Springtime boundary layer O 3 and GEM depletion at Toolik Lake, Alaska

Atmospheric surface ozone (O 3 ) was measured at Toolik Lake, Alaska, from September 2010 to August 2011, along with winter and springtime (January–May) measurements of gaseous elemental mercury (GEM). Concurrent episodic springtime depletion of both O 3 and GEM was observed between April and May 2011. To investigate these depletion events, surface O 3 measurements from Toolik Lake were compared with similar measurements from Barrow, the only Alaskan site available to use as an indicator of conditions at the Arctic Ocean coastline. Barrow is located approximately 400 km to the northwest of Toolik Lake. In all cases where O 3 and GEM depletion was observed at Toolik Lake, similar O 3 depletion events (ODEs) were observed at Barrow. Conversely, in over half of the instances where ODEs were observed at Barrow, no such events were recorded at Toolik Lake. The Lagrangian particle dispersion model FLEXPART was utilized to interpret the transport conditions and potential influence of oceanic air masses on depletion events observed at Toolik Lake. These analyses indicate that ODEs observed at Toolik Lake are correlated with depletion events observed at Barrow when the prevailing airflow is from the north and the air mass has spent substantial time over the Arctic Ocean or coast within the previous week. These observations suggest that coastal O 3 and GEM‐depleted air masses are likely transported from the Arctic Ocean up to ~200 km inland and to at least an altitude of 700 m above sea level. These observations underscore that O 3 and GEM depletion events impact not just the Arctic coastal zone but also extensive inland areas with possible implications for the cycling and bioavailability of mercury (Hg) to inland Arctic ecosystems.