Low-level pollution - health impacts: evidence review

This review explores the existing evidence on the health effects associated with low-level pollution in countries that have levels of ambient air pollution similar to Scotland.

3 Results

3.1 Search results

The final search was conducted on 6 June 2023, and a total of 333 studies were found using Scopus. The titles and abstracts were screened for relevance; 54 potentially relevant papers were identified, and full copies were obtained for detailed assessment. Of these, 46 papers were assessed as relevant and 8 were rejected. Papers were not included in the final analysis for the following reasons:

  • The paper did not explicitly assess, analyse, or evaluate the association or impact of air pollution on human health.
  • The level of evidence was not sufficient due to the methodological and data choices.
  • The paper did not recognise or consider the role of confounding factors in their analysis.
  • The interaction between air quality monitoring sites, and human geography was not appropriately considered or established.
  • The paper was focused on evaluation of methodological/modelling choices, as opposed to air pollution and human health.

Additional search results were obtained during the preliminary and supplementary searches using the search engine Google and the Scopus database. This was to capture any relevant evidence not captured by the search strategy, including reports and research specific to Scotland that fell outside of the search timeframe. The Dominski review, three reports from the HEI and three papers (published before 1 January 2020) in Scotland were found.

3.2 Categorical breakdown of results

Table 2 to Table 8 show a categorical breakdown of the continent, country, age of participants, health outcomes, whether these outcomes were short-term or long-term, and the pollutants assessed in each of the studies, as well as the year of publication.

Half of the included papers (24/46) were from European countries, most commonly the UK (or England), Sweden, Denmark and the Netherlands. Around two-thirds of papers assessed health outcome in adults, with one third on health outcomes in children. The most evaluated health outcomes were mental health and well-being, dementia and cognition, with most papers focussing on long-term outcomes. It is worth recognising that the prevalence of papers on mental health and well-being is reflective of the search strategy timescale. The evidence on the physiological health impacts of air pollution has been established for several years. Therefore most of these papers would have been published prior to 1 December 2020 and the evidence from these studies will be captured by the mapping review by Dominski et al. (2020) and the three HEI reports. Of all pollutants PM2.5 was the most evaluated, followed by NO2 and PM10.

Table 2: Geographic focus of relevant search results, by continent.
Continent #
Europe 24
North America 10
Worldwide 6
South America 1
Australia 5
Total 46
Table 3 Geographic focus of relevant search results, by country.
Country #
n/a 6
Australia 5
Sweden 5
Canada 4
England 4
Denmark 3
Netherlands 3
UK 3
France 2
Germany 2
Brazil 1
Portugal 1
Spain 1
Total 47
Table 4 Demographic age focus of relevant search results.
Age #
Adult 31
<18 15
Total 46
Table 5 Long- or short- term health outcomes assessed by relevant search results.
Health outcome duration #
Long 39
Short 7
Total 46
Table 6 Categorical health outcomes assessed by relevant search results (primary results focus, overlap may exist within papers).
Health outcome #
Mental health and well-being 11
Dementia 6
Cognition 5
Neurological 4
Respiratory 4
Development 3
Mortality 3
Cancer 2
Multiple 2
Neonatal 2
Diabetes 1
DNA methylation 1
Ocular 1
Primary care healthcare service use 1
Total 46
Table 7 Pollutants assessed[1] by relevant search results (count).
Pollutant #
PM2.5 41
NO2 23
PM10 19
O3 13
NOx 11
Other 7
BC 3
Table 8 Year of publication relevant search results.
Year of publication #
2020 1
2021 13
2022 19
2023 13
Total 46


Email: andrew.taylor2@gov.scot

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