Fig. 2: SEM images of the different graphene raw materials and the materials measured in the emission zones.

a The raw material of graphene nanoplatelets used during Study A, b graphene nanoplatelets found on the emission zone filter sampled during work task A1 during Study A, c the raw material of graphene oxide used during Study B, and d graphene oxide found on the emission zone filter sampled during work task B1–2 during Study B.