Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Traffic density, wind and air stratification influence the load of the air pollutant nitrogen dioxide

26.06.2020

Leipzig researchers use methods to calculate weather influences from air pollution data

In connection with the effects of the COVID-19 pandemic, satellite measurements made headlines showing how much the air pollutant nitrogen dioxide (NO2) had decreased in China and northern Italy.


Traffic density, wind and air stratification influence the pollution with the air pollutant nitrogen dioxide, according to the conclusion of a TROPOS study commissioned by the LfULG, for which data from Saxony were evaluated - including Dresden.

Burkhard Lehmann, LfULG

In Germany, traffic density is the decisive factor. However, weather also has an influence on NO2 concentrations, according to a study by the Leibniz Institute for Tropospheric Research (TROPOS), which evaluated the influence of weather conditions on nitrogen dioxide concentrations in Saxony 2015 to 2018 on behalf of the State Environmental Agency (LfULG).

It showed that wind speed and the height of the lowest air layer on the ground are the most important factors that determine how much pollutants can accumulate locally.
In order to determine the influence of various weather factors on air quality, the team used a statistical method that allows meteorological fluctuations to be calculated from long-term measurements.

The air quality fluctuates, in some cases very strongly, due to different emissions and the influence of the weather. Until now, however, it has been difficult to estimate:

What share do legal measures such as low emission zones or diesel driving bans have and what share does the weather have in the actual air quality? With the method used, this will be easier in the future.

Nitrogen dioxide (NO2) is an irritant gas which attacks the mucous membrane of the respiratory tract, causes inflammatory reactions as an oxidant and increases the effect of other air pollutants. As a precursor substance, it can also contribute to the formation of particulate matter. Limit values have been set in the EU to protect the population:

For nitrogen dioxide, an annual average value of 40 micrograms per cubic metre of air applies (μg/m³). To protect the health of the population, measures must be taken if these limit values are not complied with. In 2018/2019, for example, various measures were taken in Germany, ranging from a reduction in the number of lanes (e.g. in Leipzig) to driving bans for older diesel vehicles (e.g. in Stuttgart).

To evaluate the effectiveness of such measures, it would be helpful to determine the exact influence of weather conditions. The Saxon State Office for Environment, Agriculture and Geology (LfULG) therefore commissioned TROPOS to carry out a study on the influence of weather factors on NO2 concentrations and provided its measurement data from the Saxon air quality measurement network and meteorological data for this purpose.

The researchers were thus able to evaluate data from 29 stations in Saxony over a period of four years, which represent a cross-section of air pollution - from stations at traffic centres to urban and rural background stations and stations on the ridge of the Erzgebirge mountains. They also calculated the height of the soil layer in the atmosphere and incorporated data from traffic counting stations in Leipzig and Dresden into the study. A method from the field of machine learning was used for the statistical modelling, the application of which in the field of air quality was first published by British researchers in 2009.

In this way, the study was able to demonstrate that the traffic density at all traffic stations is significantly responsible for nitrogen oxide concentrations. However, two weather parameters also have a significant influence on nitrogen dioxide concentrations: wind speed and the height of the so-called mixing layer. The latter is a meteorological parameter that indicates the height to which the lowest layer of air on the ground, where the pollutants mix, extends.

"It was also shown that high humidity can also reduce the concentration of nitrogen dioxide, which could be due to the fact that the pollutants deposit more strongly on damp surfaces. However, the exact causes are still unclear," says Dominik van Pinxteren.

The statistical analysis has also enabled the researchers to "deduce" the influence of the weather from the time series of pollutant concentrations: Adjusted for the weather, the concentration of nitrogen oxides (NOx) in the average of the measuring stations close to traffic in Saxony fell by a total of 10 micrograms per cubic meter between 2015 and 2018. In urban and rural areas and on the ridge of the Erzgebirge, however, NOx concentrations tend to remain at the same level. Even though there have been some changes in air quality in recent years, there are good arguments from the point of view of science for further reducing air pollution.

