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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D24306, doi:10.1029/2005JD005908, 2005

Net radiative forcing due to changes in regional emissions of tropospheric ozone precursors

Vaishali Naik

Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, New Jersey, USA


Denise Mauzerall

Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, New Jersey, USA
Department of Geosciences, Princeton University, Princeton, New Jersey, USA


Larry Horowitz

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


M. Daniel Schwarzkopf

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


V. Ramaswamy

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


Michael Oppenheimer

Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, New Jersey, USA
Department of Geosciences, Princeton University, Princeton, New Jersey, USA


Abstract

The global distribution of tropospheric ozone (O3) depends on the emission of precursors, chemistry, and transport. For small perturbations to emissions, the global radiative forcing resulting from changes in O3 can be expressed as a sum of forcings from emission changes in different regions. Tropospheric O3 is considered in present climate policies only through the inclusion of indirect effect of CH4 on radiative forcing through its impact on O3 concentrations. The short-lived O3 precursors (NO x , CO, and NMHCs) are not directly included in the Kyoto Protocol or any similar climate mitigation agreement. In this study, we quantify the global radiative forcing resulting from a marginal reduction (10%) in anthropogenic emissions of NO x alone from nine geographic regions and a combined marginal reduction in NO x , CO, and NMHCs emissions from three regions. We simulate, using the global chemistry transport model MOZART-2, the change in the distribution of global O3 resulting from these emission reductions. In addition to the short-term reduction in O3, these emission reductions also increase CH4 concentrations (by decreasing OH); this increase in CH4 in turn counteracts part of the initial reduction in O3 concentrations. We calculate the global radiative forcing resulting from the regional emission reductions, accounting for changes in both O3 and CH4. Our results show that changes in O3 production and resulting distribution depend strongly on the geographical location of the reduction in precursor emissions. We find that the global O3 distribution and radiative forcing are most sensitive to changes in precursor emissions from tropical regions and least sensitive to changes from midlatitude and high-latitude regions. Changes in CH4 and O3 concentrations resulting from NO x emission reductions alone produce offsetting changes in radiative forcing, leaving a small positive residual forcing (warming) for all regions. In contrast, for combined reductions of anthropogenic emissions of NO x , CO, and NMHCs, changes in O3 and CH4 concentrations result in a net negative radiative forcing (cooling). Thus we conclude that simultaneous reductions of CO, NMHCs, and NO x lead to a net reduction in radiative forcing due to resulting changes in tropospheric O3 and CH4 while reductions in NO x emissions alone do not.

Received 22 February 2005; accepted 6 October 2005; published 24 December 2005.

Keywords: tropospheric ozone; radiative forcing; precursor emissions.

Index Terms: 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0478 Biogeosciences: Pollution: urban, regional and global (0345, 4251); 0485 Biogeosciences: Science policy (6620).

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Citation: Naik, V., D. Mauzerall, L. Horowitz, M. D. Schwarzkopf, V. Ramaswamy, and M. Oppenheimer (2005), Net radiative forcing due to changes in regional emissions of tropospheric ozone precursors, J. Geophys. Res., 110, D24306, doi:10.1029/2005JD005908.