Fig. 1

Schematic diagram of the modified MERDOC measurement system. The measurement setup consists of (1) three mixing chambers equipped with silica gel desiccant; (2) exhaled air water trap, and; (3) two high-efficiency particulate filters. A detailed description of the experimental setup is discussed in Madueño et al. [18]. Photos on the right show the actual sampling of study participants in different exposure scenarios, a public transport and b light walking. Please note that the exposure and exhaled BC mass concentrations were measured by separate micro-aethalometers placed in two different backpacks carried by different individuals (study supervisor (BC exposure measurement) and volunteers (exhaled BC mass concentration measurement))