Tropospheric NOx and O₃ budgets in the equatorial Pacific

By combining the results of model calculations and simultaneous measurements of O 3 , NO, HNO 3 , particulate NO 3 − , and meteorological parameters in the mid‐Pacific, we have investigated the budget and photochemistry of near surface atmospheric ozone and odd nitrogen. The observed decrease of O 3 toward the Intertropical Convergence Zone is consistent with the transport of O 3 from higher latitude and a photochemical sink for O 3 by the reaction between H 2 O and O( 1 D ). The total deposition flux of odd nitrogen deduced from the data is about 1.3×10 9 cm −2 s −1 , or 5 MT(N)/yr averaged globally. Most of the deposition flux is due to HNO 3 and particulate NO 3 − . This deposition flux is probably representative of values over most of the Pacific because the HNO 3 and particulate NO 3 − densities measured over the Pacific during the GAMETAG experiments are consistent with our values. Since the residence time of odd nitrogen in the lower troposphere is short, a widely distributed, diffuse source of odd nitrogen is required to balance the deposition flux. It seems that the NO formed by cloud to cloud lightning in the tropical upper troposphere is the most likely source.