Measurements of NO, NO<sub>y</sub>, N<sub>2</sub>O, and O<sub>3</sub> during SPURT: implications for transport and chemistry in the lowermost stratosphere

Abstract

Abstract. We present measurements of NO, NO y , O 3 , and N 2 O within the lowermost stratosphere (LMS) over Europe obtained during the SPURT project. The measurements cover all seasons between November 2001 and July 2003. They span a broad band of latitudes from 30 • N to 75 • N and a potential temperature range from 290 to 380 K. The measurements represent a comprehensive data set of these tracers and reveal atmospheric transport processes that influence tracer distributions in the LMS. Median mixing ratios of stratospheric tracers in equivalent latitude-potential temperature coordinates show a clear seasonal cycle related to the Brewer-Dobson circulation, with highest values in spring and lowest values in autumn. Vertical tracer profiles show strong gradients at the extratropical tropopause, suggesting that vertical (cross-isentropic) mixing is reduced above the tropopause. Pronounced meridional gradients in the tracer mixing ratios are found on potential temperature surfaces in the LMS. This suggests strongly reduced mixing along isentropes. Concurrent large gradients in static stability in the vertical direction, and of PV in the meridional direction, suggest the presence of a mixing barrier. Seasonal cycles were found in the correlation slopes O 3 / N 2 O and NO y / N 2 O well above the tropopause. Absolute slope values are smallest in spring indicating chemically aged stratospheric air originating from high altitudes and latitudes. Larger values were measured in summer and autumn suggesting that a substantial fraction of air takes a "short-cut" from the tropical tropopause region into the extratropical LMS. The seasonal change in the composition of the LMS has direct implications for the ozone chemistry in this reCorrespondence to: M. I. Hegglin (michaela@atmosp.physics.utoronto.ca) gion. Comparisons of measured NO with the critical NO value at which net ozone production changes from negative to positive, imply ozone production up to 20 K above the local tropopause in spring, up to 30 K in summer, and up to 40 K in autumn. Above these heights, and in winter, net ozone production is negative.

TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen

“…Beside the interference with hydrocarbons in the sample air (see Sect. 2.2) or impurities in the added CO (Hegglin et al, 2006), this could have been induced by the pure air generator through a small contamination with any other N r compound. The overall calibration performance of a multi-month observation period is given in Fig.…”

A fast and precise chemiluminescence ozone detector for eddy flux and airborne application

“…Gas-phase CI instruments are more complex and are based on the reaction of ozone with either ethene or nitrogen oxide (Ridley et al, 1992;Hegglin et al, 2006;Williams et al, 2006;Bariteau et al, 2010).…”

Model simulations and aircraft measurements of vertical, seasonal and latitudinal O<sub>3</sub> and CO distributions over Europe

“…This mirrors the seasonal and latitudinal variation of the tropopause height, which enables the aircraft to reach deeper into the stratosphere at high latitudes in winter and spring when the tropopause is lowest. Additionally, strong diabatic descent from the overworld fills the lowermost stratosphere with O 3 -rich air during late winter/early spring (Hoor et al, 2004bHegglin et al, 2005). The model overestimates stratospheric O 3 mixing ratios at low latitudes during the spring and fall season (Figs.…”

“…Details of the CO measurements can be found in Hoor et al (2004b). Ozone was measured independently by the FZJülich using UV absorption (time resolution 9 s, total uncertainty 5%) and the ETH Zürich via NO chemiluminescence (time resolution: 1 s; total uncertainty: 5%) (Hegglin, 2004;Hegglin et al, 2005). A linear regression analysis showed that both measurements agree within their uncertainty bounds (O 3 (CLD)=1.069 O 3 (UV)+5.4 (ppbv), R 2 =0.995; Hegglin, 2004).…”