15 Dec 2022
15 Dec 2022

Atmospheric Distribution of HCN from Satellite Observations and 3-D Model Simulations

Antonio Giovanni Bruno1,2, Jeremy J. Harrison1,2, Martyn P. Chipperfield3,4, David P. Moore1,2, Richard J. Pope3,4, Christopher Wilson3,4, Emmanuel Mahieu5, and Justus Notholt6 Antonio Giovanni Bruno et al.
  • 1School of Physics and Astronomy, University of Leicester, Leicester, UK
  • 2National Centre for Earth Observation, University of Leicester, Leicester, UK
  • 3School of Earth and Environment, University of Leeds, Leeds, UK
  • 4National Centre for Earth Observation, University of Leeds, Leeds, UK
  • 5Institut d’Astrophysique et de Géophysique, Université de Liège, Liège, Belgium
  • 6Institute of Environmental Physics, University of Bremen, Bremen 28334, Germany

Abstract. We use a tracer version of the TOMCAT global 3-D chemical transport model to investigate the physical and chemical processes driving the abundance of hydrogen cyanide (HCN) in the troposphere and stratosphere over the period 2004–2016. The modelled HCN distribution is compared with version 4.1 of the Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) HCN satellite data, which provides profiles up to around 42 km, and with ground-based column measurements from the Network for the Detection of Atmospheric Composition Change (NDACC). ACE-FTS has so far provided over 17 years of data, from 2004, which allow us to monitor both the seasonal and interannual variations of HCN and its transport through the atmosphere. In particular, by analysing the long time series, we are able to detect the effects on atmospheric composition of large wildfire events like those observed in 2006 and 2015 in Indonesia. Our 3-D model simulations confirm previous lower altitude balloon comparisons that the currently recommended NASA Jet Propulsion Laboratory (JPL) reaction rate coefficient of HCN with OH greatly overestimates the HCN loss. The use of the rate coefficient proposed by Kleinböhl et al. (2006) in combination with the HCN oxidation by O(1D) gives good agreement between ACE-FTS observations and the model. Furthermore, investigation of the individual photochemical loss terms shows that the reduction of the HCN mixing ratio with height in the middle stratosphere is mainly driven by the O(1D) sink with only a small contribution from reaction with OH. From comparisons of the model tracers with ground-based HCN observations we test the magnitude of the ocean sink in two different published schemes (Li et al. 2000, 2003). We find that in our 3-D model the two schemes produce HCN abundances which are very different to the NDACC observations but in different directions. A model HCN tracer using the Li et al. (2000) scheme overestimates the HCN concentration by almost a factor two, while a HCN tracer using the Li et al. (2003) scheme underestimates the observations by about one-third. To obtain good agreement between the model and observations we need to scale the magnitudes of the global ocean sinks by the factors of 0.25 and 2 for the schemes of Li et al. (2000) and Li et al. (2003), respectively. This work shows that the atmospheric photochemical sinks of HCN now appear well constrained but improvements are needed in parameterising the major ocean uptake sink.

Antonio Giovanni Bruno et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1404', Hugh C. Pumphrey, 19 Dec 2022
  • RC2: 'Review of ‘Atmospheric distribution of HCN from satellite observations and 3-D model simulations’ by A. G. Bruno et al. (2022)', Anonymous Referee #2, 09 Jan 2023

Antonio Giovanni Bruno et al.

Antonio Giovanni Bruno et al.


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Short summary
A 3-D chemical transport model, TOMCAT, satellite data and ground-based observations have been used to investigate the hydrogen cyanide (HCN) variability. We found that the oxidation by O(1D) drives the HCN loss in the mid-stratosphere and the currently JPL recommended OH reaction rate overestimates the HCN atmospheric loss. We also evaluated two different ocean uptake schemes. We found them to be unrealistic and we need to scale these schemes to obtain good agreement with HCN observations.