PSI Conversion Tables and How to Calculate the PSI (24h, 3h, and 1h)
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PSI Conversion Tables
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This table says, for example, that if the PM2.5 reading is exactly 10 μg/m³, then the PM2.5 PSI is ≈ 41.7 (which the NEA will round off to 42 in its published figure).
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Scroll to the right (→) for an explanation of how these conversions are done.
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PM2.5 (μg/m³)
PM2.5 PSI
PM10 (μg/m³)
PM10 PSISO₂ (μg/m³)SO₂ PSICO (mg/m³)CO PSIO₃ (μg/m³)O₃ PSINO₂ (μg/m³)NO₂ PSI
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00.000.000.000.000.00 to 1129
The NO₂ PSI is not reported if the NO₂ reading is less than 1130 μg/m³. This makes no sense to me and I can't find no explanation on the NEA website.
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14.211.053.10.11.020.81130200.0
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28.322.0106.30.22.041.71135200.4
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312.533.0159.40.33.062.51140200.9Breakpoints
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416.744.02012.50.44.083.41145201.3PSIPM2.5PM10SO₂ COO₃ NO₂
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520.855.02515.60.55.0104.21150201.8501250805118
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625.066.03018.80.66.0125.11155202.21005515036510157
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729.277.03521.90.77.0145.91160202.7200150350800172351130
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833.388.04025.00.88.0166.81165203.13002504201600347852260
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937.599.04528.10.99.0187.61170203.54003505002100469803000
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1041.71010.05031.3110.0208.51175204.0500500600262057.511803750
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1145.81111.05534.41.111.0229.31180204.4
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1250.01212.06037.51.212.02410.21185204.9
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1351.21313.06540.61.313.02611.01190205.3Explanation of how to convert readings to PSIs.
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1452.31414.07043.81.414.02811.91195205.8
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1553.51515.07546.91.515.03012.71200206.2
I'll only explain how the PM2.5-to-PSI conversion is done. The other pollutant-to-PSIs are similarly converted, excepted with different breakpoints (see table directly above).
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1654.71616.08050.01.616.03213.61205206.6
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1755.81717.08550.91.717.03414.41210207.1
For the PSI, the cut-off points, or breakpoints as the NEA calls them, are 0, 50, 100, 200, 300, 400, and 500 (unitless).
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1857.01818.09051.81.818.03615.31215207.5
For PM2.5, the breakpoints are 0, 12, 55, 150, 250, 350, and 500μg/m³.
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1958.11919.09552.61.919.03816.11220208.0
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2059.32020.010053.5220.04016.91225208.4
The PM2.5 PSI is constructed so that the PM2.5 breakpoints correspond to the PSI breakpoints.
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2160.52121.010554.42.121.04217.81230208.8
So for example, if the PM2.5 is 55μg/m³, then the PM2.5 PSI is 100.
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2261.62222.011055.32.222.04418.61235209.3
As another example, if the PM2.5 is 350μg/m³, then the PM2.5 PSI is 400.
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2362.82323.011556.12.323.04619.51240209.7
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2464.02424.012057.02.424.04820.31245210.2
For any other PM2.5 level, the PM2.5 PSI is calculated by simple linear interpolation.
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2565.12525.012557.92.525.05021.21250210.6
So for example, going from PM2.5 of 0μg/m³ to 12μg/m³, the PM2.5 PSI goes from 0 to 50.
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2666.32626.013058.82.626.05222.01255211.1
So if the PM2.5 is 1μg/m³, then the PM2.5 PSI is 1 × (50/12) ≈ 4.17.
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2767.42727.013559.62.727.05422.91260211.5
And if the PM2.5 is 2μg/m³, then the PM2.5 PSI is 2 × (50/12) ≈ 8.33.
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2868.62828.014060.52.828.05623.71265211.9
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2969.82929.014561.42.929.05824.61270212.4
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3070.93030.015062.3330.06025.41275212.8
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3172.13131.015563.23.131.06226.31280213.3
The other pollutant PSIs are similarly calculated, but with different breakpoints.
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3273.33232.016064.03.232.06427.11285213.7
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3374.43333.016564.93.333.06628.01290214.2
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3475.63434.017065.83.434.06828.81295214.6
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3576.73535.017566.73.535.07029.71300215.0
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3677.93636.018067.53.636.07230.51305215.5
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3779.13737.018568.43.737.07431.41310215.9
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3880.23838.019069.33.838.07632.21315216.4
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3981.43939.019570.23.939.07833.11320216.8
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4082.64040.020071.1440.08033.91325217.3
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4183.74141.020571.94.141.08234.71330217.7
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4284.94242.021072.84.242.08435.61335218.1
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4386.04343.021573.74.343.08636.41340218.6
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4487.24444.022074.64.444.08837.31345219.0
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4588.44545.022575.44.545.09038.11350219.5
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4689.54646.023076.34.646.09239.01355219.9
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4790.74747.023577.24.747.09439.81360220.4
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4891.94848.024078.14.848.09640.71365220.8
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4993.04949.024578.94.949.09841.51370221.2
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5094.25050.025079.8550.010042.41375221.7
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5195.35150.525580.75.151.010243.21380222.1
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5296.55251.026081.65.252.010444.11385222.6
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5397.75351.526582.55.353.010644.91390223.0
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5498.85452.027083.35.454.010845.81395223.5
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55100.05552.527584.25.555.011046.61400223.9
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56101.15653.028085.15.656.011247.51405224.3
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57102.15753.528586.05.757.011448.31410224.8
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58103.25854.029086.85.858.011649.21415225.2
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59104.25954.529587.75.959.011850.01420225.7
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60105.36055.030088.6660.012052.61425226.1
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61106.36155.530589.56.161.012255.11430226.5
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62107.46256.031090.46.262.012457.71435227.0
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63108.46356.531591.26.363.012660.31440227.4
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64109.56457.032092.16.464.012862.81445227.9
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65110.56557.532593.06.565.013065.41450228.3
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66111.66658.033093.96.666.013267.91455228.8
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67112.66758.533594.76.767.013470.51460229.2
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68113.76859.034095.66.868.013673.11465229.6
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69114.76959.534596.56.969.013875.61470230.1
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70115.87060.035097.4770.014078.21475230.5
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71116.87160.535598.27.171.014280.81480231.0
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72117.97261.036099.17.272.014483.31485231.4
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73118.97361.5365100.07.373.014685.91490231.9
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74120.07462.0370101.17.474.014888.51495232.3
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75121.17562.5375102.37.575.015091.01500232.7
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76122.17663.0380103.47.676.015293.61505233.2
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77123.27763.5385104.67.777.015496.21510233.6
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78124.27864.0390105.77.878.015698.71515234.1
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79125.37964.5395106.97.979.0158101.31520234.5
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80126.38065.0400108.0880.0160103.81525235.0
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81127.48165.5405109.28.181.0162106.41530235.4
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82128.48266.0410110.38.282.0164109.01535235.8
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83129.58366.5415111.58.383.0166111.51540236.3
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84130.58467.0420112.68.484.0168114.11545236.7
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85131.68567.5425113.88.585.0170116.71550237.2
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86132.68668.0430114.98.686.0172119.21555237.6
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87133.78768.5435116.18.787.0174121.81560238.1
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88134.78869.0440117.28.888.0176124.41565238.5
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89135.88969.5445118.48.989.0178126.91570238.9
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90136.89070.0450119.5990.0180129.51575239.4
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91137.99170.5455120.79.191.0182132.11580239.8
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92138.99271.0460121.89.292.0184134.61585240.3
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93140.09371.5465123.09.393.0186137.21590240.7