2012 Progress Report: Source Attribution of Radiative Forcing in Chemical Transport Models

EPA Grant Number: R835211
Title: Source Attribution of Radiative Forcing in Chemical Transport Models
Investigators: Henze, Daven K
Institution: University of Colorado at Boulder
EPA Project Officer: Callan, Richard
Project Period: June 1, 2012 through May 31, 2014 (Extended to May 31, 2016)
Project Period Covered by this Report: June 1, 2012 through May 31,2013
Project Amount: $244,446
RFA: Source Attribution of Radiative Forcing in Chemical Transport (2011) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Air Quality and Air Toxics , Climate Change , Air


The project objective is to account for the radiative forcing impacts of aerosols and tropospheric ozone (O3) from changes to their precursor emissions owing to air quality and greenhouse gas policies. This will be accomplished through the following research tasks:
  1. quantify the impacts of emissions from each sector, in each model grid cell, on the global and regional radiative forcing of tropospheric O3 and aerosols.
  2. assess the radiative forcing consequences of emissions scenarios designed to target combinations of aerosol and greenhouse gas reductions.

Progress Summary:

In the first year of this project, we have assessed the radiative forcing of both aerosols and tropospheric ozone. For aerosols, we have used chemical transport model (GEOS-Chem) simulations to evaluate the preindustrial to present-day direct radiative forcing, and adjoint sensitivity analysis to apportion this radiative forcing to contributions from aerosol and aerosol precursor emissions (NH3, NOx, SO2, OC, and BC). For ozone, remote sensing data from the TES instrument aboard the Aura satellite are used to generate Instantaneous Radiative Kernels, which quantify the dependence of observed outgoing longwave radiation on observed O3 pro les. We have developed a method for combining these measurements with the GEOS-Chem adjoint model to quantify the instantaneous radiative forcing (i.e., not including long-term feedbacks on CH4) via tropospheric ozone from emissions of NOx, CO and non-methane VOCs. We now have completed a year-long assessment of the tropospheric ozone radiative forcing, which has allowed us to begin to explore the seasonal dependence of radiative forcing efficiencies of ozone precursor emissions.

In addition to considering global radiative forcing of aerosols and ozone, we have considered radiative forcing in four separate latitudinal bands. These bands (Arctic, Northern mid-latitudes, tropics, and Southern extra-tropics) have been identifi ed in recent studies that examined regional climate responses to forcing applied in these regions. We have found that estimates of the temperature change caused by a single ton of emitted aerosol precursor can be greater when considering regional climate sensitivities than when considering only global climate sensitivities by up to 30-50%, as much of the anthropogenic emissions are located in northern mid-latitudes, where the regional climate response to forcing is greater than the global mean. A similar analysis of tropospheric ozone radiative forcing is in progress.

We also have begun work on our fourth activity assessing the radiative forcing impacts of different emissions scenarios. First, we have repeated the global radiative forcing analysis for aerosols using the emissions projections for the year 2050 from the IPCC Representative Concentration Pathways (RCPs). We have found that accounting for changes in the chemical environment can critically alter radiative forcing projections. For example, the estimated radiative forcing of NH3 changes in the year 2050 depends not only on the NH3 emissions themselves, which are projected to increase in both China and India, but also the changing NOx emissions. In RCP 6.0, NOx emissions increase in China, whereas they increase more in India and decrease in China following RCP 2.6 projections. This modulates the radiative forcing of the NH3 emissions by facilitating formation of ammonium nitrate aerosol; consequently, the radiative forcing of enhanced NH3 emissions in India is much stronger in RCP 2.5 than 6.0.

Further, the global aerosol radiative forcing estimates have been used to estimate the radiative forcing of several scenarios for U.S. emissions following di fferent policies targeting air quality and climate mitigation. These are summarized in a manuscript by Akhtar, et al. (submitted), currently under revision for publication in ES&T.

Future Activities:

The remaining eff orts will focus on radiative impacts of emissions scenarios for air quality and greenhouse gas mitigation. The regional radiative forcing sensitivities will be combined with projected changes in emissions to estimate regional climate responses. Projected emissions changes will come from the IPCC RCP scenarios for global assessment. Following on the work of Akhtar, et al. (submitted), we also will consider additional emissions scenarios for the United States resulting from national scale emissions reductions following projections based on U.S. energy systems modeling under various constraints, such as total emissions caps or emissions fees on criteria pollutants and greenhouse gases.

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

Other project views: All 15 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Akhtar FH, Pinder RW, Loughlin DH, Henze DK. GLIMPSE:a rapid decision framework for energy and environmental policy. Environmental Science & Technology 2013;47(21):12011-12019. R835211 (2012)
R835211 (2013)
R835211 (2014)
R835211 (Final)
  • Abstract from PubMed
  • Full-text: Harvard University-Full Text PDF
  • Abstract: ES&T-Abstract
  • Other: ES&T-Full Text PDF
  • Supplemental Keywords:

    adjoint sensitivity, environmental policy, air quality regulations, fi ne particulate matter, climate change, remote sensing, greenhouse gases

    Progress and Final Reports:

    Original Abstract
  • 2013 Progress Report
  • 2014 Progress Report
  • Final Report