Observations and modelling of hydrogen cyanide in the atmosphere

Abstract

Wildfires in Indonesia are seasonal events regulated mainly by the agricultural practice of burning old vegetation for land clearing in order to prepare the soil for the new planting season. El Niño exacerbates the typical extreme weather conditions of the Indonesian wildfire season, making burning events difficult to control, as they were towards the end of 2015. Indonesian land contains a high percentage of peat, a carbon-rich type of soil, which emits a large amount of hydrogen cyanide (HCN) when burning. For this reason, HCN is typically considered a good atmospheric tracer for peat fires.
In this work we present a preliminary study of HCN focused on the emissions of the 2015 Indonesian peat fires. The University of Leicester IASI Retrieval Scheme (ULIRS), originally developed to retrieve carbon monoxide profiles from IASI radiances using an optimal estimation approach, has been expanded to retrieve HCN profiles. The ULIRS HCN data are compared with HCN retrieved using a one-step non-linear retrieval scheme.
For the first time, HCN chemistry has been included in TOMCAT, a 3D state-of-the-art chemical transport model. Here we compare model outputs with HCN profiles measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS).

Full text

Introduction
Wildfires in Indonesia are seasonal events regulated mainly by the agricultural practice of burning old vegetation for land clearing in order to prepare the soil for the new planting season. El
Niño exacerbates the typical extreme weather conditions of the Indonesian wildfire season, making burning events difficult to control, as they were towards the end of 2015.
Indonesian land contains a high percentage of peat, a carbon-rich type of soil, which emits a large amount of hydrogen cyanide (HCN) when burning. For this reason, HCN is typically considered
a good atmospheric tracer for peat fires.
References
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ULIRS
ULIRS was performed for HCN choosing a wide wavenumber range of investigation (710-717 cm-1) which include the 712.5
cm-1 vibrational transition of HCN molecules.
A priori information and climatology are determined using a set of reference atmospheres designed by Remedios et al.
(2007).
The Infrared Atmospheric Sounding Instrument (IASI)
•IASI is a Michelson Interferometer onboard METOP measuring atmospheric spectra in the TIR range –645 to 2760 cm-1
(15.5 to 3.62 μm).
•Data have a spectral sampling of 0.25 cm-1 and a spectral resolution of 0.5 cm-1.
•14 orbits per day in a polar sun-synchronous orbit, local time ~09:30 (descending orbit).
•Global daily coverage due to large 2200 km swath width.
Comparison between IASI HCN total column from ULIRS (Left panels) and one-step non-linear retrieval process (Right panels)
relative to the MetOp-A IASI night-time measurement (~21:30 local solar time) on the first three days of November showing
a large enhancement of HCN concentration over Indonesia and Indian Ocean.
(Above) Viewing geometry of the IASI instrument.
(Right). An example of an IASI spectrum alongside the
major absorption bands of a number of important
trace gases in the atmosphere.
Observations and modelling of hydrogen cyanide in the
atmosphere
Antonio Giovanni Bruno1, 2, Jeremy Harrison1, 2, 3, David Moore1, 2, 3, Richard Pope4, 5, Martyn Chipperfield4, 5
(1) Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom. (2) National Centre for Earth Observation (NCEO), University
of Leicester, Leicester, United Kingdom. (3) Leicester Institute for Space and Earth Observation (LISEO), University of Leicester, Leicester, United Kingdom.
(4) School of Earth and Environment, University of Leeds, Leeds, United Kingdom. (5) National Centre for Earth Observation, University of Leeds, Leeds,
United Kingdom
ACE-FTS TOMCAT
comparison
TOMCAT is a 3-D off-line
chemical transport model
(CTM) (Chipperfield, 2006)
driven by reanalysis
meteorology (e.g. winds,
temperature). The model
has a horizontal resolution
of 2.8°x2.8°, for sixty
atmospheric layers from
the surface up to 0.1 hPa.
The sources of
atmospheric hydrogen
cyanide (HCN) come from
anthropogenic emissions
(CMIP6; Hosely et al.,
2018) and biomass
burning (GFED vn4; van
der Werf et al., 2017).
HCN sinks include ocean
deposition and chemical
loss through reaction with
OH, O(1D) and photolysis.
The ocean uptake scheme
is based on Li et al., (2000)
and chemical sinks are
based on TOMCAT off-line
fields.
Credit –David Moore, NCEO
HCN burden from one-step
retrieval over Indonesia during
2015 wildfire season. An
unprecedented amount of HCN
was released between the end of
October and the beginning of
November.
01/11/2015 01/11/2015 Credit –Jeremy Harrison, NCEO
02/11/2015 02/11/2015 Credit –Jeremy Harrison, NCEO
03/11/2015 03/11/2015 Credit –Jeremy Harrison, NCEO
Flow diagram representing ULIRS
scheme used to retrieve HCN.
(Insert) An IASI spectrum taken
on the night of 30 October 2015
over the Indonesia region
showing absorption of HCN.
Comparison between HCN averaged vertical profiles at different latitude bands for the period Oct-Dec 2009 measured
by ACE-FTS and from TOMCAT run using the ocean uptake scheme based on Li et al., (2000). Each panel represents a 10
degrees latitude band.