In atmospheric chemistry, the Leighton relationship is an equation that determines the concentration of tropospheric ozone in areas polluted by the presence of nitrogen oxides.
 Ozone in the troposphere is primarily produced through the photolysis of nitrogen dioxide at wavelengths (λ) less than 430 nm, which are able to reach the lowest levels of the atmosphere, through the following mechanism:
The Taft equation is a linear free energy relationship (LFER) used in physical organic chemistry in the study of reaction mechanisms and in the development of quantitative structure activity relationships for organic compounds.
 It was developed by Robert W. Taft in 1952 as a modification to the Hammett equation.
 While the Hammett equation accounts for how field, inductive, and resonance effects influence reaction rates, the Taft equation also describes the steric effects of a substituent.
 The Taft equation is written as:
In chemical kinetics, the entropy of activation of a reaction is one of the two parameters (along with the "enthalpy of activation") which are typically obtained from the temperature dependence of a reaction rate constant, when these data are analyzed using the Eyring equation.
 The standard entropy of activation is symbolized ΔS and equals the change in entropy when the reactants change from their initial state to the activated complex or transition state (Δ = change, S = entropy, ‡ = activation).
 It determines the preexponential factor A of the Arrhenius equation for temperature dependence of reaction rates.
 The relationship depends on the molecularity of the reaction: for reactions in solution and unimolecular gas reactions A = (ekT/h) exp(ΔS/R), while for bimolecular gas reactions A = (ekT/h) (R'T/p) exp(ΔS/R).
 In these equations e is the base of natural logarithms, h is the Planck constant, k is the Boltzmann constant and T the absolute temperature.
 R' is the ideal gas constant in units of (bar*L)/(mol*K).
 The factor is needed because of the pressure dependence of the reaction rate.
 R' = 8.3145 * 10^-2 (bar*L)/(mol*K).
Ozone (systematically named 1λ,3λ-trioxidane and "catena"-trioxygen), or trioxygen, is an inorganic molecule with the chemical formula O3 .
 It is a pale blue gas with a distinctively pungent smell.
 It is an allotrope of oxygen that is much less stable than the diatomic allotrope O2 , breaking down in the lower atmosphere to O2 or dioxygen.
 Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in very low concentrations throughout the Earth's atmosphere (stratosphere).
 Its concentration is highest in the ozone layer region of the atmosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.
A comparametric equation is an equation that describes a parametric relationship between a function and a dilated version of the same function, where the equation does not involve the parameter.
 For example, "ƒ"(2"t") = 4"ƒ"("t") is a comparametric equation, when we define "g"("t") = "ƒ"(2"t"), so that we have "g" = 4"ƒ" no longer contains the parameter, "t".
 The comparametric equation "g" = 4"ƒ" has a family of solutions, one of which is "ƒ" = "t".
The quantum Boltzmann equation is the quantum mechanical version of the Boltzmann equation, which gives the time evolution of a distribution of free particles out of equilibrium.
 Typically, the quantum Boltzmann equation is given as only the “collision term” of the full Boltzmann equation, giving the change of the momentum distribution of a locally homogeneous gas, but not the drift and diffusion in space.
 There is not a single quantum Boltzmann equation; a different equation must be written for each type of particle scattering.
The Freundlich equation or Freundlich adsorption isotherm, an adsorption isotherm, is an empirical relation between the concentration of a solute on the surface of an adsorbent to the concentration of the solute in the liquid with which it is in contact.
 In 1909, Herbert Freundlich gave an expression representing the isothermal variation of adsorption of a quantity of gas adsorbed by unit mass of solid adsorbent with pressure.
 This equation is known as Freundlich adsorption isotherm or Freundlich adsorption equation.
 As this relationship is entirely empirical, in the case where adsorption behavior can be properly fit by isotherms with a theoretical basis, it is usually appropriate to use such isotherms instead (see for example the Langmuir and BET adsorption theories).
In physics and thermodynamics, the Redlich–Kwong equation of state is an empirical, algebraic equation that relates temperature, pressure, and volume of gases.
 It is generally more accurate than the van der Waals equation and the ideal gas equation at temperatures above the critical temperature.
 It was formulated by Otto Redlich and Joseph Neng Shun Kwong in 1949.
 It showed that a two-parameter, cubic equation of state could well reflect reality in many situations, standing alongside the much more complicated Beattie–Bridgeman model and Benedict–Webb–Rubin equation that were used at the time.
 The Redlich–Kwong equation has undergone many revisions and modifications, in order to either improve its accuracy in terms of predicting gas-phase properties of more compounds, as well as in better simulating conditions at lower temperatures, including vapor–liquid equilibria.
The Arrhenius equation is a formula for the temperature dependence of reaction rates.
 The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 1884 that Van 't Hoff's equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions.
 This equation has a vast and important application in determining rate of chemical reactions and for calculation of energy of activation.
 Arrhenius provided a physical justification and interpretation for the formula.
 Currently, it is best seen as an empirical relationship.
 It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermally-induced processes/reactions.
 The Eyring equation, developed in 1935, also expresses the relationship between rate and energy.
The compressibility factor (Z), also known as the compression factor or the gas deviation factor, is a correction factor which describes the deviation of a real gas from ideal gas behavior.
 It is simply defined as the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure.
 It is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behavior.
 In general, deviation from ideal behavior becomes more significant the closer a gas is to a phase change, the lower the temperature or the larger the pressure.
 Compressibility factor values are usually obtained by calculation from equations of state (EOS), such as the virial equation which take compound-specific empirical constants as input.
 For a gas that is a mixture of two or more pure gases (air or natural gas, for example), the gas composition must be known before compressibility can be calculated.

Question: What color is the gas in the troposphere of the Leighton relationship equation?
Answer: pale blue