol-1/camp_data/config.json",
+      "override species": {
+        "M": {
+          "mixing ratio mol mol-1": 1
+        }
+      },
+      "suppress output": {
+        "M": {}
+      }
+    }
+  ]
+}
diff --git a/tests/integration/configs/mixing_ratio/ppth/my_config.json b/tests/integration/configs/mixing_ratio/ppth/my_config.json
new file mode 100644
index 00000000..c1d31f41
--- /dev/null
+++ b/tests/integration/configs/mixing_ratio/ppth/my_config.json
@@ -0,0 +1,45 @@
+
+{
+  "box model options": {
+    "grid": "box",
+    "chemistry time step [sec]": 1,
+    "output time step [sec]": 1,
+    "simulation length [sec]": 100
+  },
+  "chemical species": {
+    "A": {
+      "initial value [ppth]": 22.37646638131061
+    },
+    "B": {
+      "initial value [mol m-3]": 0
+    },
+    "C": {
+      "initial value [mol m-3]": 0
+    }
+  },
+  "environmental conditions": {
+    "pressure": {
+      "initial value [Pa]": 101253.3
+    },
+    "temperature": {
+      "initial value [K]": 272.5
+    }
+  },
+  "evolving conditions": {
+  },
+  "initial conditions": {},
+  "model components": [
+    {
+      "type": "CAMP",
+      "configuration file": "../mol mol-1/camp_data/config.json",
+      "override species": {
+        "M": {
+          "mixing ratio mol mol-1": 1
+        }
+      },
+      "suppress output": {
+        "M": {}
+      }
+    }
+  ]
+}
diff --git a/tests/integration/test_mixing_ratios.py b/tests/integration/test_mixing_ratios.py
new file mode 100644
index 00000000..6272df5c
--- /dev/null
+++ b/tests/integration/test_mixing_ratios.py
@@ -0,0 +1,116 @@
+from acom_music_box import MusicBox, Examples
+import os
+
+import math
+
+
+class TestAnalyticalWithMixingRatios:
+    def run_example(self, example):
+        box_model = MusicBox()
+        box_model.loadJson(example)
+
+        # solves and saves output
+        df = box_model.solve()
+        output = [df.columns.values.tolist()] + df.values.tolist()
+
+        conc_a_index = output[0].index("CONC.A")
+        conc_b_index = output[0].index("CONC.B")
+        conc_c_index = output[0].index("CONC.C")
+
+        # extracts model concentrations from data output
+        model_concentrations = [
+            [row[conc_a_index], row[conc_b_index], row[conc_c_index]]
+            for row in output[1:]
+        ]
+
+        # initalizes concentrations
+        analytical_concentrations = []
+        analytical_concentrations.append([1, 0, 0])
+
+        time_step = box_model.box_model_options.chem_step_time
+        sim_length = box_model.box_model_options.simulation_length
+
+        temperature = box_model.initial_conditions.temperature
+        pressure = box_model.initial_conditions.pressure
+
+        k1 = 4.0e-3 * math.exp(50 / temperature)
+        k2 = (
+            1.2e-4
+            * math.exp(75 / temperature)
+            * (temperature / 50) ** 7
+            * (1.0 + 0.5 * pressure)
+        )
+
+        curr_time = time_step
+
+        idx_A = 0
+        idx_B = 1
+        idx_C = 2
+
+        # gets analytical concentrations
+        while curr_time <= sim_length:
+
+            initial_A = analytical_concentrations[0][idx_A]
+            A_conc = initial_A * math.exp(-(k1) * curr_time)
+            B_conc = (
+                initial_A
+                * (k1 / (k2 - k1))
+                * (math.exp(-k1 * curr_time) - math.exp(-k2 * curr_time))
+            )
+            C_conc = initial_A * (
+                1.0
+                + (k1 * math.exp(-k2 * curr_time) - k2 * math.exp(-k1 * curr_time))
+                / (k2 - k1)
+            )
+
+            analytical_concentrations.append([A_conc, B_conc, C_conc])
+            curr_time += time_step
+
+        # asserts concentrations
+        for i in range(len(model_concentrations)):
+            assert math.isclose(
+                model_concentrations[i][idx_A],
+                analytical_concentrations[i][idx_A],
+                rel_tol=1e-8,
+            ), f"Arrays differ at index ({i}, 0)"
+            assert math.isclose(
+                model_concentrations[i][idx_B],
+                analytical_concentrations[i][idx_B],
+                rel_tol=1e-8,
+            ), f"Arrays differ at index ({i}, 1)"
