Ozone Absorption of UV Radiation
The ozone layer partially absorbs UVB radiation (280-320 nm) but does not absorb UVA radiation (320-400 nm). 1
Key Distinctions Between UVA and UVB Absorption
UVB and Ozone Interaction
- UVB rays (280-315 nm) are partially absorbed by the ozone layer before reaching the earth's surface 1, 2
- Only approximately 5% of UV radiation reaching earth's surface is UVB, specifically because the ozone layer filters much of it 1
- The ozone layer principally absorbs ultraviolet radiation of wavelengths below 290 nm, providing partial protection against UVB 3
- Depletion of stratospheric ozone results in measurably increased UVB radiation at ground level, with documented increases in short-wavelength UV radiation during periods of ozone depletion 3, 4
UVA and Ozone Interaction
- UVA rays (315-400 nm) are NOT absorbed by the ozone layer and pass through it completely 1, 2
- Approximately 95% of UV radiation reaching the earth's surface consists of UVA, precisely because it is not filtered by the ozone layer 1
- UVA penetrates deeply into the skin, reaching both epidermis and dermis, causing premature aging and immune suppression 1, 2
Clinical Implications of This Distinction
Why This Matters for Skin Cancer Risk
- UVB's partial absorption by ozone makes ozone depletion particularly dangerous, as it directly increases carcinogenic UVB exposure at ground level 3, 4
- UVA exposure remains constant regardless of ozone levels, representing a "substantial background that is not affected by depletion of the ozone layer" 5
- Both UVA and UVB have been linked to skin cancer development, but through different mechanisms and exposure patterns 1, 2
Practical Protection Considerations
- Sunscreen must provide broad-spectrum protection against both UVA and UVB, since UVA reaches the skin regardless of ozone layer status 1
- The recommendation for broad-spectrum sunscreens (protecting against both UVA and UVB) exists because ozone only filters UVB partially, leaving UVA completely unfiltered 1