A modeling study of the impact of winter–spring arctic outflow on the NO_x and O₃ budgets of the North Atlantic troposphere

Abstract

[1] In this study, we determine the impact of winter-spring arctic outflow events on the budgets of tropospheric NO x and ozone over the North Atlantic Ocean. An updated version of the NCAR Master-Mechanism, a detailed, explicit photochemical model, is applied to trajectories representative of arctic outflow for the months of January through May. During the simulations, peroxyacetyl nitrate (PAN) mixing ratios drop by up to 270 pptv, increasing NO x levels up to 120 pptv. However, the released NO x is quickly destroyed by efficient NO x loss reactions leading to formation of HNO 3 and, to a lesser extent, nitroaromatic compounds. As a result of elevated NO x , O 3 levels are increased. The resulting net impact on the flux of O 3 to the North Atlantic is estimated to be less than 712 Gg O 3 /month. While this source is similar in magnitude to estimates of ozone produced from aircraft emissions, both are small in comparison to the export of ozone from North America. Therefore, we conclude that while elevated levels of pollutants in arctic outflow increase the levels of NO x and O 3 in the North Atlantic region, on a seasonal basis the impact on the budgets of NO x and O 3 in this region is small.

Photostationary state deviation–estimated peroxy radicals and their implications for HOx and ozone photochemistry at a remote northern Atlantic coastal site

“…Most of the data included in this analysis were collected within continental outflows dominated by Arctic and sub‐Arctic outflows [ Peterson , 1999]. Hence this analysis supports the conclusion that arctic outflow does not contribute significantly to the springtime midlatitude ozone maximum [ Wang et al , 1998; Hamlin and Honrath , 2002]. It is likely, however, that the low temperatures in northern Newfoundland limited the NO x released from peroxyacetyl nitrate (PAN) transported from the Arctic.…”

“…It is likely, however, that the low temperatures in northern Newfoundland limited the NO x released from peroxyacetyl nitrate (PAN) transported from the Arctic. Significant levels of peroxyacetyl nitrate (S. Bertman, personal communication, 1998) remained in the arctic outflow sampled at Cape Norman, and it is expected that additional, but small [ Hamlin and Honrath , 2002], amounts of NO x release and O 3 formation would result as the air warmed over the warmer marine regions to the east.…”

“…was calculated using radiative transfer modeling in combination with the Eppley‐based measurements. First, clear‐sky actinic flux was calculated using the Phodis radiative transfer program (A. Kylling, Phodis, a program package for calculation of photodissociation rates in the Earth's atmosphere, 1995) (available via anonymous ftp at ftp://ftp.geofysikk.uio.no, cd outgoing/arveky), using the six‐stream pseudo‐spherical algorithm and assuming clear skies and conditions characteristic of arctic outflow during March, as described by Hamlin and Honrath [2002] for their March simulations. Clear‐sky was then calculated using recommended O 3 cross sections and quantum yields [ DeMore et al , 1997; Sander et al , 2000].…”

Photochemistry in the arctic free troposphere: NOx budget and the role of odd nitrogen reservoir recycling

“…Knowing the distribution of NO y and how recycling reactions redistribute NO y in the arctic free troposphere indicates whether the arctic free troposphere simply transports NO x as PAN or whether the arctic free troposphere is a region of permanent removal of odd nitrogen from the global atmosphere as HNO 3 . If a large fraction of the NO x accumulates as PAN in the arctic free troposphere, then subsequent episodic transport of these air masses to mid-latitudes along subsiding trajectories would provide large sources of NO x which could shift the O 3 budget to net O 3 production in impacted regions (Beine et al, 1997;Hamlin and Honrath, 2002). Here, we also explore the importance of other reactive odd nitrogen species, such as N 2 O 5 and HNO 4 , which rapidly inter-convert with NO x on intermediate time scales (on the order of a day), and thus impact how efficiently NO x is converted to either PAN or HNO 3 in arctic air masses.…”

“…Numerous studies have examined the role of NO y reservoir species in NO x recycling in remote environments (Schultz et al, 2000;Jacob et al, 1996;Kotchenruther et al, 2001;Hamlin and Honrath, 2002). The importance of HNO 3 and PAN as a sink/ source for NO x has been observed to vary with season and location.…”