  Effects of a single impurity potential on bulk properties of a spinful
Tomonaga-Luttinger (TL) liquid is studied. A boundary bosonization technique is
developed to include the impurity potential of {\it arbitrary} strength $V$.
Our new bosonization formula for fermion field $\psi$ smoothly connects the two
existing expressions in the strong ($V = \infty$) and the weak ($V = 0$)
impurity limits. With use of the formula, we found the TL parameters determined
from the long-distance correlation functions are renormalized due to the
partial transmission through the impurity potential.
