Enhanced Ozone Over the North American Arctic from Biomass Burning in Eurasia During April 2008 as Seen in Surface and Profile Observations

During April 2008 as part of the International Polar Year, a number of ground-based and aircraft campaigns were carried out in the North American arctic region. The ubiquitous presence during this period of biomass burning effluent, both gaseous and particulate, has been reported. Unusually high ozone readings for this time of year were recorded at surface ozone monitoring sites from northern Alaska to northern California. At Barrow, Alaska the highest April ozone readings recorded at the surface (hourly average values >55 ppbv) in 36 years of observation were measured on April 19, 2008. At Denali National Park in central Alaska an hourly average of 79 ppbv was recorded during an 8 hour period in which the average was over 75 ppb, exceeding the ozone ambient air standard threshold value in the U.S.. Elevated ozone (>60 ppbv) persisted almost continuously from April 19–23 at the monitoring site as part of this event. During the first three weeks of April 2008, near daily ozone soundings were performed at several sites in western North America as part of the Arctic Intensive Ozonesonde Network Study (ARCIONS) in conjunction with ARCTAS. These soundings showed lower tropospheric features at ~1-6 km with enhanced ozone during the times of elevated ozone amounts at the surface sites noted above. Ancillary information, such as aerosol optical thickness and back trajectories, are employed to diagnose the potential air masses that may have contributed to these elevated ozone readings. The back trajectories appear to be matched with known burning source regions in the Eurasian region during April 2008. At a few surface sites, atmospheric trace constituents in addition to ozone were measured that help identify biomass burning as a likely source of the enhanced ozone readings.