# 40 CFR 86.344-79 - Humidity calculations.

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§ 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
M air = Molecular weight of air = 28.9645
M H2O = Molecular weight of water = 18.01534
P DB = Saturation vapor pressure of water at the dry bulb temperature (Pa)
P DP = saturation vapor pressure of water at the dewpoint temperature (Pa)
P v = partial pressure of water vapor (Pa)
P WB = saturation vapor pressure of water at the wet bulb temperature (pa)
T DB = Dry bulb temperature (°K)
T WB = 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:
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:
P WB is in Pascals (Pa)
T WB = Web-bulb temperature (°K)
B = − 12.150799
F 0 = − 8.49922(10)3
F 1 = − 7.4231865(10)3
F 2 = 96.1635147
F 3 = 2.4917646(10) −2
F 4 = − 1.3160119(10) −5
F 5 = − 1.1460454(10) −8
F 6 = 2.1701289(10) −11
F 7 = − 3.610258(10) −15
F 8 = 3.8504519(10) −18
F 9 = − 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
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

Title 40 published on 2014-07-01.

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• 2015-02-19; vol. 80 # 33 - Thursday, February 19, 2015
1. 80 FR 9078 - Amendments Related to: Tier 3 Motor Vehicle Emission and Fuel Standards, Nonroad Engine and Equipment Programs, and MARPOL Annex VI Implementation
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ENVIRONMENTAL PROTECTION AGENCY
Direct final rule.
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Title 40 published on 2014-07-01

The following are ALL rules, proposed rules, and notices (chronologically) published in the Federal Register relating to 40 CFR Part 86 after this date.

• 2015-02-19; vol. 80 # 33 - Thursday, February 19, 2015
1. 80 FR 8826 - Amendments Related to: Tier 3 Motor Vehicle Emission and Fuel Standards, Nonroad Engine and Equipment Programs, and MARPOL Annex VI Implementation
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ENVIRONMENTAL PROTECTION AGENCY
Proposed rule.
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40 CFR Parts 59, 80, 85, 86, 600, 1037, 1043, 1051, 1054, 1060, 1065, and 1066