Air Pollution as a Climate Forcing: A Workshop
Day 5 Presentations
Investments with Multiple Payoffs: Cross-Cutting Research Implications
Gregory R. Carmichael
Center for Global and Regional Environmental Research, Dept. Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA, U.S.A.
You may download a MS PowerPoint version (770 MB) of this presentation.
Climate change, air quality and human health share many commonalities that can serve to guide research directions. Perhaps the most obvious is the central role that combustion plays in forming the pollutants that serve as the agents for impacts. In each topic a basic understanding of the processes that link emissions to end points (e.g., radiative forcing, regional climate responses, air quality measures, human and ecosystem health, etc.) is required. Furthermore, in each area there exist fundamental gaps in our ability to quantify aspects of sources, sinks (e.g., removal mechanisms of particulates), and causative processes (e.g., to what extent is fine particulate mass a surrogate for health outcomes — is it the mass, or a constituent (trace metal), or a property (acidity)?).
It is important to try to identify what are the most important research challenges/needs in each of these areas. However it is also important to identify what research needs are common to climate change, air quality and human health problems. One way of identifying the common research needs is to frame specific examples of cross-cutting policy/decision questions and address them through Case Studies. Candidate Case Studies could include: 1) Diesel vs. gasoline as the choice of fuel for motor vehicles; 2) Biofuels or fossil fuels as the fuel of choice for domestic uses; 3) The relative importance of combustion for energy vs. combustion for other uses (e.g., land clearing) as a source of pollutants and the range of controllable options for each.
To what extent can we quantify the pluses and minuses of such choices as diesel or gasoline? Evaluation of such a choice requires a capability to quantify many different aspects of the problem; for example, the amount of black carbon produced by the transportation sector and these specific fuels in absolute amount and in relation to other sources, their spatial and temporal distribution, the relative amount of black carbon emitted by this sector and fuels compared to scattering aerosols such as sulfate, the extent to which BC aerosols have a different health response than other aerosol types, estimation of whether the presence of BC impacts the quality or quantity of other pollutants (e.g., do reactions on BC reduce photochemical smog production?), etc.
Several cross-cutting issues emerge for such analysis. Aerosols are of critical importance. From climate, health and air quality perspectives we need better characterization of emissions by fuels and by sector. Each share common modeling and measurement tools and techniques (with important differences such as the need for measurements near the surface where people breath (indoors and outdoors) from a health perspective, and away from the surface for climate purposes). Each will benefit from a better understanding of aerosol processes including: increased attention to number distribution and chemical composition; need to characterize organic fraction by function, property (e.g., limited utility of unspeciated VOC in a chemical evaluation); improvements in utilization and tools (e.g., models and inventories) to support interpretation of data from new instruments such as single particle measurements; increased understanding of tropospheric NH3 (measurements, emissions); improvements in fundamental physical, chemical, optical properties of aerosols and mixtures in relation to mixing state, RH, etc.); and a better understanding of biological components of ambient aerosols.
There is also a need for better connections between health, air quality, and climate communities. Activities needed to enable a more complete analysis across problems include:
- Effects of ozone in health outcomes. Air quality analysis is based heavily on ozone as a pollutant and compliance with air quality standards. In cost/benefit frameworks we can evaluate health outcomes (mortality and morbidity) for particles, but similar response functions are not available for ozone.
- Improved response functions for regions with specific and/or different source characteristics (biofuels, diesel, coal, ...). Response functions are mostly related to particulate mass in general and do not distinguish between fuel types. Studies done in areas with markedly different source profiles would help to identify fuel/sector attributes (if any).
- Climate and air quality metrics by source/sector to facilitate cross end-point evaluation/comparison. What metric should be used for climate end-points (GWP, radiative forcing, temperature response/unit emission)?
- Better understanding of confounding factors involving SOx, NOx, NH3, VOC, CH4, CO from the chemistry, technology, physics and health perspectives. We need to anticipate the enhancements and the off-sets. Examples include the conditions under which NOx reductions increase ozone, the extent to which technologies such as particulate traps decrease efficiencies and increase NOx emissions, the role of ammonia in determining whether total scattering by tropospheric aerosols decrease as sulfur emissions decrease (if sufficient ammonia, then nitrate may replace sulfate in the aerosol, if ammonia is limiting then changes in sulfate aerosol may not be proportional to decreases in sulfur emissions), effect on methane emissions of sulfur deposition on wetlands, etc.
Finally there is a need to coordinate/pursue studies that meet multiple objectives. For example, can a field experiment with the primary purpose of characterization of aerosol radiative forcing in a specific region, also provide information on source characterization or air quality data that meet needs of the air quality and health communities? Or can studies be designed from the front-end that focus on high priority cross-cutting questions. One example is the need to improve emission estimates of BC. Figure 1 shows the cross-cutting research needed to better constrain the emission estimates of this key aerosol.