Deposition of atmospheric polycyclic aromatic hydrocarbons in rural areas: Current data and historical record from an ombrotrophic peatland

Abstract

Atmospheric concentrations of 18 polycyclic aromatic hydrocarbons (PAHs) were measured in a rural area in northern Spain. Both the gas phase and particulate fraction were determined to evaluate the types and abundance of PAHs taken up by vegetation and the historical record of PAH deposition in an ombrotrophic peatland over the last 300 years. The total atmospheric PAH concentration was ca. 2.5 ng m−3, a value that is slightly lower value than those found in other rural areas, consistent with those of remote areas (Pyrenees, Alps, and Caledonian Mountains), and much lower than those recorded in urban areas. The particulate fraction showed a greater content of high molecular weight PAHs, whereas the gas phase was enriched in low molecular weight homologues. The concentration of total PAHs in the gas phase was higher than that in the particulate fraction (ca. 80%) and similar to that found in other localities in remote areas. PAHs showed seasonal variability. In this regard, the highest concentrations in the gas phase occurred in winter and autumn, whereas in the particulate fraction they were found in winter and spring. Of note, the concentrations of PAHs increased in the particulate fraction during the years in which fires occurred. The PAH content in peat-forming plants in this area showed a similar distribution to that of the gas phase. The historical record of the depositional fluxes of PAHs in an ombrotrophic peatland in the study area, which was dated radiometrically, allowed to reconstruct the changes in pollutant content between 1775 and the present. In general, the PAHs detected were of pyrogenic origin (fossil fuels and wood combustion). The concentrations of these pollutants increased from uniform background levels at the turn of the second half of the 19th century, which were linked to industrial development, to maximum values during the first half of the 20th century until the beginning of the 21st century, when the extraction and combustion of coal was extensive close to the study area. In contrast, in the uppermost part of the record, PAH concentrations decreased. This reduction is attributed to the implementation of environmental policies, although the concentrations of these pollutants were still greater than during the preindustrial period. To gain a detailed understanding of the deposition and evolution of PAHs in the study area, here it is reported on a new method that integrates current atmospheric data on PAHs with information on their accumulation in plants and the historical peat record of a rural area in Spain. The methodology described herein could be applied to other scenarios in the context of PAH pollution.