Note: This data archive supersedes our previous archive: https://doi.org/10.18434/mds2-2491. See Updates document for specific major and minor changes. Here we provide hourly observations of carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) from tower- based sites in the NIST Northeast Corridor network. Each *.tgz (tar/gzip) archive contains data files for a given site location, nam ed by its 3-letter code (see NEC_sites.csv for codes and locations). To extract on a unix platform, use "tar -xvzf <filename>". Data files within the <site>.tgz archives are comma delimited (CSV); data files within the <site>_NC.tgz archives are in NetCDF format. Site locations, heights, and other information are in a separate ascii (CSV) file (NEC_sites.csv), and also within each data file. D ata in this archive is reported for the years 2015-2022. An ASCII Readme file (NEC_Readme_05052023) is also posted, along with an Up dates_05052023.txt file that includes additional information on updates. Note about calibrations: CO2 data are reported on the NOAA/ WMO X2007 calibration scale. CH4 data are reported on the NOAA/WMO X2004A calibration scale; CO data, where available, are reported on the NOAA/WMO X2014 scale. This archive, with CO2 data on the X2007 scale, will no longer be updated. A full revision of all the d ata on the NOAA/WMO X2019 scale for CO2 is forthcoming, and will be linked here; that archive will maintain its own record and DOI, include CH4 and CO, and will be continually updated. This data is being freely distributed for research, academic and related non-co mmercial purposes consistent with NIST's mandate to further the science and the promulgation of appropriate standards. Current updat e: May 5, 2023.