Projections of mid-century summer air-quality for North America: effects of changes in climate and precursor emissions

Abstract

Abstract. Ten year simulations of North American current and future air-quality were carried out using a regional airquality model driven by a regional climate model, in turn driven by a general circulation model. Three separate summer scenarios were performed: a scenario representing the years 1997 to 2006, and two SRES A2 climate scenarios for the years 2041 to 2050. The first future climate scenario makes use of 2002 anthropogenic precursor emissions, and the second applied emissions scaling factors derived from the IPCC Representative Concentration Pathway 6 (RCP 6) scenario to estimate emissions for 2050 from existing 2020 projections. Ten-year averages of ozone and PM 2.5 at North American monitoring network stations were used to evaluate the model's current chemical climatology. The model was found to have a similar performance for ozone as when driven by an operational weather forecast model. The PM 2.5 predictions had larger negative biases, likely resulting from the absence of rainwater evaporation, and from sub-regional negative biases in the surface temperature fields, in the version of the climate model used here.The differences between the two future climate simulations and the current climate simulation were used to predict the changes to air-quality that might be expected in a future warmer climate, if anthropogenic precursor emissions remain constant at their current levels, versus if the RCP 6 emissions controls were adopted. Metrics of concentration, human health, and ecosystem damage were compared for the simulations. The scenario with future climate and current anthropogenic emissions resulted in worse air-quality than for current conditions -that is, the effect of climate-change alone, all other factors being similar, would be a worsening of air-quality. These effects are spatially inhomogeneous, with the magnitude and sign of the changes varying with region. The scenario with future climate and RCP 6 emissions for 2050 resulted in an improved air-quality, with decreases in key pollutant concentrations, in acute human mortality associated with air-pollution, and in sulphur and ozone deposition to the ecosystem. The positive outcomes of the RCP 6 emissions reductions were found to be of greater magnitude than the negative outcomes of climate change alone. The RCP 6 scenario however resulted in an increase in the deposition of nitrogen, as a result of increased ammonia emissions expected in that scenario, compared to current ammonia emissions levels.The results of the study raise the possibility that simultaneous reductions of greenhouse gases and air pollution precursors may further reduce air pollution levels, with the added benefits of an immediate reduction in the impacts of air pollution on human and ecosystem health. Further scenarios to investigate this possibility are therefore recommended.

Toxic volatile organic air pollutants across Canada: multi-year concentration trends, regional air quality modelling and source apportionment

“…Ozone boundary conditions make use of a monthly 3-D climatology (Logan 1999). CO and PM 2.5 boundary conditions are simplified profiles based on satellite observations (MOPITT and MODIS) with seasonal and latitudinal variations (Kelly et al 2012). The benzene at the boundaries is derived from proton-transfer reaction mass spectrometry observations from Whistler with seasonal variations.…”

The effects of global change upon United States air quality

“…This downscaling approach has been used in a variety of studies in Europe, Canada and Asia at different timescales of climate change -e.g., Liao et al, 2006Liao et al, (2000Liao et al, to 2100; Langner et al, 2005Langner et al, (2000Langner et al, to 2060; Forkel and Knoche, 2006(2990to 2030; Meleux et al, 2007Meleux et al, (1975Meleux et al, to 1985; Kunkel et al, 2007Kunkel et al, (1990Kunkel et al, to 2090; Lin et al, 2008Lin et al, (2000Lin et al, to 2100; Spracklen et al, 2009Spracklen et al, (2000Spracklen et al, to 2050; Kelly et al, 2012. These investigations based the global emissions on future anthropogenic emissions scenarios developed from the Intergovernmental Panel on Climate Change (IPCC) assessment reports.…”

Climate-forced air-quality modeling at the urban scale: sensitivity to model resolution, emissions and meteorology

“…A significant portion of the published literature on this issue uses global-scale models to focus on the impact of climate on tropospheric ozone at the global or regional scale (Brasseur et al, 1998;Liao et al, 2006;Prather et al, 2003;Szopa et al, 2006;Szopa and Hauglustaine, 2007). More recent studies have integrated advanced chemistry schemes capable of resolving the variability of pollutant concentrations at regional scale, which spans from several hours up to a few days, with chemistry transport models (CTMs) (Colette et al, 2012Knoche, 2006, 2007;Hogrefe et al, 2004;Katragkou et al, 2011;Kelly et al, 2012;Knowlton et al, 2004;Lam et al, 2011;Langner et al, 2005Langner et al, , 2012Nolte et al, 2008;Szopa and Hauglustaine, 2007;Tagaris et al, 2009;Zanis et al, 2011). Global models with a typical resolution of a few hundreds of kilometers and regional CTMs used at resolutions of a few tens of kilometers, and their parameterization of physical and chemical processes make them inadequate for modeling airquality at the urban scale (Cohan et al, 2006;Forkel and Knoche, 2007;Markakis et al, 2014;Sillman et al, 1990;Tie et al, 2010;Valari and Menut, 2008;Valin et al, 2011;Vautard et al, 2007).…”

“…Other challenges stem from the fact that emission projections are mostly based on scenarios developed to represent changes at the global scale and are rarely suited for assessment at the regional let alone urban scale. Long-term projections are constrained by the evolution of large-scale energy supply and demand, and the link between global and regional-scale projections is a laborious task (Kelly et al, 2012).…”