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@aaronpk

aaronpk/aqi.php

Created Sep 14, 2020
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<?php
function aqiFromPM($pm) {
if($pm >= 350.5)
return scale($pm, 500, 401, 500, 350.5);
if($pm >= 250.5)
return scale($pm, 400, 301, 350.4, 250.5);
if($pm >= 150.5)
return scale($pm, 300, 201, 250.4, 150.5);
if($pm >= 55.5)
return scale($pm, 200, 151, 150.4, 55.5);
if($pm >= 35.5)
return scale($pm, 150, 101, 55.4, 35.5);
if($pm >= 12.1)
return scale($pm, 100, 51, 35.4, 12.1);
if($pm >= 0)
return scale($pm, 50, 0, 12, 0);
return '';
}
function scale($pm, $aqiHigh, $aqiLow, $pmHigh, $pmLow) {
$a = $aqiHigh - $aqiLow;
$b = $pmHigh - $pmLow;
$c = $pm - $pmLow;
return round(($a/$b) * $c + $aqiLow);
}
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