Emission trends in Germany

Given recent headlines about driving restrictions for diesel cars in several German cities, I was curious about patterns of nitrogen dioxide emissions across cities and over time in the underlying data. I find that current regulations don't have much bite because seasonal variation in emissions is large. Even at measuring stations with high average annual pollution, daily average pollution can fluctuate between 20 and 140 micro grams per cubic meter. Under the assumption that regulation is unchanged, I identify several cities and stations that were below the regulation limits in 2017 but are likely to exceed limits in 2018.

I downloaded emissions data from the website of the Umweltbundesamt (Federal Environmental Agency). As common with many German administrative sources, these data are difficult to access in bulk but, with some wrangling, one can get data on daily average and daily maximum emissions for each station going back to January 2017.

Keep in mind that there are two restrictions on nitrogen dioxide emissions (see for instance here):

• The daily maximum most not exceed 200 micro grams per cubic meter on more than 18 days per year
• The annual average must not exceed 40 micro grams per cubic meter

I will only discuss the latter as the 200 micro grams restriction does not appear to be restrictive in the data.

Annual averages

How does annual average concentration look? The figure below plots annual averages in several large German cities. 2018 data are incomplete and not directly comparable to 2017 data. It does seem, however, that the average annual concentration over all stations in a city is typically below the maximum level of 40 micro grams per cubic meter (with the exception of Munich).

Seasonal patterns

The annual average masks substantial heterogeneity over seasons, though. Berlin, Frankfurt and Hamburg display a clear seasonal pattern with higher concentration in the winter and lower concentration in the summer. Cologne and Munich have a slightly more suprising pattern with concentration typically being higher around quarter-ends. Average concentration over the past 30 days often exceeds the 40 micro grams limit.

To me this illustrates how annual averages are not really helpful. It's like having one hand in freezing water and one hand in boiling water, fine on average, but really missing the point.

Drilling down a bit further, we can evaluate data by measuring station to see where concentration within a city is most severe and driving restrictions are most likely. For my home town of Cologne, concentration is (naturally) highest at stations closer to the city center (Turiner Str and clevischer Ring).

Stations at increased risk of nearby-driving restrictions

Because of the aforementioned seasonalities, average annual concentration remains an unsatisfying measure. Nevertheless, under the assumption that average annual concentration continues to be the measure of choice, I was curious about stations most likely to exceed the 40 micro grams limit this year. To get a quick sense before 2018 is complete, I computed average annual concentration by station from Nov 11, 2017 to Nov 10, 2018. All of the top 15 places exceeded the 40 micro grams limit in 2017 already and continue to do so in 2018.

## # A tibble: 15 x 3
##    Stationsname                     Mean2017 MeanNov17ToNov18
##    <chr>                               <dbl>            <dbl>
##  1 Stuttgart Am Neckartor               73.0             76.7
##  2 Stuttgart Hohenheimer Straße         68.8             70.7
##  3 München/Landshuter Allee             78.2             60.5
##  4 Hamburg Habichtstraße                57.9             59.4
##  5 B Neukölln-Silbersteinstr.           48.7             58.9
##  6 Köln Clevischer Ring 3               62.1             57.4
##  7 Kiel-Theodor-Heuss-Ring              56.8             56.3
##  8 Ludwigsburg Friedrichstraße          50.8             55.8
## 10 Nürnberg/Von-der-Tann-Straße         42.6             53.8
## 11 Reutlingen Lederstraße-Ost           59.5             53.5
## 13 B Neukölln-Karl-Marx-Str. 76         49.5             53.1
## 14 Heilbronn Weinsberger Straße-Ost     56.5             52.8
## 15 Mannheim Friedrichsring              44.7             52.5


New stations likely above the limit by year-end 2018

A few places did not exceed the limit in 2017 but are on track to exceed the limit in 2018. Expect debates about driving restrictions to pick up there.

## # A tibble: 9 x 3
##   Stationsname                    Mean2017 MeanNov17ToNov18
##   <chr>                              <dbl>            <dbl>
## 1 Mainz-Rheinallee                    35.9             46.8
## 2 Kassel-Fünffenster-Str.             38.8             46.2
## 3 Fulda-Petersberger Str.             39.4             44.5
## 4 Leipzig Lützner Str. 36             37.1             44.2
## 5 Norderstedt                         39.4             44.0
## 6 Saarbrücken-Verkehr                 36.5             43.9
## 7 Karlsruhe Reinhold-Frank-Straße     39.3             43.9
## 8 Bremen Verkehr 1                    39.2             43.2
## 9 Offenbach-Untere Grenzstraße        37.8             43.2