Enter the AQI values corresponding to the higher and lower concentration breakpoints, the higher and lower concentration breakpoints, and the pollutant concentration into the calculator to determine the Air Quality Index.

Air Quality Index Formula

The following formula is used to calculate the Air Quality Index (AQI). 

AQI = I_high - I_low / (C_high - C_low) * (C - C_low) + I_low

Variables:

  • AQI is the Air Quality Index
  • I_high is the AQI value corresponding to the higher concentration breakpoint that encompasses
  • ‘C’ I_low is the AQI value corresponding to the lower concentration breakpoint that encompasses
  • ‘C’ C_high is the higher concentration breakpoint that encompasses
  • ‘C’ C_low is the lower concentration breakpoint that encompasses
  • ‘C’ C is the pollutant concentration

To calculate the Air Quality Index, subtract the AQI value corresponding to the lower concentration breakpoint from the AQI value corresponding to the higher concentration breakpoint. Then, subtract the lower concentration breakpoint from the higher concentration breakpoint. Divide the first result by the second result. Multiply this quotient by the difference between the pollutant concentration and the lower concentration breakpoint. Finally, add the AQI value corresponding to the lower concentration breakpoint to this product.

What is a Air Quality Index?

The Air Quality Index (AQI) is a system used to measure and report the daily air quality in a specific area. It focuses on health effects that may be experienced within a few hours or days after breathing polluted air. The AQI scale ranges from 0 to 500, where a higher AQI value represents a higher level of air pollution and a greater risk to health. It considers five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

How to Calculate Air Quality Index?

The following steps outline how to calculate the Air Quality Index (AQI) using the given formula:

  1. First, determine the value of I_high, which is the AQI value corresponding to the higher concentration breakpoint that encompasses ‘C’.
  2. Next, determine the value of I_low, which is the AQI value corresponding to the lower concentration breakpoint that encompasses ‘C’.
  3. Next, determine the value of C_high, which is the higher concentration breakpoint that encompasses ‘C’.
  4. Next, determine the value of C_low, which is the lower concentration breakpoint that encompasses ‘C’.
  5. Finally, calculate the AQI using the formula: AQI = (I_high – I_low) / (C_high – C_low) * (C – C_low) + I_low.
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

AQI: Air Quality Index

I_high: AQI value corresponding to the higher concentration breakpoint that encompasses ‘C’

I_low: AQI value corresponding to the lower concentration breakpoint that encompasses ‘C’

C_high: higher concentration breakpoint that encompasses ‘C’

C_low: lower concentration breakpoint that encompasses ‘C’

C: pollutant concentration