An increase in relative humidity of 35% can increase the emissions of formaldehyde by what factor?

• A. 0.5
• B. 3.0
• C. 1.8 - 2.6
• D. 5.0

Answer: (C)

Humidity drives formaldehyde off-gassing from building materials. When moisture increases, it facilitates desorption of formaldehyde from resins and porous substrates, so the emission rate rises nonlinearly with relative humidity. For a moderate increase in humidity, emissions are typically about twice as high, sometimes a bit more—roughly twofold to two-and-a-half times higher. That makes a doubling the best-match expectation for this change. The other possibilities would imply a reduction or a much larger jump, which isn’t consistent with how emission rates generally respond to a moderate humidity rise.