Column abundance

The interplay of physical controls is less complicated in the Polar and Trade (tropical) domains. As shown in Figure 24.11a, only one phytoplankton bloom occurs in the Polar domain, but is larger in amplitude than at mid-latitudes (Westerlies). Phytoplankton growth in the subpolar region is prolific because uniformly cold atmospheric temperatures suppress density stratification of the water column. Abundant winds ensure that... 

It was not until the late 1970s that the importance of the nitrate radical was recognized when it was first reported by Noxon and co-workers (1978) in terms of its total column abundance, i.e., the concentration integrated through a column extending through the atmosphere from the earth s surface (see Chapter ll.A.4a). N03 was subsequently confirmed to be in the troposphere by Noxon et al. (1980) and by Platt and coworkers (1980, 1984) in polluted atmospheres and rural continental air. 

The use of the sun or moon as the light source allows one to measure the total column abundance, i.e., the concentration integrated through a column in the atmosphere. This approach has been used for a number of years (e.g., see Noxon (1975) for NOz measurements) and provided the first measurements of the nitrate radical in the atmosphere (Noxon et al., 1978). As discussed later in this chapter, such measurements made as a function of solar zenith angle also provide information on the vertical distributions of absorbing species. Cloud-free conditions are usually used for such measurements as discussed by Erie et al. (1995), the presence of tropospheric clouds can dramatically increase the effective path length (by an order of... 

Atmospheric OH has been measured for a number of years using its absorption. For example, vertical column abundances of OH have been measured in a number of studies using the sun as a light source (e.g., Burnett and Burnett, 1981, 1996 Burnett et al., 1988 Burnett and Minschwaner, 1998). Over the past several decades, beginning with the measurements of Perner et al. (1976), absorption spectroscopy has been used to make measurements of OH over much shorter paths in the troposphere. The fundamental principles behind this technique have been described earlier in the discussion of DOAS spectrometry. Here we briefly discuss some of the aspects of the measurements that are unique to OH, as well as some typical applications. 

Wahner, A., and C. Schiller, Twilight Variation of Vertical Column Abundances of OCIO and BrO in the North Polar Region, J. Geophys. Res., 97, 8047-8055 (1992). 

Rinsland, C. P., J. S. Levine, A. Goldman, N. D. Sze, M. K. W. Ko, and D. W. Johnson, Infrared Measurements of HF and HC1 Total Column Abundances above Kitt Peak, 1977-1990 Seasonal Cycles, Long-Term Increases, and Comparisons with Model Calculations, J. Geophys. Res., 96, 15523-15540 (1991). 

The high quantum yield of photolysis of C02 suggests the rapid destruction of C02 and the formation of CO and 02 by sunlight of wavelengths below about 2200 A (see Section VI- 5). According to an estimate by McElroy and McConnell (675), the column abundance of C02 in the atmosphere is 2 x 1023 molec cm"2. With a dissociation rate of 2.5 x 1012 cm-2 sec-, the entire C02 may be destroyed in less than 10,000 years. 

NOx emissions from subsonic aircraft flying in the troposphere and the lowermost stratosphere lead to a significant increase in ozone in the upper troposphere. Emissions of NOx and H20 from supersonic aircraft cruising in the stratosphere are calculated to decrease the column abundance of O3. The effects of aircraft emissions are found to be strongly dependent on flight altitudes and on assumed emission indices for NOx. 

One last way to express concentration is the column abundance, which is the total amount or mass of a gas within a vertical column of air above a specific location. Column abundances have units of amount per area (i.e., mol m-2, kg m-2). In the particular case of stratospheric ozone, data are... 

Fig. 15. The diurnal variation of the column densities of HCl, CIO, Cl, CIONO2 and HOQ from Ko and Sze. Calculated values are for column abundances above 20 km, 30 km, 36 km and 44 km in panels (a), (b), (c) and (d), respectively. Calculations correspond to 19°N latitude for December conditions.

Fig. 16. The column abundance of ozone as a function of stratospheric chlorine for three assumed mixing ratios (by volume) of NO, - NO + NO2 + HONO2 taken from Prather et al.

The total ozone column abundance can be obtained by measuring the differential absorption of reflected near-UV radiance at two distinct wave-... 

Note that N2 and N3 represent the total slant column abundances (molec cm-2), and (02) and (O3) the number densities (molec cm-3), of 02 and O3, respectively. Heating rates are in degrees K/sec.)... 

Column abundance Vertically integrated number density of substance (expressed in particles m—2 (SI) or cm-2 (cgs)). In the case of ozone, the column abundance is often expressed in Dobson units (DU). One Dobson unit corresponds to the height (in 10 3 cm) of an ozone column if the gas were at standard temperature and pressure. It is equivalent to 2.687 x 1016 molecules cm-2. 

The global distribution of total ozone as a function of latitude and time deduced from the observations by the Total Ozone Mapping Spectrometer (TOMS) on board the Nimbus 7 satellite is presented in Figure 5.6. This figure shows that the ozone column abundance is typically 260-270 DU in the tropics. The peak total ozone... 

Figure 5.9. Evolution of the total ozone column abundance during 1994 at Uccle, Belgium (De Muer, private communication).

The nighttime distribution of NO3 has been measured, for example, by Naudet et al. (1981) using stellar occupation, and the distribution is close to that predicted by theory. Its total column abundance has also been reported by Noxon et al. (1978), Solomon et al. (1989a) and by Weaver et al. (1996). 

HOC1 has been observed by infrared thermal emission (Chance et al., 1996) and by infrared solar absorption (Toon et al., 1992a). The column abundance of OCIO has been measured in Antarctica using visible absorption methods, for example, by Solomon et al. (1987), and in the Arctic by Wahner and Schiller (1992). 

Stacknik et al, 1992), and by in-situ tunable diode laser spectrometry (May and Webster, 1989). In the 1990s, global distributions of this gas were obtained by the HALOE infrared instrument aboard UARS (Russell et al., 1993 Figure 5.59). The distribution and variability of the total column abundances of HC1 have been reported, for example, by Mankin and Coffey (1983). 

Burnett, C.R., and E.B. Burnett, Vertical column abundance of atmospheric OH at solar maximum from Fritz Peak, Colorado. Geophys Res Lett 9, 708, 1982. 

Mahieu, E., C.P. Rinsland, R. Zander, P. Demoulin, L. Delbouille, and G. Roland, Vertical column abundances of HCN deduced from ground-based infrared solar spectra Long-term trends and variability. J Atmos Chem SO, 299, 1995. 

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