Comparing human exposure to fine particulate matter in low and high-income countries: A systematic review of studies measuring personal PM_2.5 exposure

Background: Due to the adverse health effects of air pollution, researchers have advocated for personal exposure measurements whereby individuals carry portable monitors in order to better characterise and understand the sources of people's pollution exposure.

Objectives: The aim of this systematic review is to assess the differences in the magnitude and sources of personal PM_2.5 exposures experienced between countries at contrasting levels of income.

Methods: This review summarised studies that measured participants personal exposure by carrying a PM_2.5 monitor throughout their typical day. Personal PM_2.5 exposures were summarised to indicate the distribution of exposures measured within each country income category (based on low (LIC), lower-middle (LMIC), upper-middle (UMIC), and high (HIC) income countries) and between different groups (i.e. gender, age, urban or rural residents).

Results: From the 2259 search results, there were 140 studies that met our criteria. Overall, personal PM_2.5 exposures in HICs were lower compared to other countries, with UMICs exposures being slightly lower than exposures measured in LMICs or LICs. 34% of measured groups in HICs reported below the ambient World Health Organisation 24-h PM_2.5 guideline of 15 μg/m³, compared to only 1% of UMICs and 0% of LMICs and LICs. There was no difference between rural and urban participant exposures in HICs, but there were noticeably higher exposures recorded in rural areas compared to urban areas in non-HICs, due to significant household sources of PM_2.5 in rural locations. In HICs, studies reported that secondhand smoke, ambient pollution infiltrating indoors, and traffic emissions were the dominant contributors to personal exposures. While, in non-HICs, household cooking and heating with biomass and coal were reported as the most important sources.

Conclusion: This review revealed a growing literature of personal PM_2.5 exposure studies, which highlighted a large variability in exposures recorded and severe inequalities in geographical and social population subgroups.