This dataset provides atmospheric concentrations of CO2, CH4, CO, and N2O measured by the Harvard Quantum Cascade Laser System (QCLS) instruments during airborne campaigns conducted by NASA's Atmospheric Tomography (ATom) mission. The QCLS (DUAL and CO2) instrument package contains two separate optical assemblies and calibration systems, and a common data system and power supply. The QCLS DUAL instrument simultaneously measures CO, CH4, and N2O concentrations, in situ, using two thermoelectrically cooled pulsed-quantum cascade lasers light...