Abstract Aerosols play a major role in climate by influencing both radiative forcing and cloud condensation nuclei (CCN) formation, with organic aerosols comprising a large fraction of the global natural aerosol burden (∼20–70%). Despite this importance, long-term observations of water-soluble organic carbon (WSOC), particularly in size-segregated aerosols from natural sources, remain scarce in the southern hemisphere. Here, we present size-resolved WSOC measurements from an eight-month observational campaign (April to November 2018) at the Cape Point Global Atmosphere Watch (GAW) station, a remote coastal site at the southern tip of Africa, ideally suited for elucidating marine, continental, and mixed aerosol sources. Weekly aerosol samples were classified using air mass back trajectories, radon-222 and carbon monoxide concentrations, wildfire observations, and satellite-derived chlorophyll-a to assess source influences. Across all air mass classifications, WSOC concentrations were consistently higher in the fine mode (<1 μm) than in the coarse mode (>1 μm) aerosols (0.58 ± 0.55 μg/m3 vs 0.20 ± 0.22 μg/m3, respectively). Fine mode WSOC concentrations were highest during periods influenced by biomass burning (0.87 ± 0.49 μg/m3) and continental outflow, while marine and modified marine air masses exhibited lower fine mode WSOC concentrations. However, periods of enhanced marine biological activity were associated with increased fine-mode WSOC concentrations. The observed predominance of WSOC in the fine mode across marine, modified marine, and continental air masses highlights the importance of secondary formation and atmospheric aging processes, rather than direct primary emissions, in controlling WSOC concentrations at Cape Point. Overall, WSOC levels at this coastal site reflect an integration of natural and anthropogenic sources, transport history, and atmospheric processing. These results establish a regional baseline for WSOC aerosols in southern Africa and contribute to a broader understanding of organic aerosol formation in a data-sparse southern hemisphere coastal environment.

Anthropogenic nitrogen (N) deposition entering the ocean from the atmosphere has increased over time. Ammonia (NH3), a precursor to ammonium (NH4+), is released into the atmosphere via both natural sources (e.g., ammonification, biomass burning, waste products, surface ocean emissions) and anthropogenic sources (e.g., agriculture, industry, sewage, vehicle emissions). Studies disagree on the quantity of anthropogenic N deposition to the ocean, as well as the consequences this excess N poses to the biogeochemistry of the open ocean, particularly in the Pacific Ocean. Understanding the current role that the open ocean is playing in the N cycle and budget is essential to determine the sources of N (e.g., internal or external, recycled or excess) and to further distinguish the relationships between atmospheric and oceanic N. Therefore, in the current study, ion concentrations and ammonium isotope values (delta N-15-NH4+) were measured for aerosol samples collected on the coast of Oahu, Hawaii from 2021 to 2022 (n = 67). This location was chosen based on low anthropogenic activity, access to the open ocean, and the premise of a dominant marine signal. Particulate NH4+ concentrations ([NH4+]) averaged 3.7 +/- 7.3 ng/m(3), with no distinct seasonality (p > 0.05). The delta N-15-NH4+ values also did not exhibit distinct seasonality (p > 0.05), but did fall into three unique clusters (using a K-means clustering analysis): cluster one = 19.0 +/- 3.9 parts per thousand (n = 8), cluster two = 4.1 +/- 2.3 parts per thousand (n = 31), and cluster three = -3.3 +/- 2.4 parts per thousand (n = 13). Cluster three was best explained as an ocean emissions signature, which was determined via a phase partitioning model that incorporated N isotope fractionation associated with NH3 conversion to NH4+. Cluster one had higher than average [NH4+] along with air mass origins from two seabird sanctuaries and was hypothesized to be a seabird emission signature. Cluster two was considered a mix of these two sources (67 % marine, 33 % seabird emissions). 6 % of aerosol inorganic N (NH4+ + nitrate; annual dry inorganic N = 5.5 ng/m(3)) is from [NH4+], with 35 % resulting from seabird emissions. The annual inorganic N (IN; NO3- + NH4+) dry deposition value for this site was 1.2 +/- 1.1 Tg Ny(-1).

