PUC-Rio study reveals high concentrations of mercury in the air in fire-affected areas

The research conducted by the Laboratory of Atmospheric Chemistry, Department of Chemistry of the PUC-Rio Scientific Engineering Center, funded by FAPERJ, evaluated the concentration of mercury in particulate matter (PM_2.5) in the air at three different locations: an urban area (Gávea), an urban area affected by sugarcane burning (Campos dos Goytacazes) and a nature reserve (Parque Nacional da Serra dos Órgãos – Parnaso) in the state of Rio de Janeiro. The results showed that 63% of the samples had daily PM concentrations_2.5 higher than the standards set by the World Health Organization, which may pose potential problems to health and well-being, especially to the respiratory tract.

The work – which has just been published in the scientific journal of the Royal Society of Chemistry – is the result of a collection over the years 2022–2023. The average concentration of mercury in PM_2.5 The highest levels occurred in Campos dos Goytacazes (169 ± 139 pg m⁻³), a sugarcane plantation area, where burning is a recurrent practice and may be the main source. Although PARNASO is a conservation area, the average mercury concentration in PM_2.5 (110 ± 71 pg m⁻³) was greater than in Gávea (81 ± 116 pg m⁻³). Possible causes of this difference are the proximity of the sampling points to the highway, in addition to long-distance transportation.

“The novelty of our results lies in the quantification of mercury concentrations in particulate matter in Rio de Janeiro, identifying seasonal variations and possible sources of emissions. Rio de Janeiro, as one of the largest urban and industrial centers in Brazil, has unique characteristics that make the investigation of these pollution levels relevant, especially due to the combination of intense urbanization and industrial activity in the region”, comments Luis Fernando Mendonça da Silva, doctoral student at CTC/PUC-Rio, who developed the work.

This is the first study in Rio de Janeiro that focuses on the analysis of mercury in particulate matter carried out with a direct-reading Hg analyzer. In addition to these highlights, professor at the Scientific Technical Center at PUC-Rio and Coordinator of the Atmospheric Chemistry Laboratory, Adriana Gioda, highlights an important characteristic of the particles – that they are not static and are not limited by their geographical boundaries.

“The important factor is that fires, regardless of the type of biomass, not only cause air pollution through their particle emissions, but also through the components associated with them. In this study, mercury was used. In Parnaso, it is estimated that the concentration is lower because it is a protected forest area. However, because it is close to a highway, where the combustion of diesel fuel emits Hg, the levels are high. The particles are not static and can come from the highway or from a distance. It is important to remember that air masses are not affected by geographical boundaries, he said.

Four Seasons in a Year

Seasonal variations were also part of the CTC/PUC-Rio researchers’ evaluation. The figures show that the highest percentage of mercury is in PM_2.5 found in autumn: at 37%; followed by 28% in spring; 24% in winter and 11% in summer. The differences between mercury in the samples were found to be much more significant in spring, autumn and winter than in summer. The hypothesis is that high temperatures and greater solar radiation in summer may facilitate the transformation of gas into particles.

“Hg concentrations were approximately twice as high during the dry season compared to the summer, suggesting contributions from local sources and transboundary pollution. Furthermore, we observed significant seasonal variations, with higher fire rates in the urban hinterland (Campos), compared to the capital and protected sites”, concludes Adriana Gioda, LQA coordinator of the Chemistry Department at CTC/PUC-RIo.

According to the researchers, additional studies should be conducted in the future to understand the cycle of these pollutants in Rio de Janeiro State.