Development of plant mass is neglected. The concentration of a chemical in the plant as well as the concentration in the particles on the plant is governed by a first-order linear differential equation with constant coefficients. An analytical solution is implemented. Chemical distribution in soil, and between plant and atmosphere is calculated by help of partition coefficients. Volatilization from plantinto air, and chemical input from air into plant are governed by the conductivity of the leaves and the boundary air layer.
Metabolism is taken into consideration by using a first-order degradation rate.