The biogeochemical nitrogen (N) cycle in South Africa is influenced by, and in turn influences a number of crucially important global change processes. However, the natural N cycling in South Africa is not well-understood. The “Emissions, deposition, impacts - Interdisciplinary study of N biogeochemical cycling (EDI-SA)” project is working to improve our baseline understanding of the natural biogeochemical cycling of N in non-industrialized ecosystems across South Africa. This includes quantifying N fluxes from emissions through to deposition, identifying linkages between N cycling and related species such as sulphur (S) and ozone, and evaluating ecosystem impacts. Previous work has focused on the impact of atmospheric deposition of N and S species on ecosystems at sites almost exclusively on the industrialized Highveld. This has left large gaps of knowledge in the biogeochemical cycling and ecosystem impacts, particularly within the diverse natural ecosystems found across South Africa. In order to address this gap, EDI-SA is applying a more holistic approach using measurements (from two South African Research Infrastructures; EFTEON and BIOGRIP) and modelling to investigate multiple linkages within the biogeochemical cycling of N with a focus on improving the understanding of the natural cycling. The project is applying a variable resolution sampling approach to investigate processes which occur at multiple spatial scales, and applying multiple measurement techniques including atmospheric measurements, stable isotope analysis of aerosol particles, rainwater and soil, and analysis of soil chemistry and biology. This contribution will detail the approach of this interdisciplinary project, highlight results from the first soil and air sampling campaigns, as well as the atmospheric composition modelling that assesses the relative importance and impacts of N emissions from soil across South Africa. This baseline understanding will allow future research to assess the potential changes to N biogeochemical cycling into the future in a changing climate.

To tackle the current pressing atmospheric science issues, as well as those in the future, a robust scientific community is necessary in all regions across the globe. Unfortunately, this does not yet exist. There are many geographical areas that are still underrepresented in the atmospheric science community, many of which are in the Global South. There are also larger gaps in the understanding of atmospheric composition, processes, and impacts in these regions. In this opinion, we focus on two geographical areas in the Global South to discuss some common challenges and constraints, with a focus on our strengths in atmospheric science research. It is these strengths, we believe, that highlight the critical role of Global South researchers in the future of atmospheric science research.

Aerosols and clouds are key components of the marine atmosphere, impacting the Earth’s radiative budget with a net cooling effect over the industrial era that counterbalances greenhouse gas warming, yet with an uncertain amplitude. Here we report recent advances in our understanding of how open ocean aerosol sources are modulated by ocean biogeochemistry and how they, in turn, shape cloud coverage and properties. We organize these findings in successive steps from ocean biogeochemical processes to particle formation by nucleation and sea spray emissions, further particle growth by condensation of gases, the potential to act as cloud condensation nuclei or ice nucleating particles, and finally, their effects on cloud formation, optical properties, and life cycle. We discuss how these processes may be impacted in a warming climate and the potential for ocean biogeochemistry—climate feedbacks through aerosols and clouds.

Permissions Request permissions Contents list Environ. Sci.: Processes Impacts, 2023, 25, 1011 DOI: 10.1039/D3EM90020G This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given. Read more about how to correctly acknowledge RSC content.

This dataset provides an overview of data produced during South African voyages in the Southern Ocean aboard the R/V S.A. Agulhas II and contains a document detailing the data that are presented (AvailableData.pdf) and an .xlsx file that contains the metadata and links to the published datasets (AvailableData.xlsx). Each voyage has a dedicated sheet within the .xlsx file. This dataset will be updated, and a new version published as more data becomes available. Please refer to the most recent version on https://zenodo.org/communities/scale_south_africa/ This is a data curation document only. Any use of the data mentioned in this document should reference the original dataset and authors.

