The absorption of NO2 samples in the region of 436~470 nm was measured by incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) with a blue light emitting diode (LED) to demonstrate the performance of IBBCEAS. Mirror reflectivity at 430~490 nm is determined from the changes in transmitted intensity through the cavity due to Rayleigh scattering when the cavity is filled with pure N2 and He, and validated with the help of the absorption at 477 nm of O2-O2 collisional pair in pure oxygen. The maximum mirror reflectivity of 0.99937 is found at 461 nm, which corresponds to an effective path length of about 1.17 km based on a 73.5 cm-long cavity. Detection sensitivity (1σ) of 0.25×10-9 with an acquisition time of 20 s is achieved. The absorptions of NO2 and O2-O2 collisional pair in ambient air are simultaneously measured by IBBCEAS in open-path mode. Measuring results demonstrate that the performance of the IBBCEAS instrument deteriorats due to aerosol extinction. It is a possible solution to realize in situ calibration of absorption light path of IBBCEAS instrument by measuring O2-O2 in atmospheric air.