Ultraviolet Radiation Environment of a Tropical Megacity in Transition: Mexico City 2000-2019.

Tropical regions experience naturally high levels of UV radiation, but urban pollution can reduce these levels substantially. We analyzed 20 years of measurements of the UV index (UVI) at several ground-level locations in the Mexico City Metropolitan Area and compared these data with the UVI values derived from the satellite observations of ozone and clouds (but not local pollution). The ground-based measurements were systematically lower than the satellite-based estimates by ca. 40% in 2000 and 25% in 2019. Calculations with a radiative transfer model using observed concentrations of air pollutants explained well the difference between satellite and ground-based UVI and showed specific contributions from aerosols, O3, NO2, and SO2 in decreasing order of importance. Such large changes in UV radiation between 2000 and 2019 have important implications ranging from human health (skin cancer and cataract induction) to air pollution control (photochemical smog formation).

Climate change and its relationship with non-melanoma skin cancers.

Climate change is affecting both the environment and human behaviour. One significant impact is related to health, as detailed in the IPCC 2014 report. In the present work, and as a contribution to this commemorative special issue to Prof. Dr Jan van der Leun, we present the results of the squamous (SCC) and basal-cell carcinoma (BCC) incidence change in relation to the ambient temperature increase. This increase is produced by global warming, mainly induced by anthropogenic atmospheric emissions of greenhouse gases. We have broadened a previous study conducted by van der Leun et al. (Photochem. Photobiol. Sci., 2008, 7, 730-733), by analysing the effective carcinogenicity of UV dose, for the period 2000-2200 and four climate change scenarios (called RCP2.6, RCP4.5, RCP6.0 and RCP8.5). The corresponding percentage increases of the incidence of SCC for 2100 are 5.8, 10.4, 13.8 and 21.4%, and for 2200 they are 4.3, 12.1, 19.0 and 40.5%. In a similar way, the percentage increases of the incidence of BCC for 2100 are 2.8, 4.9, 6.5 and 9.9% and for 2200 they are 2.0, 5.8, 8.9 and 18.2%. We report the SCC and BCC percentage effective incidence results as a function of time, for the whole 21st century and we extended the analysis to the 22nd century, since people possibly affected (like the Z and T generations, born at the beginning of this century) will have a life expectancy extending up to the final decades of the present century and even to the first ones of the next century.

Combination of sunlight, oxidants, and Ce-doped TiO2 for phenol degradation.

The degradation of phenol was used as a model reaction to investigate the photocatalytic properties of cerium-doped (0.1 nominal atomic percent) TiO2 catalysts in the presence and in the absence of oxidants: persulfate (PS) or hydrogen peroxide (HP). Experiments were performed in batch reactors using either artificial light (ultraviolet or visible) or solar exposure during spring-summer seasons in La Plata City (34.90° S, 57.92° W, 15 MASL). The formation of hydroquinone, catechol, and p-benzoquinone was observed in all the experiments. Additionally, for the experiments with PS (with or without catalyst), evidence of the formation of dimers and trimers was found. Total degradation of phenol (250 µM) was achieved with doped material and 7 mM of PS (two doses) after 3 h of solar exposure (H SUV, T = 2.9 ± 0.6 105 J m-2).

Photodynamic inactivation induced by carboxypterin: a novel non-toxic bactericidal strategy against planktonic cells and biofilms of Staphylococcus aureus.

Microbial related contamination is of major concern and can cause substantial economic losses. Photodynamic inactivation (PDI) has emerged as a suitable approach to inhibit microorganism proliferation. In this work, PDI induced by 6-carboxypterin (Cap), a biocompatible photosensitizer (PS), was analyzed. The growth inhibition of Staphylococcus aureus exposed to artificial UV-A radiation and sunlight in the presence of Cap was investigated. After UV-A irradiation, 50 µM Cap was able to decrease by three orders (with respect to the initial value) the number of S. aureus cells in early biofilms. However, this concentration was 500 times higher than that needed for eradicating planktonic cells. Importantly, under solar exposure, 100 µM Cap was able to suppress sessile bacterial growth. Thus, this strategy is able to exert a bactericidal effect on sessile bacteria and to eradicate planktonic cells by exposing the Cap-containing sample to sunlight.

UV index values and trends in Santiago, Chile (33.5°S) based on ground and satellite data.

We report on the surface UV index (UVI) variations in Santiago (Chile) a city with high air pollution and complex surrounding topography. Ground-based UV measurements were continuously carried out between January 1995 and December 2011, by using a multi-channel filter radiometer (PUV-510). Ground-based measurements and satellite-derived data retrieved from the Total Ozone Mapping Spectrometer (TOMS), the Ozone Monitoring Instrument (OMI), and the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), were compared. We found that satellite-derived UVI products largely overestimate surface UVI. Our ground-based UVI measurements were significantly lower than TOMS-derived UVI data: (46.1±6.3)% (in the period 1997-2003), and OMI-derived UVI data: (47.0±6.3)% (in the period 2005-2007). Clear-sky SCIAMACHY-derived UVI were found to be also nearly systematically greater than ground-based UVI measurements in the period 2002-2011. An exceptionally long period of clear skies between December 2010 and January 2011 was used to test further satellite-derived UVI data; in the whole period, OMI and SCIAMACHY data were 53.1% and 38.3% greater than our ground-based measurements, respectively. These differences are presumably due to aerosol load associated with the local pollution and the complex topography surrounding Santiago. In addition, linear regression allowed us to estimate trends that we use for forecasting. Methodological details are provided below.