Several rocket measurements in the D region have revealed the presence of a narrow minimum (dip) and a steep gradient (ledge) in the electron density Ne in the 80- to 90-km altitude region and a rapid drop in the hydronium ions H+.(H2O)n from an altitude above about 85 km during quiet daytime conditions. In this report we have tried to reproduce these features using a detailed positive ion chemical scheme. It is found that the parameters which are responsible for the occurrence of a dip and a ledge in the Ne profile are the height distributions of q (O2) and q (NO), the electron-ion production rates due to the ionization of O2 and NO, respectively, and Hc, the height of intersection of the q (O2) and q (NO) profiles. The dip in Ne is reproducible when a narrow minimum in the NO density profile is present and the level of this minimum lies below the level of Hc. To reproduce the dip in the Ne profile as observed by Aikin et al. (1964), it is found that the NO density at the minimum should be about 105 cm-3. The ledge in Ne is obtained when the level of Hc lies below the level of the minimum in the NO profile. It is also found that the ledge in the Ne profile follows the ledge in the q (O2) profile. For the disappearance of the hydronium ions above about 85 km the rise of temperature above the mesopause is shown as the major factor which slows down the rate of transfer of molecular ions to hydronium ions, and this, coupled with the decreasing trend of total neutral particle density with height, rapidly decreases the lifetime of hydromium ions above this altitude.