Human Breathable Air in a Mediterranean Forest: Characterization of Monoterpene Concentrations under the Canopy

Abstract

Monoterpenes have been identified as potential determinants of the human health effects induced by forest exposure. The present study characterizes the total monoterpene concentrations at nose height in a Mediterranean Holm oak forest located in North-East Iberian Peninsula during the annual emission peak (summer and autumn: June to November) using a Proton Transfer Reaction–Mass Spectrometry (PTR-MS). Results show a strong variability of the total monoterpene concentrations in season and daytime. The concentration peak appears during July and August. These two months displayed two average maxima in their diel cycles: One during early morning (from 6:00 to 8:00, 0.30 ppbv for July and 0.41 ppbv for August) and another one at early afternoon (from 13:00 to 15:00, 0.27 ppbv during July and 0.32 ppbv during August). Monoterpene concentrations were strongly related with the temperature (exponentially) and solar radiation (rectangular hyperbolic relationship). The concentrations registered here are similar or higher than in previous ex situ studies showcasing the effects of forests on human health. These findings provide relevant data for the scientific and healthcare community by improving the understanding of monoterpene dynamics at nose height and suggesting further research on the effects of forests on human health, particularly in the Mediterranean region.

Forest Volatile Organic Compounds and Their Effects on Human Health: A State-of-the-Art Review

“…The biochemical composition of forest air tends to follow diurnal variations, with BVOCs concentration usually peaking early in the afternoon and, especially in summertime, even in the morning (around 2 h after dawn), and it can be markedly influenced by several factors, including meteorological conditions, altitude, seasons, sunlight exposure, and tree types [ 31 , 32 ]. For example, it has been demonstrated that the air of forests dominated by conifer trees has a higher concentration of VOCs if compared to that of forests with more deciduous trees [ 31 ].…”

“…From a quantitative point of view, studies which aimed to determine the atmospheric concentration of some categories of BVOCs under forest canopy reported heterogeneous findings, probably due to a significant influence of the abovementioned factors on the forest air composition: approximately, on the basis of available evidence, the total amount of terpenes can vary from a minimum of 3.5 to a maximum of 56.0 μg/m 3 , isoprene can range from 0.1 to 28.0 μg/m 3 , and monoterpenes may have an average concentration of 4.5 μg/m 3 , whereas the amount of LOX pathway products is usually below the upper threshold of 3.4 μg/m 3 [ 16 , 31 , 32 , 34 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ] ( Figure 3 ). In particular, if we only consider monoterpenes, the concentration range of seven of them under the canopy of a Scots pine forest was reported in a study [ 44 ] ( Figure 4 ).…”

“…It is known that forest VOCs like limonene and, even more, pinene, are mostly released by conifers (pines, fir trees, cypresses) ( Table 3 , Table 6 , and Table 7 ), and, therefore, the exposure to these volatile substances (with more documented effects on health) can be maximized by visiting a forest whose composition is rich in these trees. In general, beyond differences in tree composition, levels of BVOCs in the forest air exhibit diurnal quali-quantitative variations, with two daily peaks (early in the morning and in the afternoon) [ 31 , 32 ], and these cyclic changes may influence the magnitude and type of potential beneficial effects of their inhalation depending on the time of the day when the exposure occurs. For this reason, it would be useful to carry out additional environmental studies aimed at quantifying all concentration changes in forest VOCs in order to maximize the visitors’ exposure and, therefore, the impact of such compounds on health after inhalation.…”

“…Therefore, it is important to consider this high degree of variability when studying health and environmental effects of forest VOCs. [16,31,32,34,[38][39][40][41][42][43][44]. Abbreviations: Tot.…”

“… Atmospheric concentration of BVOCs under forest canopy [ 16 , 31 , 32 , 34 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ]. Abbreviations: Tot.…”