Gravitational wave (GW) characteristics of the SMBH binary population for four different SMBH models: purely GW driven inspirals (GW only), inspirals with environmental effects (GW+env), inspirals of eccentric SMBH binaries (GW+ecc), and inspirals of eccentric SMBH binaries with environmental effects (GW+ecc+env). Left panel: Median (solid line) and mean (dashed line) number of the strongest sources contributing half the signal at each PTA frequency band. Middle panel: Distributions of contributions from individual binaries at 1.98 nHz (solid lines) and 27.68 nHz (dashed lines). Right panel: Distributions of the GW spectra in the n × 1.98 nHz frequency bins compared to NANOGrav 15-year data (yellow violin plots).