Nitrogen oxides, collectively referred to as NOx (NO + NO2), are an important component of atmospheric chemistry involved in the production and destruction of various oxidants that contribute to the oxidative capacity of the troposphere. The primary sink for NOx is atmospheric nitrate, which has an influence on climate and the biogeochemical cycling of reactive nitrogen. NOx sources and NOx-to-NO3- formation pathways remain poorly constrained in the remote marine boundary layer of the Southern Ocean, particularly outside of the more frequently sampled summer months. This study presents seasonally resolved measurements of the isotopic composition (δ15N, δ18O, and Δ17O) of atmospheric nitrate in coarse-mode (> 1 µm) aerosols, collected between South Africa and the sea ice edge in summer, winter, and spring. Similar latitudinal trends in δ15N–NO3- were observed in summer and spring, suggesting similar NOx sources. Based on δ15N–NO3-, the main NOx sources were likely a combination of lightning, biomass burning, and/or soil emissions at the low latitudes, as well as oceanic alkyl nitrates and snowpack emissions from continental Antarctica or the sea ice at the mid-latitudes and high latitudes, respectively. Snowpack emissions associated with photolysis were derived from both the Antarctic snowpack and snow on sea ice. A combination of natural NOx sources, likely transported from the lower-latitude Atlantic, contribute to the background-level NO3- observed in winter, with the potential for a stratospheric NO3- source evidenced by one sample of Antarctic origin. Greater values of δ18O–NO3- in spring and winter compared to summer suggest an increased influence of oxidation pathways that incorporate oxygen atoms from O3 into the end product NO3- (i.e. N2O5, DMS, and halogen oxides (XO)). Significant linear relationships between δ18O and Δ17O suggest isotopic mixing between H2O(v) and O3 in winter and isotopic mixing between H2O(v) and O3/XO in spring. The onset of sunlight in spring, coupled with large sea ice extent, can activate chlorine chemistry with the potential to increase peroxy radical concentrations, contributing to oxidant chemistry in the marine boundary layer. As a result, isotopic mixing with an additional third end-member (atmospheric O2) occurs in spring.

Determining the magnitude and origins of nitrogen (N) deposition in the open ocean is vital for understanding how anthropogenic activities influence oceanic biogeochemical cycles. Excess N in the North Pacific Ocean (NPO) is suggested to reflect recent anthropogenic atmospheric deposition from the Asian continent, changes in nutrient dynamics due to marine N-fixation, and/or lateral transport of nutrients. We investigate the impact of anthropogenic and marine sources on reactive N deposition in the NPO, with a focus on ammonium (NH4+), an important bioavailable nutrient, using aerosol samples (n = 108) collected off the coast of China (Changdao Island). This study site is used as a proxy for continental emissions that can be exported and subsequently deposited to the ocean. The NH4+ concentration of aerosol samples varied seasonally (p < 0.05), with a higher average value in winter (2.8 +/- 1.1 mu g/m(3)) and spring (1.9 +/- 0.8 mu g/m(3)) compared to autumn (0.7 +/- 0.6 mu g/m(3)) and summer (1.4 +/- 0.4 mu g/m(3)). The isotopic composition of aerosol NH4+ varied seasonally, with higher averages in spring (13.3 +/- 7.9 parts per thousand) and summer (15.6 +/- 6.2 parts per thousand) compared to autumn (3.2 +/- 2.5 parts per thousand) and winter (3.8 +/- 11.4 parts per thousand). These seasonal patterns in the isotopic composition of NH4+ are investigated based on correlations of aerosol chemical species, seasonal shifts in transport patterns, partitioning of ammonia/ammonium between the gas and particle phase, and continental versus marine sources of ammonia. We find that anthropogenic activities, mainly agricultural practices (e.g., volatilization, fertilizer, animal husbandry), are the primary sources of NH4+ deposited to the NPO.

Polar environments are among the fastest changing regions on the planet. It is a crucial time to make significant improvements in our understanding of how ocean and ice biogeochemical processes are linked with the atmosphere. This is especially true over Antarctica and the Southern Ocean where observations are severely limited and the environment is far from anthropogenic influences. In this commentary, we outline major gaps in our knowledge, emerging research priorities, and upcoming opportunities and needs. We then give an overview of the large-scale measurement campaigns planned across Antarctica and the Southern Ocean in the next 5 years that will address the key issues. Until we do this, climate models will likely continue to exhibit biases in the simulated energy balance over this delicate region. Addressing these issues will require an international and interdisciplinary approach which we hope to foster and facilitate with ongoing community activities and collaborations.

