Observed time-averaged afternoon CO dry mole fraction above background (Site 01). The averaging period is 1 January – 30 April 2013. The site number is shown in the upper right corner of each plot (in blue) and the average observed CO above background (in ppb) in the upper left corner. The full y-axis scale for the plots is 40 ppb CO. Red filled circles indicate the locations of the sites, with the background Site 01 indicated by a red star. Time frame was chosen to maximize the number of sites with available data. Sites with less than 75% data availability during the selected time period were excluded. DOI: https://doi.org/10.1525/elementa.127.f11