Simultaneous measurements of 2>, , 3>, and the NO2 photo-dissociation rate coefficient, J2, were made during a one-month field study in the spring of 1988 at Mauna Loa, Hawaii, and were used to evaluate the photostationary state ratio, ϕ=J22>/k13>. Over 5600 measurements were made for clear sky conditions, allowing a detailed comparison with photochemical theory. Values of ϕ determined from the observations were consistently higher than unity, approaching 2.0 for high sun, and indicated peroxy radical mixing ratios near 60 pptv. High sun values of ϕ were independent of NOx (NO+NO2), but correlated well with ozone and water vapor through the expression ϕ-1=(0.11¿0.21)+(1.59¿0.64)¿10-3¿(2O>/3>)1/2. A photochemical box model is shown to give good agreement with the values of ϕ, the peroxy radical concentrations, and the correlations with physical and chemical environmental variables determined from the observations. The rate of photochemical production of ozone was estimated from measurements of ϕ, and the rate of photochemical ozone destruction was estimated from the box model. For free tropospheric air samples characteristic of altitudes near 3.4 km, the 24-hour average net ozone production rate is shown to be -0.5 ppbv/d (net ozone destruction), and is determined primarily by photolytic destruction. ¿ American Geophysical Union 1992