Evidence from firn air for recent decreases in non-methane hydrocarbons and a 20th century increase in nitrogen oxides in the northern hemisphere

David R. Worton, William T. Sturges, Claire E. Reeves, Mike J. Newland, Stuart A. Penkett, Elliot Atlas, Verity Stroud, Kristen Johnson, Norbert Schmidbauer, Sverre Solberg, Jakob Schwander, Jean Marc Barnola

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Abstract

The atmospheric evolution of eight non-methane hydrocarbons (ethane, acetylene, propane, n-butane, isobutane, n-pentane, isopentane and benzene) and five alkyl nitrates (2-propyl, 2-butyl, 3-methyl-2-butyl and the sum of 2+3-pentyl nitrates) are reconstructed for the latter half of the 20th century based on Arctic firn air measurements. The reconstructed trends of the non-methane hydrocarbons (NMHCs) show increasing concentrations from 1950 to a maximum in 1980 before declining towards the end of last century. These observations provide direct evidence that NMHCs in the northern hemisphere have declined substantially during the period 1980-2001. Benzene concentrations show a smaller increase between 1950 and 1980 than the other NMHCs indicating that additional sources of benzene, other than fossil fuel combustion, were likely important contributors to the benzene budget prior to and during this period. The declining benzene concentrations from 1980 to 2001 would suggest that biomass burning is unlikely to be important in the benzene budget as biomass burning emissions were reportedly increasing over the same period. Methyl and ethyl nitrate show growth patterns in the firn that suggested perturbation by in-situ production from an unidentified mechanism. However, the higher alkyl nitrates show evidence for increasing concentrations from 1950 to maxima in the mid 1990s before decreasing slightly toward the end of the last century. The differing atmospheric evolution of the alkyl nitrates relative to their parent hydrocarbons indicate an increase in their production efficiency per hydrocarbon molecule. Using a steady state analysis of hydrocarbon oxidation and alkyl nitrate production and loss we show that reactive nitrogen oxide (NO x) concentrations in the northern hemisphere have likely increased considerably between 1950 and 2001.

Original languageEnglish (US)
Pages (from-to)592-602
Number of pages11
JournalAtmospheric Environment
Volume54
DOIs
StatePublished - Jul 1 2012

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Keywords

  • Alkyl nitrates
  • Atmospheric trends
  • Benzene
  • Firn air
  • Hydrocarbons
  • Nitrogen oxides

ASJC Scopus subject areas

  • Environmental Science(all)
  • Atmospheric Science

Cite this

Worton, D. R., Sturges, W. T., Reeves, C. E., Newland, M. J., Penkett, S. A., Atlas, E., Stroud, V., Johnson, K., Schmidbauer, N., Solberg, S., Schwander, J., & Barnola, J. M. (2012). Evidence from firn air for recent decreases in non-methane hydrocarbons and a 20th century increase in nitrogen oxides in the northern hemisphere. Atmospheric Environment, 54, 592-602. https://doi.org/10.1016/j.atmosenv.2012.02.084