Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
achieve the necessary
uncertainty limits at these short
wavelengths. If changes in
column ozone from aviation are
larger than 1%, longer
wavelengths may be adequate
for detection.
In contrast to ozone changes,
UV attenuation by aerosols and
clouds varies weakly with
wavelength, except
(occasionally) when clouds
contain ozone in significant
amounts. The effects of
aerosols and clouds on groundlevel
UV irradiances have been
studied with the aid of model
simulations as well as by
measurements (Frederick and
Snell, 1990; Bais et al., 1993;
Frederick and Steele, 1995;
Blumthaler et al., 1996;
Bodeker and McKenzie, 1996;
Kylling et al., 1997). Although
an increase in aerosols will
generally lead to a reduction in
UV irradiance via
Figure 5-2: UVery as a function of latitude for the 1992
background atmosphere for January, April, July, and October.
backscattering to space, an increase in radiation is possible, depending on the relative altitudes of the aerosol and ozone layers and the solar zenith angle (Davies,
1993; Tsitas and Yung, 1996). Temporal variations in cloudiness and, to a lesser degree, aerosols lead to large variations in UV irradiance measured at a fixed site.
This degree of natural variability will complicate attempts to detect small changes in UV irradiance related to potential changes brought about by future aviation.
Thus, it appears that some existing instrumentation is capable of detecting future changes in UV caused by changes in ozone and perhaps by aerosols and clouds.
With the current state of technology, properly maintained instruments should be able to detect UV irradiances that differ from the unperturbed state by 2-5% or more.
Whether it would be feasible to distinguish UV changes caused by aircraft emissions from changes caused by the natural background variability in atmospheric
parameters depends on the relative magnitude of these variations and the duration of the data sets.
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