diff --git a/cara/models.py b/cara/models.py
index b74cdcf2..95aabe08 100644
--- a/cara/models.py
+++ b/cara/models.py
@@ -221,11 +221,9 @@ class Expiration:
         def volume(diameter):
             return (4 * np.pi * (diameter/2)**3) / 3
         total = 0
-        for i, (diameter, factor) in enumerate(zip(self.particle_sizes, self.ejection_factor)):
+        for diameter, factor in zip(self.particle_sizes, self.ejection_factor):
             contribution = volume(diameter) * factor
-            if i >= 2:
-                # TODO: It is probably the case that this term comes from the
-                #  particle diameter, rather than arbitrary position in a sequence...
+            if diameter >= 3e-4:
                 contribution = contribution * (1 - mask.exhale_efficiency)
             total += contribution
         return total
diff --git a/cara/tests/test_known_quantities.py b/cara/tests/test_known_quantities.py
index 5a11e4ae..82c3ac71 100644
--- a/cara/tests/test_known_quantities.py
+++ b/cara/tests/test_known_quantities.py
@@ -139,3 +139,12 @@ def test_periodic_hepa(baseline_periodic_hepa, baseline_room):
     aes = [baseline_periodic_hepa.air_exchange(baseline_room, t) for t in ts]
     answers = [0, rate, rate, 0, 0, 0, rate, 0, 0]
     npt.assert_allclose(aes, answers, rtol=1e-5)
+
+
+def test_expiration_aerosols():
+    mask = models.Mask.types['Type I']
+    exp1 = models.Expiration((0.751, 0.139, 0.0139, 0.059),
+                            particle_sizes = (0.8e-4, 1.8e-4, 3.5e-4, 5.5e-4))
+    exp2 = models.Expiration((0.059, 0.0139, 0.751, 0.139),
+                            particle_sizes = (5.5e-4, 3.5e-4, 0.8e-4, 1.8e-4))
+    npt.assert_allclose(exp1.aerosols(mask), exp2.aerosols(mask), rtol=1e-5)