A53F-01 INVITED
Description and status of the the AC&C Initiatives
To address issues specifically related to the interaction between chemistry and climate, a new initiative, "Atmospheric Chemistry and Climate Initiative" (AC&C), has been started up under the auspices of WCRP- SPARC (Stratospheric Processes and Their Role in Climate) and IGBP-IGAC (International Global Atmospheric Chemistry Project). The goal of AC&C is to improve our understanding of the processes involved in atmospheric chemistry-climate interactions and specifically to improve their representation in models. The initial approach to doing this is by helping the scientific community to define a common set of scientific themes and facilitating their execution. Four initial projects have been defined by the modeling community with the idea that they would serve as overarching themes that could be implemented through existing bodies, such as the Chemistry-Climate Model Validation activity of SPARC (CCM-Val), the global Aerosol model inter-Comparison (AeroCom), the European ACCENT project Model Inter-comParison (ACCENT-MIP), and the HTAP project (Hemispheric Transport of Atmospheric Pollutants). In addition, AC&C is relying on a newly created body (TropChem) that focuses on scientific issues around tropospheric chemistry. This presentation will describe these 4 initial projects and provide updates on their respective status. In addition, we will provide a brief description of the role structure and forthcoming goals of TropChem
A53F-02
Hindcasts of Chemistry and Aerosols: Results and Plans
Predictions of chemistry-climate interactions under climate change scenarios rely on large numerical models. As part of the Atmospheric Chemistry and Climate (AC&C) initiative we propose a coordinated exercise to provide guidance for the interpretation of these predictions. This exercise will initially be based on a series of hindcast simulations of the last 20-25 years which emphasize the prediction of tropospheric chemistry and aerosols (AC&C Activity 1). We propose a process oriented evaluation of these simulations along with discussion and coordinated analysis of the results. Here we present i) plans for implementing these simulations and ii) results of hindcast simulations using the Model of Ozone and Relate Trace Species (MOZART). The latter simulations consisted of two 40 year hindcasts, where MOZART was either driven by winds from the National Center for Environment Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis or from a General Circulation Model (the Community Atmosphere Model version 3, CAM3). We compare differences and similarities in these set of simulations. Sensitivity studies suggest that for many chemical species the short term variability driven by recent fluctuations in climate scales similarly to the long term variability from climate change scenarios. This suggests that future chemical changes due to climate change can be assessed from current climate simulations.
A53F-03
North Pacific Marine Tropospheric Ozone Concentrations at the West Coast of North America: Evaluation of Long-Term Trends
Activity 1 of the WCRP-SPARC and IGBP-IGAC initiative - Atmospheric Chemistry and Climate - comprises a 20- 25 year hindcast of tropospheric ozone and aerosols, This activity intends to address the following questions: Can we understand what has happened with tropospheric chemistry, and in particular ozone and aerosols? Can we replicate the observed changes over the past 20 years? For this activity to be successful, it is critical that the observed changes must be clearly and accurately defined. However, the observational record is not as extensive as would be desired, and some contradictory conclusions have been reached. These issues are particularly acute for the North Pacific region, which lies downwind of the Asian continent with its rapidly increasing emissions of ozone and aerosol precursors. This presentation will review the available data sets that can illuminate temporal trends of the tropospheric ozone concentrations in the marine air entering North America from the North Pacific, with a particular focus on springtime. The derived long-term temporal trends will be examined for confounding effects from North American influences, statistical significance, and consistency across the available data sets. The derived trends will be compared with those observed at the west coast of Europe, an analogous location that receives marine air from the North Atlantic, which is downwind from the large North American emission sources.
A53F-04
Tracer Transport by Deep Convection: Implications of the Connection Between Convective Mass Fluxes and Large-Scale Circulations
Global chemistry-transport models (CTMs) generally simulate vertical tracer transport by deep convection separately from the advective transport due to large-scale mean winds, even though a component of the large-scale transport, for instance in the Hadley and Walker cells, occurs in deep convective updrafts. This split treatment of vertical transport can have several significant implications for CTM simulations, such as numerical diffusion, misinterpretation of the transport characteristics in convectively active regions, and underestimation of the effects of convective tracer transport on ozone and other gases. Here we show that there is a significant overlap between the convective and large-scale advective vertical transport fluxes in the CTM MATCH, and discuss the main implications for tracer transport studies which can be expected due to this. We also give an outlook to the next step of this study, in which we are examining the connection between diagnosed convective mass fluxes and the vertical fluxes in the tropical Hadley and Walker Cells using the ECHAM5/MESSy GCM, which is set up with a flexible framework allowing the use of several different convection parameterizations. From the direct comparison of multiple deep convection parameterizations within the same model we expect to gain a better sense of the relationship between parameterized deep convection and large-scale circulations, as well as of the present uncertainty due to differences in convection parameterizations. This work is anticipated to contribute to the objectives of Activity 2 (vertical tracer distributions) of AC&C.
