Indoor Air Quality

Indoor air quality concerns the concentration and effects of pollutants in the air inside buildings.

Definition

The character of the air within and around buildings as it relates to the health and comfort of occupants, determined by indoor pollutant sources, outdoor air infiltration, and ventilation.

Scope

This topic covers the sources, behavior, and effects of pollutants in indoor environments where people spend most of their time. It addresses combustion products, volatile organic compounds, radon, environmental tobacco smoke, biological agents such as mold and allergens, and the role of ventilation in diluting or removing pollutants. The relationship between indoor and outdoor air and the concept of building-related illness are also covered.

Core questions

• What are the major sources of indoor air pollutants?
• How does ventilation affect indoor pollutant concentrations?
• Why can indoor pollutant levels exceed outdoor levels?
• What is radon and why is it an indoor concern?

Key theories

Source strength and ventilation balance

Indoor pollutant concentration reflects a balance between emission from indoor sources and removal by ventilation and deposition, so reducing sources or increasing fresh-air exchange lowers exposure.

Indoor accumulation of soil gases

Radon, a radioactive gas from soil and rock, can accumulate to elevated levels indoors by entering through foundations, illustrating how confined indoor spaces concentrate pollutants from outside sources.

Clinical relevance

Indoor air pollutants are associated with respiratory irritation, allergic responses, and, in the case of radon, increased lung-cancer risk; characterizing indoor sources and ventilation informs building design and exposure reduction.

Evidence & guidelines

Indoor pollutant levels are commonly compared against health-based reference values such as the WHO guidelines for indoor air quality, used here descriptively to explain how indoor air is assessed rather than as prescriptive limits.

History

Indoor air quality gained recognition in the later twentieth century as tighter, more energy-efficient buildings reduced ventilation, and as concerns over radon, environmental tobacco smoke, and building-related illness grew.

Seminal works

• spengler2001
• manahan2017
• who2010iaq

Frequently asked questions

Why can indoor air be more polluted than outdoor air?

Buildings contain many pollutant sources, such as combustion appliances, furnishings, and cleaning products, and limited ventilation lets these pollutants accumulate, so indoor concentrations can exceed those outdoors.

What is radon and why does it matter indoors?

Radon is a naturally occurring radioactive gas that seeps from soil and rock; when it enters and accumulates in buildings, prolonged exposure increases the risk of lung cancer, making it a key indoor-air concern.