Basis weight uniformity of melt-blown fibrous webs is attracting considerable interest because it directly affects the application performance of nonwovens. There are numerous studies which introduce factors of processing conditions on the basis weight uniformity based on their final applications. However, theoretical research is still scarce. This paper describes the numerical modeling (bead–viscoelastic element fibrous model) involving fibrous web structure generation and basis weight uniformity evaluation. The effects of four processing conditions, including velocity of air jet and suction, die-to-collector distance, and moving speed of collector, on the basis weight uniformity of the fibrous web were quantitatively analyzed. Additionally, computational fluid dynamics simulation was employed to study the air flow (including the suction) in the melt-blowing process. The simulated results were in good agreement with the experimental data. The numerical model was practical and could better be used to research the problems on fibrous web formation and structures.

Airborne redox-active compounds (ARC) account for a substantial fraction of atmospheric aerosols and play a vital role in chemical processes that influence global climate and human and ecological health. With the exception of the determination of total organic carbon by the expensive total organic carbon (TOC) analyzer, there is currently no easy-to-use method to quantify ARC. Here, we designed a method to detect the concentration of ARC by using the thermal-induced reduction and colorimetric behaviors of gold nanoparticles (AuNPs), in which the humic substances (HS) was used as a standard model of ARC to calculate the HS-equivalent concentration of ARC. Distinguished from the conventional complex methods, e.g., TOC analysis, the proposed approach measured localized surface plasmon resonance absorption of AuNPs and the target ARC concentration can be either directly quantified by the absorption spectrometer or qualitatively evaluated by the naked eyes. By using the absorption spectrometer, a limit of detection of 0.005 ppm by our AuNP sensor was achieved. To validate this sensing technique, aerosol samples collected from Basel (suburban), Bern (urban), and Rigi mountain (rural and high-altitude) sites in Switzerland were further investigated through the TOC combustion method. The results thereby substantiated that our plasmonic absorption-based AuNP sensor upholds a great promise for fast, cost-efficient total ARC detection and air quality assessment.

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