The inhalation of natural nanoparticles (NPs) emitted from volcanic activity may be a risk to human health. However, the literature rarely reports the fate and response of NPs once in contact with lung fluids. In this work, we studied the particle size distribution of ashfall from Popocatépetl volcano, Mexico. The collected ashes (n = 5) were analyzed with scanning electron microscopy (SEM) to obtain the elemental composition and morphology, and to determine the size of the ash particles using ParticleMetric software (PMS). The PMS reported most of the ash to have submicrometric size (<1 μm) and an average equivalent circle of 2.72 μm. Moreover, to our knowledge, this study investigated for the first time the behavior of ash NPs at different times (0 to 24 h) while in contact with in vitro lung fluid, Gamble Solution (GS) and Artificial Lysosomal Fluid (ALF) using dynamic light scattering (DLS). We found a large variability in the hydrodynamic diameter, with values less than 1 nm and greater than 5 μm. Furthermore, aggregation and disaggregation processes were recognized in GS and ALF, respectively. The results of this study increase the knowledge of the interaction between NPs and lung fluids, particularly within the alveolar macrophage region.

A Three-Way Catalyst (TWC) contains a cordierite ceramic monolith coated with a layer of Al₂O₃, Ce_xZr_1−xO₂ and platinoids mixture. Under standard operation, the platinoid concentration decreases, exposing the remaining washcoat structure. After that particle release stage, the sintering process follows where the crystalline Ce_xZr_1−xO₂ solution is broken and begins to separate into ZrO₂ and CeO₂ phases. ZrO₂ is released to the environment as micro and nanoparticles, while a small amount of CeO₂ generates a new Al_xCe_1−xO₂ composite. The main effect of Ce capture is the growth in the size of the polycrystal structure from 86.13 ± 16.58 nm to 225.35 ± 69.51 nm. Moreover, a transformation of cordierite to mullite was identified by XRD analysis. Raman spectra showed that the oxygen vacancies (Vö) concentration decreased as Ce_xZr_1−xO₂ phases separation occurred_. The SEM-EDS revealed the incorporation of new spurious elements and microfractures favouring the detachment of the TWC support structure. The release of ultrafine particles is a consequence of catalytic devices overusing. The emission of refractory micro to nanocrystals to the atmosphere may represent an emerging public health issue underlining the importance of implementing strict worldwide regulations on regular TWCs replacement.

The COVID-19 pandemic has caused several millions of deaths and forced the world population to a new normality. This study aims to analyze the air quality variation of several gaseous pollutants (CO, NO₂, SO₂, O₃, PM₁₀, and PM_2.5) during the pre-lockdown, lockdown, and unlock period in the city of Monterrey using ground-based measurements. In this research, we proposed to use a control period of previous years to identify parameter variation due to local climate. The results showed a drastic decrease in measured contaminants during the lockdown period as follows: SO₂ (−41.9%) > PM₁₀ (−30.5%) > PM_2.5 (−25.6%) > NO₂ (−14.9%) > CO (−9.8%) compared to the control period (2017–2019). The O₃ was the only air pollutant that showed an opposite trend, increasing during lockdown (+15%) and unlock (+2.2%), whereas CO (−16.6%) and NO₂ (−30.6%) were further decreased. Moreover, using OMI/AURA satellite data, we detected a NO₂ tropospheric column reduction by −1.9% during lockdown concerning the same period in the control interval. Moreover, we found a significant improvement in the Air Quality Index (AQI) due to the lockdown. Our findings indicate an association between air pollutants and economic activity and can be used in future strategies to improve urban air quality.