What is AQI, and how is it different from PM2.5?

PM 2.5 Dust Explained

These days, checking daily air pollution levels has become second nature, especially for city dwellers in Bangkok. Residents constantly monitor PM2.5 fine dust particles and other pollutants that pose significant risks to respiratory health and overall well-being, hoping for some relief soon.

While there are multiple ways to check air quality, Ticy City recommends the easiest option—your smartphone. Most devices display AQI values, but here’s where many get confused: What exactly is AQI, and how does it differ from PM2.5? Let us break it down for you.

What is AQI?
The Air Quality Index (AQI) is a comprehensive indicator of air quality, calculated from six major pollutants:

• PM2.5: Fine particulate matter with a diameter of 2.5 microns or smaller
• PM10: Particulate matter with a diameter of 10 microns or smaller
• Ozone (O3)
• Carbon monoxide (CO)
• Nitrogen dioxide (NO2)
• Sulfur dioxide (SO2)

In Thailand, the Pollution Control Department sets AQI standards, ranging from 0 to over 201. A color-coded system indicates the health impacts of these values. If the 24-hour average AQI exceeds 100, air quality is deemed unhealthy.

How AQI Works
Thailand’s AQI is divided into five levels, ranging from good to hazardous, with color indicators representing the severity of health risks. An AQI of 100 aligns with the national air quality standard. If it exceeds 100, pollutant concentrations surpass safe levels, and the air becomes harmful to health.

How PM2.5 Differs from AQI
PM2.5, or fine particulate matter, refers specifically to tiny dust particles less than 2.5 microns in size. It is just one of the pollutants factored into the AQI. However, PM2.5 is measured independently, with Thailand’s 24-hour standard set at 50 micrograms per cubic meter. Levels above this threshold are considered harmful to health.

How Pollutants Are Measured
The AQI is based on average pollutant levels over specific time frames, measured in different units:

• PM2.5 & PM10: 24-hour average (micrograms per cubic meter, µg/m³)
• Ozone (O3): 8-hour average (parts per billion, ppb)
• Carbon monoxide (CO): 8-hour average (parts per million, ppm)
• Nitrogen dioxide (NO2): 1-hour average (parts per billion, ppb)
• Sulfur dioxide (SO2): 1-hour average (parts per billion, ppb)

In short, while AQI gives a broader picture of air quality, PM2.5 focuses specifically on fine particulate matter. Both are critical tools for monitoring pollution and protecting your health.

Source: Department of Health, Ministry of Public Health
Image: https://www.istockphoto.com