Air pollutant exposure evidence review

1 Introduction

A substantial evidence base has developed which shows population level health effects of air pollutants at concentrations which do not exceed current air quality objectives ^[1]. Most of the Scottish population does not regularly experience air quality which exceeds current objectives or limit values but nevertheless experiences air quality which may affect their health. While the air quality standards and limit values are based on health evidence and are, in many ways, proxies for exposure to air pollutants, the actual relationship between measured or estimated concentrations and individuals’ exposure to those pollutants is complex. For PM_2.5 current evidence suggests that long term average concentrations have a greater effect on public health than those seen in studies of short-term fluctuations. Available studies do not allow firm conclusions to be drawn about the relative toxicity of particulates of different composition or from different sources^[2].

Different societal groups are not evenly exposed to poor air quality. For example, grouping populations by economic status, age, or race may reveal systematic differences in their average exposure^[3]. As well as being important from a social justice perspective, this can also be highly relevant to efforts to most efficiently protect public health, since different groups may also be more susceptible to the effects of poor air quality.

There is some uncertainty from international studies about the scale of health effects associated with low pollutant concentrations typical of those found across Scotland¹. Barnes et al (2023)^[4] concluded that while the global evidence is robust, the specific evidence regarding air pollution and health outcomes in Scotland is limited and inconclusive. Nonetheless, harmful effects have been extensively evidenced at concentrations below national and international air quality standards, so effective policies and interventions are necessary to reduce air pollution levels.

The objectives of this study are therefore to review existing data on pollutant concentrations and demographic features and use this to understand the strength of the evidence base on how the Scottish population is being exposed to outdoor concentrations of NO₂, PM₁₀, and PM_2.5. In particular, the outputs will focus on the potential introduction to Scottish air quality policy of an exposure reduction approach for PM_2.5 and/or NO₂ and potential implications of this approach for different demographic groups. A key focus of the study is to review whether the currently available information base could robustly be used to assess population exposure to PM₁₀, PM_2.5 and NO₂ in Scotland now and in the future, where any gaps in evidence are and how they could potentially be filled.