| The trans-Atlantic Aerosol and Ocean Science Expedition experiments were conducted to investigate the chemical and microphysical evolution of the Saharan air layer (SAL) during its long range transport into the eastern seaboard of the United States and the Caribbean, and to quantify the effects of the SAL on the regional environment and climate. Analyses of air mass history, satellite imagery, surface weather maps, and chemical and aerosol datasets allowed the characterization of four distinct meteorological regimes: marine background, dust, mixed dust and biomass burning, and biomass burning air mass regimes. During the AEROSE experiments, continuous in-situ measurements of ozone were collected during both Saharan dust and biomass burning events. Along the AEROSE-I ship track, the ship encountered air masses with significant Saharan dust loading early in the cruise, and mixed dust and biomass burning aerosols later along the cruise track. While traveling through the dominant dust regime, ozone concentrations were reduced by up to 70%. Photochemistry was not dominant within the dust regime and the reduced ozone concentrations are most likely due to dry deposition or removal by nitric oxide (NO). During the mixed dust and biomass burning regimes, smoke was observed to dominate the chemistry of the air masses. During AEROSE-II, ozone concentrations exceeding 150 ppb were observed over 4,800 km downstream of a biomass burning source region. Back trajectory analyses, satellite imagery, and streamline analyses confirmed that the ship was traveling through air masses influenced by biomass burning. Elevated ozone concentrations aloft were also apparent from observations of ozonesondes that were launched during the biomass burning regime. |
