Hydrogen cyanide in the upper troposphere: GEM-AQ simulation and comparison with ACE-FTS observations 1Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada
2NASA Langley Research Center, Hampton, Virginia, USA
3Department of Chemistry, University of York, Heslington, UK
4Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada
5Department of Physics, University of Toronto, Toronto, Ontario, Canada
6Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, Japan
7Faculty of Education and Human Sciences, Yokohama National University, Yokohama, Japan
Received: 17 Nov 2008 – Published in Atmos. Chem. Phys. Discuss.: 23 Jan 2009 – Published: 03 Jul 2009Abstract. We investigate the spatial and temporal distribution of hydrogen cyanide
(HCN) in the upper troposphere through numerical simulations and comparison
with observations from a space-based instrument. To perform the simulations,
we used the Global Environmental Multiscale Air Quality model (GEM-AQ),
which is based on the three-dimensional global multiscale model developed
by the Meteorological Service of Canada for operational weather forecasting.
The model was run for the period 2004–2006 on a 1.5°×1.5°
global grid with 28 hybrid vertical levels from the surface up to 10 hPa.
Objective analysis data from the Canadian Meteorological Centre were used to
update the meteorological fields every 24 h. Fire emission fluxes of gas
species were generated by using year-specific inventories of carbon emissions
with 8-day temporal resolution from the Global Fire Emission Database (GFED)
version 2. The model output is compared with HCN profiles measured by the
Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS)
instrument onboard the Canadian SCISAT-1 satellite. High values of
up to a few ppbv are observed in the tropics in the Southern Hemisphere;
the enhancement in HCN volume mixing ratios in the upper troposphere is most
prominent in October. Low upper-tropospheric mixing ratios of less than 100 pptv
are mostly recorded at middle and high latitudes in the Southern Hemisphere in
May–July. Mixing ratios in Northern Hemisphere peak in the boreal summer. The
amplitude of the seasonal variation is less pronounced than in the Southern
Hemisphere. The comparison with the satellite data shows that in the upper
troposphere GEM-AQ performs well globally for all seasons, except at northern
high and middle latitudes in summer, where the model has a large negative
bias, and in the tropics in winter and spring, where it exhibits large
positive bias. This may reflect inaccurate emissions or possible inaccuracies
in the emission profile. The model is able to explain most of the observed
variability in the upper troposphere HCN field, including the interannual
variations in the observed mixing ratio.
A complementary comparison with daily total columns of HCN from two middle
latitude ground-based stations in Northern Japan for the same simulation period
shows that the model captures the observed seasonal variation and also points
to an underestimation of model emissions in the Northern Hemisphere in the summer.
The estimated average global emission equals 1.3 Tg N yr−1. The average
atmospheric burden is 0.53 Tg N, and the corresponding lifetime is 4.9 months.
Citation: Lupu, A., Kaminski, J. W., Neary, L., McConnell, J. C., Toyota, K., Rinsland, C. P., Bernath, P. F., Walker, K. A., Boone, C. D., Nagahama, Y., and Suzuki, K.: Hydrogen cyanide in the upper troposphere: GEM-AQ simulation and comparison with ACE-FTS observations, Atmos. Chem. Phys., 9, 4301-4313, doi:10.5194/acp-9-4301-2009, 2009.