Canadian Smog Science Assessment Highlights and Key Messages: chapter 10

Recommendations for Future Research

• Health Effects
• Environmental Effects
• Emissions
• Monitoring and Trend Analysis
• Understanding of Processes
• Modelling

Health Effects

Sources/components--Research directed at source characterization, exposure, epidemiology, and toxicology of the different fine particulate matter (PM) components, properties and sources that may be more strongly related to health effects would reduce the uncertainties in estimating risks associated with exposure to PM.

Size fractions--Although effects of the coarse PM₁₀ size fraction are likely less than those seen in the 2.5 µm range, it is not clear if the risk management of PM_2.5 would account for PM₁₀ related effects, and thus continued investigation of such effects is warranted. For the ultra fine fraction, more precise exposure-response studies are revealing significant effects but more work is needed to determine the relative toxicity and health impacts of ultra fine particles versus other particles. As well, because the standard monitoring system does not represent this fraction well, specific studies to understand source-exposure relationships are also necessary.

Exposure--Additional research into personal and population exposures to PM and ozone (O₃), especially under conditions relevant to Canada, would enhance our understanding of exposure and the interpretation of the epidemiological evidence for these pollutants. Work could be directed at investigating the extent of exposures to various PM components and size fractions, as well as the determinants of these exposures, including source contributions, personal attributes and activities, and building-related factors. Further work to address the size of the measurement error introduced by the difference between concentrations at a central monitor and actual pollutant exposures would help in evaluating the associated error in the risk estimates of pollutant effects in epidemiological studies.

Concentration-response relationship--Further research into concentration-response functions for air pollution related morbidity and mortality, including studies at the relatively low ambient levels of PM_2.5 and O₃ measured in Canada, with a wider range of health endpoints, and (as more information becomes available) fine PM components and sources would serve to reduce uncertainties in characterizing risk.

Role of co-pollutants in health effects--Research focused on furthering our understanding in this area would inform our ability to discern the effects of these substances in the broad mix of ambient pollutants and help to direct risk management of ambient air pollution sources.

Exposure durations of concern--While there are a few studies which specifically address this subject, they do not cover most endpoints of concern, nor do they cover all the possible time frames of concern. Since toxicological studies indicate potential effects running the full gamut of ultra acute to chronic timeframes, further research to examine human responses in the field and in controlled settings is warranted and could provide additional time frames relevant for risk management. Research examining the very short time course events related to inflammatory mechanisms and especially as relates to cardiac events would be highly useful. Longitudinal studies of health outcomes in relation to chronic exposures to these pollutants have the potential to yield particularly valuable information on the health effects of air pollution. Such studies should also attempt to incorporate design features which would provide information on the degree to which air pollution plays a role in the instigation and progression of disease.

Inflammation/oxidation and range of effects--Since these mechanisms appear to be one of the fundamental aspects of the health effects of both PM and O₃, research to better understand the processes, especially but not solely related to those with pre-existing disease or susceptibilities is warranted. Given the recent appearance of more novel disease endpoints in the air pollution literature (e.g., appendicitis, bowel diseases), examination of existing cohorts for inflammatory diseases could provide new and important insights as to the impact of air pollution.

Susceptible populations--As we move towards the development of risk management tools for individuals [i.e., such tools as the Air Quality Health Index (AQHI)], the understanding of the susceptibility of specific sub-groups of the population is warranted in order to provide more targeted messaging, and to provide better estimates of how air pollution affects quality of life. As well, the appearance of information indicating that those with specific genetic makeup are more susceptible to air pollution (but are otherwise perfectly healthy) warrants considerable attention in order to better understand how such genetic factors influence susceptibility and overall population health impact. 

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Environmental Effects

Further research on exposure-response relationships for Canada-relevant plant species is recommended. This could entail a meta-analysis (combination of data from several studies to produce a single estimate) of existing information and the development of indices predicting dose-response functions for plant species that have not been directly investigated based on previously established plant O₃ sensitivities. The use of an O₃ flux approach to estimate plant uptake, in particular the quantification of plant defences to O₃ damage, is recommended for North American species and environments.

Continued studies of the linkages between O₃ and other pollutants (e.g., atmospheric carbon dioxide) in the context of impacts to forest growth and productivity are recommended. In addition, further research on the effects of PM and O₃ on an ecosystem level would better evaluate the broader ecosystem risks associated with PM and O₃ exposure to sensitive or endangered species, as well as the impacts on wildlife species.

Moving ahead, there is a need for more Canadian-based primary valuation research on the negative effects of smog on ecosystems. Further research into both the scientific basis underlying physical drivers of the impact of smog and how these impacts are valued by Canadians will help formulate effective smog abatement policies. There is a need to develop a framework capable of capturing non-linear relationships among emissions, air quality and impacts on humans and the environment through an integrated assessment approach with greater coordination among the various fields of expertise.

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Emissions

Improving the spatial and temporal quantification of precursor emissions would serve to resolve some of the discrepancies between measured ambient levels of smog and precursors and emissions inventories. Areas that would benefit from additional work include the identification and quantification of source regions of intercontinental transport (e.g., Asia), of sources and species of natural and anthropogenic primary PM_2.5 and volatile organic compounds (VOC) emissions, of sources of mobile emissions (e.g., aviation, rail, biodiesel) such as through the use of PM_2.5 compounds that mark specific emission sources. Historical emissions inventories and current non-point source emissions estimates need refinement. The latter is important in air quality model applications as it is often difficult to reconcile observed values with current emissions estimates (e.g., open sources of PM from road dust, agriculture, construction and mining).

