N2O abundance (ppb)
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 Year  measured
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 2000   315.548
 2001   316.332
 2002   316.994
 2003   317.661
 2004   318.257
 2005   319.035
 2006   319.994
 2007   320.652
 2008   321.580
 2009   322.242
 2010   323.109
 2011   324.169
 2012   325.008
 2013   325.917
 2014   327.056
 2015   328.140
 2016   328.926
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