STILT-NOx v1 (for GMD submission)

This release contains model input (e.g., preprocessed EDGARv6 files) and model scripts (r/src/chem_lifetime) for simulating tropospheric NO2 columns. These changes are initially designed for working with TROPOMI v1 and v2 data. Reference for the GMDD paper: Wu, D., Laughner, J. L., Liu, J., Palmer, P. I., Lin, J. C., and Wennberg, P. O.: A simplified non-linear chemistry-transport model for analyzing NO2 column observations, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-876, 2023. This paper is still in review and we expect possible changes to the model scripts during revisions. One can start with run_xstilt.r for generating the trajectories from each TROPOMI satellite sounding and then use run_stilt_nox.r to simulate NO2 columns [ppb]. More descriptions are included in the README.md