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Tropospheric ozone in the Northern mid and high latitudes: The impact of long-range transport of pollution and stratosphere-troposphere exchange

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Monday, October 31, 2011, 4 pm

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This is a past event.

Qing Liang
NASA GESTAR/Universities Space Research Association (USRA)
NASA Goddard Space Flight Center
Atmospheric Chemistry and Dynamics Branch

Airborne measurements from field campaigns, though limited in space and time, provide an extensive and comprehensive suite of simultaneous measurements of O3 and its precursors, e.g. reactive nitrogen (NOy) and volatile organic compound (VOCs) that are highly informative in understanding the complex O3-NOx-VOC photochemistry in the troposphere. We analyze aircraft observations obtained during the NASA (INTEX-A) (1 July – 14 August 2004) and the Arctic Research of the Composition of the Troposphere from Aircraft and Satellite (ARCTAS) (April and June-July 2008) to examine how long-range transport of pollution and stratosphere-troposphere exchange contribute to ozone in the free troposphere over North America and the Arctic. Using a set of simultaneously measured marker tracers, we distinguish various air masses from the background troposphere, including anthropogenic pollution, biomass burning emissions, convective/lightning influenced air, and air of stratospheric origin, and examine their chemical composition and photochemical characteristics. Observations from the INTEX-A mission show that Asian pollution outflow can reach North America in 3-9 days. These Asian pollution plumes display high levels of NOy and O3 and high ΔO3/ΔCO ratio reflecting active photochemistry and, in some cases, mixing with stratospheric air during long-range troposphere. This implies that that long-range transport of Asian pollution can potentially impact air quality in North America. The ARCTAS measurements suggest that although anthropogenic and biomass burning pollution from the continental source regions frequently penetrate into the Arctic, they do not contribute significantly to O3 in the Arctic troposphere except in some aged biomass burning plumes sampled during spring. Stratosphere-troposphere exchange is the most important direct source of ozone in the Arctic troposphere. In addition, air of stratospheric origin is the only notable driver of net O3 formation in the Arctic due to its sustainable high NOx and NOy concentrations. These findings have significant implication in predicting how ozone, an important radiative gas, in the Arctic troposphere may change in the coming decades.

Host Louisa Kramer


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