ML3DZSO2 is the EOS Aura Microwave Limb Sounder (MLS) daily binned on zonal and assorted vertical grids product for sulfur dioxide (SO2) derived from radiances measured by the 240 GHz radiometer. The data version is 5.1. Spatial coverage is near-global (-82 to +82 degrees latitude) at 4 degree latitude zonal increments. The recommended useful vertical range is from 215 to 10 hPa, and the vertical resolution is about 3 km. Users of the ML3DZSO2 data product should read chapter 4 and section 3.21 of the EOS MLS Level 2 Version 5 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.