ML3DBHCN is the EOS Aura Microwave Limb Sounder (MLS) daily binned on various vertical grids product for hydrogen cyanide (HCN) derived from radiances measured primarily by the 190 GHz radiometer. The data version is 4.2. Spatial coverage is near-global (-82 to +82 degrees latitude) at a spatial resolution of 4 degrees latitude by 5 degrees longitude. The recommended useful vertical range is from 21.5 to 0.1 hPa, and the vertical resolution is between 8 and 12 km. Users of the ML3DBHCN data product should read chapter 4 and section 3.11 of the EOS MLS Level 2 Version 4 Quality Document for more information. The data files are archived in the netCDF4 format, which is also compatible with HDF5 readers and tools. Each file contains six group objects: lat-lon map vs pressure, lat vs pressure zonal mean, lat-lon map vs "potential temperature", 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.