The ionospheric E-region from 100 km to 150 km is typically regarded as being in photo-chemical equilibrium (PCE) state during daytime. Incoherent scatter radar observations at Arecibo show that PCE is not always valid. During July 31--Aug. 5, 1992, the vertical ion drift was observed to increase by 50 m/s over a ten kilometer altitude range. The large divergence resulting from the steep velocity gradient reduced the electron concentration by 30%, invalidating the generally held PCE. Observations of non-PCE allow us to estimate the chemical loss rate. By assuming that the loss rate does not have a day-to-day variability, the dissociative recombination rate derived from the incoherent scatter radar (ISR) observation is about 1.0 ¿ 10-7 cm3s-1, which is significantly lower than the laboratory rate of NO+, or O2+. The most plausible explanation for the discrepancy is that the relative concentration of O2+ and NO+ changed significantly when non-PCE occurred.