Quality-controlled formic acid (HCOOH) fluxes 30-minute averaging periods at the 30-m inlet height at the WLEF very tall tower for the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD) project are contained in this dataset.  HCOOH mixing ratio measurements were made using a chemical ionization time of flight mass spectrometer (CI-ToFMS). All flux values are in ppbv cm/s. Time is in fractional day of year Central Daylight Time. For all measurements assume a 20% uncertainty, as that is the upper limit in flux uncertainty calculations. See the readme documentation for a decription of the instrument, data collection, quality control and detection method.