On December 10, 2024 the European Union (EU) updated its Ambient Air Quality Directive to bring its air quality standards more in line with the World Health Organization’s (WHO’s) recommendations. As an air dispersion modeler who has worked throughout the world over the course of my career, I have always found it interesting to compare air quality standards between different countries. Along those lines, I thought I’d take a few moments to compare EU air quality standards with those in the United States (US).
The EU refers to their air quality standards as Limit Values, while the US uses the phrase National Ambient Air Quality Standards (NAAQS). There are Limit Values for each of the Criteria Pollutants in the US, along with several toxic air pollutants. The complete list is as follows:
· Particulate matter smaller than 2.5 microns (PM2.5),
· Particulate matter smaller than 10 microns (PM10),
· Nitrogen dioxide (NO2),
· Nitrogen oxide,
· Sulfur dioxide (SO2),
· Ozone,
· Carbon monoxide,
· Lead,
· Benzene,
· Benzo(a)pyrene,
· Arsenic,
· Cadmium, and
· Nickel.
The EU has two sets of Limit Values, one that needs to be attained by December 11, 2026, and one that needs to be attained by January 1, 2030, with the 2030 Limit Values being equal to or lower than the 2026 Limit Values.
Below are bar charts that compare EU Limit Values and US NAAQS for PM2.5, PM10, NO2, and SO2. Note that these charts only show the value of the standard; the form of the standard (how many exceedances are permitted in a year) differs between the Limit Values and the NAAQS. In general, the Limit Values and NAAQS are comparable; exceptions are the Limit Values for 24-hr PM2.5 and Annual NO2 being markedly lower than the comparable NAAQS, and the 1-hr SO2 NAAQS being more restrictive than the comparable Limit Value.
In the case of PM2.5 the 24-hr Limit Value is more restrictive than the NAAQS, while for the Annual averaging period they will be nearly identical by 2030 with the Limit Value being 1 µg/m3 greater than the NAAQS at that time. Note that the Annual PM2.5 Limit Value is being reduced even more drastically than was done recently in the US, going from 25 µg/m3 (by 2026) down to 10 µg/m3 (by 2030).
The form of the 24-hr Limit Value is as follows:
· By January 1, 2030: Not to be exceeded more than 18 times in a calendar year
For 24-hr PM10 the EU and US are fairly comparable, with the 2026 Limit Value being equal to the NAAQS. By 2030 the 24-hr PM10 Limit Value is going to be reduced to 45 µg/m3, 5 µg/m3 less than the NAAQS. Note the EU has an Annual PM10 Limit Value, while the US no longer has an Annual PM10 NAAQS; that said, the values of the Annual PM10 Limit Values (40 µg/m3 and 20 µg/m3 for 2026 and 2030, respectively) are much less than what the US previously had for its Annual PM10 NAAQS (150 µg/m3).
The forms of the Limit Values are as follows:
· By December 11, 2026: Not to be exceeded more than 35 times in a calendar year
· By January 1, 2030: Not to be exceeded more than 18 times in a calendar year
The 1-hr NO2 Limit Values and NAAQS are very similar, with the Limit Values being slightly greater (200 µg/m3 vs. 188 µg/m3). On the other hand, the Annual Limit Values for NO2 (40 µg/m3 and 20 µg/m3 for 2026 and 2030, respectively) are far more restrictive than the US NAAQS of 100 µg/m3.
Note the EU also has a 24-hr Limit Value for NO2 (50 µg/m3) for 2030, but since there is no 24-hr NO2 NAAQS I did not plot it.
The forms of the Limit Values are as follows:
· 1-hr, by December 11, 2026: Not to be exceeded more than 18 times in a calendar year
· 1-hr, by January 1, 2030: Not to be exceeded more than 3 times in a calendar year
· 24-hr, by January 1, 2030: Not to be exceeded more than 18 times in a calendar year
Contrary to 1-hr NO2, there is a very large discrepancy between the 1-hr SO2 Limit Values and the 1-hr SO2 NAAQS; the NAAQS is far more restrictive than the Limit Values, at slightly more than half (196 µg/m3 as compared to 350 µg/m3).
Note the EU also has for SO2 a 24-hr Limit Value (50 µg/m3) and an Annual Limit Value (20 µg/m3), but since there aren’t SO2 NAAQS for those averaging periods I didn’t plot them.
The forms of the Limit Values are as follows:
· 1-hr, by December 11, 2026: Not to be exceeded more than 24 times in a calendar year
· 1-hr, by January 1, 2030: Not to be exceeded more than 3 times in a calendar year
· 24-hr, by December 11, 2026: Not to be exceeded more than 3 times in a calendar year
· 24-hr, by January 1, 2030: Not to be exceeded more than 18 times in a calendar year
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