Air pollutant exposure evidence review
A review of existing data on pollutant concentrations and demographic features, used to understand the strength of the evidence base on how the Scottish population is being exposed to outdoor concentrations of NO2, PM10, and PM2.5.
2 Approach
Research Questions
A series of research questions has been developed to help structure both the evidence review and the analysis of its outputs. These research questions have thus formed the basis of the project:
R1: What contemporary evidence exists which could inform the assessment of current exposure of the general population in Scotland to ambient concentrations of PM10, PM2.5 and NO2, in the context of the EU Limit Values and the Air Quality Targets and Objectives for Scotland?
R2: To what extent could this evidence base be used to assess population exposure to PM10, PM2.5 and NO2 in Scotland now and in the future?
R3: To what extent could this evidence base be used to track progress towards the achievement of an exposure reduction target, such as that in the revised EU Ambient Air Quality Directive or England’s Environmental Improvement Plan?
R4: To what extent could this evidence base be used to assess the variation in exposure for different demographic groups, such as those in more deprived communities or with protected characteristics?
R5: What are the key uncertainties, such as applicability to very low concentration situations or relationships to measurement uncertainty, and gaps with regards to the evidence base or its use?
R6: What does the project recommend in order to increase the coherence and utility of the evidence base, in the context of the outcomes of the questions above?
PM10 is covered within the review, although no exposure reduction target is currently being considered for this pollutant.
Methodology
The study identifies, collates, reviews, and interprets existing evidence on exposure levels to NO2, PM10 and PM2.5 in different geographic and demographic contexts across Scotland and comparable societies and geographies.
The project has been structured around three main tasks:
- Task 1 focused on identifying relevant sources of information.
- Task 2 was a review and appraisal of the information identified during Task 1 and sought to compile data which can be used to understand air pollution exposure in different locations within Scotland.
- Task 3 assessed whether the evidence identified in Task 2 could support the assessment of exposure to air pollution in Scotland, in order to evaluate population exposure as the basis for an exposure reduction target. Limitations and gaps in the current evidence base were also identified, as well as areas where further data collection or data analysis are needed.
Task 1: Identification of Existing Evidence
The aim of this task was to identify all available evidence and knowledge to help inform our analysis on patterns of exposure. It includes identification of relevant material under each of the following search topics:
- Search Topic 1: Identification of modelling and monitoring of ambient concentrations, and emissions of NO2, PM10 or PM2.5.
- Search Topic 2: Identification of existing evidence on public exposure to NO2, PM10 and PM2.5 in outdoor environments in Scotland.
- Search Topic 3: Identification of data and datasets containing information on demographics, socioeconomic indicators and health information.
The data sources which have been reviewed are listed in Appendix A2. The sources include:
- Coarse scale (typically 1 km2 average) modelled concentration data. This includes those available via the Scottish Air Quality data website [5] and those produced for the Scottish Government by UKCEH.
- Finer scale modelled concentration data. This focuses on any recent data which has been produced by local authorities fulfilling their Local Air Quality Management duties. Published information also exists in relation to designing and assessing a range of interventions; for example, modelling carried out by SEPA for the four Scottish cities with LEZs. Consideration has also been given to Defra’s Pollution Climate Mapping (PCM) model.
- Emissions data available at a 1 km2 resolution from the National Atmospheric Emissions Inventory.
- Monitored concentration data, including those held on the Scottish Air Quality data website 5 and Diffusion Tube data submitted annually to the Scottish Government by local authorities.
- Data in the scientific literature specific to Scotland, and more widely where relevant.
Information has been extracted into a standardised tabular format as outlined in task 2.
Task 2: Evidence review and consolidation
This task considers how the evidence collected in Task 1 can most effectively be used to understand the exposure to air pollution of the Scottish population. For key studies, a deep dive into the methodology and datasets (where available) has been undertaken, in order to fully assess applicability.
For the review, we have developed a matrix to classify each data source, which considers:
- Data collection date
- Which pollutants covered
- Resolution of data
- Robustness/ uncertainty/ quality of data
- How often the data are updated
- Summary of outcomes
- Identification of specific health information
- Identification of specific spatial trends
- Identification of specific demographic trends
Task 3: Gap analysis and identification of research needs
The main purpose of Task 3 was to provide an assessment of how the evidence base assembled under Task 2 could be used to assess the exposure of the population in Scotland to air pollution, in the context of the research questions included in section 2. An associated commentary has been provided on the strength of the evidence base for the purpose of assessing population exposure to PM10, PM2.5 and NO2 in Scotland now and in the future, as a basis for an exposure reduction approach.
During this task we have identified limitations and gaps in the current evidence base, and areas where further data collection or data analysis are needed. This covers:
- Gaps in the geographical areas and social groupings covered by the existing dedicated exposure assessments.
- Geographical areas where finer-resolution, or more up-to-date, concentration data are needed for a more detailed analysis.
- Areas where demographic information, and its spatial resolution, is lacking.
- Documentation or consistency issues in the existing datasets which have been collated.
Based on this assessment of the strengths and gaps in the current evidence base, recommendations for improvement are included in Section 5.
Note that there is a potential difference between assessing population exposure to air pollutants and assessing compliance with an exposure reduction target. The paradox in setting the target itself is that the more closely an approach tries to represent “real” exposure of the population to the pollutants, the more complex it becomes, which means that it is less transparent and any achievement is less likely to be trusted by non-specialists. The target is not simply a scientific exercise but must be legally definable – so that Government can be held to account – and the assessment method must be replicable over time. This inevitably means that the best target formulation in policy terms may not be the most scientifically accurate way of representing exposure. However, simply relying on target compliance may mean that real-world exposures do not reduce in the manner expected when setting the target. Thus, a method for tracking exposure in a scientifically robust manner will be essential in evaluating whether achievement of the target is actually delivering the anticipated social, economic and environmental benefits.