We examine the ozone production from boreal forest fires based on a case study of wildfires in Alaska and Canada in summer 2004. The model simulations were performed with the chemistry transport model, MOZART-4, and were evaluated by comparison with a comprehensive set of aircraft measurements. In the analysis we use measurements and model simulations of carbon monoxide (CO) and ozone (O₃) at the PICO-NARE station located in the Azores within the pathway of North American outflow. The modeled mixing ratios were used to test the robustness of the enhancement ratio ΔO₃/ΔCO (defined as the excess O₃ mixing ratio normalized by the increase in CO) and the feasibility for using this ratio in estimating the O₃ production from the wildfires. Modeled and observed enhancement ratios are about 0.25 ppbv/ppbv which is in the range of values found in the literature and results in a global net O₃ production of 12.9 ± 2 Tg O₃ during summer 2004. This matches the net O₃ production calculated in the model for a region extending from Alaska to the east Atlantic (9-11 Tg O3) indicating that observations at PICO-NARE representing photochemically well aged plumes provide a good measure of the O₃ production of North American boreal fires. However, net chemical loss of fire-related O₃ dominates in regions far downwind from the fires (e.g., Europe and Asia) resulting in a global net O₃ production of 6 Tg O₃ during the same time period. On average, the fires increased the O₃ burden (surface -300 mbar) over Alaska and Canada during summer 2004 by about 7-9% and over Europe by about 2-3%.
