Peroxy radical behavior during the Transport and Chemical Evolution over the Pacific (TRACE‐P) campaign as measured aboard the NASA P‐3B aircraft

Peroxy radical concentrations were measured aboard the NASA P‐3B aircraft during the Transport and Chemical Evolution over the Pacific (TRACE‐P) campaign in the spring of 2001 and varied in ways that depended on radical production rates and reactive nitrogen concentrations. Measurements of HO 2 , HO 2 + RO 2 , and OH during this study allowed calculation of radical ratios, examination of functional relationships of these ratios on controlling variables, and comparison with numerical model estimations. Radical production terms show changes in relative contributions at low, middle, and high total production rates that are understandable in terms of systematic variations in the controlling components (trace gas concentrations and photolysis rate coefficients). Ozone tendency calculations indicate net ozone production in the western Pacific basin because the concentrations of critical precursor trace gases (e.g., NO x , hydrocarbons) are highest there. The dependence of ozone tendency follows the concentration of NO systematically. Peroxy radical levels on the two aircraft (HO 2 + RO 2 on the P‐3B and HO 2 on the DC‐8) during two relatively short prescribed intercomparison periods were in good agreement in one instance and poorer in another given reasonable assumptions about the apportioning of radicals between HO 2 and RO 2 . Recommended changes to CH 2 O photolysis quantum yields, HO 2 self reaction, and O( 1 D) quenching kinetics lead to small changes (<5%) in calculated peroxy radical levels for TRACE‐P conditions. There is evidence from this campaign that peroxy radicals are lost by interaction with aerosols and cloud droplets.