Indicator: Air quality in agglomerations

Two graphs show how strongly, on average, urban background levels of three main air pollutants in German agglomerations exceeded the old and the new WHO recommendations between 2000 and 2022. The trend for the different pollutants varies. With the new, stricter WHO recommendations of 2021 for nitrogen dioxide (NO2) and particulate matter (PM2.5), the distances to the target have become significantly greater. Between 2000 and 2022 the values for NO2 range between 172 and 52 %, for ozone between 44 and 39 %. Click to enlarge
Discrepancy between average pollutant concentrations and WHO recommendations ...
Source: German Environment Agency Figure as PDF

Table of Contents


At a glance

  • After the background level in German agglomerations exceeded the old recommendations of the World Health Organisation (WHO) only for the air pollutant ozone (figure left), the background level now clearly exceeds the updated WHO recommendations from 2021 also for particulate matter (PM2.5) and nitrogen dioxide NO2 (figure right).
  • Close to sources, pollutant levels can even be significantly higher.
  • The situation regarding NO2 and PM2.5 has greatly improved since 2000, but the current WHO recommendations of 2021 are still clearly exceeded.
  • Ozone and PM2.5 pollution are very dependent on the weather. Levels thus fluctuate significantly.

Environmental importance

Nitrogen dioxide (NO2), particulate matter (PM2.5) and ozone (O3) are of particular concern to human health. All three pollutants affect the respiratory organs. Many premature deaths are also attributed to particulates, as well as damages to ecosystems.

Up to now, the indicator for ozone and particulate matter was based on air quality guideline values of the World Health Organisation WHO from 2005 (WHO 2006) and for NO2 on recommendations of a WHO research report (WHO 2013). In 2021, the WHO published new, mostly significantly lower recommendations for air quality assessment based on the latest scientific findings on the health effects of air pollutants (WHO 2021). Due to the significantly stricter assessment thresholds for PM2.5 and NO2, the distances of the average pollutant concentrations from the target increase, in some cases considerably. For ozone, the new WHO recommendation is somewhat less stringent than the old one, so that the distances to the target have even decreased somewhat.

Air quality is particularly precarious in agglomerations, where one third of the German population lives. Here, industry, traffic and residential areas exist in close proximity. The indicator incorporates data from monitoring stations which measure background urban pollution levels. At busy locations in cities pollution levels may be significantly higher. The indicator represents the average discrepancy of all monitoring stations of urban background from WHO guideline values, respectively.


Assessing the development

Levels of nitrogen dioxide and particulate matter have fallen considerably. 2019 is the first year in which nitrogen dioxide falls below the WHO recommendation in agglomerations. In 2020, the mean level of PM2.5 was also just below the WHO recommendation for the first time. However, ozone concentrations fluctuate widely. This is largely due to the influence of the weather. In hot summers such as 2003 or 2015, ozone concentrations rise sharply. Thus it is impossible to make a meaningful statement about the trend in recent years.

In 2008 the EU set out its air quality objectives in the Air Quality Directive (EU Directive – 2008/50/EC), in October 2022, the Commission presented a proposal to revise this directive (COM 2022) to take into account the new WHO recommendations 2021. Even then, large parts of Germany would still fail to meet some of the current less ambitious targets of the EU directive (UBA 2023). There is still a long way to go until the air in agglomerations is sufficiently ‘clean’.



The indicator is based on measurement data from the network of German air quality monitoring stations. All monitoring sites within an agglomeration were included in the measurement of urban and suburban background pollution levels. Measurements of these monitoring sites are used to calculate the extent to which the three pollutants NO2, PM2.5 and O3 exceed or fall short of WHO recommendations 2021. The average discrepancy between the values recorded at all monitoring stations and the WHO recommendation 2021 is calculated for each agglomeration. The average discrepancies are then averaged across all agglomerations and expressed in a standardised form with the WHO recommendation 2021.

More detailed information: 'Luftbelastung in Ballungsräumen' (in German only).