Opposing seasonal trends for polycyclic aromatic hydrocarbons and PM10: Health risk and sources in southwest Mexico City

► We determine polycyclic aromatic hydrocarbons (PAHs) in PM10 during four consecutive years. ► Seasonal variation was observed in Southwest Mexico City. ► Meanwhile a decreasing trend of PM10 was observed, a positive trend for some PAHs was found. ► Air control strategies implemented by the government were adequate for PM10 but not for PAHs. ► Combustion from gasoline and diesel engines were the main contributors to PAHs.