Effects of 2000–2050 changes in climate and emissions on global tropospheric ozone and the policy‐relevant background surface ozone in the United States

Shiliang Wu,Daniel J Jacob,David Rind,David G Streets,Loretta J Mickley

doi:10.1029/2007jd009639

Abstract

We use a global chemical transport model (GEOS‐Chem) driven by a general circulation model (NASA Goddard Institute for Space Studies GCM) to investigate the effects of 2000–2050 global change in climate and emissions (the Intergovernmental Panel on Climate Change A1B scenario) on the global tropospheric ozone budget and on the policy‐relevant background (PRB) ozone in the United States. The PRB ozone, defined as the ozone that would be present in U.S. surface air in the absence of North American anthropogenic emissions, has important implications for setting national air quality standards. We examine separately and then together the effects of changes in climate and anthropogenic emissions of ozone precursors. We find that the 2000–2050 change in global anthropogenic emissions of ozone precursors increases the global tropospheric ozone burden by 17%. The 2000–2050 climate change increases the tropospheric ozone burden by 1.6%, due mostly to lightning in the upper troposphere, and also increases global tropospheric OH by 12%. In the lower troposphere, by contrast, climate change generally decreases the background ozone. The 2000–2050 increase in global anthropogenic emissions of ozone precursors increases PRB ozone by 2–6 ppb in summer; the maximum effect is found in April (3–7 ppb). The summertime PRB ozone decreases by up to 2 ppb with 2000–2050 climate change, except over the Great Plains, where it increases slightly as a result of increasing soil NOx emission. Climate change cancels out the effect of rising global anthropogenic emissions on the summertime PRB ozone in the eastern United States, but there is still a 2–5 ppb increase in the west.

Highlights

Surface Ozone in the United States [26] Figure 2 shows the natural summer afternoon ozone levels in surface air for the 2000 climate
We find that climate change decreases mean ozone levels in the lower troposphere by up to 8%, especially in the tropics and Northern Hemisphere. This decrease reflects the shorter lifetimes of ozone and of peroxyacetylnitrate (PAN), a low-temperature NOx reservoir produced from NOx-nonmethane VOCs (NMVOCs) chemistry that provides a major source of NOx to the remote atmosphere [Wang et al, 1998]
This effect is compounded in the southeast by increasing biogenic isoprene emissions (Table 2b), which leads to net ozone destruction under low-NOx conditions [Sillman et al, 1990; Fiore et al, 2005; Wu et al, 2008]

Summary

Introduction

[2] Surface ozone is a toxic air pollutant. As of 2003 – 2005, 157 million people in the United States lived in areas exceeding the ozone National Ambient Air Quality Standards (NAAQS) of 0.08 ppm (8-h average, not to be exceeded more than 3 times per year) [U.S Environmental Protection Agency (EPA), 2007]. [7] In previous work we used a global chemical transport model (GEOS-Chem CTM) driven by meteorological fields from a general circulation model (NASA/GISS GCM 3) to investigate the effects of 2000 – 2050 global changes in climate and anthropogenic ozone precursor emissions (A1B scenario) on ozone air quality in the United States [Wu et al, 2008]. We apply this model here to study the effects on global tropospheric ozone, natural background ozone, and intercontinental transport of ozone pollution to the United States. Reference Johnson et al [1999] Stevenson et al [2000]g Stevenson et al [2000]g Stevenson et al [2000]g Zeng and Pyle [2003]g Hauglustaine et al [2005]

Various

Background

Findings

Conclusions