Anne Caroline Lange specializes in air quality and inverse atmospheric chemistry modelling.
Polluted air is a danger to health. The sources of the air pollutants are largely known, but how much the sources emit is only estimated. Researchers from Jülich have reviewed these estimates, thus providing an important tool for identifying measures that improve air quality.
The diesel scandal, criticism aimed at the location of measuring stations, lawsuits for exceeding threshold values – the topic of air quality keeps causing a stir. Even though Germany’s pollution levels of particulate matter and nitrogen dioxide (NO2), for example, have been decreasing for years, the federal and state governments will probably have to tighten their measures. In October 2022, the EU Commission proposed stricter limits. If these were to come into force from 2030 onward, pollution levels would be too high in many places.
Picture above: Anne Caroline Lange specializes in air quality and inverse atmospheric chemistry modelling.
The German Environment Agency (UBA) and the federal states operate around 600 measuring stations. In addition to the quantities of particulate matter and NO2, they also assess ozone, carbon monoxide and sulphur dioxide. Most of the stations are located in conurbations, and thus assess air pollution concentrations that directly affect people. What they do not measure, however, is where the pollutants come from and how much each source emits. Yet understanding the relationship between emissions and measured pollutants is crucial – it is the basis for taking sensible measures to improve air quality. For this reason, the UBA estimates emission levels on the basis of many different data having to do with pollutant sources, such as the number of households and what each one uses for heating, traffic density or what kind of local industry there is. Information is drawn not only from administrative bodies, but also from companies like car manufacturers who share data on the pollutant emissions of their vehicles.
UBA has commissioned Jülich atmospheric researchers to assess how good the estimates are. For this purpose, they used the complex EURAD-IM atmospheric chemistry model, which they developed themselves (see box). “Our chemical transport model takes into account more than 100 different chemical compounds in the air and how they react with each other,” says Dr. Anne Caroline Lange from the Institute of Energy and Climate Research (IEK-8).
Tracing back to the source
The biggest advantage of the model: “We can calculate backwards in time with it. For example, we start with the measured concentration of nitrogen oxides taken from one point. The model then uses meteorological data and the known reactions of nitrogen oxides in the air to calculate their previous path, how they are distributed and with which substances they have reacted.” The researchers can then compare these simulated emission data with the UBA’s estimated emission data.
After high blood pressure, smoking and poor nutrition, air pollution is one of the most important risk factors for disease and mortality worldwide.
Source: Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019
In their first analysis, the Jülich researchers had initially concentrated on the year 2016. “We chose an average year in which climate change was already evident, but which had no extreme events such as heat, drought, volcanic eruptions or Saharan dust,” says Lange. Besides, even a single year means enormous computing effort. “We calculated the average annual emissions for each town and district at a resolution of 5 by 5 kilometres – but even that took Jülich supercomputers several months.”
The good news: “The results of our model calculations agree well with the emission values determined by the German Environment Agency,” says Lange. Still, “the spatial distribution of pollutant emissions could be even more precise.” There were unexpected discrepancies at first, Lange reports: “Our calculations showed higher nitrogen oxide emissions than estimated by the UBA. It turned out that the deviation may be attributable to the diesel scandal in 2016: the exhaust emissions of diesel vehicles were, in some cases, significantly higher than stated by manufacturers. These emissions were missing from the UBA estimates available at the start of the project.”
The scientists now plan to compare the UBA estimates from other years with the calculations of their model. In addition, other chemical transport models will be used to examine whether they produce similar results. Not only can the simulations test how good the estimates are, but they could also help politicians and authorities decide which measures and mitigation strategies are effective in order to improve air quality.
With the present report on 2016, however, UBA can already analyze how the spatial distribution of pollutants can be better estimated in the future. “It may be that baseline information needs to be looked at in a more regionally differentiated way, for example in agriculture: what plants are grown in the region, what fertilizers are used?” says Lange. Measures to comply with new threshold values can then be planned more specifically.
Barbara Schunk/Christian Hohlfeld
Air quality forecast
EURAD-IM (EURopean Air pollution Dispersion – Inverse Model) is an air quality prediction and analysis system. The regional chemical transport model calculates which gases and aerosols occur in the lower atmospheric layer three-day (troposphere), and in which quantities, and simulates their dispersion. The calculations include daily weather data and data updates from satellites as well as from measuring stations on the ground. This enables 3-days forecasts of air quality, which Jülich researchers make available online every day and send to the European Union for consultative purposes.
The model continuously checks its own predictions by retroactively comparing the calculated values with the measured values in analyses and adjusting parameters if necessary.
EURAD-IM air quality forecasts:
Stricter air quality guidelines
In autumn 2021, the World Health Organization (WHO) significantly tightened its air quality guidelines. If these guideline values had been binding, pollution levels would have been too high in many places in Europe – including in Germany (see table). On 26 October 2022, the European Commission presented proposals for stricter rules more closely aligned with the WHO guidelines. They are to come into force starting in 2030.
Current EU limit value as of October 2022 Proposed EU limit value WHO guideline value Particulate matter PM10 Max. annual average value 40 μg/m3 Max. annual average value 20 μg/m3 Max. annual average value 15 μg/m3 Exceeded by measuring station: Germany 0 % 6 % 38 % Exceeded by measuring station: EU countries 0 % 39 % 70 % Particulate matter PM2,5 Max. annual average value 25 μg/m3 Max. annual average value 10 μg/m3 Max. annual average value 5 μg/m3 Exceeded by measuring station: Germany 0 % 30 % 97 % Exceeded by measuring station: EU countries 1 % 50 % 95 % Nitrogen dioxide Max. annual average value 40 μg/m3 Max. annual average value 20 μg/m3 Max. annual average value 10 μg/m3 Exceeded by measuring station: Germany 1 % 56 % 85 % Exceeded by measuring station: EU countries 1-2 % 34% 74 %
Robert Wegener, from European Environment Agency (EEA) data for 2021, preliminary evaluation.
EU Commission: Proposal for a Directive of the European Parliament and of the Council on ambient air quality and cleaner air for Europe – Annexes
Photos: Forschungszentrum Jülich/Sascha Kreklau, Sergey Nivens/Shutterstock.com