Surface Ozone and Atmospheric Transport over the Gulf of Maine during ICARTT

As part of the 2004 ICARTT summer campaign, we deployed a buoy with ozone and wind instruments about 20 km ESE of Appledore Island from late June through early September. Data from Thompson Farm, Appledore, and the buoy showed that on average, surface ozone levels over the Gulf of Maine increased with distance from the New Hampshire coast. Diurnally averaged ozone was highest at the buoy site, both in daytime and at night. The diurnal cycle at sea peaked several hours later than at Thompson Farm (3-6 PM EST vs. 1-3 PM). Trajectory and dispersion calculations showed that elevated ozone episodes were generally correlated with air masses from the New York-Boston corridor. The diurnal cycle in ozone at coastal and offshore sites at Martha's Vineyard (about 150 km to the south) was much smaller than in the Gulf of Maine (higher nighttime lows and lower daytime highs), reflecting a higher incidence of marine air at these stations. In summer 2004, the sea-breeze/land-breeze strongly influenced local transport and ozone levels at Appledore and the buoy. For onshore winds, the diurnal cycle in ozone was much smaller than for offshore winds but still present. A weekly cycle in ozone at the Gulf of Maine sites was also observed, with lowest daily ozone maxima on weekends.