The diffuse component of erythemal ultraviolet radiation.

Area of Science:

• Atmospheric Science
• Radiometry
• Photobiology

Background:

• Diffuse ultraviolet radiation (UVR) is a critical factor in human solar radiation exposure.
• Understanding the diffuse component is essential for accurate erythemal dose assessment.
• Tropical regions experience a wide range of solar zenith angles, influencing UVR patterns.

Purpose of the Study:

• To develop a semi-empirical method for calculating the diffuse erythemal dose rate (EDRDif).
• To analyze the relationship between diffuse UVR, global UVR, and cloud cover.
• To assess the contribution of diffuse UVR to total erythemal dose and its implications for skin health.

Main Methods:

• Synchronized measurements of diffuse UVR (UVDif) and global irradiances (UVG, EDRG) were utilized.
• A semi-empirical model was developed to derive the diffuse erythemal dose rate (EDRDif).
• The ratio of diffuse to global UVR (Dif/G) was analyzed in relation to cloud cover.

Main Results:

• The ratio Dif/G showed a quadratic dependence on cloud cover (r² = 0.79).
• Maximum EDRDif values frequently exceeded moderate UV-Index levels, reaching extreme ranges during spring-summer.
• The daily diffuse erythemal dose (daily EDDif) averaged 2673 J m⁻², constituting at least 48% of the daily global erythemal dose (daily EDG) under clear skies.

Conclusions:

• Diffuse UVR is a significant threat, contributing substantially to the total erythemal dose.
• High levels of EDRDif pose a risk of sunburn, particularly for individuals with lighter skin types (I and II).
• Cumulative exposure to diffuse UVR can cause long-term harm across all skin types.