Fig. 3

Gaseous portion of diesel exhaust (DE) exposures in reviewed studies. Whiskers denote minimum and maximum values, box denotes 25th and 75th percentiles, line denotes median. 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. A nitric oxide (NO), n = 63 studies, n = 95 arms; B nitrogen dioxide (NO₂), n = 69 studies, n = 107 arms; C nitrogen oxides (NO_x), n = 41 studies, n = 61 arms; D carbon monoxide (CO), n = 62 studies, n = 93 arms; E total volatile organic compounds (TVOC), n = 13 studies, n = 19 arms; F formaldehyde, n = 14 studies, n = 21 arms. For Noah et al. [61] and Pawlak et al. [54], concentrations of the gaseous portion of exposures were listed as ranges. As such, the median of each range was used in this figure. See Additional file 1 for full dataset