Effect of lockdown on air quality and everyday life
TROPOS evaluation from Leipzig shows less nitrogen dioxide and soot at traffic stations for spring 2020.
Leipzig. In connection with the effects of the COVID-19-pandemic, it has been widely discussed how much the lockdown will affect air quality and climate. An evaluation by the Leibniz Institute for Tropospheric Research (TROPOS) shows: The first lockdown in spring 2020 contributed to improving the air. At the traffic stations in the west and east of Leipzig, for example, there was a decrease in nitrogen oxide (NOx) as well as soot (BC). At the major roads and thus for many people the air became better according to the traffic reduction. The analysis is based on measurement data from various stations in Leipzig from TROPOS and the Saxon State Office for the Environment, Agriculture and Geology (LfULG), for which the influence of the weather was subsequently corrected at great expense. The analysis is preliminary, not yet scientifically peer-reviewed, and is to be submitted to a scientific journal in 2021.
To combat the pandemic in the spring of 2020, on March 22 the federal and state governments in Germany had agreed on strict exit and contact restrictions, which also ensured reduced mobility in Saxony until June 5. These restrictions entered the vernacular as lockdown and have been controversially discussed ever since. From a scientific perspective, these measures are a field experiment on an unprecedented scale: Atmospheric research is interested, for example, in what effect a reduction in traffic can have on air pollution and global warming. Researchers around the world have therefore analyzed data. One of them is a Europe-wide study of the EU research infrastructure for short-lived atmospheric components such as aerosol, clouds, and trace gases (ACTRIS), whose German contribution is coordinated by TROPOS.
To investigate the lockdown´s effect on local air quality, TROPOS evaluated various measurements in Leipzig. For this purpose, TROPOS used two stationary measuring stations: The station Permoser Straße in the northeast of Leipzig is about 150 meters away from the B6. The station in Eisenbahnstraße near the city center locates in a busy street canyon. In addition, the data set was supplemented with measurements from the LfULG station in Lützner Straße in the west of Leipzig and with traffic counts from the city of Leipzig.
It quickly became apparent that weather in spring had an influence on air quality: While a westerly weather situation with clean air from the Atlantic prevailed shortly before the lockdown, the weather situation changed in the first week of the lockdown: easterly winds brought continental and more polluted air from eastern Europe to central Germany. April and May were also characterized by low precipitation and little wind, which favors the accumulation of pollutants in the air - as researchers at TROPOS were already able to demonstrate in 2020 in a study on the air pollutant nitrogen dioxide in Saxony.
In spring 2020, two effects overlapped: On the one hand, less road traffic resulted in fewer pollutants. On the other hand, however, the pollutants remained on-site longer due to the low-exchange weather and were thus able to accumulate more. In addition, pollutants appeared due to long-distance transport from Eastern Europe, where the dry spring had already caused the first forest fires. For a well-founded analysis, it was, therefore, necessary to distinguish between the two effects. For the statistical analysis, Dr. Dominik van Pinxteren used a method from the field of machine learning. The application of this method first took place in 2009 and was published by British researchers. It has already proven its worth in "extrapolating" the weather's influence on nitrogen dioxide values in Saxony.
Using data series from 2016 to 2019 and factors such as time of day, season, weather, the height of the boundary layer, and origin of the air masses, it was thus possible to predict by computer model what pollutant concentrations could theoretically have been expected in 2020. The team then compared the prediction with the actual measured pollutant concentrations. The difference between the two values corresponds to the improvement in air quality due to reduced traffic, especially at the measuring stations near the roads.
For nitrogen oxides (NOx), the LfULG station Lützner Straße in the west of Leipzig showed an average decrease of 25 micrograms per cubic meter, which corresponds to almost one-third of the concentrations expected without lockdown under comparable weather conditions. This pollutant reduction is of a magnitude that corresponds to the decrease in traffic during this period: At the beginning of the first lockdown, the following data was counted: about 35 percent fewer cars, 15 percent fewer vans, and 10 percent fewer trucks.
For black carbon (BC), which TROPOS measures at Eisenbahnstraße east of Leipzig center, the analysis showed a decrease of up to 0.6 micrograms per cubic meter. These numbers correspond to about 40 percent of the expected concentrations. On average, soot decreased by 0.4 micrograms per cubic meter in Leipzig's Eisenbahnstraße during the two-month lockdown in spring 2020, a decrease of about 20 percent.
By comparison, the Leipzig Low Emission Zone had reduced soot by around 60 percent between 2011 and 2017. However, this reduction took place over six years, starting from an even higher level at the time, and was more sustainable because the Low Emission Zone accelerated the modernization of the vehicle fleet. This decline was demonstrated in 2017 at the LfULG station Leipzig-Mitte, which in 2020, however, could not be used for the current lockdown analysis due to construction sites in the surrounding area. The trend toward more fireplaces and wood-burning heaters is partially undoing the progress made for air quality in the transport sector in recent years by causing an increase in particulate matter and soot during the heating season, even in urban areas. "In contrast, in the urban background at our station at the institute, which is away from traffic, the effects were barely noticeable. Traffic influences are no longer as dominant. Other sources play a stronger role for both nitrogen oxide and soot. We see this as one reason for these differences," explains Dominik van Pinxteren from TROPOS.
Conclusion: The lockdown in spring 2020 also contributed to an improvement in air quality in Leipzig, especially in the vicinity of roads. Taking into account the weather effects, the air pollutants nitrogen oxide and soot significantly decreased. The data roughly corresponds to the decrease in traffic volume. However, the effects of fewer motor vehicles outweighed the effects of the dry spring weather and are therefore not directly evident in the pure measurement data.