Correction for dry air density

kebasaa · Apr 21, 2022 · 763caad · 763caad
1 parent cb83ccf
commit 763caad
Showing 1 changed file with 12 additions and 5 deletions.
diff --git a/02_laser.ipynb b/02_laser.ipynb
@@ -214,13 +214,20 @@
     "    return(RH)\n",
     "\n",
     "# Density of dry air\n",
-    "# - https://en.wikipedia.org/wiki/Density_of_air\n",
-    "def calculate_rho_dry_air(T_C, P_Pa):\n",
+    "# - https://www.licor.com/env/support/EddyPro/topics/calculate-micromet-variables.html\n",
+    "def calculate_rho_dry_air(T_C, h2o_mmol_mol, P_Pa):\n",
     "    # Constants\n",
-    "    R_dry_air = 287.058     # [J/(kg·K)] Specific gas const dry air\n",
-    "    # Calculations\n",
+    "    R_dry_air = 287.058     # [J kg-1 K-1] Specific gas const dry air\n",
     "    T_K = T_C + 273.15\n",
-    "    rho_dry_air = P_Pa / (R_dry_air * T_K) # Density of dry air (use for approximation)\n",
+    "    \n",
+    "    # Preparations\n",
+    "    R     = 8.314463             # Ideal gas constant (J K-1 mol-1)\n",
+    "    M_d   = 0.02897              # molecular weights of dry air (kg mol-1)\n",
+    "    M_h2o = 0.01802              # molecular weights of water vapour (kg mol-1)\n",
+    "    e = h2o_mol_mol * P_Pa       # Water vapor partial pressure (Pa)\n",
+    "    P_d = P_Pa - e               # Dry air partial pressure (P_d, P_a)\n",
+    "    \n",
+    "    rho_dry_air = P_d / (R_dry_air * T_K) # Density of dry air (use for approximation)\n",
     "    return(rho_dry_air)\n",
     "\n",
     "# Density of moist air\n",