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Multimodel ensemble simulations of present-day and near-future tropospheric ozone

Stevenson, D S and Dentener, F J and Schultz, M G and Ellingsen, K and van Noije, T P C and Wild, O and Zeng, G and Amann, M and Atherton, C S and Bell, N and Bergmann, D J and Bey, I and Butler, T and Cofala, J and Collins, W J and Derwent, R G and Doherty, R M and Drevet, J and Eskes, H J and Fiore, A M and Gauss, M and Hauglustaine, D A and Horowitz, L W and Isaksen, I S A and Krol, M C and Lamarque, J F and Lawrence, M G and Montanaro, V and Muller, J F and Pitari, G and Prather, M J and Pyle, J A and Rast, S and Rodriguez, J M and Sanderson, M G and Savage, N H and Shindell, D T and Strahan, S E and Sudo, K and Szopa, S (2006) Multimodel ensemble simulations of present-day and near-future tropospheric ozone. Journal of Geophysical Research: Atmospheres, 111 (D8). -. ISSN 0747-7309

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    Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing "optimistic,'' "likely,'' and "pessimistic'' options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (+/-1 standard deviation) associated with these values is about +/-25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of -50, 180, and 300 mW m(-2), compared to a CO2 forcing over the same time period of 800-1100 mW m(-2). These values indicate the importance of air pollution emissions in short-to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by +/-5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000, and 550 Tg(O-3) yr(-1), respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O-3)) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NOx production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations.

    Item Type: Journal Article
    Journal or Publication Title: Journal of Geophysical Research: Atmospheres
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 49581
    Deposited By: ep_importer_pure
    Deposited On: 07 Sep 2011 11:47
    Refereed?: Yes
    Published?: Published
    Last Modified: 20 Mar 2018 05:20
    Identification Number:

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