  The ZFIRE survey has spectroscopically confirmed two proto-clusters using the
MOSFIRE instrument on Keck 1: one at z=2.095 in COSMOS and another at z=1.62 in
UDS. Here we use an updated ZFIRE dataset to derive the properties of ionized
gas regions of proto-cluster galaxies by extracting fluxes from emission lines
H$\beta$ 4861\AA, [OIII] 5007\AA, H$\alpha$ 6563\AA, [NII] 6585\AA, and [SII]
6716,6731\AA. We measure gas-phase metallicity of members in both
proto-clusters using two indicators, including a strong-line indicator
relatively independent of ionization parameter and electron density.
Proto-cluster and field galaxies in both UDS and COSMOS lie on the same
Mass-Metallicity Relation with both metallicity indicators. We compare our
results to recent IllustrisTNG results, which reports no significant gas-phase
metallicity offset between proto-cluster and field galaxies until z=1.5. This
is in agreement with our observed metallicities, where no offset is measured
between proto-cluster and field populations. We measure tentative evidence from
stacked spectra that UDS high mass proto-cluster and field galaxies have
differing [OIII]/H$\beta$ ratios, however these results are dependent on the
sample size of the high mass stacks.
