ML3DZHCL is the EOS Aura Microwave Limb Sounder (MLS) daily binned on zonal and assorted vertical grids product for hydrogen chloride (HCl) derived from radiances measured primarily by the 640 GHz radiometer. The data version is 4.2. Spatial coverage is near-global (-82 to +82 degrees latitude), with each profile spaced 1.5 degrees or ~165 km along the orbit track (roughly 15 orbits per day). The recommended useful vertical range is from 100 to 0.316 hPa, and the vertical resolution is between 3 and 6 km. Users of the ML3DZHCL data product should read chapter 4 and section 3.10 of the EOS MLS Level 2 Version 4 Quality Document for more information.The data files contain one year of data and are archived in the netCDF4 format, which is also compatible with HDF5 readers and tools. Each file contains four group objects: lat vs pressure zonal mean, lat vs "potential temperature" zonal mean, "equivalent latitude" vs "potential temperature" zonal mean, and vortex average vs "potential temperature". Each group has a set of data (average, min, max, std dev, rms) and geolocation fields, grid attributes, and metadata.