Abstract: Although present in low concentrations in the atmosphere, mercury in particulate matter (PM) plays an important role in the biogeochemical process of mercury. With this in mind, this study aims to investigate mercury concentrations in particulate matter (PM2.5) samples from the regions of Campos dos Goycatazes (CG), Gávea (GA) and Serra dos Órgãos National Park (PARNASO). All samples were collected according to Brazilian standards (ABNT-NBR 9547/86) and the methods of the United States Environmental Protection Agency (US EPA) (Method IO – 2.1). PM concentrations were determined by gravimetric technique. The Direct Mercury Analyzer (DMA-80, Milestone Helpind Chemists) was used for total Hg analysis. Daily PM2.5 concentrations ranged from 13 to 36 μg m-3 , with a mean of 24 ± 12 μg m-3 for the GA region, and from 24 to 46 μg m-3 , with a mean of 33 ± 12 μg m-3 for the PARNASO region, and from 14 to 19 μg m-3 , with a mean of 17 ± 11 μg m-3 for the CG for the days sampled from July to October 2022. High levels of PM concentrations at PARNASO indicate a contribution from anthropogenic sources. Considering these values, no day sampled exceeded the value suggested by Brazilian legislation (60 μg m-3 ), but 65 % of the samples showed higher daily concentrations than suggested by WHO (15 μg m-3 ). Hg concentrations ranged from 223 to 366 pg m-3 , with a mean of 274 ± 65 pg m-3 for the GA region, and from 119 to 190 pg m-3 , with a mean of 155 ± 29 pg m-3 for the PARNASO region, and from 164 to 315 pg m-3 , with a mean of 258 ± 67 pg m-3 for the CG for the days sampled. Hg concentrations in the atmosphere showed significant spatial variation, with much higher values in urban areas than in the natural zone. The results showed that Hg concentrations in particulate matter are at the same level as those found in urban and industrial areas in US and northern Europe. At Parnaso, the presence of Hg may be due to anthropogenic sources, which may be local sources and/or long-range transport contributions. There exists an intriguing meteorological facet warranting consideration, pertaining to the atmospheric transport facilitated by mountain-valley interactions and sea-land breezes within the southern region of the Serra dos Órgãos. This phenomenon merits further in-depth exploration. In addition, the high concentrations of Hg found in Campos dos Goytacazes may be associated with the burning of biomass, since sugar cane is burned throughout the year in the region and also due to the application of pesticides in the most diverse crops in the municipality, many times without due control.

Keywords: Mercury, particulate matter, PM2.5, Rio de Janeiro.