Overall exposure varies but there is a baseline of risk
There exists high variation in exposure concentrations, concerning both short peaks and averages over the period of use. This characteristic is related to the "real-world" nature of the study and the different ways in which people use their stoves.
On average, participants used 9.58 pieces of solid fuel and 8.32 pieces of kindling per use. The number of fuel pieces used in a single use varied between a minimum of 7 to a maximum of 40, while kindling varied between a minimum of 1 and a maximum of 32. All participants used dried and seasoned logs, but the sizes and type of wood varied. There was also a diversity of kindling used, taking the form of firelighters, newspapers, balls of paper, twigs, sawdust, packing cardboard, greeting cards and empty egg boxes.
Echoing the findings of existing studies, this means that the same wood burner may emit different levels of air pollution depending on the quantity and type of fuel and kindling used. However, longer usage is associated with greater numbers of fuel pieces used. Therefore, instead of fuel type, the results support the stove door explanation for the ’flooding’ phenomenon observed - higher short-term peak concentrations are seen during longer periods of use because these periods are sustained by more refueling actions. This accords with existing studies that also found the lighting and refueling aspects of stove management form the main indoor pollutant-generating phases of operation.
While it appears to be less relevant to indoor air pollution, other studies show that the type of fuel used does influence the levels of PM2.5 and PM1 emitted outdoors.