This also applies, in a transferred sense, to premature conclusions from the corona crisis: in order to find out how strong the influence of the initial restrictions on air quality actually was, the influence of the weather would have to be statistically deducted in a longer series of measurements. To this end, investigations for the Leipzig area are currently underway at TROPOS, as is a Europe-wide study of the EU research infrastructure for short-lived atmospheric constituents such as aerosol, clouds and trace gases (ACTRIS), the German contribution to which is coordinated by TROPOS. Tilo Arnhold

Project:

LfULG-Projekt „Meteorologische Einflüsse auf Stickstoffdioxid“:
https://www.luft.sachsen.de/Inhalt_FuE_Projekt_Witterung_NOx_Ozon.html

Background information:

Until now, the influence of weather has made it difficult to assess the effectiveness of traffic measures in reducing the exposure to the air pollutant nitrogen dioxide. This is mainly due to its formation: Nitrogen oxides (NOx) are mainly produced in combustion processes. In conurbations, road traffic is considered the most important source, with the largest share coming from diesel engines. Diesel engines emit nitrogen dioxide and, above all, nitrogen monoxide (NO), which is converted to NO2 in the atmosphere by complex photochemical processes: High solar radiation can therefore lead to high NO2 and ozone (O3) levels, especially in urban areas. Also in summer, high temperatures, especially in rural areas, can lead to high concentrations of biogenic volatile organic compounds (BVOC) and thus to an increased conversion of NO to NO2. However, the extent to which concentrations of trace gases accumulate in the air above the ground also depends on the weather: It has long been known that weak winds can cause high concentrations of pollutants. Two unfavourable factors come together, especially in inversion weather conditions in winter: Because of the cold, there is a lot of heating and the high immissions accumulate in a small volume of air. High concentrations of pollutants are then the result. In particular, valley locations then act like a pot on which the inversion layer in the atmosphere has been put on a lid.

The concentrations of nitrogen dioxide (NO2) in Saxony have decreased on average since 2000. Until 2018, however, exceedances of the annual NO2 limit of 40 micrograms per cubic meter were still measured. In October 2019, for example, the city of Leipzig was forced to implement immediate measures from the Clean Air Plan and to throttle the traffic flow on several entry roads, because the modelling had suggested that the NO2 values in these roads were too high.

The applied method is based on so-called "enhanced regression trees". "These are decision trees, with which a mathematical algorithm is 'trained' in such a way that it can independently decide on the basis of the data whether a factor has an influence on the pollutant concentration and if so, how high this influence is. A decision tree consists of a sequence of "if-then" decisions, which in its structure resembles a tree that starts at the root and branches out further and further until it reaches the "leaves", as the final points of a decision tree are also called," explains Dr. Dominik van Pinxteren from TROPOS, who has made the method applicable to Saxony. "A disadvantage of a single regression tree is its usually only moderately good prediction quality. To improve this, modern applications therefore calculate ensembles consisting of many trees. The prediction is averaged from the entire "forest", so to speak. In this way, a "weak learner" (a single tree with limited depth) is gradually built up or strengthened to become a "strong learner", resulting in powerful models that have become widely used in areas of machine learning".

Detailed results:
The team around Dominik van Pinxteren was able to statistically calculate that e.g. at the measuring station Dresden-Bergstraße the nitrogen dioxide concentration decreases significantly due to wind: from calm to 1 m/s wind speed by 25 micrograms per cubic meter and between one and three meters per second by another 10 micrograms per cubic meter. NO2 also decreases by 10 µg/m3 when the height of the mixing layer increases from very close to the ground to an average height of 500 m.

