Seasonal Erythemal UV Doses in Belo Horizonte, Brazil

Ground-based and Satellite Measurements of Solar Spectral Irradiances at 305 nm and 380 nm at a Tropical Site

The solar radiation has been monitored through ground-based and satellite instruments all over the world for decades. This is also important for both checking and validation of satellite probing. In this work, we compare spectral irradiances at 305 nm (UV-B) and 380 nm (UV-A) from a ground-based radiometer and the Ozone Monitoring Instrument (OMI) for a tropical site in 2019-2020. Measurements had the auxiliary support of a ground-based imager to identify cloud cover. The presence of clouds introduces the largest differences between satellite and ground-based measurements. In fact, on average, for all-sky (AS, only cloudy skies) conditions such differences (satellite - ground-based) were 46% and 30% at 305 nm and 380 nm, respectively, while for cloud-free-sky (CFS) conditions the differences dropped to 17% and 8%. In addition, the linear fitting between ground-based and satellite measurements yielded a coefficient of determination (r² ) of 0.857 (for AS) and 0.984 (for CFS) at 305 nm and 0.774 (for AS) and 0.950 (for CFS) at 380 nm. The differences between these AS and CFS values of r² were 95% statistically significant. Such results imply the hindrance clouds (and also aerosols based on the results for CFS) still set to obtain UV-B and UV-A surface irradiance from satellite probing.

A Semiempirical Approach to the Determination of Daily Erythemal Doses

The maintenance of ground-based instruments to measure the incidence of ultraviolet radiation (UVR) from the Sun demands strict and well-developed procedures. A piece of equipment can be out of service for a couple of weeks or months for calibration, repair or even the improvement of the facilities where it has been set up. However, the replacement of an instrument in such circumstances can be logistically and financially prohibitive. On the other hand, the lack of data can jeopardize a long-term experiment. In this study, we introduce a semiempirical approach to the determination of the theoretical daily erythemal dose (DED_t ) for periods of instrumental absence in a tropical site. The approach is based on 5 years of ground-based measurements of daily erythemal dose (DED) linearly correlated with parameters of total ozone column (TOC) and reflectivity (R_PC ) from the Ozone Monitoring Instrument (OMI) and the cosine of solar zenith angle at noon (SZA_n ). Seventeen months of missing ground-based data were replaced with DED_t , leading to a complete 5-year series of data. The lowest and the highest values of typical DED were 2411 ± 322 J m^-2 (1σ) (winter) and 5263 ± 997 J m^-2 (summer). The monthly integrated erythemal dose (mED) varied from 59 kJ m^-2 (winter) to 162 kJ m^-2 (summer). Both of them depended mainly on cos(SZA_n ) and R_PC . The 12-month integrated erythemal dose (12-ED) ranged from 1350 kJ m^-2 to 1546 kJ m^-2 , but it can depend significantly on other atmospheric parameter (maybe aerosols) not explicitly considered here.

Outdoor Exposure to Solar Ultraviolet Radiation and Legislation in Brazil

The total ozone column of 265 ± 11 Dobson Units in the tropical-equatorial zones and 283 ± 16 Dobson Units in the subtropics of Brazil are among the lowest on Earth, and as a result, the prevalence of skin cancer due to solar ultraviolet radiation is among the highest. Daily erythemal doses in Brazil can be over 7,500 J m. Erythemal dose rates on cloudless days of winter and summer are typically about 0.147 W m and 0.332 W m, respectively. However, radiation enhancement events yielded by clouds have been reported with erythemal dose rates of 0.486 W m. Daily doses of the diffuse component of erythemal radiation have been determined with values of 5,053 J m and diffuse erythemal dose rates of 0.312 W m. Unfortunately, Brazilians still behave in ways that lead to overexposure to the sun. The annual personal ultraviolet radiation ambient dose among Brazilian youths can be about 5.3%. Skin cancer in Brazil is prevalent, with annual rates of 31.6% (non-melanoma) and 1.0% (melanoma). Governmental and non-governmental initiatives have been taken to increase public awareness of photoprotection behaviors. Resolution #56 by the Agência Nacional de Vigilância Sanitária has banned tanning devices in Brazil. In addition, Projects of Law (PL), like PL 3730/2004, propose that the Sistema Único de Saúde should distribute sunscreen to members of the public, while PL 4027/2012 proposes that employers should provide outdoor workers with sunscreen during professional outdoor activities. Similar laws have already been passed in some municipalities. These are presented and discussed in this study.