End-to-end performance modeling for the TanSat-2 NO₂ instrument: an evaluation of key design parameters for an...

China's next-generation atmospheric carbon monitoring satellite, TanSat-2, will utilize nitrogen dioxide (NO₂) as a tracer to identify anthropogenic CO₂ emissions. TanSat-2 will employ an innovative medium Earth orbit frozen, Sun-synchronous elliptical orbit with a wide-swath instrument to enhance monitoring capabilities over the Northern Hemisphere. An end-to-end simulation framework was established based on the UNL-VRTM radiative transfer model and the differential optical absorption spectroscopy algorithm. The impacts of various instrumental and observational parameters on NO₂ vertical column density retrieval were systematically assessed. Results indicate that high solar zenith angles encountered during winter significantly challenge retrieval accuracy. In addition, the variable integration time required to maintain a constant spatial resolution across the elliptical orbit results in a dynamic signal-to-noise ratio (SNR) environment. Our analysis demonstrates that a spectral resolution better than 0.6 nm and an SNR exceeding 800 are necessary to resolve the fine absorption features of NO₂ effectively. The impact of instrumental artifacts inherent to the wide-swath design was also quantified, revealing that uncorrected "smile" and "keystone" effects can introduce retrieval biases exceeding 1×10¹⁵molecules/cm². Finally, simulations of pollution plumes underscore the importance of high spatial resolution for characterizing emission structures and dispersion patterns. This study confirms the feasibility of the TanSat-2 mission concept and provides a quantitative basis for finalizing its payload specifications.