Pollution patterns in the upper troposphere over Europe and Asia observed by CARIBIC
Between May 2005 and March 2008 the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) observatory was deployed to make atmospheric observations on 42 flights between Frankfurt, Germany and Manila, the Philippines. This nearly 3 year flight series provides information about atmospheric composition in the upper troposphere over Europe and Asia during all seasons and was used to investigate seasonal and regional differences in trace gas distributions and the influence of long range transport and local convection on composition. The flight route was separated into three different regions having characteristic differences in transport and composition; these were Europe and Western Asia (5°E-60°E), Central Asia (60°E-100°E) and Southeast Asia (100°E-125°E). The region over Europe and Western Asia was strongly influenced by air masses from North America, while the region over Southeast Asia was mostly influenced by local emissions, particularly from biomass/biofuel burning as indicated by high levels of acetonitrile and carbon monoxide. Air masses over Central Asia were found to be influenced by both recent convection from the Indian subcontinent and mid-range transport from Europe, Western Asia and the Middle East. Elevated levels of propane and other non-methane hydrocarbons, both with and without concomitant elevations in other trace gases (i.e. carbon monoxide, acetonitrile) was a persistent feature over Central Asia in all seasons except summer, and were particularly prominent in fall. Influences on composition over Central Asia were investigated in detail for a case study from a series of flights in October 2006, where elevated levels of pollutants were found to be the result of convective transport of both biomass/biofuel burning and urban emissions from South Asia and fossil fuel related emissions from Eastern Europe.