The RHAPS (Redox-Activity And Health-Effects Of Atmospheric Primary And Secondary Aerosol) project was launched in 2019 with the major objective of identifying specific properties of the fine atmospheric aerosol from combustion sources that are responsible for toxicological effects and can be used as new metrics for health-related outdoor pollution studies. In this paper, we present the overall methodology of RHAPS and introduce the phenomenology and the first data observed. A comprehensive physico-chemical aerosol characterization has been achieved by means of high-time resolution measurements (e.g., number size distributions, refractory chemical components, elemental composition) and low-time resolution analyses (e.g., oxidative potential, toxicological assays, chemical composition). Preliminary results indicate that, at the real atmospheric conditions observed (i.e., daily PM₁ from less than 4 to more than 50 μg m⁻³), high/low mass concentrations of PM₁, as well as black carbon (BC) and water soluble Oxidative Potential (WSOP,) do not necessarily translate into high/low toxicity. Notably, these findings were observed during a variety of atmospheric conditions and aerosol properties and with different toxicological assessments. Findings suggest a higher complexity in the relations observed between atmospheric aerosol and toxicological endpoints that go beyond the currently used PM₁ metrics. Finally, we provide an outlook to companion papers where data will be analyzed in more detail, with the focus on source apportionment of PM₁ and the role of source emissions on aerosol toxicity, the OP as a predictive variable for PM₁ toxicity, and the related role of SOA possessing redox-active capacity, exposure-response relationships for PM₁, and air quality models to forecast PM₁ toxicity.

Background: COVID-19 containment measures curb viral spread but may hamper walking mobility. As a low daily step count is associated with increased noncommunicable diseases and mortality, assessing the relationship between pandemic responses and walking mobility can help trade-off public health measures. We investigated the association between containment stringency and walking mobility across 60 countries in the period between January 21, 2020 and January 21, 2022 and modeled how this could impact mortality hazard. Methods: Walking mobility was measured through the Apple Mobility Trends, containment measures stringency index through the Oxford COVID-19 response tracker (which considers local policies on closures, healthcare, and economy), and meteorological data by National Oceanic and Atmospheric Administration weather stations. Walking mobility was regressed over stringency in a mixed-effect model with weather variables as covariates. The impact of stringency on all-cause mortality due to reduced mobility was modeled based on regression results, prepandemic walking mobility, and the association between step count and all-cause mortality hazard. Results: Across the 60 countries, the average stringency was 55 (9) (mean [SD]) out of 100. Stringency was negatively associated with walking mobility; a log-linear model fitted data better than a linear one, with a regression coefficient for stringency on ln (walking mobility) (95% confidence interval) of −1.201 × 10⁻² (−1.221 × 10⁻² to −1.183 × 10⁻²). Increasing stringency, thus decreasing walking mobility, nonlinearly incremented the modeled all-cause mortality hazard by up to ∼40%. Conclusions: In this study, walking mobility was negatively associated with containment measures stringency; the relationship between stringency, mobility, and the subsequent impact on health outcomes may be nonlinear. These findings can help in balancing pandemic containment policies.

¹⁴C measurements on the carbonaceous fractions of atmospheric aerosol are an important tool for source apportionment. In this paper, a ¹⁴C-based source apportionment study was carried out on samples collected during winter 2021 at an urban background site in the Po Valley, one of the main pollution hot-spot areas in Europe. The samples were prepared using MISSMARPLE (MIlan Small-SaMple Automated Radiocarbon Preparation LinE for atmospheric aerosol), a recently developed sample preparation line for ¹⁴C measurements on atmospheric aerosol carbon fractions, specifically targeting small samples (about 50 μgC). ¹⁴C-based source apportionment was performed separately for elemental carbon (EC) and organic carbon (OC), after suitable optimization of model parameters. As this is the first source apportionment study using MISSMARPLE-prepared samples, our results were compared with other tracers and source apportionment outcomes obtained through parallel methodologies, demonstrating strong correlations in all tests (R > 0.87). The source apportionment results showed that fossil fuel combustion remains the main source of EC in the investigated area (60%), while modern contributions generally dominate the OC fraction (66%). However, some episodes were identified where fossil fuel combustion was the dominant contributor also to the OC fraction (up to 66%). During these episodes, the importance of secondary OC formation from fossil fuel combustion was highlighted through the EC-tracer approach. Thus, fossil fuel combustion is still a significant source of carbonaceous aerosol in the Po Valley during the winter. Both primary emissions and gaseous precursors must be targeted by future abatement policies to effectively reduce pollution in the area.