Composition and distribution of aerosols over the North Atlantic during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX)

Abstract

We report the mixing ratios of aerosol-associated soluble ions (focusing on SO4= and NO3-) and HNO3 over the North Atlantic during NASA's Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX). The SONEX campaign was designed to quantify the impacts of jet emissions in the North Atlantic Flight Corridor (NAFC) by sampling both directly within and far removed from the organized track system. Beryllium-7 activities were also measured to assess the magnitude of stratospheric influence in the SONEX study region. Mixing ratios of aerosol-associated SO4= and NO3- above 8 km during SONEX were lower than recent measurements over the central United States during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) and the same as those over the remote South Pacific during the Pacific Exploratory Mission-Tropics (PEM-Tropics), suggesting that aircraft emissions cannot yet be a major source of these ions. Furthermore, mean SO4= mixing ratios at high altitudes were 65% higher in regions away from the NAFC than they were directly in the track system just a few hours after peak traffic. Nitric acid mixing ratios at the highest DC-8 sampling altitudes were elevated during SONEX compared to PEM-Tropics, but there was no clear signal of enhancement by jet exhaust. Strong correlations with 7Be indicate that a large fraction of HNO3 and aerosol-associated SO4= measured at high altitudes during SONEX were derived from a stratospheric source. Copyright 2000 by the American Geophysical Union.