Remote atmospheric

Microwave spectroscopy is used for studyiag free radicals and ia gas analysis (30). Much laboratory work has been devoted to molecules of astrophysical iaterest (31). The technique is highly sensitive 10 mole may suffice for a spectmm. At microwave resolution, frequencies are so specific that a single line can unambiguously identify a component of a gas mixture. Tabulations of microwave transitions are available (32,33). Remote atmospheric sensing (34) is illustrated by the analysis of trace CIO, O, HO2, HCN, and N2O at the part per trillion level ia the stratosphere, usiag a ground-based millimeter-wave superheterodyne receiver at 260—280 GH2 (35). 

J. N. Galloway, R. J. Chadson, M. O. Andreae, and H. Rodhe, eds.. The Piogeochemical Cjcling of Sulfur andNitrogen in the Remote Atmosphere, Kluwer Academic Pubhshers, Inc., New York, 1985. 

Fig. 3. Relationships between the concentrations of the elements in remote atmospheric dusts (a) continental vs Antarctic atmospheric dust, (b) island vs Arctic atmospheric dust. [M] is the concentration of element M.

A summary is given in Table III of the results of the elucidation of the sources of the elements in remote atmospheric dusts. Four main sources are identified silicate o dust, marine spray, high temperature natural emissions (e.g. volcanic, plant and rock... 

The accommodation coefficients for OH and HO2 in our model are parameterised as temperature dependent accommodation coefficients (Gratpanche et al., 1996) in Table 3, with no account taken of the surface characteristics. There are a few papers reporting uptake coefficients for both OH and HO2 with lower limits quoted for the HO2 coefficients due to experimental limitations, giving rise to a low confidence in current experimental values for HO2 (Cooper and Abbatt, 1996 Hanson et al., 1992). The impact of reactions on aerosol on HO2 concentrations in the remote atmosphere could be significant if the uptake coefficient was greater than 0.1, and could dominate if it was close to unity (Saylor, 1997). 

Menzies, R. T., and M. T. Chahine. Remote atmospheric sensing with an airborne laser absorption spectrometer. Appl. Optics 13 2840-2849, 1974. 

The late 1970 s saw the birth of a new aspect of atmospheric chemistry. Thus, in addition to ozone and photochemical oxidant formed in the daytime photooxidation of VOCs, there is an important nighttime chemistry, not only in polluted urban and suburban air environments, but also in relatively remote atmospheres. 

As developed in more detail in Chapter 6, the NO concentration at which other reactions such as (11), (12), and (29) occur at approximately the same rate as the H02/R02 + NO reaction is in the 10-50 ppt range. These concentrations are sufficiently low that they are encountered only in remote atmospheres, where the influence of anthropogenic emissions is minimized. 

An informal intercomparison study of N02 measurements was carried out in a remote atmosphere at Izana, Tenerife (Zenker et al., 1998). Three techniques were used TDLS, photolysis with a chemiluminescence detector, and matrix isolation-ESR. Agreement between the three methods was good, with plots of data from one technique against the others having slopes within experimental error of unity. For example, TDLS and the photolysis technique plotted against the matrix isolation measurements had slopes of 0.90 + 0.47 and 1.04 + 0.34, respectively, over a range of NOz concentrations from 100 to 600 ppt. 

At the beginning of this book, we presented some discussion of health-based air quality standards. In the final chapter, which follows this one, the scientific bases of control measures for various pollutants are discussed. In between, the complex chemistry that occurs in both polluted and remote atmospheres, and that converts the primary pollutants into a host of secondary species, has been detailed. To provide further perspective on airborne gases and particles and human exposure levels, we briefly treat indoor air pollution in this chapter. As we shall see, for many species it is simply a question of emissions leading to elevated levels indoors. However, there is some chemistry that occurs in indoor atmospheres as well, and it is of interest to compare this to that occurring outdoors. 

Galloway, J.N., Charlson, R.J., Andreae, M.O., Rhode, H. and Marston, M.S. (eds) (1984) The Biogeochemical Cycling of Sulphur and Nitrogen in the Remote Atmosphere. NATO ASI Series, Reidel, Dordrecht. 

---