Smog Calculator

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Smog Calculator

Calculate Air Quality Index (AQI) from pollutant concentrations and understand health impacts.

Last updated: March 2026

Air Quality Index
100
Moderate
Acceptable; some pollutants may concern sensitive groups.
PollutantValueAQI
PM2.535 µg/m³99
Ozone70 ppb100
NOâ‚40 ppb38
SOâ‚20 ppb29
CO4 ppm45

What is Air Quality Index (AQI)?

The Air Quality Index (AQI) is a standardized scale developed by the EPA to communicate air quality levels to the public. It converts pollutant concentrations into a single number (0-500+) where higher values indicate worse air quality and greater health risks.

Primary pollutants measured: The AQI uses PM2.5, ozone (O₃), carbon monoxide (CO), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂). The overall AQI is the highest subindex from those pollutants.

Why AQI matters: People with asthma, heart disease, and children are most vulnerable to air pollution. The AQI helps guide outdoor activity decisions and informs public health warnings.

How AQI Calculation Works

Pollutant Breakpoints (EPA Standards)

PM2.5: 0–9.0, 9.1–35.4, 35.5–55.4, 55.5–125.4, 125.5–225.4, 225.5–325.4
Ozone: 0.000–0.054 ppm, 0.055–0.070 ppm, 0.071–0.085 ppm, 0.086–0.105 ppm, 0.106–0.200 ppm
NOâ‚‚, SOâ‚‚, CO: Calculated with the same EPA interpolation method using their 1-hour or 8-hour breakpoints

Interpreting Results

  • • Good / Moderate: Safe for outdoor activity; no restrictions needed
  • • Unhealthy for Sensitive: Limit outdoor time if you have asthma or heart disease
  • • Unhealthy / Very Unhealthy: Avoid outdoor activity; stay indoors with air filters

Example Scenario

Smog event with PM2.5 = 65 µg/m³ and Ozone = 95 ppb:

PM2.5 Calculation:
65 falls in the 55.5–125.4 PM2.5 breakpoint range
AQI = 151 + (65-55.5)×49/70 ≈ 158
Ozone Calculation:
95 ppb falls in the 0.086–0.105 ppm ozone breakpoint range
AQI = 151 + (0.095-0.086)×49/0.019 ≈ 174
Overall AQI:
174 (Unhealthy)
Highest of the pollutant subindices determines overall AQI

Frequently Asked Questions

What is PM2.5?

Fine particulate matter with diameter less than 2.5 micrometers. These tiny particles penetrate deep into lungs and bloodstream, causing respiratory and cardiovascular harm.

What is ground-level ozone?

Ozone formed when sunlight reacts with nitrogen oxides and volatile compounds. Unlike stratospheric ozone (which protects from UV), ground-level ozone damages lungs and crops.

Which AQI level requires action?

At "Unhealthy for Sensitive Groups" (AQI 101–150), sensitive individuals should limit outdoor activity. At "Unhealthy" (151–200), everyone should avoid outdoor exertion.

Do air purifiers help with AQI?

Indoor HEPA filters reduce PM2.5 inside homes, but they don't affect outdoor AQI. Outdoor ventilation systems and emission reductions improve regional AQI.

What causes smog?

Vehicle emissions, industrial facilities, wildfires, and power plants release NOx and VOCs. Sunlight converts these to ozone and PM2.5, especially in warm, stagnant air.

How often does AQI update?

EPA and local agencies update AQI hourly or every 3-6 hours. Check official air quality websites for real-time data in your area.

AQI Scale Reference

0–50
Good
Air quality is satisfactory.
51–100
Moderate
Acceptable; some pollutants may concern sensitive groups.
101–150
Unhealthy (Sensitive)
Sensitive groups may experience health effects.
151–200
Unhealthy
Everyone may begin to experience health effects.
201–300
Very Unhealthy
Health warnings of emergency conditions.
301–500
Hazardous
Health alert: everyone may experience serious effects.

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