The file emars_experimental_MY34_Ls180.nc is the dataset used in "An investigation of the encirclement of Mars by dust in the 2018 global dust storm using the Ensemble Mars Atmosphere Reanalysis System (EMARS)",
 authored by H. E. Gillespie, S. J. Greybush, and R. J. Wilson and published in Journal of Geophysical Research - Planets for the 2018/MY34 Global Dust Storm special issue.

The dataset is a self-describing NetCDF file. The data available here is mostly a subset of what would be available in a full EMARS dataset. 
Further details about the EMARS dataset can be found in The Ensemble Mars Atmosphere Reanalysis System (EMARS) Version 1.0,
 authored by Greybush et al. in 2019, at [https://doi.org/10.1002/gdj3.77].

The available variables are accm1, accm2, accm3, bk, pk, dod, o1, o2, o3, omega, ps, t, u, and v. The variables can have the dimensions time, pfull, lat, and lon. 
All of these variables that are also in EMARS have the same meaning in this dataset. This dataset starts on the sol when MY 34, Ls 180 occurs, and hourly output is provided from EMARS.
accm1, accm2, and accm3 are new variables for this dataset. These variables represent the amount of dust on the surface of Mars at each model grid point and time,
 for each of the three tracer sizes tracked by EMARS. The units of the accm variables are kg m^-2.