Abstract
Concentrations of atmospheric trace species in the United States have changed dramatically over the past several decades in response to pollution control strategies, shifts in domestic energy policy and economics, and economic development (and resulting emission changes) elsewhere in the world. Reliable projections of the future atmosphere require models to not only accurately describe current atmospheric concentrations, but to do so by representing chemical, physical and biological processes with conceptual and quantitative fidelity. Only through incorporation of the processes controlling emissions and chemical mechanisms that represent the key transformations among reactive molecules can models reliably project the impacts of future policy, energy and climate scenarios. Efforts to properly identify and implement the fundamental and controlling mechanisms in atmospheric models benefit from intensive observation periods, during which collocated measurements of diverse, speciated chemicals in both the gas and condensed phases are obtained. The Southeast Atmosphere Studies (SAS, including SENEX, SOAS, NOMADSS and SEAC4RS) conducted during the summer of 2013 provided an unprecedented opportunity for the atmospheric modeling community to come together to evaluate, diagnose and improve the representation of fundamental climate and air quality processes in models of varying temporal and spatial scales.This paper is aimed at discussing progress in evaluating, diagnosing and improving air quality and climate modeling using comparisons to SAS observations as a guide to thinking about improvements to mechanisms and parameterizations in models. The effort focused primarily on model representation of fundamental atmospheric processes that are essential to the formation of ozone, secondary organic aerosol (SOA) and other trace species in the troposphere, with the ultimate goal of understanding the radiative impacts of these species in the southeast and elsewhere. Here we address questions surrounding four key themes: gas-phase chemistry, aerosol chemistry, regional climate and chemistry interactions, and natural and anthropogenic emissions. We expect this review to serve as a guidance for future modeling efforts.
Highlights
The southeastern US has been studied extensively because it includes intense emissions of biogenic volatile organic compounds (BVOCs; the definitions for the abbreviations used in this paper can be found in Appendix A) and has multiple large sources of anthropogenic emissions (e.g., Chameides et al, 1988; Trainer et al, 1987)
In this review we focus on the intersection of these two approaches, which is on analyses of observations that test and inform the construction of 3-D chemical weather models
Epoxide reactions in cloud droplets are predicted to lead to minor amounts of Secondary OA (SOA) due to the pH dependence of isoprene epoxydiol (IEPOX) hydrolysis (Fahey et al, 2017; McNeill, 2015)
Summary
The southeastern US has been studied extensively because it includes intense emissions of biogenic volatile organic compounds (BVOCs; the definitions for the abbreviations used in this paper can be found in Appendix A) and has multiple large sources of anthropogenic emissions (e.g., Chameides et al, 1988; Trainer et al, 1987). In turn, influence surface air quality, but even the sign of the effect is unknown in the southeast (Weaver et al, 2009) Part of this uncertainty has to do with complexities in the mechanism of isoprene oxidation, the details of which are still emerging from laboratory experiments and field campaigns (Liao et al, 2015; Fisher et al, 2016; Marais et al, 2016). The influence of day-to-day weather on surface ozone and particulate matter (PM2.5) has not been fully quantified, and climate models simulate different regional climate responses Resolving these uncertainties is important, as climate change in the coming decades may impose a “climate penalty” on surface air quality in the southeast and elsewhere (Fiore et al, 2015)
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