The effect of different atmospheres and differently composed dispersions on spin-casted nanoporous ZnO field-effect transistors has been investigated. Devices were fabricated by multiple spin-casting of ZnO nanoparticle dispersions with MeOH, water and chlorine containing solvents onto bottom-gate/ bottom-contact Si/SiO₂ substrates with gold electrodes commercially available through Fraunhofer IPMS, Dresden. This was possible by a synthesis route which allowed for an easy exchange of the solvents by dialysis. In all cases transistors exhibit a nanoporous ZnO channel resulting from the globular shape of the individual nanoparticles. These transistors allow for an easy access of gases and liquids to the transistor channel. For a single spin-coating process it will be shown that the coverage of the transistor channel is insufficient for a reasonable transistor performance which is why multiple coatings (at least two) have been utilized successfully. In addition, for all solvents an annealing step at temperatures between 50°C to 250°C for 15 min was found to be necessary to activate charge transport through the removal of remainders of acetate groups from the nanoparticle surface. Such acetate groups are leftovers of nanoparticle synthesis and hinder the neck-forming between particles, latter being a prerequisite for charge transport. With increasing temperature the charge carrier mobility improves up to values of 9 x10^-3 cm²/(Vs) and the threshold voltage or equivalently the trap density at the ZnO/SiO₂ interface diminishes. The reason for the decrease of the threshold voltage is shown to be due to the removal of adsorbed oxygen molecules from the surface with increasing temperature or with decreasing pressure of the surrounding oxygen atmosphere. When prepared in a water-based dispersion a two orders of magnitude larger on-current and a 3 order of magnitude higher off-current compared to the MeOH based dispersion is observed. The higher on-current can be explained by the better filtration of the acetate groups during dialysis performed for the substitution of MeOH by water. This reduction of spacer groups leads to an easier neck formation between particles, which also explains the higher off-currents. An amazing performance change is obtained when chlorine-based dispersions are employed such as chloroform and dichloromethane. Apparently the transistor characteristics seem to be destroyed and a highly conducting device is obtained within the experimentally possible voltage windows. The function of the chlorine was unraveled by adding different concentrations of HCl or KCl to a MeOH based dispersion. A concentration dependent shift of the threshold voltage has been observed indicating increased n-doping with increasing chlorine concentration allowing for a potential adjustment of the threshold voltage. A phenomenological model will be presented.