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Daily Maximum Erythemal Dose Rates in the Tropics.
Abel A Silva1, Ana L C Yamamoto2, Marcelo P Corrêa2
1Instituto de Estudos Avançados (IEAv), São José dos Campos, Brazil.
Photochemistry and Photobiology
|November 23, 2018
Summary
Clouds significantly impact the timing and intensity of maximum erythemal dose rate (EDRmax), often increasing it beyond clear-sky levels. Factors like solar zenith angle, altitude, ozone, and aerosols also influence daily EDRmax in tropical regions.
Area of Science:
- Atmospheric Science
- Solar Radiation
- Photobiology
Background:
- Maximum erythemal dose rate (EDRmax) typically peaks at local noon but is influenced by atmospheric conditions.
- Clouds, solar zenith angle, altitude, ozone, and aerosols are key determinants of EDRmax timing and magnitude.
Purpose of the Study:
- To analyze the daily incidence of EDRmax in Belo Horizonte, Brazil, over a five-year period.
- To investigate the influence of clouds, solar zenith angle, and other factors on EDRmax variations.
Main Methods:
- Collected five years of daily EDRmax data for Belo Horizonte (19.92°S, 43.94°W, 858 m a.s.l.).
- Analyzed EDRmax variations in relation to solar zenith angle, total ozone column (TOC), cloud cover, cloud genera, and aerosols.
- Quantified radiation enhancement events caused by specific cloud types.
Main Results:
- Daily EDRmax values ranged from 0.063 W m⁻² (winter) to 0.486 W m⁻² (summer).
- Cloudless day EDRmax varied seasonally, from 0.143 W m⁻² (winter) to 0.336 W m⁻² (summer).
- Cloud-induced radiation enhancement increased EDRmax by up to 45%, with Cumulus, Altocumulus, Altostratus, and Stratocumulus being primary contributors. Aerosols attenuated EDR by an average of 22%.
Conclusions:
- Cloud cover and type significantly alter EDRmax timing and intensity, often leading to radiation enhancement.
- Seasonal variations in solar zenith angle and TOC also play a crucial role in EDRmax.
- Aerosols can notably attenuate erythemal UV radiation at ground level.
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