Liquid chromatography coupled to a photodiode array detector (HPLC-DAD) and atmospheric pressure chemical ionization ion sources (LC-APCI-MS) were used for the determination of a variety of nitrophenols in air and rainwater samples after solid-phase extraction using silica gel and XAD-7 resin adsorbents (rainwater). Five field experiments were performed: (1) in a preliminary campaign air samples were obtained in 1998 in an urban site in the northern part of Milano; (2) in winter 1999, air samples were obtained in three urban sites in the Great Milano area, in one semirural site and in a rural site in the Protected Area named Ticino Valley; (3) in summer 1999, air samples were obtained in one urban site in Central Milano; (4) in summer 1999, air samples were obtained in an urban tunnel in Central Milano; (5) in spring 1999, rainwater was collected in five occasions in two urban sites located in the northern part of Milano area. Benzene, toluene, phenol, 2-nitrophenol, 4-nitrophenol, 3-methyl-4-nitrophenol,...