In Chiba Prefecture, Japan, air samples were collected at 1.5, 5, 30, 50, and 100 m height using a radio-controlled helicopter, and at 150, 300, and 800 m using a regular helicopter, and concentrations of dialkyl phthalates were measured. The analytical methods used are described. Concentrations of dimethyl phthalate, diethyl phthalate, and diisobutyl phthalate were detected only at ground level, and the concentrations of benzyl butyl phthalate, di-n-butyl phthalate, di(2-ethylhexyl) phthalate, and dioctyl adipate decreased with altitude. The concentrations of all dialkyl phthalates were higher in July than in March at the same altitudes. Maximum concentrations of di(2-ethylhexyl) phthalate were highest, followed in decreasing order by di-n-butyl phthalate; dioctyl adipate; diisobutyl phthalate; benzyl butyl phthalate, di-n-nonyl phthalate, and diethyl phthalate; and dimethyl phthalate. All relevant concentration data are tabulated.