+            assert math.isclose(
+                model_concentrations[i][idx_C],
+                analytical_concentrations[i][idx_C],
+                rel_tol=1e-8,
+            ), f"Arrays differ at index ({i}, 2)"
+
+
+    def test_mol_mol_1(self):
+        current_dir = os.path.dirname(__file__)
+        example = os.path.join(current_dir, "configs", "mixing_ratio", "mol mol-1", "my_config.json")
+        self.run_example(example)
+    
+    def test_ppth(self):
+        current_dir = os.path.dirname(__file__)
+        example = os.path.join(current_dir, "configs", "mixing_ratio", "ppth", "my_config.json")
+        self.run_example(example)
+
+    def test_ppm(self):
+        current_dir = os.path.dirname(__file__)
+        example = os.path.join(current_dir, "configs", "mixing_ratio", "ppm", "my_config.json")
+        self.run_example(example)
+    
+    def test_ppb(self):
+        current_dir = os.path.dirname(__file__)
+        example = os.path.join(current_dir, "configs", "mixing_ratio", "ppb", "my_config.json")
+        self.run_example(example)
+
+    def test_ppt(self):
+        current_dir = os.path.dirname(__file__)
+        example = os.path.join(current_dir, "configs", "mixing_ratio", "ppt", "my_config.json")
+        self.run_example(example)
+
+
+if __name__ == "__main__":
+    test = TestAnalytical()
+    test.test_run()
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
new file mode 100644
index 00000000..c77fa57e
--- /dev/null
+++ b/tests/unit/test_utils.py
@@ -0,0 +1,59 @@
+import pytest
+from acom_music_box.utils import (
+    convert_time, 
+    convert_pressure, 
+    convert_temperature, 
+    convert_concentration, 
+    calculate_air_density
+)
+import math
+
+@pytest.mark.parametrize("data, key, expected", [
+  ({'time [sec]': 60}, 'time', 60),
+  ({'time [min]': 1}, 'time', 60),
+  ({'time [hour]': 1}, 'time', 3600),
+  ({'time [day]': 1}, 'time', 86400),
+])
+def test_convert_time(data, key, expected):
+  assert convert_time(data, key) == expected
+
+
+@pytest.mark.parametrize("data, key, expected", [
+  ({'pressure [Pa]': 101325}, 'pressure', 101325),
+  ({'pressure [atm]': 1}, 'pressure', 101325),
+  ({'pressure [bar]': 1}, 'pressure', 100000),
+  ({'pressure [kPa]': 101.325}, 'pressure', 101325),
+  ({'pressure [hPa]': 1013.25}, 'pressure', 101325),
+])
+def test_convert_pressure(data, key, expected):
+  assert convert_pressure(data, key) == expected
+
+@pytest.mark.parametrize("data, key, expected", [
+  ({'temp [K]': 273.15}, 'temp', 273.15),
+  ({'temp [C]': 0}, 'temp', 273.15),
+  ({'temp [F]': 32}, 'temp', 273.15),
+])
+def test_convert_temperature(data, key, expected):
+  assert convert_temperature(data, key) == expected
+
+
+@pytest.mark.parametrize("data, key, temperature, pressure, expected", [
+  ({'concentration [mol m-3]': 1}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [mol cm-3]': 1e-3}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [molec m-3]': 6.02214076e+23}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [molec cm-3]': 6.02214076e+20}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [molecule m-3]': 6.02214076e+23}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [molecule cm-3]': 6.02214076e+20}, 'concentration', 298.15, 101325, 1),
+  ({'concentration [ppth]': 1e-3}, 'concentration', 298.15, 101325, 1e-6 * calculate_air_density(298.15, 101325)),
+  ({'concentration [ppm]': 1}, 'concentration', 298.15, 101325, 1e-6 * calculate_air_density(298.15, 101325)),
+  ({'concentration [ppb]': 1}, 'concentration', 298.15, 101325, 1e-9 * calculate_air_density(298.15, 101325)),
+  ({'concentration [ppt]': 1}, 'concentration', 298.15, 101325, 1e-12 * calculate_air_density(298.15, 101325)),
+  ({'concentration [mol mol-1]': 1}, 'concentration', 298.15, 101325, 1 * calculate_air_density(298.15, 101325)),
+])
+def test_convert_concentration(data, key, temperature, pressure, expected):
+  assert math.isclose(convert_concentration(data, key, temperature, pressure), expected)
+
+def test_invalid_concentration():
+    data = {'invalid_concentration': 100}
+    with pytest.raises(ValueError):
+        convert_concentration(data, 'invalid_concentration', 298.15, 101325)