Abstract
Abstract. We investigate the impact of biogenic emissions on carbon monoxide (CO) and formaldehyde (HCHO) in the Southern Hemisphere (SH), with simulations using two different biogenic emission inventories for isoprene and monoterpenes. Results from four atmospheric chemistry models are compared to continuous long-term ground-based CO and HCHO column measurements at the SH Network for the Detection of Atmospheric Composition Change (NDACC) sites, the satellite measurement of tropospheric CO columns from the Measurement of Pollution in the Troposphere (MOPITT), and in situ surface CO measurements from across the SH, representing a subset of the National Oceanic and Atmospheric Administration's Global Monitoring Division (NOAA GMD) network. Simulated mean model CO using the Model of Emissions of Gases and Aerosols from Nature (v2.1) computed in the frame work of the Land Community Model (CLM-MEGANv2.1) inventory is in better agreement with both column and surface observations than simulations adopting the emission inventory generated from the LPJ-GUESS dynamical vegetation model framework, which markedly underestimate measured column and surface CO at most sites. Differences in biogenic emissions cause large differences in CO in the source regions which propagate to the remote SH. Significant inter-model differences exist in modelled column and surface CO, and secondary production of CO dominates these inter-model differences, due mainly to differences in the models' oxidation schemes for volatile organic compounds, predominantly isoprene oxidation. While biogenic emissions are a significant factor in modelling SH CO, inter-model differences pose an additional challenge to constrain these emissions. Corresponding comparisons of HCHO columns at two SH mid-latitude sites reveal that all models significantly underestimate the observed values by approximately a factor of 2. There is a much smaller impact on HCHO of the significantly different biogenic emissions in remote regions, compared to the source regions. Decreased biogenic emissions cause decreased CO export to remote regions, which leads to increased OH; this in turn results in increased HCHO production through methane oxidation. In agreement with earlier studies, we corroborate that significant HCHO sources are likely missing in the models in the remote SH.
Highlights
Carbon monoxide (CO) is ubiquitous throughout the troposphere and is an important ozone (O3) precursor; it originates from both primary emission sources and in situ chemical production
In this paper we address the sensitivity of CO and HCHO distributions in the Southern Hemisphere (SH) to biogenic emissions of isoprene and monoterpenes as provided by the LPJ_GUESS emission inventory (Arneth et al, 2007a, b; Schurgers et al, 2009) and the MEGANv2.1 model (Guenther et al, 2012) across the models included in Southern Hemisphere Model Intercomparison Project (SHMIP)
We have updated the National Institute of Water and Atmospheric Research (NIWA)-UK Chemistry and Aerosols Model (UKCA) chemical mechanism from that described in Morgenstern et al (2013) to account for emissions and degradations of ethene (C2H4), propene (C3H6), methanol (CH3OH), isoprene, a representative monoterpene, and a lumped species that accounts for missing non-methane volatile organic compounds (NMVOCs) in the model similar to the approach taken in the IMAGES model (Müller and Brasseur, 1995), with primary emission sources
Summary
Carbon monoxide (CO) is ubiquitous throughout the troposphere and is an important ozone (O3) precursor; it originates from both primary emission sources (fossil fuel and biomass combustion, biogenic, and oceanic processes) and in situ chemical production. Bottom-up estimates of annual isoprene emissions vary between 400 and 600 Tg C yr−1 (Arneth et al, 2008), and the typical range of annual total isoprene emissions implemented in global atmospheric chemistry models is ∼ 200–600 Tg C yr−1 (Stevenson et al, 2006) The effect of such uncertainties in biogenic emissions on SH composition, such as CO and HCHO, has not been adequately assessed. Given the relatively low anthropogenic emissions in the SH and the dominance of biogenic emissions of VOCs (mainly isoprene), we determine the influence that different emission inventories of isoprene and monoterpenes have regarding their effects on modelled CO and HCHO columns in the SH. We provide the description of the simulations performed, the common emission inventories employed, a brief description of each model, the meteorological drivers, and the observations used for evaluating the performance of the models
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