An air mass originating in the Pacific Ocean near the equator would be labeled?

The circulation system is called a Hadley Cell.
The wind patterns it generates are called Trade Winds.

A Hadley cell is a circulation pattern that usually occurs in the atmosphere in the tropics.

It rises near the equator, travels towards the north or south poles at an altitude of about 10-15 kilometers, and decends in the subtropics.

This circulation is has a major influence on the trade winds, tropical rainbelts, and jet streams.

The air mass, which is a product of the Hadley Cell dynamics and influenced by the Earth's Coriolis Effect, would be labled a Maritime Tropical air mass (mT).