2007 Progress Report: Global Change and Air Pollution (GCAP) Phase 2: Implications for U.S. Air Quality and Mercury Deposition of Multiple Climate and Global Emission Scenarios for 2000-2050

EPA Grant Number: R833370
Title: Global Change and Air Pollution (GCAP) Phase 2: Implications for U.S. Air Quality and Mercury Deposition of Multiple Climate and Global Emission Scenarios for 2000-2050
Investigators: Jacob, Daniel J. , Byun, Daewon , Fu, Joshua , Mickley, Loretta J. , Rind, David , Seinfeld, John , Streets, David G.
Institution: Harvard University , Argonne National Laboratory , California Institute of Technology , NASA Goddard Institute for Space Studies , University of Houston , University of Tennessee - Knoxville
EPA Project Officer: Chung, Serena
Project Period: May 1, 2007 through April 30, 2011
Project Period Covered by this Report: May 1, 2007 through April 30, 2008
Project Amount: $900,000
RFA: Consequences of Global Change For Air Quality (2006) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Climate Change , Air


The objective of GCAP Phase 2 is to better quantify and understand the effects of global change on air quality and mercury deposition in the United States over the coming decades. As the United States tightens its controls on domestic emissions, we need to determine how external perturbations associated with global change may affect the success of these controls. Such external perturbations include changes in climate (driven in particular by greenhouse gas emissions) and changes in pollutant emissions outside North America. We will apply the coupled global-regional model capability developed under GCAP Phase 1 to address three critical issues over the 2000-2050 time horizon: (1) assessment of the potential range of global change impacts on air quality through consideration of multiple scenarios, (2) intercontinental transport of pollution, and (3) mercury deposition to ecosystems, including the role of climate change in perturbing the cycling of mercury between the atmosphere and surface reservoirs.

Progress Summary:

In Liao et al. [2007], we validated present-day surface aerosol concentrations calculated by the GCAP model. The GCAP model consists of the chemical transport model GEOS-CHEM driven by meteorology archived from the GISS GCM III. The model reproduces fairly well the observed concentrations of sulfate, black carbon (BC), organic carbon (OC), nitrate, and PM2.5, with biases from +75% to -50%. Isoprene is predicted to contribute about half of the biogenic secondary organic aerosol (SOA) burden over the United States, with the rest explained by the oxidation of terpenes. On an annual basis, SOA is predicted to contribute 10–20% of PM2.5 mass in the Southeast, as high as 38% in the northwest and about 5–15% in other regions, indicating the important role of SOA in understanding air quality and visibility over the United States.
In Wu et al. [2008], we again used GCAP to investigate the effects of 2000-2050 global change in climate and emissions (IPCC 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 examined separately and then together the effects of changes in climate and in anthropogenic emissions of ozone precursors. We found 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%, mostly due 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.

In Pye et al. [ms. in preparation],  we performed global simulations of sulfate, nitrate , and ammonium aerosols for the present-day and 2050 using the GCAP model. Changes in climate and emissions projected by the IPCC A1B scenario were imposed separately. Climate change alone is predicted to decrease annually averaged levels of sulfate and ammonium in the Southeast, but increase the levels of these aerosols in the Midwest and Northeast. Nitrate concentrations, on the other hand, are expected to decrease across the United States as a result of climate change. Changes in ventilation, precipitation, oxidant levels, and temperature are the most important factors influencing aerosol levels, although changes in the boundary layer depth, cyclone frequency, and vertical transport also contribute. We found that changes in inorganic aerosol levels due to simultaneous emissions and climate changes are similar to those resulting from changes in emissions alone. Domestic sulfate concentrations are projected to decrease due to SO2 emissions reductions, and nitrate concentrations are predicted to increase due to higher ammonia emissions combined with decreases in sulfate. Global burdens of ammonium and sulfate are predicted to increase as a result of emissions changes, regardless of climate change. Considering both emissions and climate changes, ammonium increases from 0.24 Tg to 0.36 Tg, and sulfate increases from 0.28 Tg S to 0.40 Tg S. The nitrate burden, however, is predicted to remain essentially constant at 0.35 Tg as a result of the competing effects of higher precursor emissions and increased temperature.

