Twenty years of ambient observations of nitrogen oxides and specified hydrocarbons in air masses dominated by traffic emissions in Germany
Twenty years of ambient observations of nitrogen oxides and specified hydrocarbons in air masses dominated by traffic emissions in Germany
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DOI：
10.1039/c5fd00180c
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发表时间：
2016-01-01
影响因子：
3.4
通讯作者：
Wahner, Andreas
中科院分区：
文献类型：
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作者：
Ehlers, Christian;Klemp, Dieter;Wahner, Andreas
对碳氢化合物(VOC)混合物的单独组成的分析使我们能够将观测到的VOC-浓度转换为它们各自相对于OH自由基的总VOC-反应性(R-VOC=Sigma(k(OH+voci)x[voci]))。这是特别有用的，因为当地臭氧的产生基本上取决于这一单一参数，而不是基础碳氢化合物混合物的细节(Klemp等人，Schiften des Forschungszentum Julich，能源与环境，2012，21)。挥发性有机化合物的成分也使我们能够确定城市地区碳氢化合物的主要排放来源是催化剂效率暂时降低的汽油车(所谓的冷启动情况)，而目前氮氧化物(NOx=NO+NO2)的来源预计将以柴油车为主。在德国城市主要道路附近的观察表明，VOC和NO2的OH反应性比率(R-VOC/R-NO2)在1994-2014年间下降了7.5倍。这比这一时期德国VOC和NOx交通排放估计趋势的预期降幅2.9倍要大(德国UmWeltbundesamt，2015年德国大气排放报告国家趋势表)。观测到的R-VOC/R-NO2比率的下降导致当地臭氧产量在碳氢化合物减少的推动下急剧下降。分析显示，臭氧排放量的整体减少得益于道路交通产生的NOx排放量减少较少，这是由于柴油车到目前为止最终没有用于去除氮氧化物的催化转换器所致。
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 (R-VOC = Sigma(k(OH+VOCi) x [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 Julich, 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 (R-VOC/R-NO2) 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 R-VOC/R-NO2 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.