diff --git a/cara/models.py b/cara/models.py
index cf2ffb8f..794ed21b 100644
--- a/cara/models.py
+++ b/cara/models.py
@@ -616,7 +616,10 @@ _ExpirationBase.types = {
 
 @dataclass(frozen=True)
 class Activity:
+    #: Inhalation rate in m^3/h
     inhalation_rate: _VectorisedFloat
+
+    #: Exhalation rate in m^3/h
     exhalation_rate: _VectorisedFloat
 
     #: Pre-populated examples of activities.
@@ -671,6 +674,8 @@ class InfectedPopulation(Population):
 
         """
         # Emission Rate (infectious quantum / h)
+        # Note on units: exhalation rate is in m^3/h, aerosols in mL/cm^3
+        # and viral load in virus/mL -> 1e6 conversion factor
         aerosols = self.expiration.aerosols(self.mask)
 
         ER = (self.virus.viral_load_in_sputum *
@@ -855,6 +860,9 @@ class ExposureModel:
     #: The number of times the exposure event is repeated (default 1).
     repeats: int = 1
 
+    #: The fraction of viruses actually deposited in the respiratory tract
+    fraction_deposited: _VectorisedFloat = 0.6
+
     def quanta_exposure(self) -> _VectorisedFloat:
         """The number of virus quanta per meter^3."""
         exposure = 0.0
@@ -870,7 +878,7 @@ class ExposureModel:
         inf_aero = (
             self.exposed.activity.inhalation_rate *
             (1 - self.exposed.mask.inhale_efficiency()) *
-            exposure
+            exposure * self.fraction_deposited
         )
 
         # Probability of infection.
diff --git a/cara/tests/conftest.py b/cara/tests/conftest.py
index 44b25423..023e4e5a 100644
--- a/cara/tests/conftest.py
+++ b/cara/tests/conftest.py
@@ -32,5 +32,6 @@ def baseline_exposure_model(baseline_model):
             presence=baseline_model.infected.presence,
             activity=baseline_model.infected.activity,
             mask=baseline_model.infected.mask,
-        )
+        ),
+        fraction_deposited = 1.,
     )
diff --git a/cara/tests/models/test_exposure_model.py b/cara/tests/models/test_exposure_model.py
index 009cf092..35c5ac0c 100644
--- a/cara/tests/models/test_exposure_model.py
+++ b/cara/tests/models/test_exposure_model.py
@@ -55,22 +55,25 @@ populations = [
 
 
 @pytest.mark.parametrize(
-    "population, cm, expected_exposure, expected_probability",[
-    [populations[1], KnownConcentrations(lambda t: 1.2),
+    "population, cm, f_dep, expected_exposure, expected_probability",[
+    [populations[1], KnownConcentrations(lambda t: 1.2), 1.,
      np.array([14.4, 14.4]), np.array([99.6803184113, 99.5181053773])],
 
-    [populations[2], KnownConcentrations(lambda t: 1.2),
+    [populations[2], KnownConcentrations(lambda t: 1.2), 1.,
      np.array([14.4, 14.4]), np.array([97.4574432074, 98.3493482895])],
 
-    [populations[0], KnownConcentrations(lambda t: np.array([1.2, 2.4])),
+    [populations[0], KnownConcentrations(lambda t: np.array([1.2, 2.4])), 1.,
      np.array([14.4, 28.8]), np.array([98.3493482895, 99.9727534893])],
 
-    [populations[1], KnownConcentrations(lambda t: np.array([1.2, 2.4])),
+    [populations[1], KnownConcentrations(lambda t: np.array([1.2, 2.4])), 1.,
      np.array([14.4, 28.8]), np.array([99.6803184113, 99.9976777757])],
+
+    [populations[0], KnownConcentrations(lambda t: 2.4), np.array([0.5, 1.]),
+     28.8, np.array([98.3493482895, 99.9727534893])],
     ])
-def test_exposure_model_ndarray(population, cm, 
+def test_exposure_model_ndarray(population, cm, f_dep,
                                 expected_exposure, expected_probability):
-    model = ExposureModel(cm, population)
+    model = ExposureModel(cm, population, fraction_deposited = f_dep)
     np.testing.assert_almost_equal(
         model.quanta_exposure(), expected_exposure
     )
@@ -148,5 +151,5 @@ def test_exposure_model_integral_accuracy(exposed_time_interval,
         10, presence_interval, models.Mask.types['Type I'],
         models.Activity.types['Standing'],
     )
-    model = ExposureModel(conc_model, population)
+    model = ExposureModel(conc_model, population, fraction_deposited=1.)
     np.testing.assert_allclose(model.quanta_exposure(), expected_quanta)
diff --git a/cara/tests/test_known_quantities.py b/cara/tests/test_known_quantities.py
index a3b1e5db..4af1c06f 100644
--- a/cara/tests/test_known_quantities.py
+++ b/cara/tests/test_known_quantities.py
@@ -349,7 +349,8 @@ def build_exposure_model(concentration_model):
             presence=infected.presence,
             activity=infected.activity,
             mask=infected.mask,
-        )
+        ),
+        fraction_deposited = 1.,
     )