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Monitoring and Trend Analysis

As PM and O₃ precursor emissions continue to decline in North America, the influence of background PM and O₃ concentrations on local air quality may become increasingly important. Additional measurements, particularly for PM_2.5 at remote (or background), high-elevation, and Arctic sites are recommended. In addition, further research is recommended to understand the contribution of intercontinentally transported pollutants to ambient concentrations in Canada. The establishment of more PM_2.5 speciation sites across Canada would facilitate tracking the fraction of chemicals transported from other continents to determine which play the largest role in contributing to local PM_2.5 concentrations.

Measurement sites are recommended near roads to better track motor vehicle emissions as these appear to dominate observed ambient PM and O₃ precursors and can provide a platform to carry out special studies. A sampling shortcoming is the bias in nitrogen oxides (NO_X) measurements, leading to over-prediction of NO_X in rural areas, and which needs to be quantified through urban/rural sampling of NO_X and other nitrogen species.

Carefully designed long- and short-term studies, which may include measurements of compounds that mark specific emissions sources, are required to minimize some of the discrepancies between emission inventory estimates and observations of ambient PM and VOC (both anthropogenic and natural). Considerable opportunity exists to extend remote sensing applications currently being developed elsewhere to Canadian-specific objectives to improve observations of surface air quality, provide constraints on emissions and track long range transport.

To understand the role of ammonia (NH₃) in PM formation, especially as emissions of other precursors are expected to decline, more measurements of NH₃ and PM are recommended in areas downwind of agriculturally intensive areas both in Canada and the U.S. This is required in order to investigate the sensitivity of PM_2.5 to changing NH₃ emissions as well as to quantify the transboundary flow of these emissions.

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Understanding of Processes

There is a continued need to increase the understanding of processes affecting smog formation, as these feed into air quality models used to assess the impacts of proposed risk management measures. A combination of both field and laboratory studies along with integrated analyses of existing monitoring data are required to elucidate these non-linear chemical, physical and meteorological processes. In particular, these include the role of different VOC species, sea salt, local meteorology, local atmospheric chemical composition, cloud, urban, and coastal influence on smog formation. As well, there is a need to better characterize local/regional scale processes for inclusion into higher spatial resolution air quality models for human exposure assessments.

Further research is needed to better understand the relationship between O₃, sulphur, dust and organic matter during intercontinental transport for better integration of global results into a regional modelling system to assess the intercontinental influence in more detail.

Atmospheric turbulence plays a key role in influencing air pollutant concentrations, yet the mechanisms of turbulence in urban settings are still being studied. Further observations and evaluation of models of turbulence are required to improve accuracy in air pollution model simulation, particularly in urban and shoreline environments.

Finally, systematic studies tailored to specific smog formation processes of importance at a regional-scale at adequate resolution are needed, while simultaneously accounting for both climate change and changing regional emissions.

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Modelling

As scenario analyses become increasingly relied upon, continued efforts to develop and evaluate air quality models will help improve their accuracy and increase confidence in the guidance provided by scenario studies. In particular, the improvement in model representations of emissions sources and the processes affecting the production of secondary aerosols is needed. Model development and evaluations are dependent on the availability of pertinent observational data of O₃, PM_2.5 mass, and the chemical composition of PM_2.5 and other important precursors from monitoring and field studies. These data, along with satellite based observations, can also be assimilated into models for improving forecasts and correspondingly, improve emissions estimates through inverse modelling. Continued research into these methods is recommended.

The influence of individual emissions source sectors on ambient PM and O₃ levels on a national scale, as estimated by modelling scenarios, needs to be verified and in some cases further investigated through more comprehensive studies. Aside from sources already routinely monitored and for which emissions data are available, approaches to include intermittent sources (e.g., wildfires, wind, dust) in model analyses should also be considered. The significance of these sources will likely increase as precursor emissions are reduced and climate change influences become more pronounced.

Studies where models can exchange information interactively between global, regional and local scales are also recommended to obtain complete spatial information on air quality, including the background influence and better quantification of the influence of point sources, local sources and smog formation processes.

A number of model evaluation approaches are available, including operational evaluation (comparison of model prediction against routine monitoring data), dynamic evaluation (model response to changes in meteorology or emissions) and diagnostic evaluation (simulation of atmospheric processes), all of which require continued development. The latter two are of particular importance in ensuring model credibility when evaluating emission control scenarios. Probabilistic modelling approaches based on uncertainties in model inputs and formulations should also be considered for assessing model uncertainties in forecasting and policy applications.

Models are currently the best available means of estimating the effects of climate change on air quality. There have been relatively few studies simulating both climate change and air quality, and additional work is needed in this area. An integral part of characterizing the impact of climate change will be initially to understand the inherent variability induced by year-to-year changes in meteorology. The development of multi-year air quality simulations to characterize inter-annual variability is especially important in the investigation of the potential influence of climate change on the conclusions drawn from modelling analyses evaluating the efficacy of proposed emissions regulations. Furthermore, multi-year simulations would enable the assessment of incremental emissions reductions and associated effects over a number of years rather than all at once as currently simulated. Multi-year simulations are also needed to characterize the inter-annual variability of trans-Pacific transport.