Oxygenates atmospheric chemistry

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

Example 7.17 illustrates the utility of the reaction coordinate method for solving equilibrium problems. There are no more equations than there are independent chemical reactions. However, in practical problems such as atmospheric chemistry and combustion, the number of reactions is very large. A relatively complete description of high-temperature equilibria between oxygen and... 

We will now discuss some very recent applications of the soft El ionization method for product detection in CMB experiments. We will first deal with two polyatomic reactions of ground state oxygen atoms with unsaturated hydrocarbons (acetylene and ethylene) these reactions are characterized by multiple reaction pathways and are of great relevance, besides being from a fundamental point of view, in combustion and atmospheric chemistry. 

Of these, photodissociation is by far the most pervasive and important in atmospheric chemistry. For example, the photodissociation of N02 into ground-state oxygen atoms,... 

Certain highly exothermic thermal and photochemical reactions of ozone could conceivably give rise to electronically excited molecular oxygen, and could be of considerable importance in atmospheric chemistry (see Sect. VI). Some of these reactions are discussed in this section, and the experimental evidence available is described. 

Singlet molecular oxygen is of interest in connection with atmospheric chemistry with respect both to its mode of excitation and to the consequences of its presence in the upper or lower atmosphere. The first part of this section deals with processes of importance in normal, unpolluted atmospheres, while the second part examines the possibility, only recently appreciated, that singlet molecular oxygen may play a part in the chemistry of polluted urban atmospheres. 

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

Thus, when studying atmospheric chemistry, it is necessary always to take into account the vertical and horizontal movements in the atmosphere, as well as the conditions controlling those chemical reactions that do not spontaneously lead to photochemical equilibrium. These conditions are applicable not only to ozone in the lower stratosphere, but also to atomic oxygen in the upper mesosphere above 75 km. In fact, equation (4) shows that, with increasing height, the formation of O3 becomes less and less important because of the decrease in the concentration of 02 and N2. Above 60 km the concentration of atomic oxygen exceeds that of ozone, but it is still in photochemical equilibrium up to 70 km. However, at the mesospause (85 km), it is subject to atmospheric movements, and its local concentration depends more on transport than on the rate of production. 

Thus a number of catalytic reactions are associated with the re-formation of 02 already indicated in equation (5). In other words, a halogen, or any other atom which attacks ozone, always reappears as a result of the reaction between its oxide and atomic oxygen, and hence there is a permanent cycle leading to the destruction of ozone. In atmospheric chemistry, therefore, it is important to find out how these constituents appear, and to assess their importance. 

An example from atmospheric chemistry is the reaction of an oxygen atom with an HC1 molecule to give an OH molecule and a chlorine atom ... 

The catalytic oxidation of sulphurous acid in aqueous medium to sulphuric acid [138, 84] has been suggested as a probe reaction for the ability of a carbon to activate molecular oxygen at ambient conditions. Besides this remarkable property the reaction is of interest in atmospheric chemistry where it provides a sink for all nonphotochemically oxidized sulfur dioxide [215]. Carbon plays a special role in this environmental application as both pure carbon and active particles (iron oxide [84] for example) anchored to carbon can act as efficient catalysts. The detailed analysis of the reactivity of various types of carbon [138] reveal that basic surface oxides (see Fig. 23) are important to fix the educt HSOj ion. It was found, in addition, that the... 

Oxygenated Sulfur Radicals Relevant to Atmospheric Chemistry. .111... 

Baulch DL, Cox RA, Crutzen PJ, Hampson RF, Kerr JA, Troe J, Watson RT (1998) Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry Supplement I, J. Phys. Chem. Ref. Data 11, No. 2 327-496 cited in Laszlo Zs, Ilisz I, Peintler G, Dome A (1998) VUV Intensity Measurement of a 172 nm Xe Excimer Lamp by means of Oxygen Actinometry, Ozone Sci. Eng. 20 421-432. 

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