Fig. 1

Target or achieved PM concentration for diesel exhaust (DE) exposures within reviewed studies. n = 76 studies, n = 118 DE arms. PM concentration not available for 3 studies (representing 5 arms). Achieved PM concentrations were used when available. Otherwise, target PM concentration was used. When studies included exposures to multiple different PM concentrations (“arms”), each exposure condition contributed to the number of exposure arms. For studies with multiple DE exposure sessions per participant, each session was counted as a separate arm. For studies involving multiple cohorts, exposure conditions for each cohort were counted as separate arms. FA arms not included. See Additional file 1 for full dataset