Twenty years of ambient observations of nitrogen oxides and specified hydrocarbons in air masses dominated by traffic emissions in Germany.

Christian Ehlers,Astrid Kiendler-Scharr,Franz Rohrer,Andreas Wahner,Robert Wegener,Djuro Mihelcic,Dieter Klemp

doi:10.1039/c5fd00180c

Christian Ehlers, Astrid Kiendler-Scharr + Show 5 more

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https://doi.org/10.1039/c5fd00180c

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Abstract

The analysis of the individual composition of hydrocarbon (VOC) mixtures enables us to transform observed VOC-concentrations into their respective total VOC-reactivity versus OH radicals (RVOC = Σ(kOH+VOCi × [VOCi])). This is particularly useful because local ozone production essentially depends on this single parameter rather than on the details of the underlying hydrocarbon mixture (Klemp et al., Schriften des Forschungszentrums Jülich, Energy & Environment, 2012, 21). The VOC composition also enables us to pin down the major emission source of hydrocarbons in urban areas to be petrol cars with temporarily reduced catalyst efficiency (the so-called cold-start situation) whereas the source of nitrogen oxides (NOx = NO + NO2) is expected to be nowadays dominated by diesel cars. The observations in the vicinity of main roads in German cities show a decrease in the ratio of OH reactivities of VOC and NO2 (RVOC/RNO2) by a factor of 7.5 over the time period 1994-2014. This is larger than the expected decrease of a factor of 2.9 taking estimated trends of VOC and NOx traffic emissions in Germany (Umweltbundesamt Deutschland, National Trend Tables for the German Atmospheric Emission Reporting, 2015), during this time period. The observed reduction in the RVOC/RNO2 ratio leads to a drastic decrease in local ozone production driven by the reduction in hydrocarbons. The analysis reveals that the overall reduction of ozone production benefits from the low decrease of NOx emissions from road traffic which is a consequence of the eventual absence of catalytic converters for nitrogen oxide removal in diesel cars up to now.

Highlights

Over the last 20 years (1994–2014), the compliance with ozone regulations of the European Union (EU) for the protection of human health has slowly improved in Germany
Since we have shown in Section 1.3.1, that the observed concentration trend in traffic dominated inner city districts of Germany follows the estimated trend for nitrogen oxides (NOx) traffic emissions, this discrepancy has to come from the trend of traffic VOC emissions
Traffic emissions of NOx did not show the same decline as the VOC emissions

Summary

Introduction

Over the last 20 years (1994–2014), the compliance with ozone regulations of the European Union (EU) for the protection of human health has slowly improved in Germany. Paper remained almost constant over the last 25 years (Fig. 1) To put this into a proper perspective, these observations in Germany can be compared to ozone data from the GAW station at the western coast of Europe in Mace Head, Ireland. The magnitude of this decrease at Hohenpeissenberg relative to Mace Head is on the order of 10–15% over 25 years This decrease has been caused by changes in Germany since air parcels on their way from the Atlantic pass France and other European countries. These observations show a general trend towards smaller ozone production in Western Europe

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