Definition
The branch of chemistry that studies chemical reactions caused or influenced by light energy. In aviation contexts, photochemistry explains how sunlight triggers reactions in materials such as aircraft finishes, plastics, fabrics, and fuels, often causing fading, weakening, or breakdown over time.
Plain English
The study of how light makes chemical changes happen. Sunlight can slowly alter materials -- bleaching paint, weakening plastic, or breaking down rubber -- and photochemistry is the science that explains why.
Context Anchor
Seen in aviation weather and atmosphere discussions, especially when explaining haze, smog, and visibility changes caused by sunlight acting on pollutants.
Derivation
From the Greek 'photo' meaning light, plus 'chemistry'. The name simply tells you it is the chemistry that happens because of light.
Why Pilots Care
Photochemical effects are why aircraft paint fades, why plastic windshields yellow and craze, and why fabric-covered surfaces deteriorate when left in the sun. Understanding this helps explain why hangaring, covers, and UV-resistant finishes matter for keeping an aircraft airworthy and presentable.
Grounding Statement
On a sunny day, light can make gases in polluted air change into new substances that make the air look hazy.
Intuition Check
Photochemistry is not photography, and it is not just any chemical process. In photochemistry, light is what starts or changes the chemical reaction.
Example Sentence 1
The yellowing of the old canopy was a result of photochemistry, with years of sunlight slowly breaking down the plastic.
Example Sentence 2
Over time, photochemistry caused by sunlight can degrade the paint and plastic parts on an aircraft.