🧪 Hosur Air Quality Index, AQI Based on Indian CPCB standards

🇮🇳 Indian vs 🇺🇸 US AQI Calculation: Key Differences

Air Quality Index (AQI) helps communicate how polluted the air is. While both India and the United States use AQI systems, they differ in calculation methods, pollutant limits, and update frequency. Here's a side-by-side comparison:

1. Agencies and Standards

Country	Agency	System
India	CPCB (Central Pollution Control Board)	National AQI (NAQI)
USA	EPA (Environmental Protection Agency)	US EPA AQI

2. Averaging Time

Pollutant	India (CPCB)	USA (EPA)
PM2.5	24-hour average	NowCast (real-time weighted)
PM10	24-hour average	24-hour average
O₃	8-hour average	8-hour and 1-hour (worst)
NO₂	1-hour average	1-hour average

Note: The US uses NowCast to reflect recent trends more accurately, while India uses fixed 24-hour or 8-hour averages.

3. AQI Breakpoints for PM2.5

Category	India (µg/m³)	USA (µg/m³)
Good	0–30	0–12.0
Satisfactory / Moderate	31–90	12.1–35.4
Poor / Unhealthy	91–250+	35.5–500.4

4. AQI Categories

AQI Range	India (CPCB)	USA (EPA)
0–50	Good	Good
51–100	Satisfactory	Moderate
101–200	Moderate	Unhealthy for Sensitive Groups
201–300	Poor	Unhealthy
301–400	Very Poor	Very Unhealthy
401–500	Severe	Hazardous

5. Summary Comparison

Aspect	India (CPCB)	USA (EPA)
Primary Method	24-hour averages	NowCast (real-time)
PM2.5 Thresholds	More lenient	Stricter
AQI Update Frequency	Daily / Hourly (limited)	Hourly
Category Design	Adapted to Indian context	WHO-aligned
NowCast Support	No	Yes

Conclusion

While both systems aim to protect public health by simplifying air quality data, the Indian AQI is tuned to local environmental baselines, whereas the US EPA system emphasizes real-time responsiveness. Understanding the differences helps users interpret AQI data accurately in both regional and international contexts.

PM 2.5

Of all air pollution measures, PM2.5 pollution poses the greatest health threat. Due to its small size, PM2.5 can remain suspended in the air for long periods of time and can be absorbed deep into the bloodstream upon inhalation.

PM 10

PM10 particles are small enough to get into your throat and lungs. High levels of PM10 can make you cough, your nose run and eyes sting.

CO

Carbon Monoxide (CO) pollution is a significant environmental and health concern, primarily stemming from incomplete combustion of fuels like gasoline in vehicles. It's a colorless, odorless gas that can be toxic, even in low concentrations, especially for individuals with pre-existing heart conditions. CO exposure can lead to various health issues, including headaches, fatigue, and, in severe cases, coma or death.

NO2

NO2 along with other NOx reacts with other chemicals in the air to form both particulate matter and ozone. Both of these are also harmful when inhaled due to effects on the respiratory system.

O3 Ozone

Ozone can damage the tissues of the respiratory tract, causing inflammation and irritation, and result in symptoms such as coughing, chest tightness and worsening of asthma symptoms.

SO2

Sulfur dioxide affects the respiratory system, particularly lung function, and can irritate the eyes. Sulfur dioxide irritates the respiratory tract and increases the risk of tract infections. It causes coughing, mucus secretion and aggravates conditions such as asthma and chronic bronchitis.