Solar Ultraviolet Radiation in Pretoria and Its Relations to Aerosols and Tropospheric Ozone during the Biomass Burning Season

Abstract

Biomass burning has an impact on atmospheric composition as well as human health and wellbeing. In South Africa, the biomass burning season extends from July to October and affects the aerosol loading and tropospheric ozone concentrations which in turn impact solar ultraviolet radiation (UVR) levels at the surface. Using ground-based observations of aerosols, tropospheric ozone and solar UVR (as well as modelled solar UVR) we investigated the impact of aerosols and tropospheric ozone on solar UVR in August, September, and October over Pretoria. Aerosol optical depth (AOD) and tropospheric ozone reached a peak between September and October each year. On clear-sky days, the average relative difference between the modelled and observed solar Ultraviolet Index (UVI) levels (a standard indicator of surface UVR) at solar noon was 7%. Using modelled UVR—which included and excluded the effects of aerosols and tropospheric ozone from biomass burning—aerosols had a larger radiative effect compared to tropospheric ozone on UVI levels during the biomass burning season. Excluding only aerosols resulted in a 10% difference between the modelled and observed UVI, while excluding only tropospheric ozone resulted in a difference of −2%. Further understanding of the radiative effect of aerosols and trace gases, particularly in regions that are affected by emissions from biomass burning, is considered important for future research.

Monitoring Solar Radiation UV Exposure in the Comoros

“…In the southern Indian Ocean, evidence of frequent occurrence of UVI enhancement by clouds was found [ 11 ]. Depending on quantities and their nature, aerosols may also contribute to UVR variability at the surface by scattering or by absorption [ 18 ]. Surface albedo also modulates surface UVI values, and these modulations can be an increase to the order of a 40% for snow covered surfaces [ 19 ].…”

Research trends in the field of ambient air quality monitoring and management in South Africa: A bibliometric review

“…Findings were that the difference between modelled and observed solar ultraviolet index at solar noon was 7 % while on the other hand excluding aerosols resulted in 10 % between modelled and observed UVI. ( Du Preez et al., 2021 ) Ambient Gaseous Pollutants in an Urban Area in South Africa: Levels and Potential Human Health Risk Annual levels of different criteria pollutants were as follows; NO 2 (39.442 µg/m 3 ), SO 2 (22.464 µg/m 3 ), CO (722.003 µg/m 3 ). while the 8-hour concentration was CO (649.902 µg/m 3 ) and O 3 (33.556 µg/m 3 ) and did not exceed the South African ambient National Air Quality Standards.…”

“…Over the city of Cape Town ( Kuyper et al., 2020 ) estimated that toluene and benzene concentrations were between 7.2 and 3.5 × 10 molecules cm while those of Hydroxyl were high in Cape Town and this was attributed to various anthropogenic activities around the city. Besides, the strides which have been made with regards air quality monitoring activities there have also been some progress regarding alternative prediction mechanisms as performed by ( De Lange et al., 2021 , Du Preez et al., 2021 ) experimented the use of Advanced Research Weather Research and Forecasting (WRF-ARW) model with four PBL schemes and ground-based measurements integrated with modelled solar ultraviolet respectively. Both approaches showed a lot of potential within the South African context as instruments of air quality monitoring.…”

Solar Ultraviolet Radiation Temporal Variability Analysis from 2-Year of Continuous Observation in an Amazonian City of Brazil

“…This spectrum of solar radiation has a direct effect on human health, terrestrial and aquatic ecosystems, and the degradation of materials [4,5]. The amount of UVR reaching the Earth's surface depends on solar variations (such as Schwabe solar cycle), on the variations in the Earth's position relative to the Sun, on atmospheric, geographical, and temporal parameters which include the angle 2 of 13 of incoming UVR (affected by latitude, season and time of day), altitude, albedo, clouds, aerosols, and others atmospheric constituents [6][7][8].…”