Ozone Differences Between Near-coastal and Offshore Sites In New England: Role of Meteorology

Abstract

Time series from two ozone monitoring stations are evaluated, one on an island several km off the New England coast, the other several km inland in New Hampshire. In the summer of 2002, during the New England Air Quality Study 2002 (NEAQS-2002), ozone measurements at the island station, Appledore Island (ADI), were consistently higher than at the inland station, Thompson Farm (TF). We hypothesized that the differences in ozone concentrations were due to transport differences driven by mesoscale meteorology, since neither site was in a source region. We found that the Appalachian Trough, coastal cold fronts and coastal stationary fronts at times caused TF to have westerly component flow while ADI had southerly component flow. In these situations, the southwesterly flow along the New England coast brought ozone and precursors to ADI from metropolitan areas to the southwest (e.g., Boston). Conversely, the air transported to TF from the west was contaminated by fewer upstream sources, and therefore the ozone was lower at TF. The sea breeze was also a factor, which tended to have the contrasting effect of nearly equalizing the ozone concentrations at the two sites by transporting ozone-rich air already impacting ADI inland to TF. Enhanced measurements from the NEAQS-2002 study were used in the analysis, including radar wind profilers, Doppler and ozone profiling lidars, and radiosondes launched from a ship. We also assessed model performance for two models, WRF/Chem and MM5/Chem, for four key days.