Total Column GHG Ratios From Ground-Based Measurements Inform Emissions Inventories

Accurately characterizing greenhouse gas (GHG) emissions is essential for improving inventories and evaluating mitigation efforts. However, this remains particularly challenging in urban environments with heterogeneous emissions and complex meteorological conditions. One effective approach which addresses these challenges uses trace gas ratios of atmospheric measurements to evaluate emissions. This study leverages total column concentration ($X_{\text{gas}}$) measurements from a single EM27/SUN spectrometer in Utah's Salt Lake Valley (SLV) to analyze $X_{C{H}_4}:X_{C{O}_2}$ and $X_{\text{CO}}:X_{C{O}_2}$ ratios across multiple spatiotemporal scales. By applying a rolling ratio method on sub-day time windows, we identify periods of strongly covarying concentration enhancements throughout the multi-year data set. This method reveals seasonal trends that are obscured using approaches from previous literature. We also examine how ratio variations correspond to changing wind conditions, facilitating more granular spatial emissions attribution. Comparisons with CO and CO₂ from the publicly available GRA²PES inventory reveal that the CO:CO₂ inventory ratios align well with observations, supporting the inventory's methodology. In contrast, comparisons with the GRA²PES CH₄ inventory beta, which is still under development, indicate that it does not adequately capture the spatial distribution of CH₄ sources in the SLV, highlighting areas for improvement. These findings demonstrate that a single sun-tracking spectrometer can provide valuable emissions insights and inventory constraints, without requiring multiple instruments or computationally intensive inversion models.