A summer simulation of biogenic contributions to ground‐level ozone over the continental United States

Abstract

The role of biogenic emissions in the production of ground‐level ozone has been the subject of considerable scientific investigation. However, because existing studies generally draw their conclusions from simulations of episodes lasting days to a week, there is a need to evaluate the biogenic impact over a relatively long timescale. Moreover, the magnitude of synergistic interaction between anthropogenic and biogenic emissions should be carefully quantified, and this issue is not accounted for in most previous investigations. In this study, we performed a summer seasonal (June to August 1995) model evaluation of surface ozone across the continental United States. A three‐dimensional regional climate, emissions, and air quality modeling system was used to do the simulations. The factor separation (FS) technique was applied to quantify the contributions from biogenic emissions alone and those from the synergy between anthropogenic and biogenic emissions. In the first step of this study, U.S. Environmental Protection Agency's National Emission Trends (NET) 1996 and 2020 “control case” raw anthropogenic emissions inventories were processed through Sparse Matrix Operator Kernel Emissions (SMOKE), an emissions model, to generate the speciated, gridded, and hourly emissions data needed for the air quality model. Next, six air quality simulations were carried out assuming zero emissions, biogenic only emissions, 1995 anthropogenic only emissions, biogenic plus 1995 anthropogenic emissions, 2020 anthropogenic only emissions, and biogenic plus 2020 anthropogenic emissions. The model results show that ground‐level ozone concentrations decrease moderately under the EPA's 2020 emissions scenario for many areas within the continental United States, with large reductions in vast areas of the eastern United States. They also show that the 1995 summer average “total biogenic contribution” to daily maximum surface ozone concentrations can reach 34 ppb. Biogenic emissions are associated with at least 20% of surface ozone concentrations for the most areas of the continental United States, with the peaks reaching more than 40% in California coastal areas, the southeastern states, and northeastern areas. A sizable portion of this “total biogenic contribution,” however, (up to 80% in some areas) is due to the synergy between anthropogenic and biogenic emissions and would thus be influenced by controls on anthropogenic source emissions.

Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds

“…In terms of isoprene oxidation it has been shown that the implicit loss of intermediates in the modified CBM4 mechanism can introduce significant differences of up to ∼30-60 % (equivalent to 10 ppb) in tropospheric O 3 when compared against other alternative mechanisms employed in CTMs (von Kuhlmann et al, 2004). The isoprene oxidation mechanism in the modified CB05 scheme is more extensive than that in the modified CBM4 mechanism, where it includes an intermediate tracer species which lumps both methacrolein and methyl vinyl ketone together (designated as ISPD) in order to provide a better representation of the principle oxidation products of isoprene and the monoterpenes (Atkinson, 2000).…”

“…For reasons of numerical stability associated with the Eulerian Backward Iterative (EBI) solver (Hertel et al, 1993) we omit the formation of higher PAN compounds, although these tend to be more reactive thus making smaller contributions to the long range transport of nitrogen oxides (NO x ) out of the main source regions than PAN itself (von Kuhlmann et al, 2004). For higher aldehydes (denoted ALDX in CB05) we assume a short atmospheric lifetime and therefore introduce the main oxidation products instead.…”

“…For the vertical distribution it is assumed that the gradient in the boundary layer and lower free troposphere is shallow allowing the constraint to be imposed in the first few kilometers of the troposphere. Adopting such offline CH 4 emission fields has been shown to improve both the regional and seasonal distribution at the surface compared to using a fixed latitudinal gradient (van Weele et al, 2013). For the emission of trace gases from Guenther et al (2006) biomass burning (BB) and wildfires we adopt the emission estimates provided in the monthly GFEDv3 inventories for all simulations (van der Werf et al, 2010).…”

“…Simpson, 1995;Roberts et al, 2006; or the composition of the global troposphere (e.g. von Kuhlmann et al, 2004;Folberth et al, 2006;Fiore et al, 2011). By exploiting the sensitivity studies described in Sect.…”

“…von Kuhlmann et al, 2004;Pfister et al, 2008;Williams et al, 2009) andregional (e.g. Simpson, 1995;Tao et al, 2003;Roberts et al, 2006;Li et al, 2007;Curci et al, 2009) scales. Sensitivity studies have shown that there is generally an enhancement in the oxidative capacity of the troposphere as a result of an increase in the resident molar mixing ratios of O 3 , and thus OH, due to the presence of BVOCs.…”