化 (hu`a/ change) is a derivation-like affix. Chinese derivation-like affixes are bound morphemes consisting of prefixes and suffixes that can be attached to free words and bound roots to form new nouns and verbs.
化 (hu`a/ change) normally serves as a nominalizer indicating the process of change in compound words. For instance, the noun 老化 (l˘ao-hu`a/ aging) is consist of an adjective 老 (l˘ao/ old) and an suffix 化 (hu`a/ change). By adding the nominal suffix -hu`a to the word l˘ao, a new word which emphasizes the process of aging is created.
There are several suffixes functioning as nominalizers in Chinese as well. For example, 度 (d`u/ degree) is a suffix relating to a different degree of measure. In compound words such as 透明度 (t`ou-m´ıng-d`u/ transparency), the nominal suffix -d`u is attached to the adjective 透明 (t`ou-m´ıng/ transparent) in order to nominalize the concept of transparency and underline the sense of measurement encompassed in this compound word.
Reference: Chinese: a linguistic introduction by Chao Fen Sun