Influence of future climate and emissions on regional air quality in California

Abstract

[1] Using a chemical transport model simulating ozone concentrations in central California, we evaluate the effects of variables associated with future changes in climate and ozone precursor emissions, including (1) increasing temperature; (2) increasing atmospheric water vapor; (3) increasing biogenic VOC emissions due to temperature; (4) projected decreases in anthropogenic NOx, VOC, and CO emissions in California for 2050; and (5) the influence of changing ozone, CO, and methane at the western boundary. Climatic changes expected for temperature, atmospheric water vapor, and biogenic VOC emissions each individually cause a 1-5% increase in the daily peak ozone. Projected reductions in anthropogenic emissions of 10-50% in NOx and 50-70% in VOCs and CO have the greatest single effect, reducing ozone by 8-15% in urban areas. Changes to the chemical boundary conditions lead to ozone increases of 6% in the San Francisco Bay area and along the west coast but only 1-2% inland. Simulations combining climate effects predict that ozone will increase 3-10% in various regions of California. This increase is partly offset by projected future emissions reductions, and a combined climate and emissions simulation yields ozone reductions of 3-9% in the Central Valley and almost no net change in the San Francisco Bay area. We find that different portions of the model domain have widely varying sensitivity to climate parameters. In particular, the San Francisco Bay region is more strongly influenced by temperature changes than inland regions, indicating that air quality in this region may worsen under future climate regimes.

Effect of climate change on air quality

“…Model perturbation studies consistently identify temperature as the single most important meteorological variable affecting ozone concentrations in polluted regions (Morris et al, 1989;Aw and Kleeman, 2003;Sanchez-Ccoyllo et al, 2006;Steiner et al, 2006;Dawson et al, 2007a). This is consistent with the strong observed correlation of ozone pollution episodes with temperature.…”

“…The model dependence of ozone on temperature is due to two principal factors Sillman and Samson, 1995): (1) the temperature-dependent lifetime of peroxyacetylnitrate (PAN), a major sequestering reservoir for NO x and HO x radicals even at high temperatures; and (2) the temperature dependence of biogenic emission of isoprene, a major VOC precursor for ozone formation under high-NO x conditions. Model slopes (v½O 3 =vT ) are typically in the range 2-10 ppb K À1 , with maximum values in urban areas having high ozone formation potential (Sillman and Samson, 1995;Baertsch-Ritter et al, 2004;Steiner et al, 2006). They tend to be lower than the observed ozone-temperature regression slopes (d [O 3 ]/dT) (Sillman and Samson, 1995).…”

“…The effect on PM is uncertain but potentially significant. When assuming business-as-usual future scenarios without significant emission reductions beyond current regulations, models find that the combined effects of emissions changes and climate change in the U.S. will result in increased ozone pollution (Hogrefe et al, 2004;Steiner et al, 2006;Tao et al, 2007;Chen et al, submitted for publication). Simulations that assume emission reductions far beyond the full implementation of current regulations indicate that climate change will partly offset the benefit of the emissions reductions Tagaris et al, 2007;Nolte et al, 2008).…”

The effects of global change upon United States air quality

“…In the US, a combined effort between the Environmental Protection Agency and the academic community resulted in a set of modeling studies that adopted a variety of modeling methods (Hogrefe et al, 2004;Leung and Gustafson, 2005;Liang et al, 2006;Steiner et al, 2006;Tagaris et al, 2007;Liao et al, 2006;Adams, 2006, 2008;Huang et al, , 2008Nolte et al, 2008;Wu et al, 2008a, b;Chen et al, 2009b;Avise et al, 2009;Dawson et al, 2009). These US investigations based their current and future climate realizations on the results of GCMs using the various IPCC emissions scenarios (IPCC, 2007) projected to the 2050s.…”

Effects of temperature-dependent NO<sub>x</sub> emissions on continental ozone production

“…In contrast, there is little consensus about the mechanisms responsible for temperature-dependent changes in ozone concentrations in rural and remote environments. Arguments in favor of large-scale changes in atmospheric circulation and in favor of local changes in the chemical production and loss of ozone have both been presented (Barnes and Fiore, 2013;Steiner et al, 2006).…”