出典:Wiktionary
Sha'anxi
In the Hanyu Pinyin romanization system for Mandarin Chinese, the syllable-dividing mark (隔音符號/隔音符号 (géyīn fúhào)) should usually be added before a non-initial syllable beginning with a, o, or e. In the unique context of the word Shaanxi, the first syllable is shaan (spelled with two a's to distinguish the two Chinese provinces Shaanxi かつ Shanxi) and hence there should be no syllable-dividing mark.