At the end of January 2019, calculations by an external engineering firm determined that, in addition to the Parcusstraße measuring station, NO2 limit values exceeding the annual average of 40 µg/m³ also occur in Mainz along the Rhine axis. The calculations showed values between 40 and 52 micrograms/m³ on Rheinstraße, Peter-Altmeier-Allee, and Rheinallee. These calculated values did not correspond to the measurement results at the fixed measuring station on Rheinallee/Frauenlobstraße operated by the State Office for the Environment (LfU), where values below the limit have been measured since 2016. In order to verify the calculations, the LfU carried out passive sampler measurements, three of which were on the Rhine axis. After several months of measurements, it became apparent that the calculations were largely confirmed and that an annual average NO2 limit value of 8 micrograms/m³ must be assumed on some sections of the Rhine axis.

The city of Mainz was therefore requested to update the valid clean air plan with the aim of achieving or falling below the limit value throughout the city.

Public participation
The first draft of this update was made available for public inspection from February 27, 2020, to March 26, 2020, and objections could be submitted to the city of Mainz until April 9, 2020. This opportunity was actively taken advantage of. 

The coronavirus pandemic and the associated restrictions led to a decline in traffic volume. The lower traffic figures and the initial effects of the various air pollution control measures that were introduced resulted in a significant reduction in emissions. Since February 2020, the monthly average limit value has been complied with or significantly exceeded. This necessitated a reassessment of the situation and an adjustment of further measures. In particular, it was possible to dispense with the introduction of the planned driving ban for diesel vehicles (Euro 5/V and below) for the time being. As a further measure, a speed limit of 30 km/h was introduced from Holzhofstraße to Kaiser-Karl-Ring, accompanied by further measures to stabilize traffic. Great attention was also paid to promoting cycling and expanding environmental lanes. This took into account the positive trend of increasing bicycle traffic in the city and gave more space to cycling and public transport. These significant changes required renewed public participation. It ended with the expiry of the objection period on August 11, 2020. Objections that had already been raised during the first public participation process were taken into account in full, provided they had not become obsolete as a result of the changes in the update.
All submissions were reviewed during the further processing of the update to the clean air plan and taken into account where appropriate. 

This plan was made available to the public from September 15, 2020, to September 28, 2020, in accordance with Section 47 (5) of the Federal Immission Control Act (BImSchG).

The proceedings brought by Deutsche Umwelthilfe e.V. against the city of Mainz, which were still ongoing at that time, were concluded with a settlement in the oral hearing on October 28, 2020, before the Higher Administrative Court in Koblenz.

The effectiveness of the broad-based action plan for air pollution control in the city of Mainz was therefore recognized by all parties involved and confirmed in its implementation. Many of the measures described in the clean air plan have already been implemented and are therefore having a direct impact on the quality of our air in Mainz. This is also evident from a recent evaluation of data from all federal states by the Federal Environment Agency, according to which the introduction of 30 km/h zones and the retrofitting of buses to reduce pollutants, as implemented in Mainz, is a major factor in reducing air pollution in cities.

At a press conference on February 22, 2024, Janina Steinkrüger, head of the environmental department, provided an update on the clean air plan. The good news:

The legal limits, especially for all relevant pollutants affected by traffic, such as nitrogen dioxide and particulate matter, were safely complied with in Mainz in 2023.

This is due, among other things, to the fact that

• the measures from the City of Mainz's Clean Air Plan have been largely implemented or further developed,
• traffic figures in Mainz (especially on Parcusstraße) have not yet returned to pre-coronavirus levels,
• the composition of the vehicle fleet in Mainz is steadily changing towards lower-emission vehicles, and
• weather conditions in 2023 were above average for ground-level air exchange.

The three graphs in the image gallery show the key developments and some of the efforts made by the city of Mainz that have contributed to what has been achieved so far.

Outlook:
The current legal limits will be complied with in Mainz for the foreseeable future. Significantly stricter limits, especially for nitrogen dioxide and particulate matter, are expected to be set by the EU in a new directive and are likely to come into force in 2030. In order to achieve these targets in Mainz, additional air pollution control measures will be necessary in the foreseeable future – and not only in the city of Mainz.