How Is the Air Quality Index Monitored?

The Air Quality Index – more colloquially known as the AQI – is a system by which the air pollution in a given location is monitored and presented to the general public. Although different governments around the world have implemented different models for their AQI (measuring different contaminants and grading them on different scales), they all share the same basic characteristics.

For the sake of simplicity, this article will focus on the US AQI, which was one of the first to be launched anywhere in the world. In particular, we’ll take a closer look at which pollutants are monitored, how the information is gathered and the format in which it is presented to internet users. For those keen to learn even more about this fascinating topic, the Air Quality and Emissions (AQE) Show 2022 is set to take place later this year in Telford UK and will explore the subject in far greater detail.

Which pollutants does the AQI measure?

In the USA, the AQI is responsible for monitoring concentrations of the five most common contaminants. These are, in no particular order, particulate matter (PM), ground-level ozone, nitrogen dioxide, carbon monoxide and sulphur dioxide. The system has been in place since 1968, though regular reporting to the public only began in 1976 and the AQI as we know it today was launched in 1999.

By monitoring these pollutants on a continual basis, concerned citizens can access the AQI at any hour of the day and see, at a glance, the real-time levels of each of these contaminants. For those interested, there is also an archive of historical data available which stretches back to 1980. This allows for a like-for-like comparison of the quality of our airwaves today versus in the past.

How is air quality information measured?

The AQI would not be possible without the presence of a sophisticated network of sensors. This comprises both governmental facilities featuring sensors that are fixed in place, as well as remote sensing equipment that is capable of assessing air quality levels while on the move. In recent years, real world vehicle emissions data has proven to be a game-changer in monitoring and managing urban air quality.

Meanwhile, the use of satellites to gather information from outer space and transmit it back to the Earth is another key method of monitoring air quality as well. This supplementary data provides a more general overview of the air pollution situation and allows the scientific community to back up their on-the-ground investigations with a more comprehensive picture of the planet’s pollution hotspots.

How is the AQI presented to the public?

The American AQI uses a numbered system of between 0 and 500 for each pollutant. The lower the figure is to zero, the higher the quality of air in any given region. This scoring system is further subdivided into six different categories, each of which is colour-coded.

Green indicates a value of between 0 and 50 and is considered good air quality. Yellow accounts for 51 to 100 and is regarded as moderate, while orange comprises the numbers 101 through 150 and is deemed unhealthy for vulnerable groups such as the very young, the very old and those suffering from respiratory complications. 151 to 200 is coded red and dubbed unhealthy, while 201 to 300 is very unhealthy and coloured purple. Anything over 300 is tagged maroon and regarded hazardous to human health. In this way, users of the AQI can check the concentration of pollutants in their area and tailor their travel plans accordingly.