CFR > Title 40 - Protection of Environment > CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY > SUBCHAPTER C—AIR PROGRAMS (Parts 50–99) > PART 86—CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND ENGINES > SUBPART D—Emission Regulations for New Gasoline-Fueled and Diesel-Fueled Heavy-Duty Engines; Gaseous Exhaust Test Procedures (§86.301-79 to §86.348-79) > 86.344-79—Humidity calculations.

86.344-79—Humidity calculations.

(a) The following abbreviations (and units) are used in this section:
BARO = barometric pressure (Pa)
H = specific humidity, (gm H2O/gm of dry air)
K = 0.6220 gm H2O/gm dry air
Mair = Molecular weight of air = 28.9645
MH2O = Molecular weight of water = 18.01534
PDB = Saturation vapor pressure of water at the dry bulb temperature (Pa)
PDP = saturation vapor pressure of water at the dewpoint temperature (Pa)
Pv = partial pressure of water vapor (Pa)
PWB = saturation vapor pressure of water at the wet bulb temperature (pa)
TDB = Dry bulb temperature (°K)
TWB = Wet bulb temperature (°K)
Y = Water-vapor volume concentration
(b) The specific humidity on a dry basis of the intake air (H) is defined by equation (1).
(c) The partial pressure of water vapor may be determined in two manners:
(1) A dew point device may be used. In that case:

Code of Federal Regulations

P v=P DP
(2) A wet-bulb, dry-bulb method may be used. In that case “Ferrels equation” (eq. (2)) is used.
(d) (1) The saturation vapor pressure (P WB) of water at the wet-bulb temperature is defined by equation (3) (Ref. Wexler and Greenspan, equation (23), National Bureau of Standards).
where:
PWB is in Pascals (Pa)
TWB = Web-bulb temperature (°K)
B = − 12.150799
F0 = − 8.49922(10)3
F1 = − 7.4231865(10)3
F2 = 96.1635147
F3 = 2.4917646(10) −2
F4 = − 1.3160119(10) −5
F5 = − 1.1460454(10) −8
F6 = 2.1701289(10) −11
F7 = − 3.610258(10) −15
F8 = 3.8504519(10) −18
F9 = − 1.4317(10) −21
(2) The table in Figure D79-5 may be used in lieu of equation (3).
(e) The saturated vapor pressure of water at the dry-bulb temperature (P DB) is found (if required) by using dry-bulb absolute temperature (°K) in equation (3).
(f) The percent of relative humidity (RH) (if required) is defined by equation (4).
(g) The water-vapor volume concentration on a dry basis of the engine intake air (Y) is defined by equation (5).
Figure D79-5—Saturation Vapor Pressure Over Water (pascals)
Temperature °C 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0 610.752 615.207 619.690 624.203 628.744 633.315 637.916 642.545 647.205 651.894
1 656.614 661.364 666.144 670.955 675.796 680.669 685.572 690.507 695.473 700.471
2 705.500 710.562 715.655 720.781 725.939 731.130 736.354 741.611 746.901 752.224
3 757.581 762.971 768.396 773.854 779.347 784.874 790.436 796.033 801.664 807.331
4 813.034 818.771 824.545 830.355 836.200 842.082 848.001 853.956 859.948 865.978
5 872.045 878.149 884.291 890.470 896.688 902.945 909.239 915.573 921.945 928.357
6 934.808 941.298 947.828 954.399 961.009 967.660 974.351 981.083 987.856 994.670
7 1001.53 1008.42 1015.36 1022.34 1029.37 1036.43 1043.54 1050.70 1057.89 1065.13
8 1072.41 1079.74 1087.11 1094.52 1101.98 1109.48 1117.03 1124.63 1132.27 1139.95
9 1147.68 1155.46 1163.28 1171.15 1179.07 1187.04 1195.05 1203.11 1211.21 1219.37
10 1227.57 1235.83 1244.13 1252.48 1260.88 1269.32 1277.82 1286.37 1294.97 1303.62
11 1312.32 1321.07 1329.87 1338.73 1347.63 1356.59 1365.60 1374.67 1383.78 1392.95
12 1402.17 1411.45 1420.78 1430.16 1439.60 1449.10 1458.64 1468.25 1477.91 1487.62
Code of Federal Regulations 658
13 1497.39 1507.22 1517.11 1527.05 1537.04 1547.10 1557.21 1567.39 1577.62 1587.90
14 1598.25 1608.66 1619.12 1629.65 1640.24 1650.88 1661.59 1672.36 1683.18 1694.08
15 1705.03 1716.04 1727.12 1738.26 1749.46 1760.73 1772.06 1783.45 1794.91 1806.43
16 1818.01 1829.67 1841.38 1853.17 1865.02 1876.93 1888.91 1900.96 1913.08 1925.27
17 1937.52 1949.84 1962.23 1974.69 1987.21 1999.81 2012.48 2025.21 2038.02 2050.90
18 2063.85 2076.87 2089.97 2103.13 2116.37 2129.68 2143.07 2156.53 2170.06 2183.66
19 2197.34 2211.10 2224.93 2238.84 2252.82 2266.88 2281.02 2295.23 2309.52 2323.89
20 2338.34 2352.86 2367.47 2382.15 2396.91 2411.76 2426.68 2441.68 2456.77 2471.93
21 2487.18 2502.51 2517.93 2533.42 2549.00 2564.66 2580.41 2596.24 2612.16 2628.16
22 2644.25 2660.42 2676.68 2693.02 2709.46 2725.98 2742.59 2759.28 2776.07 2792.94
23 2809.91 2826.96 2844.11 2861.34 2878.67 2896.09 2913.60 2931.20 2948.89 2966.68
24 2984.56 3002.54 3020.61 3038.77 3057.03 3075.39 3093.84 3112.39 3131.03 3149.78
25 3168.62 3187.55 3206.59 3225.73 3244.96 3264.30 3283.73 3303.27 3322.91 3242.65
26 3362.49 3382.43 3402.48 3422.63 3442.89 3463.24 3483.71 3504.28 3524.95 3545.73
27 3566.62 3587.62 3608.72 3629.93 3651.25 3672.67 3694.21 3715.86 3737.61 3759.48
28 3781.46 3803.55 3825.75 3848.07 3870.50 3893.04 3915.70 3938.47 3961.36 3984.36
29 4007.48 4030.71 4054.06 4077.53 4101.12 4124.83 4148.65 4172.59 4196.66 4220.84
30 4245.15 4269.58 4294.13 4318.80 4343.60 4368.52 4393.56 4418.73 4444.02 4469.44