The box-and-whisker plots in Figure show that on-road mobile NOx emissions representing 19% of domain emissions may be underestimated in the model and need to be scaled up by a median factor of 1.68, which is consistent with findings using the FD method. Similarly, the MLR found railyard NOx emissions should by increased by a median factor of 1.5. In contrast, the shipping NOx emissions representing 17% of domain emissions may be overestimated and should be scaled by a median factor of 0.77, which is also consistent with findings using the FD method, though it should be noted that the sign of the shipping adjustment changes with the regularization factor. The EGU point sources are close to a scale factor of one, which is expected given the use of emissions obtained from CAMPD measurements. The "other" sources representing 54% of domain NOx emissions are underestimated, although this factor is particularly sensitive to the regularization factor because it encompasses a diverse set of point and nonpoint sources. Finally, the boxplot suggests that the NO2 background concentration is underestimated by CAMx by a median value of 0.7 x 10 15 molec/cm 2 , which equates to a scaling factor of 2.2, and is consistent with qualitative findings discussed earlier. Results from an "Optimized NOx" CAMx simulation. We then performed a new "Optimized NOx"