Offline analysis of secondary formation markers in ambient organic aerosols by liquid chromatography coupled with time-of-flight mass spectrometry.

The present study provides a comprehensive assessment of the quantitative analysis by high-performance liquid chromatography coupled with dual orthogonal electrospray ionization time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) of pinene markers, biomass-burning related phenols, and other relevant carboxylic acids in atmospheric aerosol samples. Significant insights into the quantitative determination are offered on the basis of systematic experiments targeting the optimization of chromatographic separation, ionization source, and mass spectrometer performance. After testing three analytical columns, the best separation of the compounds of interest was achieved on a Poroshell 120 ECC18 column (4.6 × 50 mm, 2.7 µm) thermostated at 35 °C, operating in gradient elution mode with 0.1% acetic acid in water and acetonitrile at a 0.8 mL min-1 flow rate. Optimal operational conditions for the ESI-TOF-MS instrument were identified as a 350 °C drying gas temperature, 13 L min-1 drying gas flow rate, 60 psig nebulizer pressure, 3000 V for the ion transfer capillary, 60 V for the skimmer, and 150 V for the fragmentor. Additionally, the matrix effect on the ESI efficiency and the spike recovery factors of the compounds were tested. Method quantification limits can go as low as in the 0.88-48.0 µg L - 1 (3.67-200 pg m - 3, at 120 m3 of sampled air) range. The developed method was shown to be reliable for the quantification of the targeted compounds in real atmospheric aerosol samples. The accuracy in the molecular mass determination of less than 5 ppm and the acquisition in the full scan mode were shown to bring additional insights into the organic constituents in atmospheric aerosols.

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, meteorological 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 α-/ß-pinene and two nitroaromatics (i.e., 4-nitrophenol and 4-nitrocatechol). Aromaticity equivalent (XC), carbon oxidation state (OSC), H/C and O/C ratios, and van Krevelen diagrams, were used to discriminate between: i) the aliphatic 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 µm, it is believed that determination of their abundances and size distribution in ambient aerosols might provide direction for future studies such as to enhance the knowledge on their toxic potential levels for the human health.

Gas-Phase Ozone Reaction Kinetics of C5-C8 Unsaturated Alcohols of Biogenic Interest.

Unsaturated alcohols are volatile organic compounds (VOCs) that characterize the emissions of plants. Changes in climate together with related increases of biotic and abiotic stresses are expected to increase these emissions in the future. Ozonolysis is one of the oxidation pathways that control the fate of unsaturated alcohols in the atmosphere. The rate coefficients of the gas-phase O3 reaction with seven C5-C8 unsaturated alcohols were determined at 296 K using both absolute and relative kinetic methods. The following rate coefficients (cm3 molecule-1 s-1) were obtained using the absolute method: (1.1 ± 0.2) × 10-16 for cis-2-penten-1-ol, (1.2 ± 0.2) × 10-16 for trans-2-hexen-1-ol, (6.4 ± 1.0) × 10-17 for trans-3-hexen-1-ol, (5.8 ± 0.9) × 10-17 for cis-3-hexen-1-ol, (2.0 ± 0.3) × 10-17 for 1-octen-3-ol, and (8.4 ± 1.3) × 10-17 for trans-2-octen-1-ol. The following rate coefficients (cm3 molecule-1 s-1) were obtained using the relative method: (1.27 ± 0.11) × 10-16 for trans-2-hexen-1-ol, (5.01 ± 0.30) × 10-17 for trans-3-hexen-1-ol, (4.13 ± 0.34) × 10-17 for cis-3-hexen-1-ol, and (1.40 ± 0.12) × 10-16 for trans-4-hexen-1-ol. Alkenols display high reactivities with ozone with lifetimes in the hour range. Rate coefficients show a strong and complex dependence on the structure of the alkenol, particularly the relative position of the OH group toward the C═C double bond. The results are discussed and compared to both the available literature data and four structure-activity relationship (SAR) methods.

Assessment of the Anthropogenic Impact and Distribution of Potentially Toxic and Rare Earth Elements in Lake Sediments from North-Eastern Romania.

Chemical analysis was performed on sediment samples collected in two sampling sessions (July and October) from Podu Iloaiei Dam Lake, one of the most important water resources used for aquaculture in north-eastern Romania. The concentration of 15 trace elements (TEs), 8 refractory elements (REs), and 15 rare earth elements (REEs)-determined using inductively coupled plasma mass spectrometry-showed variability largely dependent of the sampling points and collection time. Manganese was the most abundant TE, V and Cr were the most abundant REs, while Ce was one of the most abundant REEs. The cerium negative anomaly and Gd positive anomaly were observed in the Chondrite-normalized distributions. In October, the Ce anomaly showed significant negative correlation with Mn, emphasizing the water body oxidation potential. The identified positive Gd anomaly was most likely associated with the use of Gd-chelating agents in magnetic resonance imaging in Iasi, the largest medical hub in north-eastern Romania. Principal component analysis extracted three factors explaining 96.0% of the observed variance, i.e., rock weathering, leaching from soil surface, contributions from urban stormwater and atmospheric deposition (50.9%), pedological contributions (23.7%), and mixed anthropogenic sources (e.g., traffic, waste discharge, agricultural activities; 21.4%). The evaluation of pollution indices highlighted low and moderate degrees of contamination for most of the elements and a considerable degree of contamination for Cd. Assigned Cd sources included fertilizers and pesticides used in the near agricultural areas or the high traffic road located near the lake. Since contamination of aquatic ecosystems with harmful elements is a human health concern, further monitoring of specific vectors in the food chain of the investigated dam lake will be of the utmost importance.