This study provides the first comprehensive characterisation of the chemical and mineralogical composition of mineral dust from Southern Africa, a major global dust source with significant impacts on regional climate and marine ecosystems. Laboratory-generated dust aerosol samples were produced using soils collected from key natural and emerging anthropogenic dust sources in Southern Africa. The chemical properties of mineral dust across Southern Africa were characterised using the elemental ratios Si/Al, (Ca+Mg)/Al, and K/Al, together with clay content. These indicators distinguish dust aerosols originating from arid western coastal areas from those originating from more humid eastern inland regions. They also provide information about the source-area environments and sediment weathering regimes, which are influenced by current and past temperature and precipitation patterns. The results of this study indicate that Southern African dust contains essential micronutrients such as iron (Fe), phosphorus (P) and manganese (Mn), which can become soluble and bioaccessible during atmospheric transport. In particular, emerging anthropogenic dust can be distinguished by its high content of certain nutrients. This affects the biogeochemistry of nearby and remote marine ecosystems, including the Southern Ocean. Southern African dust also contains higher levels of carbonates than Northern African dust sources, which can promote heterogeneous reactions and particle ageing, and contribute to cloud condensation nuclei in the extensive stratocumulus deck over the northern Benguela Upwelling System. Our findings also suggest that Southern African dust contains higher levels of K-feldspar than Northern African dust, and could therefore be an important source of ice-nucleating particles for low mixed-phase clouds over the Southern Ocean.

Southern Africa (SAf) is a key region for dust emissions, characterised by a wide variety of natural and anthropogenic sources, but also a critical knowledge gap in the mineral dust budget of the Southern Hemisphere. Projected climate warming is expected to lead to an increase in mineral dust emissions, which are increasingly linked to human activity. Although the transport and deposition pathways of SAf dust suggest that it can directly affect the regional climate and nearby marine ecosystems through dust-aerosol interaction and indirectly through aerosol-cloud/ice interaction and nutrient deposition, the extent of this impact is highly uncertain due to significant uncertainties in atmospheric loads and climate-relevant properties.This study provides the first comprehensive characterisation of the chemical and mineralogical composition of SAf dust aerosols. Aerosol samples were laboratory-generated using soils collected from key dust sources in southern Africa, including the Namib gravel plain, coastal ephemeral riverbeds, the Etosha salt pan, the Kalahari Desert, and anthropogenic sources such as agricultural soils from the Free State, savannah soils from the Kruger National Park, and a copper mine in Namibia.A geographical distribution of the chemical and mineralogical properties of SAf dust was identified based on the elemental ratios Si/Al, (Ca + Mg)/Al, and K/Al. This is influenced by both the regional geology and rainfall distribution, which shows an increase in the Si/Al ratio and a decrease in the (Ca + Mg)/Al and K/Al ratios, in areas with higher rainfall inland compared to the arid coast, while the salt pans exhibit unique features with significantly higher (Ca+Mg)/Al and Si/Al ratios.The SAf dust appears to be more enriched in Ca, Mg, and K than other dust sources in the Southern Hemisphere and northern African dust. Although Fe, a key micronutrient, occurs at similar levels in dust from both hemispheres, SAf dust contains more P, highlighting its potential significance in biogeochemical cycling. Despite limited mineralogical observations in the Southern Hemisphere, our results indicate that SAf dust contains more feldspar minerals than northern African dust, and may strongly influence the load of ice-nucleating particles over the Southern Ocean and, in turn, the regional radiative budget.