Permissions Request permissions Contents list Environ. Sci.: Processes Impacts, 2023, 25, 889 DOI: 10.1039/D3EM90015K This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given. Read more about how to correctly acknowledge RSC content.

Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx=NO+NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling and NOx to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean, where pristine conditions serve as a useful proxy for the pre-industrial atmosphere. Here, we measured the isotopic composition (δ15N and δ18O) of atmospheric nitrate in coarse-mode (>1 µm) aerosols collected in the summertime marine boundary layer of the Atlantic Southern Ocean from 34.5 to 70∘ S and across the northern edge of the Weddell Sea. The δ15N–NO3- decreased with latitude from −2.7 ‰ to −42.9 ‰. The decline in δ15N with latitude is attributed to changes in the dominant NOx sources: lightning at the low latitudes, oceanic alkyl nitrates at the mid-latitudes and photolysis of nitrate in snow at the high latitudes. There is no evidence of any influence from anthropogenic NOx sources or equilibrium isotope fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ15N signature of -21.8±7.6 ‰. Given that measurements of alkyl nitrate contributions to remote nitrogen budgets are scarce, this may be a useful tracer for detecting their contribution in other oceanic regions. The δ18O–NO3- was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NOx oxidation pathway during summer. Unusually low δ18O–NO3- values (less than 31 ‰) were observed at the western edge of the Weddell Sea. The air mass history of these samples indicates extensive interaction with sea-ice-covered ocean, which is known to enhance peroxy radical production. The observed low δ18O–NO3- is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ18O, relative to ozone, which has a high δ18O. This study reveals that the mid- and high-latitude surface ocean may serve as a more important NOx source than previously thought and that the ice-covered surface ocean impacts the reactive nitrogen budget as well as the oxidative capacity of the marine boundary layer.

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%).

The production and removal of ammonium (NH4+) are essential upper-ocean nitrogen cycle pathways, yet in the Southern Ocean where NH4+ has been observed to accumulate in surface waters, its mixed-layer cycling remains poorly understood. For surface seawater samples collected between Cape Town and the Marginal Ice Zone in winter 2017, we found that NH4+ concentrations were 5-fold higher than is typical for summer and lower north than south of the Subantarctic Front (0.01–0.26 µM versus 0.19–0.70 µM). Our observations confirm that NH4+ accumulates in the Southern Ocean's winter mixed layer, particularly in polar waters. NH4+ assimilation rates were highest near the Polar Front (12.9 ± 0.4 nM d−1) and in the Subantarctic Zone (10.0 ± 1.5 nM d−1), decreasing towards the Marginal Ice Zone (3.0 ± 0.8 nM d−1) despite the high ambient NH4+ concentrations in these southernmost waters, likely due to the low temperatures and limited light availability. By contrast, rates of NH4+ oxidation were higher south than north of the Polar Front (16.0 ± 0.8 versus 11.1 ± 0.5 nM d−1), perhaps due to the lower-light and higher-iron conditions characteristic of polar waters. NH4+ concentrations were also measured along five transects of the Southern Ocean (Subtropical Zone to Marginal Ice Zone) spanning the 2018/19 annual cycle. These measurements reveal that mixed-layer NH4+ accumulation south of the Subantarctic Front derives from sustained heterotrophic NH4+ production in late summer through winter that, in net, outpaces NH4+ removal by temperature-, light-, and iron-limited microorganisms. Our observations thus imply that the Southern Ocean becomes a biological source of CO2 to the atmosphere in autumn and winter not only because nitrate drawdown is weak but also because the ambient conditions favour net heterotrophy and NH4+ accumulation.

This commentary paper from the recently formed International Global Atmospheric Chemistry (IGAC) Southern Hemisphere Working Group outlines key issues in atmospheric composition research that particularly impact the Southern Hemisphere. In this article, we present a broad overview of many of the challenges for understanding atmospheric chemistry in the Southern Hemisphere, before focusing in on the most significant factors that differentiate it from the Northern Hemisphere. We present sections on the importance of biogenic emissions and fires in the Southern Hemisphere, showing that these emissions often dominate over anthropogenic emissions in many regions. We then describe how these and other factors influence air quality in different parts of the Southern Hemisphere. Finally, we describe the key role of the Southern Ocean in influencing atmospheric chemistry and conclude with a description of the aims and scope of the newly formed IGAC Southern Hemisphere Working Group.

