Dynamics and transport of sulfur dioxide in the north Pacific troposphere

The rapid industrialization in Asia in past two decades has raised serious concerns about how the anthropogenic activities would impact the global climate. NASA conducted the Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission over the Northwest Pacific during February–April 2001. The objectives of TRACE-P were to identify the major pathways for Asian outflow over the western Pacific and to better understand the chemical and dynamical evolution of the Asian outflow over the western Pacific.; Fast time resolution (>1 Hz) sulfur dioxide (SO₂) measurements were obtained using an atmospheric pressure ionization mass spectrometer with isotopically labeled internal standard (APIMS/ILS) on the NASA P-3B during the TRACE-P mission. The high time resolution data allowed a view into the dynamics of SO₂ transport, including the effects of clouds. Two of the 24 flights were flown on consecutive days with quite different weather conditions along 124.5°E over the East China Sea and the Yellow Sea. The observed SO₂ concentrations were markedly different in vertical and horizontal distributions. Below 2 km SO₂ layers of a few hundred meters depth were often isolated from the mixed layer. The relatively slow process of entrainment limited the loss of SO₂ to the marine mixed layer. When compared to chemical transport models (CTMs) predications of SO ₂ along the flight track, the deviations between the observations and the CTMs appear to be related to the treatment of the boundary layer dynamics.; Long-range transport of SO₂ from East Asia to the central North Pacific troposphere was observed on the transit flights across the Pacific Ocean. The enhanced SO₂ layers in the Central Pacific were associated with low water vapor and low turbulence and were usually dynamically isolated from the marine boundary layer. Atmospheric dynamics were the major factor in determining the SO₂ distributions. Trajectory studies revealed that the SO₂ came from both volcanic and anthropogenic sources in East Asia and the routes of SO₂ transport were at mid-latitudes (30°–60°N) and mid-altitude (2–4 km). A comparison of SO₂ observations and results of CTMs indicated that SO₂ was primarily removed by heterogeneous processes. Another important observation was that Miyakejima volcano made a major contribution to the SO₂ in the central Pacific troposphere during March and April 2001.