This study investigated the chemical composition and shortwave absorption coefficient, β abs ( λ ), of aerosols collected from sites on the Highveld, a major industrial and highly polluted region of South Africa. Local anthropogenic mineral dust was found to be the dominant chemical component, accounting for (53 ± 14)% of the aerosol mass concentrations. Carbonaceous aerosols (34 ± 12)%, mainly from domestic and waste biomass burning, and secondary inorganic aerosols (13 ± 6%) from anthropogenic combustion sources were also found. High β abs ( λ ) was observed at all sites, with an estimated mass absorption efficiency, MAE( λ ), from (1,296 ± 472) 10 −3 m 2 g −1 at 375 nm to (621 ± 239)10 −3 m 2 g −1 at 850 nm. The contributions of the primary light‐absorbing aerosols to β abs ( λ ) were determined using chemical tracers for two optical clusters identified based on the estimated MAE for black carbon (BC). BC was the major contributor to β abs ( λ ) at all wavelengths (>60%). The brown carbon contribution decreased with λ from (8–40) % at 375 nm to (1–23) % at 532 nm, and was higher in Cluster 1 than Cluster 2. Anthropogenic mineral dust in Cluster 2 appeared to be more light absorbing than pure desert dust and was a significant contributor to β abs ( λ ), constant with wavelength at ∼16%. The levels of light‐absorbing aerosols identified have implications for the radiation budget and atmospheric stability. Although BC dominates light absorption on the South African Highveld, mineral dust contributes significantly to aerosol mass concentrations and enhanced light‐absorption.

The complex refractive index (CRI; n−ik) and the single scattering albedo (SSA) are key parameters driving the aerosol direct radiative effect. Their spatial, temporal, and spectral variabilities in anthropogenic–biogenic mixed environments are poorly understood. In this study, we retrieve the spectral CRI and SSA (370–950 nm wavelength range) from in situ surface optical measurements and the number size distribution of submicron aerosols at three sites in the greater Paris area, representative of the urban city, as well as its peri-urban and forested rural environments. Measurements were taken as part of the ACROSS (Atmospheric Chemistry of the Suburban Forest) campaign in June–July 2022 under diversified conditions: (1) two heatwaves leading to high aerosol levels, (2) an intermediate period with low aerosol concentrations, and (3) an episode of long-range-transported fire emissions. The retrieved CRI and SSA exhibit an urban-to-rural gradient, whose intensity is modulated by the weather conditions. A full campaign average CRI of 1.41−0.037i (urban), 1.52−0.038i (peri-urban), and 1.50−0.025i (rural) is retrieved. The imaginary part of the CRI (k) increases and the SSA decreases at the peri-urban and forest sites when exposed to the influence of the Paris urban plume. Values of k > 0.1 and SSA < 0.6 at 520 nm are related to a black carbon mass fraction larger than 10 %. Organic aerosols are found to contribute to more than 50 % of the aerosol mass and up to 10 % (urban), 17 % (peri-urban), and 22 % (forest) of the aerosol absorption coefficient at 370 nm. A k value of 0.022 (370 nm) was measured at the urban site for the long-range-transported fire episode.

Background Exposure to fine particulate matter (PM2.5) is linked to many adverse outcomes, including respiratory and cardiovascular diseases. South Africa's reliance on coal combustion has led to poor air quality. Indoor air pollution exacerbates health risks in low-income households, necessitating thorough assessment. In this study, a human health risk assessment (HHRA) provided an understanding of health risks posed by indoor and outdoor PM2.5 concentrations in rural and urban settings. Methods During two campaigns, PM2.5 concentrations were monitored indoors (low-cost sensors in households) and outdoors (Zephyr sensors). We employed the method of the US Environmental Protection Agency in 22 urban households and 22 rural households. Results During a cooler period, indoor PM2.5 concentrations in all households exceeded the World Health Organization (WHO) Air Quality Guidelines. In Soweto, the winter 24-h PM2.5 concentrations reached as high as 491.4 mu g/m(3) (Household 19), surpassing all the WHO guideline targets, with the highest at 75 mu g/m(3). Even with conditions of higher atmospheric dispersion and less solid fuel burning, almost half of rural households had Hazard Quotients (HQs) > 1. In both seasons in urban areas and winter in rural areas, HQ values consistently remained >1, signalling greater health risks. Indoor PM2.5 concentrations almost consistently exceeded outdoor reference limits in both rural and urban locations throughout the year, underscoring the additional pollution burden due to indoor solid fuel burning and personal smoking habits. One Agincourt household recorded a warm period 24-h peak PM2.5 concentration of 1054 mu g/m(3) indoors, far higher than any corresponding outdoor values. Conclusions There is an urgent need for interventions to mitigate indoor air pollution that presents significant health risks to household occupants. Reducing health risks associated with high PM2.5 concentrations require interventions to mitigate outdoor PM2.5 levels and solid fuel use indoors. (347 words)

