As aluminum center cannot be completely bleached with a plateau value in the ESR spectra

the residual dose must be subtracted from the equivalent dose in order to obtain the real paleo-dose.Two types of quartz samples extracted from granite and littoral sand were exposed directly to sun-light at four cities of different latitudes in China

in an attempt to study the latitude effect on bleaching results of the Al center ESR signal and to see the dependence of quartz origins.No significant difference was found in samples bleached at different latitudes

but significant differ- ence was found in samples of different sources.For quartz from granite

the bleaching rate is 40% to 50%

while only about 20% for littoral sand.