ИСТИНА

For several years carrying on non targeted analyses of environmental samples we keep finding pyridine and its closest homologues and derivatives (C1-C3). Due to the presence of nitrogen in the aromatic cycle they are better dissolved in water than their carbocyclic analogues and may easily penetrate ground or cloud waters. These compounds were reliably identified in the samples of snow in Moscow collected in 2011-2018 and Arctic island Novaya Zemlya collected in 2017, in rain water collected in Moscow in 2017 and in Valparaiso, Chile in 2003-2015, as well as in cloud water in central France. Since GCxGC-HRMS tool was used in these cases there are no doubts in the reliability of the identifications. Moreover, identification of 6 pyridines was confirmed by the subsequent analysis of the standards. The levels of pyridine reached mkg/l values while methylpyridines were detected up to hundreds nanograms per liter levels. Surprisingly there are not many papers mentioning detection of pyridines in the environmental samples. Maybe it is due to the fact that mainly target analysis is carried out in the majority of the laboratories all over the world. Moreover, pyridines are not included into the lists of priority pollutants, although pyridine and 2-methylpyridine are listed in EPA 8270 Method proposed for the detection of semi volatile pollutants. Anyway, the sources of pyridines in the environment are not reliably established. Pyridine and its derivatives may be treated as a group of industrial contaminants. They are formed in coal chemistry, present in waste waters of petrochemical and pharmaceutical enterprises, and widely used as solvents, dyes and pesticides. Heterocyclic aromatic compounds with single N atom were recently identified in biomass burning aerosol samples collected from test burns of rice straw and it is worth mentioning that N-heterocyclics including pyridines are often ascribed to volatilization from plant material and pyrolysis of biopolymers. One more possible source of pyridines in the atmosphere might involve automobile exhausts as similar benzene derivatives are observed. Definitely the higher is the level of nitrogen containing compounds in the fuel, the higher should be the levels of pyridines. In the present study we decided to elucidate the source of pyridines in the atmosphere carrying out model laboratory experiments on peat burning, peat pyrolysis, automobile exhaust followed by qualitative and quantitative GC/MS analysis. The burning experiments were carried out in a home-built smoking machine, while the burning products were collected on the wool, glass, solvent, and in cryo trap. All experiments were performed using time-of-flight (TOF) high resolution mass-spectrometer Pegasus GCxGC-HRT (LECO Corporation, Saint Joseph, MI, USA) with an Agilent 7890A Gas Chromatograph (Agilent, Palo Alto, CA, USA). The system was controlled by the ChromaTOF-HRT® software version 1.91 (LECO Corporation), which was also used for spectra collection and data processing. Despite of the numerosity of the organic compounds there was not a single pyridine in the diesel exhaust sample. This result allowed as delete car engine exhausts as a possible source of pyridines. On the contrary, quite a number of light pyridines were identified and quantified among the peat burning products. It is worth mentioning that the levels of the detected pyridines are in the same ratio as in our previous environmental studies. The principal component among the targeted group in pyrolysis experiments is pyridine itself, with isomeric methylpyridines being the next in abundance. The levels of other detected pyridines are an order of magnitude lower. This fact perfectly matches the results of the peat burning as well as the results of our previous environmental studies. Therefore, laboratory burning, pyrolysis, and thermodesorption experiments with peat samples demonstrated that these processed may be responsible for the appearance of lower alkylpyridines in the Earth atmosphere. The distribution of pyridine homologues remains the same in the conducted experiments and in the environmental studies carried out in Arctic, Central Russia, and Central France.