Here's why:
* Combining vowels are used in medical terms to ease pronunciation when combining root words. They are typically inserted between a root and a suffix.
* Pulmonology is derived from the Latin word "pulmo" (lung) and the Greek suffix "-logia" (study of).
* The "o" in "pulmo" acts as a connecting vowel, making the word pronounceable without needing an additional combining vowel.
Therefore, "pulmonology" is a correctly formed word, and the use of a combining vowel is not necessary.