The initial [VOC] = 1.0 ppmC, [NOx] = 0.2 ppm. Assume that a reduction in the VOC and NOx emissions is equivalent to the reduction in their respective concentrations. If [VOC] and [NOx] are both reduced by 50%, the change in [O3] is estimated to be _______ %. (Hint: Use Figure 9-4, p. 487)