Hourly observations of CO2 and CH4 from tower-based sites in the NIST Northeast Corridor network (currently 23, but more may be added in future updates); CO observations from one site. Files are comma delimited (CSV). Measurements of each species is made at two different heights above ground. Machine-readable (CSV) site information is in a separate file (NEC_sites.csv). Data is reported for the years 2015-2018. An ASCII Readme file (NEC_Readme_10012019) is also posted.