Fig. 2
Effects of diesel exhaust (DE) on symptom categories by exposure group. Symptoms were recorded before, and at 4 and 24 h after the start of exposures to filtered air and DE standardized to 20, 50 and 150 µg/m3 PM2.5. X axes show represent change in symptom scores from baseline; Y axes show nominal exposure conditions. Horizontal dashed lines represent 0 (no change from baseline). Linear mixed effects models were fitted with participant ID as a random effect: **P ≤ 0.05, *P = 0.051–0.1