A review and analysis of personal and ambient PM 2.5 measurements: Implications for epidemiology studies

In epidemiology studies, ambient measurements of PM 2.5 are often used as surrogates for personal exposures. However, it is unclear the degree to which ambient PM 2.5 reflects personal exposures. In order to examine potential sources of bias in epidemiology studies, we conducted a review and meta-analysis of studies to determine the extent to which short-term measurements of ambient PM 2.5 levels are related to short-term measurements of personal PM 2.5 levels. We conducted a literature search of studies reporting both personal and ambient measurements of PM 2.5 published in the last 10 years (2009–2019) and incorporated studies published prior to 2009 from reviews. Seventy-one studies were identified. Based on 17 studies reporting slopes, a meta-analysis revealed an overall slope of 0.56 μg/m 3 (95% CI: [0.39, 0.73]) personal PM 2.5 per μg/m 3 increase in ambient PM 2.5. Slopes for summer months were higher (slope = 0.73, 95% CI: [0.64, 0.81]) than for winter (slope = 0.46, 95% CI: [0.36, 0.57]). Based on 44 studies reporting correlations, we calculated an overall personal-ambient PM 2.5 correlation of 0.63 (95% CI: [0.55, 0.71]). Correlations were stronger in studies conducted in Canada ( r  = 0.86, 95% CI: [0.67, 0.94]) compared to the USA ( r  = 0.60, 95% CI: [0.49, 0.70]) and China ( r  = 0.60, 95% CI: [0.46, 0.71]). Correlations also were stronger in urban areas ( r  = 0.53, 95% CI: [0.43, 0.62]) vs. suburban areas ( r  = 0.36, 95% CI: [0.21, 0.49]). Our results suggest a large degree of variability in the personal-ambient PM 2.5 association and the potential for exposure misclassification and measurement error in PM 2.5 epidemiology studies.