Frequency spectrum of the foreground‐cleaned EE and BB power spectra outside the P06 mask for ﹩l=2{\mbox{--}} 9﹩. Black shows EE, blue shows BB, and green, cyan, and orange show the EE ﹩yi-yj﹩ spectra (the BB ones are similar). For cosmological analysis, only the QQ, QV, and VV frequency channels are used (the "QV combination," indicated by red triangles on the bottom of each panel). The dotted black line shows the EE signal for ﹩\tau =0.09﹩. The dashed brown line shows the MEM dust temperature spectrum scaled by 0.0025 to indicate the level of 5% polarization (most evident near 90 GHz at ﹩l=2﹩). Averaged over the region outside the P06 mask, this is most likely an overestimate. The red curve shows the synchrotron spectrum scaled to 0.15 the precleaned K‐band temperature value. Based on the foreground model and discussion in text, it is unlikely that there is a significant residual foreground contamination in the Q and V bands. Note that for all frequency combinations above 40 GHz (excluding KW), BB is clearly consistent with zero, also indicating the efficacy of the foreground cleaning.