Abstract
Abstract. The capability of global chemistry and transport models (CTMs) to simulate atmospheric composition and its spatial and temporal changes highly relies on the input data used by the models, in particular the emission inventories. Biomass burning emissions show large spatial, diurnal, seasonal and year-to-year variability. In the present study, we applied a global 3-D CTM to evaluate uncertainties in the computed atmospheric composition associated with the use of different biomass burning emissions and identify areas where observational data can help to reduce these uncertainties. We find the emission inventory choice to lead to regional differences in the calculated load of aerosols up to a factor of 4. Assumptions on the injection height of the biomass burning emissions are found to produce regionally up to 30% differences in the calculated tropospheric lifetimes of pollutants. Computed changes in lifetimes point to a strong chemical feedback mechanism between emissions from biomass burning and isoprene emissions from vegetation that are linked via NOx-driven oxidant chemistry, NOx-dependent changes in isoprene oxidation products, aerosol emissions and atmospheric transport. These interactions reduce isoprene load in the presence of biomass burning emissions by 15%, calculated for the same amount of isoprene emitted into the troposphere. Thus, isoprene load and lifetime are inversely related to the quantities of pollutants emitted by biomass burning. These interactions are shown to be able to increase the global annual secondary aerosol yield from isoprene emissions, defined as the ratio of tropospheric loads of secondary aerosol from isoprene oxidation to isoprene emissions, by up to 18%.
Highlights
Atmospheric composition is affected by emissions of reactive gases and aerosols to the atmosphere by several natural and anthropogenic sources
Terpenes and biogenic volatile organic compound (BVOC) emissions in the TM4-ECPL model are taken from the MEGAN-MACC (Model of Emissions of Gases and Aerosols from Nature–Monitoring Atmospheric Composition and Climate) inventory (Sindelarova et al, 2014) for the year 2008, which is a product of the MEGANv2.1 model (Guenther et al, 2012)
Anthropogenic emissions of all basic pollutants are used: carbon monoxide (CO), nitrogen oxides (NOx), black carbon aerosol (BC), particulate organic carbon (OC), sulfur dioxide and sulfates (SOx) as well as speciated non-methane volatile organic compounds (NMVOCs; for a list of the NMVOCs used in the model see Supplement S1)
Summary
Atmospheric composition is affected by emissions of reactive gases and aerosols to the atmosphere by several natural (e.g., soils, vegetation, oceans, volcanoes, wildfires) and anthropogenic sources (e.g., industrial and residential activities, transport, and shipping). The Leung et al (2007) global modeling study of the impact of boreal fire emissions on air pollutants levels found a much larger enhancement in ozone when about half the emissions were released above the boundary layer than when all emissions were occurring in the boundary layer They attributed these differences to the role of peroxyacetyl nitrate (PAN) as carrier of NOx downwind of burning areas. The study aims to identify locations where additional observations can provide constrains for biomass burning emission estimates For this purpose, a global 3-D chemistry and transport model (CTM) is applied to evaluate uncertainties in the atmospheric composition and major pollutant lifetimes computed using recently updated and commonly used biomass burning emissions. Based on the computed model sensitivity to biomass burning emissions, we identify areas where observational data can help to reduce these uncertainties
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