| Abstract : | Exoplanets exhibit a wide range in their parameter space, including equilibrium temperature, radius, mass, orbital properties, and metallicity, which can alter the exoplanet atmospheric composition. Atmospheric metallicity is one such parameter, which affects the atmospheric equilibrium abundance, chemical conversion time scales and the location of the quenching point. We have constructed a model to study the atmospheric compositions of exoplanets and have investigated the effects of changing the metallicity on the atmosphere. The model solves the mass continuity equation with chemical kinetics, transport-flux (Eddy and molecular diffusion), and photochemistry. The photodissociation rates are calculated using the two-stream approximation method. To understand the effect of metallicity as the temperature and pressure change in the atmosphere, we ran a series of models to make a 3D grid in the temperature, pressure, and metallicity space. First, we studied the effect of metallicity on the equilibrium abundance and compared our results with the literature. Then we studied the effect of metallicity on the CH4-CO conversion time scale on the 2D T-P grid using a chemical network with H-C-N-O elements in the presence of transport. We found that the CH4/CO equal abundance curve moves towards low temperature and CO2/CO abundance curve moves towards high temperature with increased metallicity. The rate-limiting step in the conversion scheme between CH4-CO changes its region of dominance in the T-P space marginally. The quenching point of CO lies in the high-pressure region compared to the CH4 quenching point. The CO quenching point moves from low to high pressure region with increasing metallicity. The CH4 quenching point moves from high to low pressure region for moderately high metallicity ([Fe/H] < 300 x solar metallicity) and from low to high pressure region for high metallicity ([Fe/H] > 300 x solar metallicity). |
