The settling and deposition behavior of small particles significantly impacts many environmental and industrial processes. Although particle settling dynamics within turbulent environments have been extensively studied through theory and simulation, more experimental investigation is needed to test the idealized results against real-world turbulent flows. In this work, we infer the settling velocity of particles in Rayleigh–Bénard (RB) turbulence through the measurement of declines in particle concentration due to deposition within a (Formula presented.) convection chamber. Oil droplets from (Formula presented.) to (Formula presented.) and glass beads from (Formula presented.) to (Formula presented.) were used as the particle material, yielding Kolmogorov-based particle Stokes numbers in the range of (Formula presented.) to (Formula presented.) Our measurements reveal a linear scaling with particle diameter, rather than the diameter-squared scaling expected for these Stokes numbers. Direct numerical simulations (DNS) designed to mirror the experimental configuration were also performed; these yielded the familiar diameter-squared scaling. We suggest that the discrepancy between the experimental results and the theoretical framework and DNS, which makes standard assumptions regarding lift and drag, may be due to unresolved physics near the domain boundary, which dictates overall removal rates. Future work employing more direct observational methods of particle settling within RB turbulence is required to better understand these near-wall removal processes. The departure from Stokes settling within this set of experiments brings to question the limits of the applicability of the “stirred settling” model commonly invoked for estimating particle removal rates, suggesting that adjustments to traditional assumptions may be required. Such corrections may prove especially important in the design of future cloud convection chambers.

Previous studies have shown that the presence of gas-phase Polycyclic Aromatic Hydrocarbons (PAHs) during biogenic Secondary Organic Aerosol (SOA) formation can significantly enhance SOA formation, resulting in higher mass loadings, and alter properties of SOA particles. Compared to “pure” biogenic SOA, these particles have higher viscosity, lower bulk volatility, and are composed of a higher fraction of low-volatility compounds, i.e., oligomers. The in-situ aerosol mass spectrometry of α-pinene ozonolysis SOA particles indicates that while PAHs significantly enhance oligomer formation, the “extra mass” is dominated by α-pinene oxidation products. To understand the potential chemical mechanisms responsible for the increased SOA formation yields and formation of oligomers we utilized an ultrahigh resolution Orbitrap Elite mass spectrometer (resolving power 240,000 @ m/z 400). Multiple ionization methods were used to provide a comprehensive perspective of the molecular composition. Here, we present the differences in molecular composition resulting from the presence of three different PAHs during α-pinene SOA formation compared to a sample of pure α-pinene SOA. First, we report the presence of unique α-pinene + pyrene oligomers potentially responsible for low particle volatility observed in previous studies. We also report low-oxygen α-pinene oligomers only observable using atmospheric pressure photoionization. These oligomers are seemingly enhanced by the presence of benzo[a]anthracene, suggesting a potential role for certain PAHs in their formation. These results imply that our understanding of the oxidative reaction pathways may be incomplete, especially with regard to the interaction of biogenic and anthropogenic emissions.

Assessing workers’ exposure during the molding of glass fiber-reinforced polymer composites is a complex task, influenced by both the materials used, and the manufacturing processes involved. Besides the possible presence of volatile organic compounds (VOCs), there is growing concern about the release of micro- and nanoparticles, which could lead to long-term exposure that should not be underestimated. In this pilot study, for the first time, therelease of glass fibers and nano-microplastics was evaluated according to Tier 1 and Tier 2 of the multi-metric tiered approach proposed by the Organization for Economic Cooperation and Development (OECD). Multi-metric real-time instruments were used to determine particle number concentration (PNC), particle average diameter (Davg), and lung deposited surface area (LDSA), along with time-integrated instrumentation to collect airborne dust for off-line chemical and morphological characterization. The results of the workplace monitoring campaign showed a significantly higher level of airborne particles, particularly at the nanoscale, compared to the background levels. The sampling of airborne dust revealed the presence of ultrafine particles (UFPs), fiber-like structures mainly composed of carbon and oxygen, and aerodispersed SiO2 fibers. According to the OECD guidelines, since significant exposure can not be excluded, based on the results of Tier 2 measurements, an extensive monitoring campaign (Tier 3) has to be conducted with the aim of thoroughly defining the exposure scenario and, consequently, recommending appropriate protection and prevention measures to safeguard workers’ health and safety.