Organic components of fine particles, especially polycyclic aromatic hydrocarbons (PAHs), play an essential role in the toxicity of fine particulate matter (PM2.5). The chemical and bioreactive properties of PM2.5 in indoor environments were investigated from 2014 to 2016 in Hong Kong among 33 residential indoor environments. All analyzed components revealed higher concentrations in winter than in summer, except for organic carbon (OC). High molecular weight PAHs (4–6 rings) contributed higher total PAH compositions than low molecular weight PAHs (2–3 rings). The study results suggested that the major sources of indoor PM2.5 originated from outdoor vehicle emissions, indoor cooking activities, and incense burning. Cytotoxicity tests only revealed significant associations in winter. The cell viability demonstrated strong negative correlations between OC (r = − 0.8, p < 0.05), total PM2.5-bound PAHs (r = − 0.6, p < 0.05), and United States Environmental Protection Agency (US EPA) priority PAHs (r = − 0.7, p < 0.05). Cell lactate dehydrogenase (LDH) and 8-isoprostane were positively associated with OC (r = 0.8, p < 0.05; r = 0.7, p < 0.05), total PM2.5-bound PAH (r = 0.7, p < 0.05; r = 0.7, p < 0.05), and US EPA priority PAH (r = 0.6, p < 0.05; r = 0.5, p = 0.07) concentrations. IL-6 had the only positive association with OC (r = 0.5, p < 0.05). This study focused on indoor PM2.5 levels and the associated cytotoxicity in the absence of environmental tobacco smoke.
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