Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 9983-9996, 2015
https://doi.org/10.5194/acp-15-9983-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
07 Sep 2015
Diesel-related hydrocarbons can dominate gas phase reactive carbon in megacities
R. E. Dunmore1, J. R. Hopkins2,1, R. T. Lidster1, J. D. Lee2,1, M. J. Evans2,1, A. R. Rickard2,1, A. C. Lewis2,1, and J. F. Hamilton1 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
2National Centre for Atmospheric Science, University of York, Heslington, York, YO10 5DD, UK
Abstract. Hydrocarbons are key precursors to two priority air pollutants, ozone and particulate matter. Those with two to seven carbons have historically been straightforward to observe and have been successfully reduced in many developed cities through air quality policy interventions. Longer chain hydrocarbons released from diesel vehicles are not considered explicitly as part of air quality strategies and there are few direct measurements of their gaseous abundance in the atmosphere. This study describes the chemically comprehensive and continuous measurements of organic compounds in a developed megacity (London), which demonstrate that on a seasonal median basis, diesel-related hydrocarbons represent only 20–30 % of the total hydrocarbon mixing ratio but comprise more than 50 % of the atmospheric hydrocarbon mass and are a dominant local source of secondary organic aerosols. This study shows for the first time that 60 % of the winter primary hydrocarbon hydroxyl radical reactivity is from diesel-related hydrocarbons and using the maximum incremental reactivity scale, we predict that they contribute up to 50 % of the ozone production potential in London. Comparing real-world urban composition with regulatory emissions inventories in the UK and US highlights a previously unaccounted for, but very significant, under-reporting of diesel-related hydrocarbons; an underestimation of a factor ~4 for C9 species rising to a factor of over 70 for C12 during winter. These observations show that hydrocarbons from diesel vehicles can dominate gas phase reactive carbon in cities with high diesel fleet fractions. Future control of urban particulate matter and ozone in such locations requires a shift in policy focus onto gas phase hydrocarbons released from diesels as this vehicle type continues to displace gasoline world-wide.

Citation: Dunmore, R. E., Hopkins, J. R., Lidster, R. T., Lee, J. D., Evans, M. J., Rickard, A. R., Lewis, A. C., and Hamilton, J. F.: Diesel-related hydrocarbons can dominate gas phase reactive carbon in megacities, Atmos. Chem. Phys., 15, 9983-9996, https://doi.org/10.5194/acp-15-9983-2015, 2015.
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Short summary
Technological shifts between fuel sources have had unexpected impacts on atmospheric composition and these significant changes can go undetected if source-specific monitoring infrastructure is not in place. We present chemically comprehensive, continuous measurements of organic compounds in a developed megacity (London), that show diesel-related hydrocarbons can dominate reactive carbon and ozone formation potential, highlighting a serious underestimation of this source in emission inventories.
Technological shifts between fuel sources have had unexpected impacts on atmospheric composition...
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