Atmospheric brown carbon (BrC) is an important contributor to the radiative forcing of climate by organic aerosols. Because of the molecular diversity of BrC compounds and their dynamic transformations, it is challenging to predictively understand BrC optical properties. OH radical and O3 reactions, together with photolysis, lead to diminished light absorption and lower warming effects of biomass burning BrC. The effects of night-time aging on the optical properties of BrC aerosols are less known. To address this knowledge gap, night-time NO3 radical chemistry with tar aerosols from wood pyrolysis was investigated in a flow reactor. This study shows that the optical properties of BrC change because of transformations driven by reactions with the NO3 radical that form new absorbing species and lead to significant absorption enhancement over the ultraviolet–visible (UV-vis) range. The overnight aging increases the mass absorption coefficients of the BrC by a factor of 1.3–3.2 between 380 nm and 650 nm. Nitrated organic compounds, particularly nitroaromatics, were identified as the main products that contribute to the enhanced light absorption in the secondary BrC. Night-time aging of BrC aerosols represents an important source of secondary BrC and can have a pronounced effect on atmospheric chemistry and air pollution.

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Bitumen is a highly viscous and chemically complex petroleum-derived material, which is applied as a binder in road construction. However, the asphalt undergoes hardening, cracking, and embrittlement not only due to oxidative short-term aging during the mixing and paving process but also due to long-term aging during the service time of the pavement. In this study, chemical changes occurring during short-term aging, mimicked by a prolonged rotating flask procedure, are investigated for an artificial bitumen model at the molecular level. The model bitumen enables the application of two complementary analytical techniques for obtaining a comprehensive insight into the aging effects: high-resolution Fourier-transform ion cyclotron mass spectrometry (FT-ICR MS) coupled to thermogravimetry was applied to investigate the aging effects on polar to semipolar high-molecular-weight compounds ionized by atmospheric pressure chemical ionization. Aromatic core structures were analyzed by alternating collision-induced dissociation. In order to support structural assignments from FT-ICR MS data in the semivolatile region, comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC–HRTOFMS) with electron ionization at 70 eV was applied for the group-type analysis and the investigation of particular chemical functionalities. Oxidation processes were revealed to be the prevalent reactions caused by short-term aging of the hydrocarbons (CH-class) and sulfur-containing classes. Aromatic species with low steric hindrance or activated carbon positions as well as high aromatic core structures are favorably oxidized, forming carbonyl functionalities. For molecules with one sulfur atom (S1-class), nonaromatic species such as tetrahydrothiophenes decrease, whereas aromatic S1-compounds remain constant. Nonaromatic S1O1-species tend to further oxidize, while higher aromatic species are formed with ongoing aging time. Moreover, this study highlights the aging behavior of nitrogen-containing compounds, such as carbazoles. A significant reduction of the N-classes was observed during aging, indicating thermal-induced condensation reactions as well as favored oxidation of highly aromatic core structures.

On January 1, 2020, new International Maritime Organization (IMO) legislation will reduce the maximum sulfur content for marine fuels outside of sulfur emission control areas (SECA) from now 3.50% (m/m) to 0.50% (m/m) to lower the emission of SO x . In order to enable a smooth transition to the new-generation fuels and to cope with a widely diversified spectrum of heavy fuel oils, a comprehensive chemical description of such bunker fuels will become more important to investigate differences which may cause incompatibility with current engines or to avoid a negative impact for the storage stability. Comprehensive two-dimensional gas chromatography with mass-spectrometric detection (GC × GC-MS) has become one of the most potent analytical methods for detailed analysis of hydrocarbon composition in complex petroleum fractions. However, matrices that contain significant amounts of less-or nonvolatile constituents, such as marine fuels, cannot entirely be targeted by gas chromatography alone. In order to extend the application range of a GC × GC high-resolution time-of-flight mass spectrometry platform (GC × GC-HRTOFMS), we applied and compared thermogravimetric analysis (TGA-HRTOFMS) and direct inlet probe (DIP-HRTOFMS) as additional thermal sample introduction techniques. In this study, we investigated five different marine fuels with GC × GC-, DIP-, and TGA-HRTOFMS to analyze volatile as well as residual compounds. Since each of the deployed techniques showed unique advantages and possibilities, the complementarity of the combined approach is demonstrated. The combination of GC × GC-, DIP-, and TGA-HRTOFMS data enabled the generation of comprehensive chemical fingerprints for differentiation and chemical classification.

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Widespread smoke from wildfires and biomass burning contributes to air pollution and the deterioration of air quality and human health. A common and major emission of biomass burning, often found in collected smoke particles, is spherical wood tar particles, also known as “tar balls”. However, the toxicity of wood tar particles and the mechanisms that govern their health impacts and the impact of their complicated chemical matrix are not fully elucidated. To address these questions, we generated wood tar material from wood pyrolysis and isolated two main subfractions: water-soluble and organic-soluble fractions. The chemical characteristics as well as the cytotoxicity, oxidative damage, and DNA damage mechanisms were investigated after exposure of A549 and BEAS-2B lung epithelial cells to wood tar. Our results suggest that both wood tar subfractions reduce cell viability in exposed lung cells; however, these fractions have different modes of action that are related to their physicochemical properties. Exposure to the water-soluble wood tar fraction increased total reactive oxygen species production in the cells, decreased mitochondrial membrane potential (MMP), and induced oxidative damage and cell death, probably through apoptosis. Exposure to the organic-soluble fraction increased superoxide anion production, with a sharp decrease in MMP. DNA damage is a significant process that may explain the course of toxicity of the organic-soluble fraction. For both subfractions, exposure caused cell cycle alterations in the G2/M phase that were induced by upregulation of p21 and p16. Collectively, both subfractions of wood tar are toxic. The water-soluble fraction contains chemicals (such as phenolic compounds) that induce a strong oxidative stress response and penetrate living cells more easily. The organic-soluble fraction contained more polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs and induced genotoxic processes, such as DNA damage.

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