Outflow Pathways for North American Pollution in Summer: A Global 3-D Model Analysis of MODIS and MOPITT Observations

• Main Authors: Qinbin Li, Daniel J. Jacob, Rokjin Park, Yuxuan Wang, Colette L. Heald, Rynda Hudman, Robert M. Yantosca, Randall V. Martin, Mathew Evans
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2004
• Subjects: Newfoundland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.58.5419; http://www-as.harvard.edu/chemistry/trop/geos/./publications/li2004b.pdf

We examine the major outflow pathways for North American pollution to the Atlantic in summer by conducting a 4-year simulation with the GEOS-CHEM global chemical transport model, including a coupled ozone-aerosol simulation with 1 # # horizontal resolution for summer 2000. The outflow is driven principally by cyclones tracking eastward across North America at 45-55 # N, every 5 days on average during 2000. The cold fronts associated with these cyclones sweep across the northeastern United States, and the warm conveyor belts (WCBs) ahead of the fronts lift U.S. pollution to the upper troposphere on a northeastward track toward Newfoundland. Anthropogenic and fire effluents from western North America are mostly transported north and east, eventually merging with the eastern U.S. pollution outflow to the Atlantic. The WCBs typically do not reach the southeastern United States unless associated with occasional Atlantic cyclones originating along the east coast (only three in 2000). Deep convection is a more important pathway for ventilation of the southeastern and central United States. A semi-permanent upper-level anticyclone traps the convective outflow and allows it to age in the upper troposphere over the United States for several days. Rapid ozone production takes place in this outflow driven in part by anthropogenic and lightning NO x , and in part by HO x radicals produced from convectively lifted CH 2 O that originates from biogenic isoprene. This mechanism could explain ozonesonde observations of elevated ozone in the upper troposphere over the southeastern United States. Asian and European pollution influences in the North American outflow to the Atlantic are found to be dispersed into the background and do not generate distinct plumes. Satellite observations.