Isoprene emissions modelling for West Africa: MEGAN model evaluation and sensitivity analysis 1School of Environmental Sciences, University of East Anglia, Norwich, UK
2CESAM & Department of Environment and Planning, University of Aveiro, 3810–193 Aveiro, Portugal
3Department of Chemistry, University of Toronto, Toronto, Canada
4Institute for Climate and Atmospheric Science, University of Leeds, UK
Received: 27 January 2010 – Published in Atmos. Chem. Phys. Discuss.: 11 March 2010 Abstract. Isoprene emissions are the largest source of reactive carbon to the
atmosphere, with the tropics being a major source region. These natural
emissions are expected to change with changing climate and human impact on
land use. As part of the African Monsoon Multidisciplinary Analyses (AMMA)
project the Model of Emissions of Gases and Aerosols from Nature (MEGAN) has
been used to estimate the spatial and temporal distribution of isoprene
emissions over the West African region. During the AMMA field campaign,
carried out in July and August 2006, isoprene mixing ratios were measured on
board the FAAM BAe-146 aircraft. These data have been used to make a
qualitative evaluation of the model performance.
Revised: 03 August 2010 – Accepted: 05 August 2010 – Published: 07 September 2010
MEGAN was firstly applied to a large area covering much of West Africa from
the Gulf of Guinea in the south to the desert in the north and was able to
capture the large scale spatial distribution of isoprene emissions as
inferred from the observed isoprene mixing ratios. In particular the model
captures the transition from the forested area in the south to the bare
soils in the north, but some discrepancies have been identified over the
bare soil, mainly due to the emission factors used. Sensitivity analyses
were performed to assess the model response to changes in driving
parameters, namely Leaf Area Index (LAI), Emission Factors (EF), temperature
and solar radiation.
A high resolution simulation was made of a limited area south of Niamey,
Niger, where the higher concentrations of isoprene were observed. This is
used to evaluate the model's ability to simulate smaller scale spatial
features and to examine the influence of the driving parameters on an hourly
basis through a case study of a flight on 17 August 2006.
This study highlights the complex interactions between land surface
processes and the meteorological dynamics and chemical composition of the
PBL. This has implications for quantifying the impact of biogenic emissions
on the atmospheric composition over West Africa and any changes that may
occur with changing climate.
Citation: Ferreira, J., Reeves, C. E., Murphy, J. G., Garcia-Carreras, L., Parker, D. J., and Oram, D. E.: Isoprene emissions modelling for West Africa: MEGAN model evaluation and sensitivity analysis, Atmos. Chem. Phys., 10, 8453-8467, doi:10.5194/acp-10-8453-2010, 2010.