Annual average concentration scales adapted to the stricter WHO guideline values

Introduction

In November 2022, the BelAQI air quality index was adapted to the new and stricter guideline values ​​of the World Health Organization (WHO). The BelAQI index is used to qualify air quality in the short term (hours/days). An index scale is used from 1 to 10, with 1 indicating excellent air quality and 10 indicating extremely poor air quality. More information about the new BelAQI index can be found here: https://www.irceline.be/en/air-quality/measurements/air-quality-index-november-2022/info_nov2022

Need for adjustment of annual scales

In addition to its short-term impact, air pollution also has a chronic or long-term impact on health. Annual average concentrations are used as an indicator for the long-term impact. The long-term health impact is more important than the short-term one. The guideline values ​​to protect us against the long-term impact of air pollution were also tightened by the WHO in 2021. The new WHO guideline values are the result of meta-analysis studies: based on the most recent epidemiological studies, it appeared that there is still a significant health impact even at lower concentrations than the (old) guideline values from 2005.

The European Union (via EU Directive 2008/50) also uses (legally enforceable) annual limit values. The current EU annual limit values ​​are less strict than the WHO guideline values.

The table below lists the EU limit values, the old and new WHO guideline values ​​for particulate matter (PM2.5 and PM10) and nitrogen dioxide (NO2):

(*) indicative limit value from 2020

Table 1: current European annual limit values ​​and the old (2005) and new (2021) WHO annual guideline values

Because the concentration scales that IRCEL and the three Belgian regions use to visualize the long-term impact were no longer in accordance with the new WHO guideline values, they were adjusted. Three benchmarks were used:

- Annual average concentrations that are higher than the WHO guideline value are in the 5th class or higher

- Annual average concentrations that are higher than the (legally enforceable) EU limit value are placed in the highest class

- Annual average concentrations that are lower than half the WHO annual guideline value are in class 2 or lower

The other concentration classes are completed in a pragmatic manner.

This then leads to the following 10 concentration classes:    

Table 2: concentration classes annual average concentrations of PM10, PM2.5 and NO2

There are no EU annual limit values ​​and WHO guideline values ​​for ozone (O3) and Black Carbon (BC). The annual average concentration classes for ozone have not been adjusted. For BC, the class limits for the annual average were derived via the correlation that exists between BC and NO2 annual average concentrations.

Air quality is not getting worse

Compared to the previously used concentration classes, the maps will turn more "red". However, this does not mean that air quality itself is deteriorating. On the contrary, we note that air quality has been improving for several decades. It does mean that there are already health risks at lower concentrations than previously estimated.

To further reduce the negative effects of air pollution on health, the three regions have formulated air quality plans with ambitious objectives.

BelAIR app

The BelAIR smartphone application maps the current air quality for every location in Belgium. The app also displays the long-term concentrations (annual averages) for the last 5 years for each location. The new annual average concentration scales are used to qualify long-term air quality.