Abstract
Abstract. The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze, which is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning emissions dominated the ARCTAS-A period and have been the focus of many ARCTAS related studies. This study determines mean transport characteristics of anthropogenic emissions during ARCTAS-A. Trajectories are initiated each day from three significant regions of anthropogenic emissions (Asia, North America, and Europe). The fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectory calculations indicate: origins of emissions that reach the Arctic (defined as north of 70° N) within fifteen days, pathways of these emissions, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled from the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived transport characteristics and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases.
Highlights
Since the Arctic is far removed from most industrial locations and other sources of pollution, its atmosphere once was believed to be very clean
To derive general transport statistics during Aircraft and Satellites (ARCTAS)-A, fifteen day forward trajectories were initialized within the domains of each of the areas of enhanced anthropogenic emisnoted that most of the moisture at the start of a warm conveyor belt (WCB) is converted to precipitation, thereby producing decreased humidity and an increase in potential temperature
We present an example of Asian anthropogenic transport Asian outflow consists of a complex mixture of industrial, using chemical tracers sampled by the DC-8 and backward biofuel, and biomass burning emissions
Summary
Since the Arctic is far removed from most industrial locations and other sources of pollution, its atmosphere once was believed to be very clean. The Arctic atmosphere is dominated by strong temperature inversions that trap air near the surface, especially during the winter and early spring when there is little or no sunlight (Curry, 1983, 1987; Raatz, 1991; Bradley et al, 1992) Since these inversions limit turbulent mixing, dry deposition is greatly reduced (Hileman, 1983). Since the atmosphere during the winter and early spring is cold, dry, and stable, precipitating cloud systems are inhibited, thereby limiting wet deposition (Shaw, 1995) Another phenomenon that influences cold season Arctic transport is the “dome” of cold potential temperature that forms over the polar region (Klonecki et al, 2003; Stohl, 2006; Law and Stohl, 2007).
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