Daily and monthly averaged O3 mixing ratio (left axis; black circles and thick lines) and zero-out contribution from the US and east Asia (right axis; light blue and light red bars, respectively) summarized over four time zones of Pacific, Mountain, Central, and Eastern Standard Time (PST, MST, CST, and EST) in the US. The units of the left and right axes are ppbv. On a monthly average basis (center panel), whiskers indicates daily minimum and maximum. Note that the axis of zero-out contributions is different in the left (PST and MST) and right panels (CST and EST).