Ozone production from the 2004 North American boreal fires

Kurzfassung

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 O₃production 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%.