First insights into the molecular characteristics of atmospheric organic aerosols from Iasi, Romania: Behavior of biogenic versus anthropogenic contributions and potential implications

The present study reports first data on the organic molecular composition and evolution of secondary organic aerosols (SOAs) markers in aerosol samples from an urban environment in Romania. Targeted and non-targeted approaches of liquid chromatography tandem with time-of -flight mass spectrometry (LC-ToF-MS) were used as powerful analytical approaches for aerosol characterization at the molecular level. Four distinct organic molecular groups (CHO, CHON, CHONS, and CHOS) were classified as relevant for both warm (with 847 assigned molecular formulae) and cold (with 432 assigned molecular formulae) periods. Different formation mechanisms, physico-chemical processing, me-teorological conditions, and sources origin or strengths (biogenic versus anthropogenic), were identified as governing factors of the mass concentration size distribution for the first generation and second-generation oxidation products of alpha-/beta-pinene and two nitroaromatics (i.e., 4-nitrophenol and 4-nitrocatechol). Aromaticity equivalent (XC), carbon ox-idation state (OSC), H/C and O/C ratios, and van Krevelen diagrams, were used to discriminate between: i) the ali-phatic or aromatic nature of the identified organic aerosol constituents, ii) the oxidation state of the aerosol samples (e.g., more oxidized molecular formulae during the highly insolated period, more intense photochemistry), and iii) sources role in controlling OAs constituents abundances and behavior (e.g., higher relative contributions of aliphatic CHO formulae with a wider range of carbon numbers and CHOS molecular group with higher contribution during the warm period due to increased biogenic emissions or secondary formation from the biogenic precursors). Since in the present study >88 % of the 4-nitrocatechol and 4-nitrophenol was determined in the aerosol size fraction below 1 mu m, it is believed that determination of their abundances and size distribution in ambient aerosols might pro-vide direction for future studies such as to enhance the knowledge on their toxic potential levels for the human health.

Automated summary

This study provides the first data on the molecular composition and evolution of secondary organic aerosols (SOAs) markers in aerosol samples from an urban environment in Romania. Liquid chromatography tandem with time-of-flight mass spectrometry (LC-ToF-MS) was used to analyze the aerosols at the molecular level. Different factors such as formation mechanisms, physico-chemical processing, meteorological conditions, and sources origin or strengths were found to govern the mass concentration size distribution of the organic aerosols. The study also suggests that determining the abundances and size distribution of certain organic aerosol constituents in ambient aerosols can provide insights into their potential toxic levels for human health.