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Air Quality Index

Convert pollutant concentrations (PM2.5, PM10, ozone, CO, SO₂, NO₂) to the EPA Air Quality Index. Get health recommendations, mask guidance, and activity safety.

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AQI > 150: limit outdoor exposure N95 recommended when Unhealthy or worse PM2.5 is the most common driver

Ready to run the numbers?

Why: Air quality affects respiratory health, especially for sensitive groups. Knowing your local AQI helps you decide when to limit outdoor activity or wear a mask.

How: We use EPA 2024 breakpoints to convert each pollutant concentration to a sub-index. The overall AQI is the maximum of all sub-indices.

AQI > 150: limit outdoor exposureN95 recommended when Unhealthy or worse
Sources:EPA AirNowEPA AQI Breakpoints

Run the calculator when you are ready.

Calculate AQIUse the calculator below to check your health metrics

🌬️ Sample Scenarios — Click to Load

Pollutant Concentrations

aqi_report.sh
CALCULATED
$ aqi_calc --pm25=12 --pm10=45 --location="N/A"
Overall AQI
56
Category
Moderate
Primary Pollutant
PM2.5
Outdoor Safe?
✅ Generally
Health: Acceptable for most. Unusually sensitive people should consider limiting prolonged outdoor exertion.
Mask: Optional for sensitive groups.
Windows: Windows can stay open.
Share:
Air Quality Index
56
Moderate
Primary: PM2.5
numbervibe.com/calculators/health/air-quality-index-calculator

Sub-index by Pollutant

Pollution Profile (Radar)

Primary Pollutant Contribution

📐 Calculation Breakdown

SUB-INDICES
PM2.5 sub-index56
SUB-INDICES
PM10 sub-index42
SUB-INDICES
O₃ (8-h) sub-index42
SUB-INDICES
CO sub-index14
SUB-INDICES
SO₂ sub-index29
SUB-INDICES
NO₂ sub-index33
RESULT
OVERALL AQI56
Primary PollutantPM2.5
CategoryModerate

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

🏥 Health Facts

😷

N95 masks filter 95% of airborne particles

— CDC

📋 Key Takeaways

  • • The US EPA AQI uses six pollutants: PM2.5, PM10, O₃, CO, SO₂, NO₂. The highest sub-index becomes the reported AQI.
  • • PM2.5 breakpoints were updated in May 2024 — Good now ends at 9 µg/m³ (was 12 µg/m³).
  • • N95 masks filter ~95% of PM2.5; surgical masks offer minimal protection against fine particles.
  • • Chinese AQI and Indian AQI use different breakpoints — same PM2.5 can yield different index values globally.

💡 Did You Know?

🌫️PM2.5 particles are 30x smaller than a human hair — they penetrate deep into lungs and bloodstreamSource: EPA
🔥Wildfire smoke can push AQI above 500 in affected areas — Bay Area 2020 fires reached AQI 300+Source: AirNow
😷N95 masks filter 95% of PM2.5; surgical masks filter only ~20-30% of fine particlesSource: CDC
☀️Ground-level ozone forms when NOx + VOCs react in sunlight — often worst on hot summer afternoonsSource: EPA
🏠Indoor PM2.5 can be 2-5x higher than outdoor during cooking, candles, or poor ventilationSource: EPA
📡AirNow uses ~900 monitoring stations; PurpleAir low-cost sensors supplement official dataSource: AirNow

📖 How the EPA AQI Works

Each pollutant has breakpoint tables mapping concentration to AQI (0-500). The formula: AQI = ((I_high - I_low) / (BP_high - BP_low)) × (C - BP_low) + I_low

PM2.5 vs PM10: PM2.5 (≤2.5 µm) penetrates alveoli; PM10 (≤10 µm) is coarser. Wildfire smoke is mostly PM2.5.

🎯 Expert Tips

Check Before Exercise

AQI >100: sensitive groups should reduce prolonged exertion. Use Fire Weather Index during wildfire season.

Indoor Air Quality

Close windows when AQI >150. Use HEPA purifiers. Cooking and candles add PM2.5 indoors.

Mask Selection

N95 or better for PM2.5; surgical masks inadequate. Fit matters — ensure seal.

Wildfire Smoke

PM2.5 spikes fast. Create a clean room, run AC on recirculate, avoid adding indoor pollution.

❓ Frequently Asked Questions

What is the AQI formula?

AQI = ((I_high - I_low) / (BP_high - BP_low)) × (C - BP_low) + I_low. Each pollutant has breakpoint tables from the EPA.

How is the overall AQI determined?

The overall AQI is the maximum of all pollutant sub-indices. The pollutant with the highest sub-index is the primary pollutant.

What is the difference between PM2.5 and PM10?

PM2.5 are particles ≤2.5 µm (fine); PM10 are ≤10 µm. PM2.5 penetrates deeper and is more harmful. Wildfire smoke is mostly PM2.5.

When should I wear an N95 mask?

EPA recommends N95 when AQI exceeds 150 (Unhealthy) for prolonged outdoor exposure. Sensitive groups may use at AQI >100.

Do Chinese and US AQI differ?

Yes. China uses different breakpoints; the same PM2.5 concentration can yield different index values.

How do air quality monitors work?

Federal Reference Method monitors use gravimetric or beta-attenuation. PurpleAir uses laser scattering; data may need correction.

What causes ozone pollution?

Ground-level ozone forms when nitrogen oxides and VOCs react in sunlight. Peak levels occur on hot, sunny days.

Is indoor air better during wildfires?

Usually yes if windows are closed and HVAC is on recirculate. Avoid adding indoor sources. HEPA purifiers help.

⚠️ Disclaimer: This calculator uses US EPA AQI breakpoints (2024). For official real-time AQI, use AirNow.gov. Not a substitute for medical advice.

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