Add Australian AAQ NEPM AQI algorithm

[libokj]

NO2, O3, SO2: 1-hour average;
CO: 8-hour average;
PM10, PM2.5: 24-hour average

Sources:
https://soe.environment.gov.au/theme/ambient-air-quality/topic/2016/air-quality-index
https://soe.environment.gov.au/theme/ambient-air-quality/topic/2016/national-air-quality-standards

[libokj]

https://www.der.wa.gov.au/your-environment/air/air-quality-index

It seems that Western Australia has one more level beyond Very Poor: 200+ for Extreme.

[hrbonz]

This looks like a very straightforward index:

• If PM2.5 is 25µg/m³ over 24h then AQI is 100
• if PM2.5 is 5µg/m³ over 24h then AQI is 20
• if PM2.5 is 100µg/m³ over 24 then AQI is 400

Looks like there's no global AQI which avoids comparing numbers that have nothing to do with each other.

[libokj]

• if PM2.5 is 5µg/m³ over 24h then AQI is 20

Yes, the concentration is directly proportional to the AQI and vice versa.

AQI = measurement concentration / maximum concentration * 100
measurement concentration = AQI / 100 * maximum concentration

So we can simply use the formula for conversion.