A new field emission model of carbon nanotubes (CNTs) to simulate gas detection mechanism in CNT based ionization gas sensor has been developed. The new model consists of three modules which are combined together and embedded in the standard particle-in-cell/Monte Carlo collision codes. The functionality of the enhanced model is checked by varying the gas pressure and gap spacing in the simulations. From the results, around one order of magnitude decrease in the breakdown voltages and two orders of magnitude faster response time is observed. The lowest breakdown voltages are observed when intertube spacing is equal to height of the nanotube. The field enhancement factor β is calculated from our model and compared with the β of the well established model. The closeness among the values of β validates the performance of our field emission model. Furthermore, the β of our model is compared with the β of the existing ionization gas sensors. It was found that the β of our sensor is around 3 times better than the β of the gold nanowire based ionization gas sensor and 28 times better than the β of the other CNT based ionization gas sensor. These results suggest that by properly controlling the growth of CNT structures, an optimized CNT based ionization gas sensor can be realized. © 2013 American Institute of Physics.