Understanding Air Quality Index (AQI)
The Air Quality Index measures how clean or polluted the air is and what health effects might concern you. NearWeather displays real-time AQI data for every location, sourced from the OpenWeatherMap Air Pollution API.
What Does AQI Measure?
AQI is calculated from concentrations of several pollutants:
- PM2.5 — Fine particulate matter (< 2.5 micrometers). The most health-relevant pollutant. Penetrates deep into lungs.
- PM10 — Coarser particles (< 10 micrometers). Includes dust, pollen, and industrial particles.
- O₃ (Ozone) — Ground-level ozone, formed by sunlight reacting with vehicle and industrial emissions.
- NO₂ (Nitrogen Dioxide) — Primarily from vehicle exhaust and power plants.
- SO₂ (Sulfur Dioxide) — From burning fossil fuels, especially coal.
- CO (Carbon Monoxide) — From incomplete combustion of fuels.
AQI Scale
| AQI Level | Rating | Health Implications |
|---|---|---|
| 1 | Good | Air quality is satisfactory. Little or no risk. |
| 2 | Fair | Acceptable. Sensitive individuals may experience minor effects. |
| 3 | Moderate | Sensitive groups may experience health effects. General public less likely affected. |
| 4 | Poor | Health effects possible for everyone. Sensitive groups may experience more serious effects. |
| 5 | Very Poor | Health alert. Everyone may experience health effects. |
How to Protect Yourself
- AQI 1-2: Enjoy outdoor activities normally
- AQI 3: Sensitive individuals (asthma, heart disease, elderly, children) should limit prolonged outdoor exertion
- AQI 4: Everyone should reduce prolonged outdoor exertion. Keep windows closed.
- AQI 5: Avoid outdoor activities. Use air purifiers indoors. Wear N95 masks if going outside.
Seasonal Patterns
Air quality varies by season and location:
- Summer: Higher ozone levels due to sunlight + heat
- Winter: Higher PM2.5 from heating, temperature inversions trapping pollution
- Monsoon/Rainy season: Rain washes pollutants from the air, temporarily improving AQI
- Post-harvest: Agricultural burning (e.g., North India in November) can spike AQI dramatically
Data Source
NearWeather's AQI data comes from the OpenWeatherMap Air Pollution API, which aggregates data from ground monitoring stations and atmospheric models worldwide. Data is refreshed every 5 minutes.