“…NO 2 in urban atmosphere originates mainly from primary emissions of combustion processes and oxidation of NO. Recently, primary vehicular NO 2 raised much interest and concern in NO 2 control in urban areas (Harrison and Shi, 1996;Beevers, 2004a, b, 2005;Soltic and Weilenmann, 2004 EGU 2-5% to ∼30% (Lenner and Lindqvist, 1983;Cariappa et al, 1994;Harrison and Shi, 1996;Clapp and Jenkin, 2001;Jimenez et al, 2001;Beevers, 2004a, b, 2005;Jenkin, 2004a, b;Soltic and Weilenmann, 2004). The lower ratio (2-5%) is the widely accepted value for gasoline engines under normal driving conditions (Hilliard and Wheeler, 1979).…”