NMR Aerosolomics

Since 2015, we have been developing a new approach to the analysis of polar organic substances (WSOC) from aerosols. In our group, the identification of compounds by NMR is based on the comparison of the chemical shifts of the signals in the ¹H NMR spectrum of the aerosol with the spectrum of a given compound in the library. For this purpose, we use Chenomx software, which is designed for the identification of substances in complex matrices, such as body fluids, and which uses its own spectra library. For the analysis of aerosols, we purposefully expanded the library with the compounds commonly contained in aerosols; hence, we operate with a library comprising about 150 compounds. In this way, we are able to identify up to 60 substances in real aerosol samples. The testing series of samples came from Prague – Suchdol, where they were collected during the summer and winter campaigns as PM_2.5 and PM₁₀ fractions. Thanks to the developed approach, three new substances were identified and the presence of four other substances, predicted by laboratory experiments, was confirmed in aerosol particles for the first time. The concentration profiles of the identified substances can further serve as an input for advanced statistical analysis. Summer and winter samples showed a high degree of separation in a multivariate statistical analysis, and some interesting trends were observed in the composition of individual size fractions when attempting to separate the samples on the basis of aerosol particle size. The compounds responsible for group separation can be identified using univariate statistical analysis. The compounds with elevated concentrations in winter are coming mainly from anthropogenic sources, while the substances elevated in summer are the products of both biogenic and anthropogenic sources.

• ACS Omega 2020, 5(36), 22750 – 22758. DOI: 10.1021/acsomega.0c01634

The NMR aerosolomics was subsequently applied to the detailed analysis of WSOC in size-resolved aerosol collected during summer and winter again in a Prague suburban area. The samples were resolved during collection using a prototype of a high-volume slit cascade impactor into six fractions according to particle size. This enabled determination of distribution profiles of identified compounds. In total, 73 compounds were identified and classified into nine groups according to their chemical nature. Based on their distribution profiles, connections between individual compounds were revealed facilitating compound association with probable sources. For example, a relationship among carbohydrates and trimethylglycine and choline in the coarse summer aerosol was found. In the winter series, similar distribution profiles of several compounds indicated biomass burning as their common source. Naturally, multivariate statistical analysis revealed differences in chemical composition between both seasons and stressed the main features of the fine and coarse aerosol matter. The identification of aerosol sources remains the main interest of our further research in this field.

• Atmos. Environ. 2021, 267, 118757. DOI: 10.1016/j.atmosenv.2021.118757