Also in year one of GCAP phase 2, we worked on the development of future global mercury emissions. This task has never been done before, due to the difficulties of combining mercury emission characteristics with global forecasts. We are tackling this project by building on two previous projects. The first consisted of the development of a forecasting capability for carbonaceous aerosols. The second consisted of the development of a present-day mercury emission inventory for China that addressed some of the emission characteristics of unconventional and inefficient sources. To calculate future mercury emissions, we first developed a global mercury inventory for 1996, the base year of our previous BC/OC inventory. The second step of the process was to update the 1996 inventory to 2006 to give a more current representation of emissions and also to make the inventory congruent with the inventory presently being used in GEOS-Chem. This second step has also been completed. 

In year one, we also investigated issues of downscaling the GISS GCM meteorology with MM5.  We first developed an interface tool, “GISS2MM5,” which performs vertical interpolation, converting data from the hybrid sigma-pressure coordinates of the GISS GCM to the pressure coordinates of MM5. The GISS2MM5 tool also performs horizontal regridding, converting the latitude-longitude based GISS data to the map projection of MM5.  Since the GISS output has coarse resolution (5° x 4°), we use a 108-km grid as an intermediate step to the 36-km grid simulation. We perform four-dimensional data assimilation (FDDA),  using the grid nudging option in order to maintain dynamic consistency between GISS, the MM5 108-km simulation, and MM5 36-km simulation.  We are currently validating our downscaling methods.

Finally, we are now preparing 2050 emissions of ozone and aerosol precursors for use in the regional chemical model CMAQ.  Two preliminary CMAQ simulations have been completed, using (1) present-day emissions and present-day climate and (2) present-day emissions and 2050 climate.  For these simulations, we used GCAP boundary conditions for chemistry and meteorology.

Future Activities:

Our planned activities for Year 2 of GCAP, Phase 2 are as follows:

  • Finish global emission projections for mercury in the different IPCC SRES scenarios (Argonne)
  • Complete GISS GCM 1950-2050 simulations for the IPCC A2 and B2 scenarios; archive output for GEOS-Chem and MM5 (Harvard/ GISS)
  • Conduct GEOS-Chem ozone-aerosol simulations for the 2000 and 2050 GCM atmospheres for each IPCC scenario, interpret results, archive output for CMAQ (Harvard/ Caltech)
  • Conduct GEOS-Chem mercury simulations for the 2000 and 2050 GCM atmospheres (5-year ensembles) of each IPCC scenario, interpret results, archive output for CMAQ (Harvard)
  • Continue investigation of GISS-MM5 dynamical interface through stepwise downscaling; examine issues of tropopause height and strat-trop exchange (U Houston)
  • Finish CMAQ ozone simulations for the 2000 and 2050 GCM atmospheres, and begin CMAQ mercury simulations (U Tennessee)

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 52 publications 24 publications in selected types All 24 journal articles
Type Citation Project Document Sources
Journal Article Wu S, Mickley LJ, Leibensperger EM, Jacob DJ, Rind D, Streets DG. Effects of 2000-2050 global change on ozone air quality in the United States. Journal of Geophysical Research--Atmospheres 2008;113(D6):D06302 (12 pp.). R833370 (2007)
R833370 (2008)
R833370 (2009)
R833370 (Final)
R830959 (Final)
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  • Supplemental Keywords:

    chemical transport, volatile organic compounds (VOCs), nitrogen oxides, sulfates, organics, pollution prevention, environmental chemistry, modeling, climate models, tropospheric ozone, tropospheric aerosol, mercury, mercury deposition,, RFA, Scientific Discipline, Air, climate change, Air Pollution Effects, Environmental Monitoring, Ecology and Ecosystems, Atmosphere, air quality modeling, mercury deposition, Baysian analysis, climate models, atmospheric models

    Progress and Final Reports:

    Original Abstract
  • 2008 Progress Report
  • 2009 Progress Report
  • Final Report