Health impacts associated with exposure to atmospheric aerosols are of global concern and are not completely understood. In addition, health studies are, especially, complicated in developing countries such as South Africa. Oxidative potential (OP), defined as a measure of the capacity of aerosols to oxidise target molecules, has been proposed as a viable alternative relevant biological metric to better quantify toxicological responses related to atmospheric aerosol exposure in health studies. The dithiothreitol (DTT) assay is the most commonly used method to determine OP of aerosols, which was used in this study to quantify the OP of outdoor and indoor atmospheric particulates collected at three low-income settlements in South Africa. This technique is easy-to-operate, low-cost, effective and reproducible. The DTT methodology had to be modified according to previous applications, which required choosing a suitable extraction procedure and -setup. The redox activity of size-resolved sampled aerosols was evaluated and related to their chemical composition with correlation analysis. The seasonal variations of DTT redox activity were established by normalizing in terms of aerosol mass and sampled volume for indoor and outdoor particulate samples. Higher redox activity was determined for the smallest aerosols (aerodynamic diameter

South Africa, with its industrialised economy, faces unique air pollution challenges. Our study investigates aerosol composition and absorption in the Highveld region. Understanding aerosol absorption is critical as it affects climate, air quality, and public health. Aerosol absorption in the lower atmosphere affects the evolution of the boundary layer and the dispersion of pollutants, which in turn affects air quality and public health. Aerosol filter samples (PM10 fractions) were collected from residential, traffic, and industrial sites during the dry season. Chemical analyses, including X-ray fluorescence, thermo-optical analysis, and ion chromatography, were carried out to determine elemental species, carbonaceous species, and water-soluble ions, respectively. Based on this, a mass closure calculation was performed to define the contribution of five major aerosol components. The calculated aerosol mass concentrations were in good agreement with the measurements (Normalised Mean Bias, NMB < 7%). No significant variation in PM10 concentration was observed between site types. Mineral dust appeared to be the main contributor to PM10, varying from about 48%-60% at different sites, followed by organic matter (OM, 22%-35%), secondary inorganic aerosols (SIA, 9%-12%), elemental carbon (EC, 4%-7%), and sea salt (ss, 1%-2%). Aerosol spectral absorption was obtained from multi-wavelength absorbance analysis (MWAA) measurements at 375, 407, 532, 635, and 850 nm. High absorption was measured in the following order: industrial> residential> traffic sites. The estimated absorption Ångström exponent (AAE) varied from 0.8 to 2 at different sites, indicating the contribution of several sources. At 850 nm absorption correlates well with EC as expected (r = 0.85). The obtained mass absorption efficiency (8 m2/g) is in line with expectations. Specific tracers were used to determine the contribution of the main absorbing aerosol components - black carbon (BC), brown organic carbon (BrC) from incomplete biomass combustion, and mineral dust - using correlations between estimated mass and measured absorption. Preliminary results indicate that although BC is the major contributor to absorption, accounting for 30%-60% absorption at 375 nm, followed by BrC 10%-50%, the contribution of the less absorbing but more abundant mineral dust is not negligible and can range from 2% to 50% in different samples. These results underline the complexity of aerosols in the region and their high absorption properties, and the need for a comprehensive understanding of its various components to accurately assess its impact.

