Ozone loss driven by nitrogen oxides and triggered by stratospheric warmings can outweigh the effect of halogens

Abstract

Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar regions, is driven mainly by halogens and nitrogen oxides (NOx). Whereas the stratospheric chlorine levels are expected to decrease in the future, the role of NOx for the O3 budget in a changing climate is not well quantified. Here we combine satellite measurements and model simulations to diagnose the accumulated O3 loss during winter and spring 2002–2003 in the Arctic polar stratosphere. We show that in a winter stratosphere strongly disturbed by warmings, O3 loss processes driven by halogens and NOx can significantly overlap within the polar column and become comparable in magnitude even if a significant, halogen‐induced O3 loss has occurred. Whereas, until the beginning of March 2003, polar column O3 loss was mainly caused by the halogen chemistry within the vortex at an altitude around 18 km, the chemical O3 destruction in March and April was dominated by the NOx chemistry in O3‐rich air masses transported from the subtropics and mixed with the polar air above the region affected by the halogens. This NOx‐related O3 loss started around mid‐December 2002 in subtropical air masses above 30 km that moved poleward after the major warming in January, descended to 22 km with an increasing magnitude of O3 loss and reached surprisingly high values of up to 50% local loss around the end of April. To some extent, the NOx‐driven O3 loss was enhanced by mesospheric air trapped in the vortex at the beginning of the winter as a layer of few km in the vertical and transported downward within the vortex. The effect of NOx transported from the subtropics dominated the O3 loss processes in the polar stratosphere in spring 2003, both relative to the effect of the halogens and relative to the contribution of the mesospheric NOx sources. A comparison with the 1999/2000 Arctic winter and with the Antarctic vortex split event in 2002 shows that wave events triggered by stratospheric warmings may significantly enhance O3 loss driven by NOx when O3‐ and NOx‐rich air masses from the subtropics are transported poleward and are mixed with the vortex air.

A long term study of polar ozone loss derived from data assimilation of Odin/SMR observations

“…The occurrence of major mid-winter SSW and the attending warmer temperature in the lower stratosphere are common to those winters. Similar ozone decreases are seen in previous studies, e.g., Sonkaew et al (2013), Kuttippurath et al (2010) and Konopka et al (2007). NO x photochemistry has 5 been suggested to be important for ozone loss in this altitude range (Osterman et al, 1997) .…”

“…However Konopka et al (2007) showed that,above 600 K (∼ 24 km), the chemical loss induced by the horizontal transport of NO x from lower latitudes is as great as the halogen-induced loss below 500 K (∼ 20 km) in the Northern Hemisphere in 2002/2003. In this paper we have extended the vertical analysis region up to PT of 950 K (∼ 40 km) in order to show the effect of NO x 5 transport on ozone losses. This paper contains the following sections.…”

MIPAS: an instrument for atmospheric and climate research

“…The continuous intrusion of NO x , reaching up to 100 ppbv in the upper stratosphere, led, via formation of N 2 O 5 and water ion cluster chemistry, to the formation of a second HNO 3 maximum at altitudes between 35 and 45 km with maximum vmrs of 14 ppbv . Although downward transport of mesospheric air as low down as 25 km also happened in the Arctic winter 2002/2003, the deposition of NO x rich air was considerably lower during this winter Konopka et al, 2007). This was due to a major stratospheric warming in midwinter which interrupted the downward transport, diluted the vortex air into midlatitudes, and led to conditions without significant subsidence afterwards.…”

Ozone depletion in the 2006/2007 Arctic winter

“…ECMWF temperature fields, however, indicate that regions with temperature low enough to sustain polar stratospheric clouds were smaller than in the 2002/2003 and 2004/2005 winters. Ozone loss driven by NO x chemistry [Konopka et al, 2007], is one possible cause for the ozone loss inferred on the 575 K potential temperature level at the end of the winter. To determine the full consequences of the 2007 Arctic ozone depletion for the northern hemisphere it would furthermore be necessary to study regions below the 475 K potential temperature level which is near the lowest level ($450 K) for reliable Odin/SMR 501.5 GHz ozone data.…”