27AtChem TEMPO CLDO4 cloud algorithm and product

TEMPO (Tropospheric Emission: Monitoring of Pollution) measures atmospheric trace gases and aerosols for North America from a geostationary orbit hourly at high spatial resolution. TEMPO has been collecting UV and Visible spectra since its first light on 2 Aug 2023, providing the data needed to reveal local time variations of pollutants. The TEMPO L1b spectra are used to derive a suite of L2 and L3 trace gas products (e.g., O₃, NO₂, HCHO) that are important for monitoring air quality and understanding atmospheric chemistry. To this end, cloud information is needed to calculate the Air Mass Factors (AMFs) to convert the slant column densities (SCDs) retrieved from spectra to vertical column densities of trace gases and to filter the data with various cloud fractions and pressures.

We will present the operational TEMPO O₂-O₂ cloud (CLDO4) algorithm which assumes Lambertian clouds with an albedo of 0.8. The effective cloud fraction (ECF) and cloud optical centroid pressure (OCP) derived from this algorithm are used to quantify the light paths for TEMPO trace gases through consistently calculated Air Mass Factors (AMFs). This greatly simplifies the retrievals and increases computational efficiency. The ECF is derived from the reflectance at 466 nm which is relatively free from gas absorption but relies fundamentally upon the quality of L1b calibration. The OCP is derived from the O₂-O₂ SCD retrieved from 439 – 488 nm using the direct spectrum fitting code shared among all the TEMPO trace gases. Ancillary inputs to the algorithm include surface reflectance (GLER – Geometry dependent Lambertian Equivalent Reflectance) and meteorological variables (from GEOS-CF). Look-Up-Tables (LUTs) computed using radiative transfer model (VLIDORT) are employed to match the observed and calculated top of atmosphere reflectance and O₂-O₂ SCDs. We present the sensitivities of TEMPO CLDO4 ECF and OCP to a number of input parameters. We test the influence of TEMPO CLDO4 product on TEMPO trace gases. The TEMPO CLDO4 and trace gas products are publicly available through NASA Earth Data Atmospheric Science Data Center (ASDC).