Urban air mobility (UAM) is expected to be a new alternative future transportation system to overcome the limitations of infrastructure investment and resolve traffic congestion cost issues in urban areas. This study aims to estimate the parameters of the mode choice model incorporating the cleaner transportation mode and evaluate the environmental impact by calculating the reduction of greenhouse gas emissions from ground traffic. A stated preference survey is employed to estimate the parameters for each travel mode, including the emerging travel mode. The awareness and experience of the air travel modes remove the hesitation concerning travel mode choice having positive values, but concerns about taking new types of air mobility reduce the probability of choosing urban air mobility. The macroscopic travel demand forecasting program simulates the travel demand of urban air mobility to calculate the reduction of CO2 emissions between before and after the introduction. While about 30 thousand of urban air mobility travel demand are generated after the introduction of urban air mobility in the urban area, it reduces about 90 thousand tons of CO2 emissions from the ground traffic. The introduction of urban air mobility causes modal shifts from ground traffic, reducing climate change and global warming. Policymakers should evaluate the feasibility of introducing urban air mobility, including environmental impact assessment, and an appropriate transit fare policy is required for the proliferation of urban air mobility.