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As recognized risk factor to pose a health threat to humans and wildlife globally, atmospheric particulate matter (PM) were collected from a North African coastal city (Bizerte, Tunisia) for one year, and were characterized for their chemical compositions, including mercury (Hg PM), as well as organic contaminants (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs)), organic carbon (OC) and organic nitrogen (ON), determined in a previous study. Then, we applied an in vitro reporter gene assay (DR-CALUX) to detect and quantify the dioxin-like activity of PM-associated organic contaminants. Results showed that average Hg PM concentration over the entire sampling period was found to be 13.4 ± 12 pg m−3. Seasonal variation in the Hg PM concentration was observed with lower values in spring and summer and higher values in winter and autumn due to the variation of meteorological conditions together with the emission sources. Principal component analysis suggested that fossil fuel combustion and a nearby cement factory were the dominant anthropogenic Hg PM sources. Aryl hydrocarbon receptor (AhR)-mediated activities were observed in all organic extracts of atmospheric PM from Bizerte city (388.3–1543.6 fg m−3), and shows significant positive correlations with all PM-associated organic contaminants. A significant proportion of dioxin-like activity of PM was related to PAHs. The dioxin-like activity followed the same trend as PM-associated organic contaminants, with higher dioxin-like activity in the cold season than in the warm season, indicating the advantage and utility of the use of bioassays in risk assessment of complex environmental samples. Image 1 • The first investigation of atmospheric particulate Hg (Hg PM) in whole Africa. • PCA analysis showed that Hg PM in Bizerte city was mainly produced by fossil fuel combustion. • Ambient temperature, precipitation and wind speed were identified as the major factors influenced Hg PM concentrations. • All atmospheric PM organic extracts from Bizerte city showed dioxin-like activity. • PAHs are responsible for 40% of dioxin-like activity of atmospheric PM. [ABSTRACT FROM AUTHOR]