Background of the Project
Objective of the Project
Location of the Project
Air Quality Basics

Vehicle Emissions Reduction

Air Quality Monitoring and Evaluation

Air Quality Standards
Air Quality Index (AQI)

Air Quality Policies and Legislation
Useful links
Contacting AQMP
Return to DoE Home

Air Quality Index (AQI)  

What is Air Quality Index (AQI)?

Air Quality Index (AQI) is an index number for reporting daily air quality. This is a simple way of describing the air pollution level in a particular area or region that can easily be understood by the public in general. AQI tells you how clean or polluted the air you are breathing and whether it is healthy or not for to breathe this air.

AQI focuses on short term health effects that can happen within a few hours or days after breathing polluted air. This index is calculated by comparing the measured concentration of the major air pollutants with their respective health effect. These pollutants are NO2, SO2, O3, CO, and particulate matter (PM10 and PM2.5)
AQI is a scale of numbers that runs from 0 to 500. Higher the AQI value, greater is the level of air pollution. For example, an AQI value less than 100 represents good air quality, while an AQI value over 100 represents poor air quality.

The AQI scale is divided into four categories. A specific colour is assigned to each AQI category. These categories are as follows:

AQI Categories

Air Quality Index (AQI) Value Category Colour
0-100 Good GREEN
101-200 Unhealthy ORANGE
201-300 Very unhealthy VIOLET
301 to 500 Extremely unhealthy RED

How is the AQI calculated?
Concentrations of common air pollutants are measured at a Continuous Air Monitoring Station (CAMS). Each pollutant concentration is converted into an AQI number according to the methodology developed by the US EPA. The highest AQI number attributed to a particular pollutant becomes the overall AQI value of that day. For example, on a particular day, if a certain area has an AQI value of 120 for PM2.5 and 88 for SO2, then the AQI value reported would be 120 and the responsible pollutant would be PM2.5 for that day. The AQI is linked to the National Ambient Air Quality Objectives. These are long term objectives that aim to protect public health. An AQI value less than or equal 100 means the air quality complies with the objectives. An AQI value greater than 100 means that air quality exceeds the AQI limit and so it may have potential health impacts.

How is the AQI reported?

The AQI calculation is based on measured pollutant concentrations for the past 24 hours up to 4pm of the reported day. The AQI is reported along with the weather news in the evening news and in the newspapers the following day.

Initially, DoE is releasing the AQI information for the public, each alternate day. However, in the coming months, the AQI will be released every day for the evening news.


» Communication Strategic Plan
» Communication Procedure and Guideline
» Communication Actions


PM samplers at CAMS

Air Quality Monitoring Equipment at CAMS

Working at CAMS staff Particulate Matter (PM) Sampler


:: © Air Quality Management Project 2004 ::