As an employee of the Los Angeles Air Quality Com- mission, you have been asked to develop a model for computing the distribution of NO2 in the atmosphere. The molar flux of NO2 at ground level,NA",0, is pre- sumed known. This flux is attributed to automobile and smoke stack emissions. It is also known that the concentration of NO2 at a distance well above ground level is zero and that NO2 reacts chemically in the atmosphere. In particular, NO2 reacts with unburned hydrocarbons (in a process that is activated by sun- light) to produce PAN (peroxyacetylnitrate), the final product of photochemical smog. The reaction is first order, and the local rate at which it occurs may be expressed as NA =-k1CA.
(a) Assuming steady-state conditions and a stagnant atmosphere, obtain an expression for the vertical distribution CA(x) of the molar concentration of NO2 in the atmosphere.
(b) If an NO2 partial pressure of pA = 2 X 10-6 bar is sufficient to cause pulmonary damage, what is the value of the ground level molar flux for which you would issue a smog alert? You may assume an isothermal atmosphere at T = 300 K, a reaction coefficient of k1 = 0.03 s-1, and an NO2-air diffusion coefficient of DAB = 0.15 X 10-4 m2/s. may be neglected. For this condition what are the molar concentrations of NO2 at ground level and at 100-m elevation 3 h after the start of the emissions, if NA" , 0 = 3 X 10-11 kmol/s · m2 and DAB = 0.15 X 10-4 m2/s?