Changes in light absorption by brown carbon in soot particles due to heterogeneous ozone aging in a smog chamber

The effects of photochemical aging and interactions with secondary organic aerosols on cellular toxicity of combustion particles

Fine particulate matter (PM2.5) is associated with numerous adverse health effects, including pulmonary and cardiovascular diseases and premature death. Significant contributors to ambient PM2.5 include combustion particles and secondary organic aerosols (SOA). Combustion particles enter the atmosphere and undergo an aging process that changes their shape and composition, but there is limited study on the health effects of combustion particle aging and interactions with SOA. This study aimed to understand how biological responses to combustion particles would be affected by atmospheric aging and interaction with anthropogenic SOA. Fresh combustion particles underwent photochemical aging in a potential aerosol mass (PAM) oxidation flow reactor and interacted with SOA produced by the oxidation of toluene vapor in the PAM reactor. Photochemical aging and SOA interactions lead to significant changes in the PAH content and oxidative potential of the particle. Photochemical aging and SOA interactions also affected the biological responses, such as the inflammatory response and CYP1A1 induction of the particles in monoculture and coculture cells. These findings highlight the significance of photochemical aging and SOA interactions on the composition and cellular responses of combustion particles.

Ageing Significantly Alters the Physicochemical Properties and Associated Cytotoxicity Profiles of Ultrafine Particulate Matters towards Macrophages

There are still significant concerns about the detrimental effects and health risks of particulate matters (PMs) on the respiratory system. Notably, a largely overlooked knowledge gap is whether the environmental ageing process would change the physicochemical properties of PMs as well as the toxic influences of PMs on macrophages. Here, we applied ambient treatment of model PMs to mimic the real O3-induced ageing process and investigated ageing-determined cytotoxicity profile changes of PMs towards macrophages. The consequent distinct bioreactivity and toxicity towards macrophages are largely attributed to the changes of species of surface O-functional groups. Importantly, we unveiled the specific interactions between aged PMs and macrophages due to the variant contents of the surface carboxyl group, resulting in the divergent inflammatory activations and immune balance in the lung. Collectively, this study unearths the significance of ageing in altering particle cytotoxicity, and also provides additional understandings for consecutive investigations on the adverse effects of air pollution on the respiratory system.

Effect of Diesel Soot on the Heterogeneous Reaction of NO2 on the Surface of γ-Al2O3

Soot and aged soot are often found to be mixed with atmospheric particles, which inevitably affect various atmospheric heterogeneous reactions and secondary aerosol formation. Previous studies have investigated the heterogeneous reaction of NO2 with different types of soot, but there are few studies on the heterogeneous reaction of NO2 with mixtures containing diesel soot (DS) or aged DS and mineral dust particles. In this study, the effects of DS and aged DS on the heterogeneous reaction of NO2 on the surface of γ-Al2O3 were investigated via in-situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS). The results showed that the DS or DS n-hexane extract significantly inhibited the formation of nitrate on γ-Al2O3 particles and promoted the formation of nitrite. At 58% RH, with the increase of DS or DS n-hexane extract loading amount, the effect of DS or DS n-hexane extract on the formation of nitrate changed from promotion to inhibition, but DS or DS n-hexane extract always promoted the formation of nitrite. The results also showed that light was conducive to the formation of nitrate on the DS-γ-Al2O3 or DS-n-hexane extract-γ-Al2O3 particles. Furthermore, the influence of soot aging on the heterogeneous reaction of NO2 was investigated under light and no light. In the dark, O3-aged DS-γ-Al2O3 or O3-aged DS-n-hexane extract-γ-Al2O3 firstly inhibited the formation of nitrate on the mixed particles and then promoted it, while the effect of aged DS on nitrite formation was complex. Under light, the O3-aged DS-γ-Al2O3 firstly promoted the formation of nitrate on the mixed particles and then inhibited it, while the O3-aged DS-n-hexane extract-γ-Al2O3 promoted the formation of nitrate on the mixed particles. Our results further showed that the production of nitrate on the O3-aged particles under light or no light was greater than that of the UV-nitrate-aged particles. This study is helpful to deeply understand the atmospheric chemical behavior of soot and the heterogeneous conversion of atmospheric NO2.

Effect of ozone aging on light absorption and fluorescence of brown carbon in soot particles: The important role of polycyclic aromatic hydrocarbons

The evolution of brown carbon (BrC) during atmospheric aging, including the changes in optical properties and chemical compositions, is still unclear. Light absorption and fluorescence of BrC fraction extracted from fresh and ozonized propane soot particles by methanol were systematically measured, which showed that (1) the mass absorption efficiencies (MAE) sharply decreased by ozone (O₃) aging (e.g., 1.2 ± 0.3-0.8 ± 0.1 m² g^-1 for MAE₃₆₅), but changed slowly with increased O₃ concentration (e.g., from 0.7 ± 0.2-0.8 ± 0.1 m² g^-1 for MAE₃₆₅); (2) the fluorescence emission peaks were blue shifted, implying a loss of conjugated structures; (3) excitation-emission matrix analysis suggested that humic-like substances, charge transfer complexes, and polycyclic aromatic hydrocarbon (PAH)-like substances were the main chromophores. The PAH loss, accompanied by the decline of surface C˭C content, contributed more to the change of optical properties than the oxygenated PAH formation, thereby leading to the decrease in light absorption and fluorescence with O₃ aging. This research reveals the importance of identifying the components responsible for optical properties in investigating the evolution of BrC during atmospheric aging, and is benefit for improving the evaluation of BrC's radiative forcing.