Ozone 12-hour treatment meansz, SUM0y, SUM06x, and the number of hours above 120 ppb.
↵z 12-hour (9:00 A.M. to 9:00 P.M.) ozone treatment means.
↵y SUM0 24-hour sum of all hourly ozone concentrations.
↵x SUM06 24-hour sum of all hourly ozone concentrations ⊕ 60 ppb.