Fig. 2
PM2.5 concentration for diesel exhaust (DE) exposures of reviewed studies, categorized by duration of exposure. Achieved PM2.5 concentration was used if available, otherwise target PM2.5 concentration was used. Only studies that reported PM2.5 concentrations were included (n = 37 studies). When studies included exposures to multiple different PM concentrations, 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. This resulted in a total of n = 59 exposure arms. FA arms not included. See Additional file 1 for full dataset