In order to study aerosols in environments influenced by anthropogenic and biogenic emissions to variable extents, PM1 samples were collected during summer 2022 in the greater Paris area (ACROSS campaign, Atmospheric Chemistry Of the Suburban Forest, 14 June to 25 July) at two locations that represent the urban Paris and the suburban forested areas. They were analyzed using high-resolution mass spectrometry (HRMS) together with total carbon (TC) with a thermo-optical method. Both sites are compared here to explore differences in aerosol composition from urban and forested environments. The TC analysis shows similar organic carbon (OC) concentrations at both sites (3.2 ± 1.8 µg m−3 for Paris and 2.9 ± 1.5 µg m−3 for Rambouillet) and higher elemental carbon (EC) values in the urban area. Both OC and EC concentrations did not show significant variations for daytime and nighttime conditions. This work highlights the influence of anthropogenic inputs on the chemical composition of urban and forested areas, derived from the presence of CHO and CHON compounds but also the detection of two sulfur-containing compounds (C5H12SO7 and C10H17NSO7), which could be tentatively assigned as organosulfates. A smaller number of aromatic compounds were observed for clean periods that better represent the local biogenic and anthropogenic contributions in Rambouillet and Paris, respectively.

Household air pollution (HAP) is responsible for millions of premature deaths each year. Exposure to household air pollutants as a risk factor for poor health has not been adequately quantified in many parts of the world, especially Sub-Saharan Africa. We aimed to assess HAP, specifically PM2.5, and its associations with dwelling and household characteristics in urban (Soweto) and rural (Agincourt) settings in South Africa. We monitored indoor PM2.5 concentrations in 40 unique households using low-cost sensors, across two study sites and seasons. Lowcost sensors were calibrated by collocation, and associations between dwelling and household characteristics with indoor PM2.5 concentrations were assessed using a log-linear regression model. PM2.5 concentrations were greater in urban households in the summer (50 mu g/m3 (95% CI: 41-63) and in the winter (82 mu g/m3 (95% CI: 62-109)) compared to rural households (summer: 19 mu g/m3 (95%: CI 14-26) and winter: 48 mu g/m3 (95% CI: 44-53)). The log-linear model (n = 39) explained 74% of the variance in leave-one-out cross validation. Significant associations with household PM2.5 were observed with the following: the season, study setting, presence of tobacco smoking, presence of incense burning inside the dwelling, and the use of heating. This study found significant variations in HAP concentrations within and across the urban and rural communities, likely influenced by differences in ambient outdoor concentrations and individual behaviours such as incense burning. It is crucial to enhance community and policy maker awareness regarding the dangers of indoor smoking and the harmful effects of burning incense indoors.

Data on respiratory syncytial virus (RSV) incidence and household transmission are limited. To describe RSV incidence and transmission, we conducted a prospective cohort study in rural and urban communities in South Africa over two seasons during 2017-2018. Nasopharyngeal swabs were collected twice-weekly for 10 months annually and tested for RSV using PCR. We tested 81,430 samples from 1,116 participants in 225 households (follow-up 90%). 32% (359/1116) of individuals had ≥1 RSV infection; 10% (37/359) had repeat infection during the same season, 33% (132/396) of infections were symptomatic, and 2% (9/396) sought medical care. Incidence was 47.2 infections/100 person-years and highest in children <5 years (78.3). Symptoms were commonest in individuals aged <12 and ≥65 years. Individuals 1-12 years accounted for 55% (134/242) of index cases. Household cumulative infection risk was 11%. On multivariable analysis, index cases with ≥2 symptoms and shedding duration >10 days were more likely to transmit; household contacts aged 1-4 years vs. ≥65 years were more likely to acquire infection. Within two South African communities, RSV attack rate was high, and most infections asymptomatic. Young children were more likely to introduce RSV into the home, and to be infected. Future studies should examine whether vaccines targeting children aged <12 years could reduce community transmission.

Contact matrices are a commonly adopted data representation, used to develop compartmental models for epidemic spreading, accounting for the contact heterogeneities across age groups. Their estimation, however, is generally time and effort consuming and model-driven strategies to quantify the contacts are often needed. In this article we focus on household contact matrices, describing the contacts among the members of a family and develop a parametric model to describe them. This model combines demographic and easily quantifiable survey-based data and is tested on high resolution proximity data collected in two sites in South Africa. Given its simplicity and interpretability, we expect our method to be easily applied to other contexts as well and we identify relevant questions that need to be addressed during the data collection procedure.

