The impact of monsoon outflow from India and Southeast Asia in the upper troposphere over the eastern Mediterranean

[摘要] A major objective of the Mediterranean INtensive Oxidant Study (MINOS) was to investigatelong-range transport of pollutants (notably ozone precursor species). Here we present tracegas measurements from the DLR (German Aerospace Organization) Falcon aircraft in theeastern Mediterranean troposphere. Ten day backward trajectories and a coupledchemistry-climate model (ECHAM4) were used to study the nature and origin of pollutionobserved in the upper troposphere between 6 and 13 km altitude. We focus on a largepollution plume encountered over the eastern Mediterranean between 1 and 12 Augustoriginating in South Asia (India and Southeast Asia), referred to as the Asian plume,associated with the Asian Summer Monsoon. Vertical as well as longitudinal gradients ofmethane, carbon monoxide, hydrocarbons including acetone, methanol, andacetonitrile, halocarbons, ozone and total reactive nitrogen (NO_y) are presented, showing the chemicalimpact of the Asian plume compared to westerly air masses containing pollution from NorthAmerica. The Asian plume is characterized by enhanced concentrations of biomass burningtracers (acetylene, methyl chloride, acetonitrile), notably from biofuel use. Concentrations ofthe new automobile cooling agent HFC-134a were significantly lower in the Asian plumethan in air masses from North America. Relatively high levels of ozone precursors (CO,hydrocarbons) were found in both air masses, whereas lower ozone concentrations in theAsian plume suggest NO_x-limited conditions. Consistently, ECHAM model simulationsindicate that the expected future increase of NO_x-emissions in Asia enhances thephotochemical ozone production in the Asian plume. The size and location of the Asianplume near the tropopause provides an important potential for pollution transport into thelowermost stratosphere. We present observations indicative of Asian pollution transport intothe lower stratosphere.

[学科分类] 大气科学