Slopes of relative attenuation distribution in the blue histograms of the linear fitting for [S II] λλ 4069,4076/[S II] λλ 6716,6731 (left) and [O II] λλ 7320,7330/[O II] λλ 3726,3729 (middle), and [S III] λ 6312/[S III] λλ 9068,9531 (right) of all the sub-bins. The green lines represent the slopes of relative attenuation from F99, and the red lines represent the median slopes of 168 bins. The values of median slopes are presented in Table 2.