Health-related impacts e.g. respiratory and cardiovascular morbidity and mortality, associated with exposure to atmospheric particulate matter (PM) are globally considered important and are not completely understood. Oxidative potential (OP), defined as a measure of the capacity of PM to oxidise target molecules, has been previously proposed as an alternative relevant biological metric in health studies to better quantify toxicological responses associated with PM exposure than aerosol mass alone. Several methods are currently used to assess the oxidative capacity of PM. In this study, the dithiothreitol (DTT) assay was used, which is the most commonly used technique to estimate OP. This assessment is easy-to-operate, low-cost, effective and reproducible. The first step was to modify the DTT methodology based on previous applications, which entailed choosing an appropriate extraction procedure and -setup. The redox activity of size-resolved PM samples collected in three low-income urban settlements in South Africa, i.e. Jouberton, KwaZamokuhle and Zamdela was evaluated and related to their chemical composition through correlation analysis. Furthermore, it was attempted to determine seasonal variations of DTT redox activity through normalisation according to PM mass (DTTm) and sampled volume (DTTv) for outdoor and indoor environments. The results indicated higher redox activity for the finest (<1 mu m) particles compared to the coarser particulates (1-10 mu m) for both outdoor and indoor environments. DTT redox activity of PM, especially, in the PM1-10 particle size fraction, had strong correlations with elemental (EC) and organic carbon (OC), as well as trace elements and water-soluble inorganic species for outdoor and indoor samples. Possible atmospheric aerosol emission sources suggested from these correlations include primary emissions from domestic- and open biomass burning, vehicles and industrial activities, as well as secondary particle formation (e.g. sulphate).

The complex refractive index (CRI) is one of the key parameter driving aerosol spectral optical properties and direct radiative effects (DRE). Its value and spectral variation under different conditions, such as anthropogenic− and biogenic−dominated environments and anthropogenic−biogenic mixing situations, remains not fully understood. As a consequence, oversimplified representations of aerosol optical properties are generally used in climate models. Therefore, measurements of aerosol CRI in different environments and their inclusion in models are needed. The field observations from the ACROSS campaign, performed in June-July 2022 in the Ile de France region, are used in this study to deepen the knowledge of aerosol optical properties, aiming to improve the aerosol representation in the CHIMERE model and provide the best constraint for DRE simulations. Measurements obtained both at the Paris city center and the Rambouilllet rural forest sites during ACROSS are considered, in order to explore the CRI variability from anthropogenic−dominated to biogenic−dominated environments, including anthropogenic−biogenic mixing situations. The CRI retrievals at seven different wavelengths, performed by combining the Mie theory with optical and size distribution measurements, are representative of different atmospheric conditions, aerosol loadings as well as type and chemical compositions. In fact, the June-July 2022 period was characterized by highly diversified weather conditions: 1) two strong heatwaves, promoting SOA build-up and favoring the export of the Paris pollution plume towards the forest site; 2) Saharan dust events transported from the upper atmosphere to the ground; 3) biomass burning episode; 4) periods with reduced anthropogenic influence. The CRI retrievals under these different conditions and their link to particulate chemical composition is investigated. Hence, the CRI dataset presented here constitutes a unique dataset from which models can benefit to validate and constrain simulations and DRE estimations, under both urban and biogenic emissions influence. These data, in conjunction with those from the aircraft observations during ACROSS, are used to initialize and perform sensitivity studies on the aerosol DRE, using the CHIMERE−WRF coupled model, the OPTSIM model for the aerosol optical properties and the Rapid Radiative Transfer Model for GCMs (RRTMG).Keywords: Complex refractive index, direct radiative effect, aerosol mixing, urban, forest

