  Ratios of polycyclic aromatic hydrocarbon (PAH) vibrational bands are a
promising tool for measuring the properties of the PAH population and their
effect on star formation. The photometric bands of the MIRI and NIRCam
instruments on JWST provide the opportunity to measure PAH emission features
across entire galaxy disks at unprecedented resolution and sensitivity. Here we
present the first results of this analysis in a sample of three nearby
galaxies: NGC 628, NGC 1365, and NGC 7496. Based on the variations observed in
the 3.3, 7.7, and 11.3 $\mu$m features, we infer changes to the average PAH
size and ionization state across the different galaxy environments. High values
of F335M$_{\rm PAH}$/F1130W and low values of F1130W/F770W are measured in H II
regions in all three galaxies. This suggests that these regions are populated
by hotter PAHs, and/or that the PAH ionization fraction is larger. We see
additional evidence of heating and/or changes in PAH size in regions with
higher molecular gas content as well as increased ionization in regions with
higher H$\alpha$ intensity.
