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N.C. Air Awareness Program >> Air Quality Forecast Center >> AQI Calculation Table

Tables for converting 8-hour averaged ozone concentrations in parts per million (ppm)
to the Air Quality Index (AQI)

Green

ILO = 0
IHI = 50
BPLO = 0.000
BPHI = 0.059

O3 Conc.   AQI
0.000   0
0.001   1
0.002   2
0.003   3
0.005   4
0.006   5
0.007   6
0.008   7
0.009   8
0.010   9
0.012   10
0.013   11
0.014   12
0.015   13
0.016   14
0.018   15
0.019   16
0.020   17
0.021   18
0.022   19
0.023   20
0.024   20
0.025   21
0.026   22
0.027   23
0.028   24
0.029   25
0.031   26
Green

ILO = 0
IHI = 50
BPLO = 0.000
BPHI = 0.059

O3 Conc.   AQI
0.032   27
0.033   28
0.034   29
0.035   30
0.036   31
0.037   31
0.038   32
0.039   33
0.040   34
0.041   35
0.042   36
0.043   37
0.045   38
0.046   39
0.047   40
0.048   41
0.049   42
0.050   42
0.051   43
0.052   44
0.053   45
0.054   46
0.055   47
0.056   48
0.057   48
0.058   49
0.059   50
Yellow

ILO = 51
IHI = 100
BPLO = 0.060
BPHI = 0.075

O3 Conc.   AQI
0.060   51
0.061   54
0.062   58
0.063   61
0.064   64
0.065   67
0.066   71
0.067   74
0.068   77
0.069   80
0.070   84
0.071   87
0.072   90
0.073   93
0.074   97
0.075   100
Orange

ILO = 101
IHI = 150
BPLO = 0.076
BPHI = 0.095

O3 Conc.   AQI
0.076   101
0.077   104
0.078   106
0.079   109
0.080   111
0.081   114
0.082   116
0.083   119
0.084   122
0.085   124
0.086   127
0.087   129
0.088   132
0.089   135
0.090   137
0.091   140
0.092   142
0.093   145
0.094   147
0.095   150
Red

ILO = 151
IHI = 200
BPLO = 0.096
BPHI = 0.115

O3 Conc.   AQI
0.096   151
0.097   154
0.098   156
0.099   159
0.100   161
0.101   164
0.102   166
0.103   169
0.104   172
0.105   174
0.106   177
0.107   179
0.108   182
0.109   185
0.110   187
0.111   190
0.112   192
0.113   195
0.114   197
0.115   200
Purple

ILO = 201
IHI = 300
BPLO = 0.116
BPHI = 0.374

O3 Conc.   AQI
0.116   201
0.117   201
0.118   202
0.119   202
0.120   203
0.121   203
0.122   203
0.123   204
0.124   204
0.125   204
0.126   205
0.127   205
0.128   206
0.129   206
0.130   206
0.131   207
0.132   207
0.133   208
0.134   208
0.135   208
 
AQI Conversion Formula
 AQI = [(Index value at higher limit of category minus Index value at lower limit of category) / (Break-point concentration at upper limit of category minus Break-point concentration at lower limit of category)] multiplied by [8-hour ozone concentration minus Break-point concentration at lower limit of category] plus Index value at lower limit of category

AQI = Air Quality Index
ILO = Index value at the lower limit of the AQI category
IHI = Index value at the upper limit of the AQI category
BPLO = Break-point concentration at lower limit of AQI category
BPHI = Break-point concentration at upper limit of AQI category
CO3 = 8-hour ozone concentration

 

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Last Modified: Fri June 13 10:26:42 2008
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