Grantee Research Project Results

Major activities of this research have been to further develop adjoint sensitivity and data assimilation tools and to use them in novel applications directed at reducing the uncertainties in ambient BC distributions and their associated environmental impacts, and in better informing decision makers. To illustrate the later point, we have conducted full-year global adjoint calculations in GEOS-Chem for speciated aerosol emissions sensitivities, direct radiative forcing (globally and in four latitude bands), and population-weighted concentrations. Simulations have employed present-day and RCP 2050 emissions scenarios to support development of emissions elasticity curves. From these, we have calculated radiative forcing metrics, including Forcing Amplifier and Emissions Reduction Efficiency by sector and region, for all megacities. A key result has been identifying locations and sectors where global, regional, and Arctic radiative forcing and warming are orders of magnitude more sensitive to emissions reductions than global population-weighted PM_2.5 (Figure A). We have thereby, for the first time, identified regions and activities where air quality improvements can be considered a co-benefit to mitigating SLCF by aerosols. 

 

 

To more comprehensively calculate climate impacts, we added latitudinal parameterizations of speciated aerosol indirect radiative forcing and radiative effects of black carbon on snow. We further calculated air pollution impacts on premature mortalities using five concentration-response functions. We also analyzed megacity sectoral contributions in economic context, considering sectoral contributions to GDP estimates from Brookings Institute Global MetroMonitor and PWC Global City GDP rankings. Key findings include a global assessment of emissions reduction efficiency for BC and SO2 (Figure B). We plan a regional application in Asia building on emissions sensitivity results from Zhang et al. (2014), which will identify the impacts of emissions uncertainties on policy-relevant metrics findings and assess the roles of megacities at higher spatial and temporal resolution. 

 

 

Work also hasadvanced on building and applying the WRF-Chem adjoint. The duel role of BC in air quality and weather/climate motivated the development of sensitivity analysis for the coupled WRF-Chem model. Our goal for this aspect of the project is to provide capability for sensitivity studies and 4D variational data assimilation (4DVar) for WRF-Chem. We have developed tangent linear (TL) and adjoint (AD) components for critical subgrid-scale mechanisms, including emissions, dry deposition, BC aging, PBL mixing, two land surface models (LSM), and two surface layer models. AD and TL versions of cumulus convection are can be included once a chemical tracer is added to the forward model. The AD enables a user to track the sensitivity of a receptor backwards in time to emission sources. The TL model additionally enables incremental 4D-Var data assimilation by calculating the affect of perturbing emissions on modeled observation values. 

 

We have also advanced the capabilities to assimilate pm and AOD into the a comprehensive version of WRF-Chem by building the adjoint of various WRF-Chem modules that handle aerosol feedbacks to meteorology, including the aerosol mixing-activation and a microphysics parameterization that deal with indirect effects, and the radiation and optical properties routines used in the direct and semi-direct interactions. These components have been added to the operational Gridpoint Statistical Interpolation (GSI) tool, which is being used in assimilation studies designed to produce optimized fields of PM2.5 and BC for use in subsequent studies. These tools have been used in a series of studies related to improving the analysis state of PM via assimilation of mutliwavelength AOD from polar orbiting (Saide et al., 2013 ) and geostationary (Saide et al., 2014b) satellites, in improving biomass burning emission estimates (Saide et al., 2014c) and in investigating the impact of smoke on severe storms (Saide et al., 2014a).