Air pollution and environmental justice: a systematic literature review on methodological approaches

<h2>Abstract</h2> Air pollution is the greatest environmental risk to human health, according to the WHO and other international entities like the UN Human Rights Council and EEA. However, not everyone is equally affected by air pollution, depending on exposure and vulnerability. The objective of this systematic literature review is to investigate whether and how concepts related to environmental inequalities or justice have been considered when assessing health impacts of air pollution, identify possible gaps in knowledge, and offer suggestions for future research. A total of 99 articles are assessed considering framework, study region, time scale, data and indicators used and finally, the method applied (statistical, numerical or survey). Results show that EJ studies took place in 21 different countries, led by the United States of America (53 %), followed by Canada (6 %) and China (5 %). In terms of temporal coverage, more than 50 % of the studies were published in the last 5 years and are mainly focused on long-term studies. As regards proxy data, most of the studies focused on PM2.5, but only 50 % explicitly include health or exposure data. All studies evaluated EJ questions related to socio-economic status (SES) or race/ethnicity. The socio-economic indicators mostly used are associated with income (99 %), followed by population characterization and housing. The most common method used was statistical analysis (71 %), with 14 % applying surveys and 15 % using modelling for scenario approaches. These results point out that there is space for other case studies in Europe among other regions of the world, with more robust statistical models based on advanced mixed methods to deal with such multivariable research. At small geographic units, studies supported by survey information would be recommended to include both individual and contextual socio-economic indicators. A limited number of studies deal with social perceptions and citizen engagement. Future research is suggested. It should be noticed that this literature review only looks for occurrences of "environmental justice" related to air pollution/quality.