Lung deposition fractions of nine experimental particle number distributions emitted by various light duty diesel vehicles with different after-treatment devices and fuels were calculated with a stochastic lung deposition model. The emitted volatile and non-volatile mass fractions were treated separately as the corresponding biological response in the human respiratory tract differs. The health related effects of the volatile mass fraction, referred to as the chemical effect, were associated with the deposited volatile mass. The deposited volatile mass depends on the total emitted volatile mass concentration, on its distribution (mass median diameter of nucleation mode and surface area median of the accumulation mode), and on the ratio of the volatile mass in the nucleation and accumulation modes. The effect of the non-volatile mass fraction, referred to as the physical effect, was associated with the surface area distribution of the accumulation mode. The deposited surface area of the non-volatile fraction depends on its emitted concentration and on the surface area median diameter of the size distribution. The calculations suggest the importance of selecting the appropriate distribution (surface, volatile or non-volatile mass) for an assessment of the health effects of diesel exhaust particles, and the importance of combined particulate mass and number distribution measurements. (C) 2009 Elsevier Ltd. All rights reserved.