Using Ultrasound-Treated Washout from Conifer Needles and Fresh Snow Samples in Air Pollution Monitoring

Snow precipitation and snowpack are commonly used to assess the condition of the aerial environment. Another way to monitor air quality is to study trees and shrubs, which are natural barriers for capturing air pollution, including atmospheric particulate matter. The hypothesis of the current study was that using fresh snow precipitation and washout from vegetation for the monitoring of air pollution can produce comparable results. In this study, we compared the results of laser diffraction analysis of suspended particular matter in melted fresh snow and ultrasound-treated washout from conifer needles. The samples were collected at several sites in Primorsky Krai, Russian Federation, and analyzed according to the same scheme. We observed that the content of particulate matter with a smaller aerodynamic diameter in the ultrasound-treated washout from conifer needles was higher than that in the melted fresh snow. The content of PM10 in the ultrasound-treated washout from conifers was increased by 6–27% depending on the site, showing greater efficacy of this method. This method can be used as an alternative to the sampling of snow for the monitoring of ambient air pollution, taking into account several limitations.

Accumulation of heavy metals in needles and bark of Pinus species

During the research, cumulative properties of conifer needles P. armandii, P. banksiana, P. mugo, P. nigra, P. sylvestris and P. wallichiana in reference to Cu, Ni, Mn, Fe, Zn and Cd were analysed, and the factors which have an impact on the chemical composition of the bark of those species were identified. During the study, the age of needles and the content of the examined components in soil was taken into consideration. The content of metals in the needles varied, depending on a species and the age of the coniferous needles. In most cases, a higher level of content of those metals was determined in 2 years old needles, except for Cu and Zn (P. banksiana) as well as Zn (P. nigra), in which case, higher concentration of metals in 1 year old needles was determined. The obtained results indicate that the heavy metals’ concentration in the samples of needles was relatively low, except for Ni (P. armandii, P. sylvestris, P. wallchiana) and Cd (P. armandii, P. banksiana), which showed higher levels. Among the examined elements, Mn was accumulated in the largest volume in the needles of P. banksiana, Fe and Cu in the needles of P. wallchiana, Ni in the needles of P. sylvestris, Zn in the needles of P. nigra and Cd in the needles of P. armandii. The bark samples represented a clearly acidic reaction, with pH levels from 3.7 (P. sylvestris) to 4.9 (P. armandii). The highest quantities of Mn, Fe, Cu and Cd were accumulated by the bark of P. armandii, Ni in the bark of P. sylvestris and Cu in the bark of P. mugo.

Role of needle surface waxes in dynamic exchange of mono- and sesquiterpenes

Biogenic volatile organic compounds (BVOCs) produced by plants have a major role in atmospheric chemistry. The different physicochemical properties of BVOCs affect their transport within and out of the plant as well as their reactions along the way. Some of these compounds may accumulate in or on the waxy surface layer of conifer needles and participate in chemical reactions on or near the foliage surface. The aim of this work was to determine whether terpenes, a key category of BVOCs produced by trees, can be found on the epicuticles of Scots pine (Pinus sylvestris L.) and, if so, how they compare with the terpenes found in shoot emissions of the same tree. We measured shoot-level emissions of pine seedlings at a remote outdoor location in central Finland and subsequently analysed the needle surface waxes for the same compounds. Both emissions and wax extracts were clearly dominated by monoterpenes, but the proportion of sesquiterpenes was higher in the wax extracts. There were also differences in the terpene spectra of the emissions and the wax extracts. The results, therefore, support the existence of BVOC associated to the epicuticular waxes. We briefly discuss the different pathways for terpenes to reach the needle surfaces and the implications for air chemistry.