Surface ozone trends reversal for June and December in an Atlantic natural coastal environment.

Surface ozone and temperature trends were investigated using records from 2000 to 2021 in Southwestern Europe, at El Arenosillo observatory, focusing on June and December. The ozone trends for daily percentiles were increasing in June for lower percentiles (2.5 ± 1.2 ppb decade-1 for the 5th percentile) and decreasing for higher (- 2.2 ± 1.4 ppb decade-1 for the 95th percentile); in December, the trends were growing in the entire range of percentiles, with a peak of 2.2 ± 0.8 ppb decade-1. A declining trend was obtained for the geopotential height at the pressure level of 850 hPa (Z850) in June while highlighting the upward trend in December (26.3 ± 6.5 m decade-1). The hourly trends for ozone and temperature were also explored in these months. In June, the nocturnal ozone trends were growing (4.0 ± 1.2 ppb decade-1 or 10% decade-1 at 8:00 UTC) associated with temperature rises while in the daytime, a decrease in temperature was observed along with an ozone decreasing trend (- 2.6 ± 1.6 ppb decade-1 or - 5% decade-1 at 18:00 UTC). Hourly ozone and temperature trends in December were increasing with peaks of 3.0 ± 0.9 ppb decade-1 (~ 8% decade-1) at 12:00 UTC and 1.6 ± 0.3 °C decade-1 at 19:00 UTC. Two representative scenarios of these months were studied. The ozone decreases in June could be associated with several factors, decreasing in temperatures and a possible weakening of the anticyclonic conditions leading to changes in the mesoscale processes' development. The strengthening of the Azores anticyclone in December could be enhancing the upward ozone trend observed. It is unknown whether the reversal ozone pattern trends found in this region are a local phenomenon; although we suggest that it could be happening on a larger scale as well, future studies should be carried out.

A simple and precise methodology to determine particulate matter mass in atmospheric filters; validation and application cases.

In the past decades, particulate matter (PM) measurements have been used extensively in atmospheric sciences, as it allows studying the evolution of tracers for different atmospheric processes and the effects of atmospheric pollution on human health. However, measuring PM mass requires a constant control of the laboratory conditions due to its capacity to absorb humidity. For this reason, this study was focused on developing a novel, simple and precise methodology to determine the corrections of the filter mass due to humidity changes. The control and corrections are possible using a "control filter", which is always adapted to the environmental conditions of the laboratory. To check the consistency of this method, it was proved that the mass of any problem filter and that of the control filter behave in a very similar way. This allows quantifying the mass changes of any problem filter by using the control filter, where the problem filters and the control filter must have the same chemical composition and dimensions. To validate this methodology, a comparison was made between the methodology proposed in this study (Method-1) and the one proposed by the EPA (Method-2), which is generally applied. The particulate matter mass (m) was obtained for a problem filter for different weights, achieving similar values using both methods. However, Method-1 still provided reliable mass measurements for relative humidities very different from 50%, even as low as 18%. It was also proved that the adsorption or loss of water by the particulate matter can be neglected, since m is much smaller than the blank filter mass. Method-1 was also employed in several samplings carried out using three PM10 samplers to determine contaminants, such as 7Be and 210Pb, obtaining a good agreement between all particulate masses and activities measured by the three samplers for all samplings.

Evaluation of the radioactive pollution in the salt-marshes under a phosphogypsum stack system.

Next to the city of Huelva (SW of Spain), around 100 Mt of phosphogypsum (PG) are stored in stacks on the salt-marshes of the Tinto River estuary covering a surface of about 1000 ha. Due to the high content of 238U series natural radionuclides of the PG, its acidic nature (pH about 3), and the fact that PG stacks were disposed without any kind of isolation from the substrate, they could produce a potential radioactive impact into the underlying sediments. The aim of this work is to assess the pollution of the underlying sediments by natural radionuclides coming from the PG stacks. To this end, seven cores were taken, and PG and sediments samples collected at different depths were analysed. The activity concentrations of the main long half-live natural radionuclides of interest were determined by applying both gamma-ray and alpha-particle spectrometry radiometric techniques. The results of this study showed that the first decimeters of salt-marsh sediment act as a "barrier" for the radionuclides coming from the PG stacks decreasing rapidly its activity concentration in depth, affecting mainly sediments located in the first 20 cm below the contact due to mixing processes. While 230Th, 226Ra and 210Pb pollution is mainly restricted to the first 20 cm of sediments, U-isotopes can reach higher depths (up to around 50 cm) by leaching processes due to their lower reactivity and higher concentration in the polluted leachates. The obtained results have high relevance for the design of the perimeter channel which is projected to build in the restoration project, suggesting that should has around 1 m deep under the base of the PG stacks, to ensure the full collection of polluting leachates, and to prevent their release into the estuary of the Tinto River.

Pollution evaluation on the salt-marshes under the phosphogypsum stacks of Huelva due to deep leachates.

In the salth-marshes of the Tinto River (Huelva estuary, SW Spain), are stored in stacks around 100 Mt of PG, covering a surface of 1000 ha without any type of isolation, which produce an important impact in the surrounding environment. On the other hand, this ecosystem it is affected by acid mine drainage (AMD) from sulphide mines located upstream the Tinto River. The aim of this study is to evaluate the deep pollution of the underlain salt-marsh sediments due to leachates from the PG stacks. For that purpose, 7 cores were collected from zones 2 and 3 of the stacks, and PG and salt-marsh sediments samples from different depths were analyzed. The physicochemical parameters, mineralogy, granulometry and the concentration of the main elements of interest were determined in the samples. Most analysed salt-marsh sediments are not affected by PG stacks pollution, because sediments act as a "barrier" for the leachates from the PG, concentrating the contaminants in the first decimetres (0.5 m) under PG-sediments contact, and the deep infiltration is very limited. The obtained results suggest that the perimeter channel which is projected to build in the restauration project, should has a depth of 1 m below the level of the PG stacks for assuring the complete collection of leachates from the stacks, and avoid their liberation into the Tinto River estuary.