What standard addresses Indoor Environmental Quality?

ASHRAE 62.1 is the standard for ventilation and acceptable indoor air quality in commercial and institutional buildings. It specifies the minimum ventilation rates and other measures to provide good indoor air quality for occupants. LEED v4 references ASHRAE 62.1 as a prerequisite for the Indoor Environmental Quality credit category.

ASHRAE 62.1 from the LEED v4 Green Associate Candidate Handbook, page 18.

Enhance Indoor Environmental Quality (IEQ) from the WBDG website, section on Adequate Ventilation and Exhaust.