FIGURE 11.14 Measurement of NO, using DOAS in Riverside, California, on the evening of September 12, 1979 (adapted from Piatt et al, 1980b).
environment in Ireland at concentrations up to 6 ppt (Alicke et al., 1999).
Table 11.3 gives detection limits reported for DOAS measurements of OH and the halogen oxide radicals at a path length of 5 km and assuming a detectable absorbance of 10~4. This method provides ppt to sub-ppt sensitivities for these radicals.
grow in as the sun comes up, initiating photolysis which forms OH (see Chapter l.B).
As discussed in Chapter 6.J.4, there is a halogen-catalyzed destruction of surface-level 03 at polar sunrise in the Arctic and bromine atoms are believed to be the major reactant destroying 03:
In this case, BrO should be generated, and indeed, it has been observed by DOAS under these conditions at concentrations up to ~30 ppt (Tuckermann et al., 1997). Figure 11.16 shows a DOAS spectrum taken at polar sunrise at Alert in April 1992 and a reference spectrum of BrO (instrument features are included in this); clearly, BrO is present, in this case at a concentration of 17 ppt (Piatt and Hausmann, 1994). BrO has also been detected at the Dead Sea, Israel, and attributed to heterogeneous reactions of the sea salt. CIO has also been detected at concentrations up to ~40 ppt under these conditions using DOAS (Tuckermann et al., 1997), and IO in a midlatitude coastal marine a o c co .o
308.00 308.05 308.10 Wavelength (nm)
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