A53F-05
Effect of chemistry-aerosol-climate coupling on global predictions of future climate and future levels of tropospheric ozone and aerosols
Radiative forcing from changing aerosols and tropospheric ozone has the potential to modify climate effects of greenhouse gases, especially regionally. Ozone and aerosols also interact tightly through tropospheric chemical processes, which themselves will be affected by future climate change. In this study we investigate the extent to which chemistry-aerosol-climate feedbacks affect the ultimate levels of year 2100 ozone and aerosols as well as the climate response to changes in long-lived greenhouse gases, tropospheric ozone, and aerosols over 2000- 2100. We simulate tropospheric ozone-NOx-hydrocarbon chemistry and sulfate, nitrate, ammonium, black carbon, primary organic carbon, and secondary organic carbon aerosols online in the Goddard Institute for Space Studies (GISS) general circulation model II'. Year 2100 CO2 concentration as well as the anthropogenic emissions of ozone precursors and aerosols/aerosol precursors are based on IPCC scenario A2. Results indicate that chemistry-aerosol-climate coupling is influential on predicted future ozone and aerosols and consequently on simulated year 2100 climate. For example, as compared to year 2100 climate simulated using offline ozone and aerosol fields calculated based on present-day climate and year 2100 emissions (a commonly used approach in previous studies), predicted year 2100 surface-layer temperatures in the fully coupled simulation are higher over populated areas as a result of regionally higher ozone and aerosol (especially BC) concentrations; changes in temperature there relative to year 2000 are 10-30% higher in the coupled climate simulation if aerosols are internally mixed. Sensitivity studies are performed to identify some key coupling processes in predicting future ozone, aerosols, and climate.
A53F-06
Measuring the seasonal cycle of H2 and its stable isotope HD
The goal of the EUROHYDROS project is to improve our understanding of the atmospheric cycle of H2 in order to identify and quantify the possible effects of the introduction of a hydrogen economy on global climate. For this reason, the various sources and sinks contributing to the global budget, the seasonal cycles and the inter- hemispheric gradient are studied by performing H2 and stable isotope measurements at different sites distributed over Europe and the Atlantic meridian. Global models will be employed to assess the global budget and possible climate effects. This work presents the first measurement results and interpretation of the seasonal isotopic variability over the Atlantic meridian and West-to-East European transect. The results were obtained using online Isotope Ratio Mass Spectrometry combined with a novel technique to separate hydrogen from the main constituents of air, recently developed by Rhee et al., 2003.
A53F-07
Interactions between trace gases, aerosols, and clouds in polluted troposphere: preliminary results from field studies in spring and summer 2007 at Mt Tai in central-eastern China
As part of China's National Basic Research Project (National '973 Project) on sulfur and acid deposition, a large suite of trace gases, aerosols (physical and chemical properties), and cloud water composition were measured in the spring and summer of 2007 at the summit of Mount Tai, the highest mountain (1534 m above the sea level) in the polluted central-eastern plains of China. The main objective was to study the chemical transformation of trace gases and aerosols and their interactions with clouds under conditions of high SO2 and particulate matter. We report here the preliminary results from the two-phase measurements. High concentrations of trace gases and aerosols were observed during the spring phase. Two major dust events were observed in the end of March with the PM10 concentration reaching > 1500 £gg/m3 at the mountain top. Pollution plumes with SO2 of 40-60 ppbv were frequently observed during the spring study indicating strong transport of surface pollution to the upper Planetary Boundary Layer and the free troposphere. Cloud water acidity showed a vary large variation ranging from very acidic to basic, with high concentrations of ions such as sulfate, nitrate, ammonia and calcium. The data in the two seasons will be compared to show the influence of dust and photochemical processes on the chemical composition, and the budget of reactive nitrogen and the ozone production efficiencies will be examined. The relationship between major trace gases, aerosols, and cloud water composition will also be shown.
A53F-08
An Integrated Approach to Economic and Environmental Aspects of Air Pollution and Climate Interactions
Emissions of greenhouses gases and conventional pollutants are closely linked through shared generation processes and thus policies directed toward long-lived greenhouse gases affect emissions of conventional pollutants and, similarly, policies directed toward conventional pollutants affect emissions of greenhouse gases. Some conventional pollutants such as aerosols also have direct radiative effects. NOx and VOCs are ozone precursors, another substance with both radiative and health impacts, and these ozone precursors also interact with the chemistry of the hydroxyl radical which is the major methane sink. Realistic scenarios of future emissions and concentrations must therefore account for both air pollution and greenhouse gas policies and how they interact economically as well as atmospherically, including the regional pattern of emissions and regulation. We have modified a 16 region computable general equilibrium economic model (the MIT Emissions Prediction and Policy Analysis model) by including elasticities of substitution for ozone precursors and aerosols in order to examine these interactions between climate policy and air pollution policy on a global scale. Urban emissions are distributed based on population density, and aged using a reduced form urban model before release into an atmospheric chemistry/climate model (the earth systems component of the MIT Integrated Global Systems Model). This integrated approach enables examination of the direct impacts of air pollution on climate, the ancillary and complementary interactions between air pollution and climate policies, and the impact of different population distribution algorithms or urban emission aging schemes on global scale properties. This modeling exercise shows that while ozone levels are reduced due to NOx and VOC reductions, these reductions lead to an increase in methane concentrations that eliminates the temperature effects of the ozone reductions. However, black carbon reductions do have significant direct effects on global mean temperatures, as do ancillary reductions of greenhouse gases due to the pollution constraints imposed in the economic model. Finally, we show that the economic benefits of coordinating air pollution and climate policies rather than separate implementation are on the order of 20% of the total policy cost.