 Solution

The observed value is about 4 ppb higher than the local chemical–dry deposition balance predicts. Entrainment from the ozone-richer free troposphere adds a term $(w_e/H)({\chi }_{\mathrm{FT}}-{\chi }_{\mathrm{BL}})$; horizontal Advection can likewise import ozone or longer-lived precursors from other regions. Time dependence, including the day–night cycle of photodissociation and changes in mixing depth, is also omitted. The approximately four-day model adjustment time means that air arriving at the measurement location need not have attained the assumed local steady state. These transport and history terms can raise ozone without changing the given local chemical constants.