Satellite observations of stratospheric hydrogen fluoride and comparisons with SLIMCAT calculations

Abstract

Abstract. The vast majority of emissions of fluorinecontaining molecules are anthropogenic in nature, e.g. chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Many of these fluorine-containing species deplete stratospheric ozone and are regulated by the Montreal Protocol. Once in the atmosphere they slowly degrade, ultimately leading to the formation of hydrogen fluoride (HF), the dominant reservoir of stratospheric fluorine due to its extreme stability. Monitoring the growth of stratospheric HF is therefore an important marker for the success of the Montreal Protocol.We report the comparison of global distributions and trends of HF measured in the Earth's atmosphere by the satellite remote-sensing instruments ACE-FTS (Atmospheric Chemistry Experiment Fourier transform spectrometer), which has been recording atmospheric spectra since 2004, and HALOE (HALogen Occultation Experiment), which recorded atmospheric spectra between 1991 and 2005, with the output of SLIMCAT, a state-of-the-art threedimensional chemical transport model. In general the agreement between observation and model is good, although the ACE-FTS measurements are biased high by ∼ 10 % relative to HALOE. The observed global HF trends reveal a substantial slowing down in the rate of increase of HF since the 1990s: 4.97 ± 0.12 % year −1 (1991-1997; HALOE), 1.12 ± 0.08 % year −1 (1998 HALOE), and 0.52 ± 0.03 % year −1 (2004-2012 ACE-FTS). In comparison, SLIMCAT calculates trends of 4.01, 1.10, and 0.48 % year −1 , respectively, for the same periods; the agreement is very good for all but the earlier of the two HALOE periods. Furthermore, the observations reveal variations in the HF trends with latitude and altitude; for example, between 2004 and 2012 HF actually decreased in the Southern Hemisphere below ∼ 35 km. An additional SLIMCAT simulation with repeating meteorology for the year 2000 produces much cleaner trends in HF with minimal variations with latitude and altitude. Therefore, the variations with latitude and altitude in the observed HF trends are due to variability in stratospheric dynamics on the timescale of a few years. Overall, the agreement between observation and model points towards the ongoing success of the Montreal Protocol and the usefulness of HF as a metric for stratospheric fluorine.

Shift of subtropical transport barriers explains observed hemispheric asymmetry of decadal trends of age of air

“…Similar hemispheric asymmetries of trends of stratospheric trace species have been derived from other observational data sets by various groups, corroborating the results from the MIPAS AoA analysis, e.g. for ozone (Eckert et al, 2014;Gebhardt et al, 2014;Nedoluha et al, 2015a, b;Pawson et al, 2014), hydrogen fluoride (Harrison et al, 2016), hydrogen chloride (Mahieu et al, 2014), (H)CFCs (Chirkov et al, 2016;Kellmann et al, 2012), nitrous oxide (Nedoluha et al, 2015a), and carbonyl sulfide (Glatthor et al, 2017). Ploeger et al (2015b) performed an analysis of the time series of AoA as derived from the MIPAS SF 6 observations and the AoA derived from a Chemical Lagrangian Model of the Stratosphere (CLaMS) model run with a clock tracer G. P. Stiller et al: Shift of subtropical transport barriers included.…”

Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine‐Containing Very Short Lived Substances

“…These trends, associated with lower stratospheric phosgene, are influenced by changing stratospheric dynamics over the period of the observations and reveal differences between southern and northern hemispheres. The off-line formulation of TOMCAT, which uses specified ECMWF meteorology, does not allow for any rigorous explanation of the changing stratospheric dynamics that are responsible for the observed trends; however, these are in line with previous observations of stratospheric species (e.g., Harrison et al, 2016;Mahieu et al, 2014).…”

“…TOMCAT/SLIMCAT (hereafter simply TOMCAT) is a state-of-the-art off-line global three-dimensional CTM (Chipperfield, 2006). Its outputs have been widely evaluated against observations of tropospheric and stratospheric composition; for example, it reproduces well the tropospheric abundance of chlorine-containing VSLS (Hossaini et al, 2015) and the stratospheric abundance of hydrogen fluoride (Harrison et al, 2016). The model is forced with meteorological fields, including winds and temperatures, from European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalyses.…”

Recent Trends in Stratospheric Chlorine From Very Short‐Lived Substances

“…The version of the stratospheric model employed here was recently used by Chipperfield et al () to investigate lower stratospheric ozone trends and is used by Harrison et al () to interpret long‐term COCl 2 observations from ACE. It has also been extensively evaluated in terms of both chemistry and transport (e.g., Harrison et al, ; Wales et al, ).…”