A modified microwave cavity technique was used to measure the decay rates of electron densities in air afterglows. Measurements of low‐duty cycle or single discharges which were not affected by the discharge products of preceding events were obtained by monitoring the shifts of the resonant frequencies. Results of measurements in late afterglows show that one loss mechanism can be described by an effective ambipolar diffusion coefficient representing participation of two positive ions in the process; the ions being most likely O2+and NO+. The other loss mechanism is due to two‐body attachment of electrons, the likely attaching specie being NO2. The measurements on two differentx‐band cavities in the pressure range 0.1‐10.0 Torr for ambipolar diffusion yielded:Da,eff p = 122 ± 18cm2/secTorr and for attachment:hav1 = (4.9 ± 0.15) × 103sec−1Torr−1.