---

The Leibniz-Institute for Tropospheric Research (TROPOS) is member of the Leibniz Association, which connects 96 independent research institutions that range in focus from the natural, engineering and environmental sciences via economics, spatial and social sciences to the humanities. Leibniz Institutes address issues of social, economic and ecological relevance. They conduct knowledge-driven and applied basic research, maintain scientific infrastructure and provide research-based services.
The Leibniz Association identifies focus areas for knowledge transfer to policy-makers, academia, business and the public. Leibniz institutions collaborate intensively with universities – in the form of “Leibniz ScienceCampi” (thematic partnerships between university and non-university research institutes), for example – as well as with industry and other partners at home and abroad.
They are subject to an independent evaluation procedure that is unparalleled in its transparency. Due to the importance of the institutions for the country as a whole, they are funded jointly by the Federation and the Länder, employing some 20,000 individuals, including 10,000 researchers.
The entire budget of all the institutes is approximately 1.9 billion Euros. They are financed jointly by the Federal Government and the Länder. The basic funding of the Leibniz Institute for Tropospheric Research (TROPOS) is therefore financed by the Federal Ministry of Education and Research (BMBF) and the Saxon State Ministry of Science and the Arts (SMWK). The Institute is co-financed with tax revenues on the basis of the budget approved by the Saxon State Parliament.
https://www.leibniz-gemeinschaft.de/en/home/
https://www.bmbf.de/en/index.html
https://www.smwk.sachsen.de/

Wissenschaftliche Ansprechpartner:

Dr. Dominik van Pinxteren
Scientist, Atmospheric Chemistry Department at the Leibniz-Institute for Tropospheric Research (TROPOS), Leipzig
Phone +49 341 2717- 7029
https://www.tropos.de/en/institute/about-us/employees/dominik-van-pinxteren
und
Prof. Hartmut Herrmann
Head of the Atmospheric Chemistry Department at the Leibniz-Institute for Tropospheric Research (TROPOS), Leipzig
Phone +49 341 2717- 7024
https://www.tropos.de/en/institute/about-us/employees/hartmut-herrmann
or
Tilo Arnhold
Public Relations at the Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
Phone: +49-341-2717-7189
https://www.tropos.de/en/current-issues/press-releases

Originalpublikation:

Dominik van Pinxteren, Sebastian Düsing, Alfred Wiedensohler, Hartmut Herrmann (2020): Meteorological influences on nitrogen dioxide: Influence of weather conditions and weathering on nitrogen dioxide concentrations in outdoor air 2015 to 2018. series of publications of the LfULG, issue 2/2020
https://publikationen.sachsen.de/bdb/artikel/35043
This study was commissioned by the State Office for Environment, Agriculture and Geology (LfULG).

Weitere Informationen:

COVID-19 campaigns by ACTRIS:
http://www.actris.eu/Outreach/News/ACTRISUpdates.aspx

Tilo Arnhold | Leibniz-Institut für Troposphärenforschung e. V.

More articles from Ecology, The Environment and Conservation:

nachricht Road access for all would be costly, but not so much for the climate
10.07.2020 | Potsdam-Institut für Klimafolgenforschung

nachricht Innovative grilling technique improves air quality
01.07.2020 | Fraunhofer Institute for Building Physics IBP

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The spin state story: Observation of the quantum spin liquid state in novel material

New insight into the spin behavior in an exotic state of matter puts us closer to next-generation spintronic devices

Aside from the deep understanding of the natural world that quantum physics theory offers, scientists worldwide are working tirelessly to bring forth a...

Im Focus: Excitation of robust materials

Kiel physics team observed extremely fast electronic changes in real time in a special material class

In physics, they are currently the subject of intensive research; in electronics, they could enable completely new functions. So-called topological materials...

Im Focus: Electrons in the fast lane

Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful.

Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light....

Im Focus: The lightest electromagnetic shielding material in the world

Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range – and they are unrivalled in terms of weight.

Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic...

Im Focus: Gentle wall contact – the right scenario for a fusion power plant

Quasi-continuous power exhaust developed as a wall-friendly method on ASDEX Upgrade

A promising operating mode for the plasma of a future power plant has been developed at the ASDEX Upgrade fusion device at Max Planck Institute for Plasma...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Contact Tracing Apps against COVID-19: German National Academy Leopoldina hosts international virtual panel discussion

07.07.2020 | Event News

International conference QuApps shows status quo of quantum technology

02.07.2020 | Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

 
Latest News

X-ray scattering shines light on protein folding

10.07.2020 | Life Sciences

Looking at linkers helps to join the dots

10.07.2020 | Materials Sciences

Surprisingly many peculiar long introns found in brain genes

10.07.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>