&lt;p&gt;Southern Africa, and in particular its western part, Namibia, is considered a climate change hotspot by the IPCC and is at risk of severe temperature-related changes. As examples, models projections suggest by the end of the century: 1) Increase of surface temperature of +4 to +7&amp;#176;C; 2) destruction of the stratocumulus cloud deck along the western coast; and 3) decrease of the fog inland. The role of aerosols in this context is still not completely quantified, due to their high spatial and temporal variability, the many sources responsible for the complex mixture and the lack of continuous observations. Most of the past regional climate modelling (RCM) and intensive field campaigns focussed primarily on constraining the radiative effects of the seasonal biomass burning aerosols generally occurring in the end of the austral winter (August to October). However, the aerosol spectral optical properties, aerosol optical depth and the organic fractions are not studied enough to provide a firm understanding of regional aerosol load, interaction with radiation and interplays in relation to particle chemistry.&lt;/p&gt; &lt;p&gt;In this work, we present the first analysis of new long-term ground-based aerosol observations conducted since april 2022 at Gobabeb Namib Research Institue (23&amp;#176;33&amp;#8217;40&amp;#8216;&amp;#8217;S, 15&amp;#176;02&amp;#8217;24&amp;#8217;&amp;#8217;E) in Namibia. Gobabeb is located in the hyperarid Namib desert and it is under the influence of different air masses, transporting maritime and biomass burning aerosols, amongst others. The measurements of optical and physical properties of the aerosol mixtures are analysed to provide with the aerosol single scattering albedo and mass absorption, scattering and extinction efficiencies which are needed to evaluate the first Africa-based Earth system model by the Global Change Institute at the University of Witwatersrand in South Africa. The in situ surface data are complemented by the analysis of pre-existing observations such as those from the AERONET sunphotometers.&lt;/p&gt;

The Namibian coast is one of the areas of international interest for aerosol studies. This is due to the region’s importance for the global radiation budget because of the presence of a semi-permanent stratocumulus cloud along the coast. Aerosol particles may scatter/absorb radiation and directly influence how long clouds last by modifying their properties. This is all dependent on the particles’ chemical and physical properties because of the sources they were emitted from. In this study, we identified and investigated episodes of high (HAE) and low (LAE) PM concentrations and the meteorology that may favour their occurrence. Here, we investigated PM2.5 (particles with an aerodynamic diameter of 2.5 µm or less) and PM10 (particles with an aerodynamic diameter of 10 µm or less) at Henties Bay, Namibia. Daily aerosol measurements were taken with E-samplers between 15 and 29 July 2019. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to investigate the long-range atmospheric transport of air masses that reached Henties Bay. The study found that during HAEs, the average PM2.5 concentration was 28.40 ± 18.10 µg/m3 and the average PM10 concentration was 68.20 ± 44.3 µg/m3. In contrast, during LAEs, the average PM2.5 concentration was 13.3 ± 9.52 µg/m3 and the average PM10 concentration was 30.00 ± 23.00 µg/m3. In both fractions, there was an observed dominant contribution from marine sources.

In South Africa, the Highveld region and the Johannesburg-Pretoria megacity are known as global NOx (NOx = NO + NO2) “hotspots” identified by satellite-based instruments. The ultimate sink for atmospheric NOx is conversion to aerosol nitrate. However, measurements of aerosol nitrate concentrations do not provide information on which NOx sources served as nitrate precursors at that location. This complicates efforts to reduce concentrations of particulate matter (PM) in these air quality priority areas. Here, we measured the nitrogen stable isotopic composition of nitrate from daily wintertime collections of coarse mode PM2.5-10 (PM ≤ 10 and >2.5 µm in diameter) at three air quality monitoring stations located in the Vaal Triangle Air-Shed Priority Area (VTAPA). The overall aim of this case study was to evaluate the use of the distinct stable isotopic signatures of various NOx sources to identify their relative contribution to aerosol nitrate across the Highveld. The nitrogen isotopic ratios of aerosol nitrate were similar across the three sites, with greater day-to-day variability than site to site variability. Air mass history was the main driver of the variability in the nitrogen isotopic ratios of aerosol nitrate, with significantly higher isotopic ratios observed for air masses originating from the southwest. Using an isotope mixing model we determined that NOx from coal-burning is the dominant contributor to aerosol nitrate (66%), followed by biomass burning (16%), vehicles (12%), and soil emissions (6%).