Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 8269-8283, 2017
https://doi.org/10.5194/acp-17-8269-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
07 Jul 2017
Changes to the chemical state of the Northern Hemisphere atmosphere during the second half of the twentieth century
Mike J. Newland1, Patricia Martinerie2,a, Emmanuel Witrant3, Detlev Helmig4, David R. Worton5, Chris Hogan1, William T. Sturges1, and Claire E. Reeves1 1Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
2Univ. Grenoble Alpes/CNRS, LGGE, 38000 Grenoble, France
3Univ. Grenoble Alpes/CNRS, GIPSA-Lab, 38000 Grenoble, France
4Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA
5National Physical Laboratory, Teddington, Middlesex, UK
anow at: Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK
Abstract. The NOx (NO and NO2) and HOx (OH and HO2) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NOx and HOx are highly variable in space and time, and so the measurements of these species are of limited value for examining long-term, large-scale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the production efficiency of which is dependent on the atmospheric [NO] ∕ [HO2] ratio. We derive long-term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 3–5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NOx, lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increased from around 1970 to the late 1990s. This is consistent with large changes to the [NO] ∕ [HO2] ratio in the Northern Hemisphere atmosphere during this period. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.

Citation: Newland, M. J., Martinerie, P., Witrant, E., Helmig, D., Worton, D. R., Hogan, C., Sturges, W. T., and Reeves, C. E.: Changes to the chemical state of the Northern Hemisphere atmosphere during the second half of the twentieth century, Atmos. Chem. Phys., 17, 8269-8283, https://doi.org/10.5194/acp-17-8269-2017, 2017.
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Short summary
We report increasing levels of alkyl nitrates in the Northern Hemisphere atmosphere between 1960 and the mid-1990s. These increases are symptomatic of large-scale changes to the chemical composition of the atmosphere, particularly with regards to the amounts of short-lived, reactive species. The observed increases are likely driven by increasing levels of nitrogen oxides. These changes have direct implications for the lifetimes of climate-relevant species in the atmosphere, such as methane.
We report increasing levels of alkyl nitrates in the Northern Hemisphere atmosphere between 1960...
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