Refer to the Environmental Science & Technology study of sorption of organic vapors, Exercise 12.7. The independent variables used to model the retention coefficient y are

x₁ = Temperature (degrees)

x₂ = Relative humidity (percent)

Organic compound = (benzene, toluene, chloroform, methanol, and anisole)

a. Write a first-order, main effects model for E(y) as a function of temperature and organic compound. Draw a sketch of the model.

b. Interpret the β parameters of the model, part a.

c. Write a model for E(y) as a function of relative humidity and organic compound that hypothesizes different retention–relative humidity slopes for the five compounds. Draw a sketch of the model.

d. Give the slopes of the five compounds (in terms of the β’s) for the model, part c.

Data from Exercise 12.7

Environmental Science & Technology (Oct. 1993) published an article that investigated the variables that affect the sorption of organic vapors on clay minerals. The independent variables and levels considered in the study are listed here. Identify the type (quantitative or qualitative) of each.