  We numerically studied magnetic reconnection in a high $\beta$
hydrogen-helium plasma at different altitudes from the photosphere to the upper
chromosphere. The time dependent ionization degrees were included to get more
realistic diffusivities and viscosity, and appropriate radiative cooling models
were applied. Our numerical results indicate that the plasmoid instability
always plays a vital role in speeding up magnetic reconnection at different
atmospheric layers. In addition, both the strong radiative cooling and the
magnetic diffusion caused by the electron-neutral collision ($\eta_{en}$) can
significantly accelerate magnetic reconnection below the middle chromosphere.
On the other hand, both the ambipolar diffusion and the viscosity result in
higher temperature and plasma pressure in the reconnection region in the upper
chromosphere, which then hinder the fast reconnection process from developing.
The local compression heating triggered by turbulent reconnection mediated with
plasmoids is the dominant heating mechanism in the unstable reconnection stage
at different atmospheric layers, but the viscous heating and the ambipolar
diffusion heating are equally important in the upper chromosphere. The Joule
heating contributed by $\eta_{en}$ dominates during the early quasi-steady
reconnection stage below the middle chromosphere, the strong radiative cooling
also leads to much stronger compression heating and more generation of thermal
energy in this region. Though the plasma $\beta$ is the same in all the
simulation cases at different altitudes, the temperature increase is more
significant in the upper chromosphere with much lower density and weaker
radiative cooling.