Nearshore water quality can be highly impacted by anthropogenic activities ongoing along the coast, the effects of which on natural environments can be permanent and irreversible, with consequences for ecosystem biodiversity and functioning, as well as for associated services. Benthic filter feeders (e.g., mussels) provide several services for coastal regions, including improving water quality by reducing eutrophication, being a major source of food for humans, and as a habitat-forming species. Here, we seek to understand the role of benthic filter feeders in enhancing water quality in an urban coastal system in order to assess their role as ecosystem service providers and how they should be included in ecosystem-based evaluations. Using as a model False Bay, South Africa's largest natural bay and a socio-economic hotspot, this multidisciplinary study was designed to identify possible pollution sources to a highly-urbanised coastal region, assess their effects on several biological and biogeochemical parameters, and evaluate the role of mussels in mitigating these anthropogenic inputs. We consider several sources of pollution, including nutrient loading from wastewater and river outflows, heavy metals, and aerosol deposition. We find that pollutant inputs are largely attenuated by the circulation of the bay and by the presence of filter feeders that bioaccumulate contaminants, thereby removing them from coastal waters. Our work thus emphasizes the potential for mussels and natural abiotic processes to ameliorate anthropogenic impacts, although these mitigation strategies are not without environmental risk. We recommend that such information should be included in national assessments used to develop appropriate strategies and policies for coastal environmental management and conservation.

Understanding the transport and accumulation of microplastics is useful to determine the relative risk they pose to global biodiversity. The exact contribution of microplastic sources is hard to elucidate; therefore, investigating the Antarctic Weddell Sea, an area known for its remoteness and little human presence (i.e. limited pollution sources), will help us to better understand microplastic transportation. Here, we investigate the presence of microplastics in a range of Antarctic sample media including air, seawater, and sediment. We hypothesised that multiple transportation processes including atmospheric and oceanic vectors determine the presence of microplastics in the Antarctic. Using techniques including Polarised Light Microscopy and Raman Spectrometry, we identified mostly fibres and categorised them based on their optical and chemical properties. A total of 47 individual microplastic categories (45 of which were fibres) were identified in the air, seawater, and sediment samples. The majority of categories did not overlap multiple media (42/47); however, four fibre categories were present in both air and water samples, and another fibre category was found in all three media (category 27). We suggest that the large variety of fibres identified and the overlap of fibre categories among media indicates that the pollution may result from multiple diffuse sources and transportation pathways. Additionally, our Air Mass Back Trajectory analyses demonstrates that microplastic fibres are being transported by air masses or wind, and strongly suggests that they are transported to the Antarctic from southern South America. We also propose that fibres may be transported into the Antarctic in subsurface waters, and as pollution was identified in our sediment and additional sea ice samples, we suggest that the coastal and Antarctic deep sea may be a sink for microplastic fibres. The results shown here from a remote, near-pristine system, further highlight the need for a global response to the plastic pollution crisis.

Table S1: The starting and ending date, latitude (°S), and longitude(°E) are presented for each aerosol filter deployment.The wind speed (WS; m s⁻¹), atmospheric temperature (Atm T; °C), relative humidity (RH; %), and the number of daylight hours (hrs) were calculated as an average (Avg) over the duration of each filter deployment.For WS, Atm T and RH the standard deviations (SD) are also shown.Filter deployments are separated into early Summer (ES), Weddell Sea (WS) and late Summer (LS) depending on the location and time of sampling. Cruise

The Indian Ocean has been highlighted as an important region for SOLAS science and is included in the list of key environments under the Integrated Studies of High Sensitivity Systems of the SOLAS science mission. The main aim of this workshop was to present and discuss current, ongoing, and planned SOLAS research and initiatives taking place in the Indian Ocean and help forge collaborations between different institutions. Another aim of the workshop was to reinvigorate the Indian SOLAS community and develop community actions and strategies supported by SOLAS.