Molecular signatures of organic particulates as tracers of emission sources

Abstract

Chemical signature of airborne particulates and deposition dusts is subject of study since decades. Usually, three complementary composition markers are investigated, namely, (i) specific organic compounds; (ii) concentration ratios between congeners, and (iii) percent distributions of homologs. Due to its intrinsic limits (e.g., variability depending on decomposition and gas/particle equilibrium), the identification of pollution sources based on molecular signatures results overall restricted to qualitative purposes. Nevertheless, chemical fingerprints allow drawing preliminary information, suitable for successfully approaching multivariate analysis and valuing the relative importance of sources. Here, the state-of-the-art is presented about the molecular fingerprints of non-polar aliphatic, polyaromatic (PAHs, nitro-PAHs), and polar (fatty acids, organic halides, polysaccharides) compounds in emissions. Special concern was addressed to alkenes and alkanes with carbon numbers ranging from 12 to 23 and ≥ 24, which displayed distinct relative abundances in petrol-derived spills and exhausts, emissions from microorganisms, high vegetation, and sediments. Long-chain alkanes associated with tobacco smoke were characterized by a peculiar iso/anteiso/normal homolog fingerprint and by n-hentriacontane percentages higher than elsewhere. Several concentration ratios of PAHs were identified as diagnostic of the type of emission, and the sources of uncertainty were elucidated. Despite extensive investigations conducted so far, the origin of uncommon molecular fingerprints, e.g., alkane/alkene relationships in deposition dusts and airborne particles, remains quite unclear. Polar organics resulted scarcely investigated for pollution apportioning purposes, though they looked as indicative of the nature of sources. Finally, the role of humans and living organisms as actual emitters of chemicals seems to need concern in the future.

Keywords: Air pollution; Diagnostic concentration ratios; Molecular signature of sources; Particulate organic matter (POM); Toxicants.

Fig. 1

GC–MS profiles of the non-polar fraction (m/z = 85) of airborne particulates collected at four sites variously influenced by emission sources. A Road traffic site; B rural region; C urban location (city garden). Symbols: nC_i indicates the n-alkane with carbon number equal to i. [Personal communication. The samples were collected in the frame of a cooperative research project of our institute with INAIL-DIPIA, Rome, Italy, by applying the procedure described in Cecinato A, Marino F, Di Filippo P, Lepore L, Possanzini M (1999). Distribution of n-alkanes, polynuclear aromatic hydrocarbons and nitrated polynuclear aromatic hydrocarbons between the fine and coarse fractions of inhalable atmospheric particulates. J Chromatog A 846, 255–264, 10.1016/S0021-9673(99)00,129–6]

Fig. 2

GC–MS profile of the non-polar fraction of diesel exhaust. A Total ion current signal; B Ion trace corresponding to m/z = 85 (labeling n-alkanes); C m/z = 95 ion trace (branched alkanes). Both a and b humps occur in the UCM. Symbols: nC_i indicates the n-alkane with carbon number equal to i. [Personal communication. The samples were collected in the frame of a cooperative research project of our institute with Istituto Motori CNR, Naples, Italy, by applying the procedure described in Ciccioli P, Cecinato A, Brancaleoni E, Draisci R, Liberti A (1989). Evaluation of nitrated polycyclic aromatic hydrocarbons in anthropogenic emission and air samples: a possible means of detecting reactions of carbonaceous particles in the atmosphere. Aerosol Sci Technol 10, 296–310, 10.1080/ 02786828908959266]

Fig. 3

GC–MS chromatograms of airborne particulate extracts. A1 El Bey, Tunisia, m/z = 85 (n-alkanes); A2 El Bey, Tunisia, m/z = 83 (n-alkenes); B1 Tipaza, Algeria, m/z = 85 (n-alkanes); B2 Tipaza, Algeria, m/z = 83 (n-alkenes); C1 Reggio Calabria, Italy, m/z = 85 (n-alkanes); C2 Reggio Calabria, Italy, m/z = 83 (n-alkenes). [Personal communication. The samples were collected in the frame of a cooperative research project of our institute with Kasdi Merbah University of Ouargla, Dept. Mathematics and Sciences of Matter, Touggourt, Algeria, by applying the procedure described in Romagnoli P, Balducci C, Perilli M, Perreca E, Cecinato A (2016). Particulate PAHs and n-alkanes in the air over Southern and Eastern Mediterranean Sea. Chemosphere 159, 516-525. https://doi.org/10.1016/j.chemosphere.2016.06.024]