International air quality standards: how do they compare?

International air quality standards: how do they compare?

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Last Updated

11 April 2024


30 September 2015



What is an air quality standard?

Just as air quality varies depending on where you are in the world, so to do the air quality standards. In this blogpost we’ll talk about the different standards in effect around the globe, how they compare, and who in the world has the toughest standards (as well as the weakest).

An ambient air quality standard (AAQS) simply put is a limit on the amount of a given pollutant in the air. These standards are usually enshrined in national (or federal) law and are legally binding. The standards are designed to protect people’s health and have been calculated to allow a margin for people most at risk e.g. the young and old and people with pre-existing health problems.

Looking around the world, most AAQS cover a handful of key pollutants that are collectively referred to as ‘criteria pollutants’:  ozone, particulate matter, sulphur oxides, nitrogen oxides, carbon monoxide, and lead. Although countries often have standards for the same types of air pollutants, the limits themselves are quite different.

Limits, targets and averages

An air quality standard may state a limit i.e. the level of pollutant x must not exceed amount y. Alternatively a standard may stipulate a target i.e. by year z the level of pollutant x must not exceed amount y. In some cases the air quality standards will have a mix of both.

To further complicate matters, standards are under periodic review and the limits or targets may be reduced. This link shows how the US EPA’s ozone standard has changed over the years, and a further reduction is now under review.

The other thing you will notice looking at international standards is that they contain a mix of averages and units. For example the US favours stating standards in part per million (ppm) whereas in the EU they state values in µg/m3. In some cases the limits are stated as an average over 1 hour, 8 hours or even 24 hours. This variability makes inter-comparison more difficult.

How do international standards compare?

The ambient air quality standards most often compared include those of the European Union, the United States, and the WHO. The WHO air quality standards are not legally binding; they are there as a guideline for countries who may or may not choose to adopt them. China’s standards have also come under close scrutiny in recent years.

The best comparison we have seen comes courtesy of the National Environmental Research Institute of Denmark. In this analysis the AAQS of the EU, US and WHO are compared to those found in China, Japan, and Switzerland. A link to the complete analysis can be found here.

The standards proposed by the WHO are significantly tougher than those imposed by any of the countries listed. This is perhaps not surprising – the WHO does not to answer to voters or taxpayers! The table also shows that the standards in the US (National Ambient Air Quality Standards, NAAQS) are more forgiving than the standards in other countries.

Looking at the variability in international standards we can’t help but wonder: what limits are truly safe for people? and are citizens in the US being exposed to more air pollution than the people who live within the borders of the European Union?

The answer to both questions is – it depends…

The problem with air quality standards

The first major problem with air quality standards is that the science is constantly advancing. What we thought was OK for human health 30 years ago no longer looks quite as safe. This explains the reduction in limits over the years such as the US EPA’s ozone standard referred to above.

Then there are all the things not included in most national air quality standards. Many experts believe we should include Volatile Organic Compounds (VOCs) which are a very large group of chemicals which include some extremely toxic substances.  As yet none of the major standards discussed here includes such pollutants.

The second major problem relates to the way the limits are measured and reported against. The methods that can be used to measure and report air quality levels are defined alongside the ambient air quality standards in law. The methods mandate equipment that is by nature expensive, immobile and complicated.

The problem with such equipment is that most governments can afford only a handful of ‘stations’ where measurement of air quality takes place. In Auckland, for example, where we live, a city of 1.5 million people is covered by just five monitoring stations. We can be confident that the air quality is as reported in the vicinity of the station, but what about people who live 20 km away from the nearest station?

As a result the US EPA and other organisations responsible for setting air quality standards are now looking for alternative methods of measuring air quality – equipment that is less expensive but still accurate and more mobile (which means we can have more of them).

One such example is Aeroqual’s AQM 65 compact air quality station.

See our air quality monitors

View Aeroqual’s full range of outdoor air quality monitors.