The magnetic properties of indoor dust fractions as markers of air pollution inside buildings

• Magnetometry is a good tool to study the air pollution inside the buildings.
• The concentration of magnetic particles increases as size of pollution decreases.
• The pollution inside building is mainly traffic-related.
• The medium- and fine-grained fractions revealed magnetite and Fe-rich particles.
• The metallic Fe affects magnetic susceptibility, hysteresis parameters and ratios.

The distribution of indoor dust into size fractions can be a convenient way to characterize the pollution in apartments located in the city center and suburbs. Magnetic properties revealed that concentration of magnetic particles increases with decreasing granulometric size. The coarse- and medium-grained dust from the suburbs show the higher concentration of magnetic particles than the same fractions from the city center. The finer-grained fractions from the center contain more magnetic particles than the dust from suburbs. The coarse-grained dust contains mixture of single-domain to multi-domain magnetite. Magnetite and metallic iron are present in the medium- and fine-grained fractions. In these fractions, the metallic Fe contributes to the relatively high values of magnetic susceptibility and saturation magnetization, and affecting the values of hysteresis parameters and ratios. The medium-grained fraction is dominated by shaving-shape particles containing metallic iron or/and traffic-related elements as Ca–Mg–Si–Ti–K–Al–Ba. Spherules of very diverse surface morphologies (orange-peel, hexagonal-pattern, thread-like and druse-like), were observed in fine-grained fraction of indoor dust. Magnetic mineralogy, metallic iron affects the values of coercivity and remanence causing the shift of ratios hysteresis parameters towards region characteristic for MD grains of magnetite in the Day–Dunlop plot.