Fig. 1. Schematic diagram for the cell used in the photodegradation study (modified from Balmer et al., 2000). Pyrex glass is adequate for our experiment in which near-soil-surface sunlight (terrestrial light) (wavelength > 290 nm; Schwarzenbach et al., 1993) is of interest. Pyrex glass does not completely block UV light between 290 and 325 nm. It is more transparent to UV light with wavelength > 325 nm than quartz.