Introduction to Atmospheric Photochemistry

FIGURE 20.28 The variation of the temperature of the atmosphere with altitude, showing the layered structure of the atmosphere. 

Research in atmospheric chemistry dates back to the 18th century. Cavendish, Priestley, Lavoisier, and Ramsay were the first scientists to study the composition of the atmosphere. In recent years, atmospheric chemistry has developed in two different but related directions. First, the sensitivity of chemical analysis has greatly improved, and analyses for substances at concentrations below the part-per-billion (ppb) level are now carried out routinely. Airplanes and satellites enable scientists to map the global distributions of trace substances. Second, advances in gas-phase chemical kinetics have led to a better quantitative understanding of the ways in which substances in the atmosphere react with one another and with light. Much of the impetus for these studies of atmospheric chemistry comes from concern about the effect of air pollution on life. 

The bond dissociation energy of O2 is 496 kj mol Calculate the maximum wavelength of light that can photodissociate an oxygen molecule. 

Because 496 kJ dissociates 1.00 mol of O2 molecules, the energy to dissociate one molecule is found by dividing by Avogadro s number  

A photon carrying this energy has a wavelength A, given by 

---