Reactive Nitrogen, Ozone and Ozone production in the Arctic Troposphere and the Impact of Stratosphere-Troposphere Exchange
Abstract
We analyze the aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellite (ARCTAS) mission to examine O3 and NOy in the Arctic and sub-Arctic region and their source attribution. Using a number of marker tracers, we distinguish various air masses from the background troposphere and examine their contribution to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has mean O3 of ~ 60 ppbv and NOx of ~ 25 pptv throughout spring and summer with CO decreasing from ~ 145 ppbv in spring to ~ 100 ppbv in summer. These observed CO, NOx and O3 mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in the past two decades in processes that could have changed the Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses with mean O3 concentration of 140-160 ppbv are the most important direct sources of O3 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 (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer) levels. Several STE plumes sampled during ARCTAS-B also show elevated levels of CH3CHO and active conversion of HNO3/NOx to PAN. The most likely source of CH3CHO in the STE air is ethane, which has a relatively long lifetime and higher molar yields of CH3CHO under high NOx conditions. This photochemical process contributes an average of ~ 100 pptv net formation of PAN in the STE air masses. These findings imply that an adequate representation of stratospheric O3 and NOy input are essential to accurately simulate O3, NOx and PAN in tropospheric chemistry transport models of the Arctic. Anthropogenic and biomass burning pollution plumes observed during ARCTAS show highly elevated hydrocarbons and NOy (mostly in the form of NOx and PAN), but do not contribute significantly to O3 in the Arctic troposphere except in some aged biomass burning plumes sampled during spring. Convection and/or lightning influences are negligible sources of O3 in the Arctic troposphere but can have significant impacts in the upper troposphere in the continental sub-Arctic during summer.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A14B..06L
- Keywords:
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- Tropospheric Ozone