AirWare Online Reference Manual
 Release Level  5.6 
 Release Date  2009 09 
 Revision Level  1.0 
Last modified on:
Monday, 20Jul09 14:03 CEST

PSI air quality Index
In addition to the basic set of air pollutants,
AirWare can also compute and display air quality indices such as PSI.
PSI requires values from several pollutants and for different aggregation periods
that are generated by the
photochemical model CAMx, both a daily forecats and as
hourly nowcasts with the corresponding moving averages over the most recent 24 hours,
including the current hour.
 All CAMx result matrices show averages over a time period.
The period can be 1 hour, 8 hours or 24 hours.
All matrices are assigned to their ending time.
For example, the 8houraveragematrix of 10:00  18:00 is assigned to
18:00. The 24houraveragematrix of September 29th, 7:00  September
30th, 7:00 is assigned to September 30th, 7:00.
 For calculation of PSI matrices the following matrices are generated
for each timestep:
 CO: maximum of the 8houraverages of the last 24 hours (in reference to
the timestep) is taken for each grid cell.
 O3: maximum of the 1houraverages of the last 24 hours (in reference to
the timestep) is taken for each grid cell.
 NO2: maximum of the 1houraverages of the last 24 hours (in reference
to the timestep) is taken for each grid cell.
 SO2: 24houraveragematrix (ending at the timestep) is taken.
 PM10: 24houraveragematrix (ending at the timestep) is taken
 The concentration values are transformed into PSI values using the
following formula:
psip = ( psi(hi)  psi(lo) ) * (concp  bp(lo) ) / ( bp(hi)  bp(low) ) + psi(low)
where:
psip  calculated psi index for the pollutant 
concp  the concentration of the pollutant 
bp(lo)  lower breakpoint of the interval of pollutant concentration 
bp(hi)  higher breakpoint of the interval of pollutant concentration 
psi(lo)  PSI values corresponding to bp(lo) 
psi(hi)  PSI values corresponding to bp(hi) 
bp(lo), bp(hi), psi(lo) and psi(hi) are taken from the PSI color
definition.
If the concentration is above the upper limit of the table, PSI is not
defined.
In this case the maximum PSI value + 1 is assigned ( psip=301 )
 PSI matrix is generated by taking the maximum of the psip value of
the 5 pollutants for each grid cell.