露点（Dew point），又称露点温度（Dew point temperature），在气象学中是指在固定气压之下，空气中所含的气态水达到饱和而凝结成液态水所需要降至的温度。在这温度时，凝结的水飘浮在空中称为雾、而沾在固体表面上时则称为露，因而得名露点。
那么气体湿度、露点和PPM含量怎样换算？请参考下列对照表。
| 湿度\露点\PPM对照表 |
|
| 露点摄氏度℃ | 露点华摄氏度F | 水蒸气压力 | PPM水份的体积比 | 相对湿度 | PPM水份的质量比 |
| -150 | -238 | 7*10-15 | 9.2*10-12 | － | 5.7*10-12 |
| -140 | -220 | 3*10-10 | 4.0*10-7 | － | 2.5*10-7 |
| -130 | -202 | 7*10-8 | 9.2*10-5 | － | 5.7*10-5 |
| -120 | -184 | 10*10-8 | 1.3*10-4 | 5.4*10-7 | 8.1*10-5 |
| -118 | -180 | 0.00000016 | 0.00021 | 0.0000009 | 0.00013 |
| -116 | -177 | 0.00000026 | 0.00034 | 0.0000014 | 0.00021 |
| -114 | -173 | 0.00000043 | 0.00057 | 0.0000023 | 0.00035 |
| -112 | -170 | 0.00000069 | 0.00091 | 0.0000037 | 0.00057 |
| -110 | -166 | 0.0000010 | 0.00132 | 0.0000053 | 0.00082 |
| -108 | -162 | 0.0000018 | 0.00237 | 0.0000096 | 0.0015 |
| -106 | -159 | 0.0000028 | 0.00368 | 0.000015 | 0.0023 |
| -104 | -155 | 0.0000043 | 0.00566 | 0.000023 | 0.0035 |
| -102 | -152 | 0.0000065 | 0.00855 | 0.000035 | 0.0053 |
| -100 | -148 | 0.0000099 | 0.0130 | 0.000053 | 0.0081 |
| -98 | -144 | 0.000015 | 0.0197 | 0.000080 | 0.012 |
| -96 | -141 | 0.000022 | 0.0289 | 0.00012 | 0.018 |
| -94 | -137 | 0.000033 | 0.0434 | 0.00018 | 0.027 |
| -92 | -134 | 0.000048 | 0.0632 | 0.00026 | 0.039 |
| -90 | -130 | 0.000070 | 0.0921 | 0.00037 | 0.057 |
| -88 | -126 | 0.00010 | 0.132 | 0.00054 | 0.082 |
| -86 | -123 | 0.00014 | 0.184 | 0.00075 | 0.11 |
| -84 | -119 | 0.00020 | 0.263 | 0.00107 | 0.16 |
| -82 | -116 | 0.00029 | 0.382 | 0.00155 | 0.24 |
| -80 | -112 | 0.00040 | 0.526 | 0.00214 | 0.33 |
| -78 | -108 | 0.00056 | 0.737 | 0.00300 | 0.46 |
| -76 | -105 | 0.00077 | 1.01 | 0.00410 | 0.63 |
| -74 | -101 | 0.00105 | 1.38 | 0.00559 | 0.86 |
| -72 | -98 | 0.00143 | 1.88 | 0.00762 | 1.17 |
| -70 | -94 | 0.00194 | 2.55 | 0.0104 | 1.58 |
| -68 | -90 | 0.00261 | 3.43 | 0.0140 | 2.13 |
| -66 | -87 | 0.00349 | 4.59 | 0.0187 | 2.84 |
| -64 | -83 | 0.00464 | 6.11 | 0.0248 | 3.79 |
| -62 | -80 | 0.00614 | 8.08 | 0.0328 | 5.01 |
| -60 | -76 | 0.00808 | 10.6 | 0.0430 | 6.59 |
| -58 | -72 | 0.0106 | 13.9 | 0.0565 | 8.63 |
| -56 | -69 | 0.0138 | 18.2 | 0.0735 | 11.3 |
| -54 | -65 | 0.0178 | 23.4 | 0.0948 | 14.5 |
| -52 | -62 | 0.0230 | 30.3 | 0.123 | 18.8 |
| -50 | -58 | 0.0295 | 38.8 | 0.157 | 24.1 |
| -48 | -54 | 0.0378 | 49.7 | 0.202 | 30.9 |
| -46 | -51 | 0.0481 | 63.3 | 0.257 | 39.3 |
| -44 | -47 | 0.0609 | 80.0 | 0.325 | 49.7 |
| -42 | -44 | 0.0768 | 101 | 0.410 | 62.7 |
| -40 | -40 | 0.0966 | 127 | 0.516 | 78.9 |
| -38 | -36 | 0.1209 | 159 | 0.644 | 98.6 |
| -36 | -33 | 0.1507 | 198 | 0.804 | 122.9 |
| -34 | -29 | 0.1873 | 246 | 1.00 | 152 |
| -32 | -26 | 0.2318 | 305 | 1.24 | 189 |
| -30 | -22 | 0.2859 | 376 | 1.52 | 234 |
| -28 | -18 | 0.351 | 462 | 1.88 | 287 |
| -26 | -15 | 0.430 | 566 | 2.30 | 351 |
| -24 | -11 | 0.526 | 692 | 2.81 | 430 |
| -22 | -8 | 0.640 | 842 | 3.41 | 523 |
| -20 | -4 | 0.776 | 1020 | 4.13 | 633 |
| -18 | 0 | 0.939 | 1240 | 5.00 | 770 |
| -16 | 3 | 1.132 | 1490 | 6.03 | 925 |
| -14 | 7 | 1.361 | 1790 | 7.25 | 1110 |
| -12 | 10 | 1.632 | 2150 | 8.69 | 1335 |
| -10 | 14 | 1.950 | 2570 | 10.4 | 1596 |
| -8 | 18 | 2.326 | 3060 | 12.4 | 1900 |
| -6 | 21 | 2.765 | 3640 | 14.7 | 2260 |
| -4 | 25 | 3.280 | 4320 | 17.5 | 2680 |
| -2 | 28 | 3.880 | 5100 | 20.7 | 3170 |
| 0 | 32 | 4.579 | 6020 | 24.4 | 3640 |
| 2 | 36 | 5.294 | 6970 | 28.2 | 4330 |
| 4 | 39 | 6.101 | 8030 | 32.5 | 4990 |
| 6 | 43 | 7.013 | 9230 | 37.4 | 5730 |
| 8 | 46 | 8.045 | 10590 | 42.9 | 6580 |
| 10 | 50 | 9.209 | 12120 | 49.1 | 7530 |
| 12 | 54 | 10.52 | 13840 | 56.1 | 8600 |
| 14 | 57 | 11.99 | 15780 | 63.9 | 9800 |
| 16 | 61 | 13.63 | 17930 | 72.6 | 11140 |
| 18 | 64 | 15.48 | 20370 | 82.5 | 12650 |
| 20 | 68 | 17.54 | 23080 | 93.5 | 14330
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