Scale 0–500 covering PM2.5, PM10, O₃, NO₂, SO₂, CO.
Piecewise linear formula from EPA-454/B-18-007.
Good · Moderate · USG · Unhealthy · Very Unhealthy · Hazardous.
PM2.5: 5 µg/m³ annual / 15 µg/m³ 24h
PM10: 15 µg/m³ annual / 45 µg/m³ 24h
NO₂: 10 µg/m³ annual / 25 µg/m³ 24h
O₃: 60 µg/m³ peak season · SO₂: 40 µg/m³ 24h
PM2.5: 25 µg/m³ annual
PM10: 50 µg/m³ daily (max 35 exceed./yr)
NO₂: 200 µg/m³ 1h / 40 µg/m³ annual
O₃: 120 µg/m³ 8h target value
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