Figure 2

Number of subjects reporting symptoms after exposure to filtered air, unfiltered diesel exhaust (DE), diesel exhaust with filter A (ultrafine particle filter) and with filter B (ultrafine particle filter with active charcoal). McNemar´s Chi-square test was performed to analyze the difference between the number of subjects reporting symptoms after exposure to unfiltered DE and diesel exposure filtered with filters A and B. Data were considered significant at ^*P < 0.05, ^**P < 0.01