Juha Sulo

Coral reefs are among the most biologically important ecosystems on Earth and are highly sensitive to climate change. The Great Barrier Reef (GBR) is the largest coral reef system globally, yet the extent to which it contributes to local atmospheric particle loading remains poorly understood. Here, we present a case study focusing on particle formation processes observed during a six-week measurement campaign at Heron Island on the GBR. Our results show that when air masses spent considerable time over the reef itself, we observed a number of new particle formation events. These events were preceded by an increase in dimethylsulfoxide (DMSO) concentrations and led to increased sulfate and ammonium in the resulting particle population. Importantly, DMSO concentrations were not higher during event days in comparison to other days, suggesting that both precursor availability and favorable photochemical conditions such as increased solar irradiance played a role in initiating particle formation over the reef. These findings provide evidence that the GBR ecosystem can influence local aerosol formation processes, with implications for regional cloud formation and climate feedbacks in marine ecosystems.

Coral reefs are among the most biologically important ecosystems on Earth and are highly sensitive to climate change. The Great Barrier Reef (GBR) is the largest coral reef system globally, yet the extent to which it contributes to local atmospheric particle loading remains poorly understood. Here, we present a case study focusing on particle formation processes observed during a six-week measurement campaign at Heron Island on the GBR. Our results show that when air masses spent considerable time over the reef itself, we observed a number of new particle formation events. These events were preceded by an increase in dimethylsulfoxide (DMSO) concentrations and led to increased sulfate and ammonium in the resulting particle population. Importantly, DMSO concentrations were not higher during event days in comparison to other days, suggesting that both precursor availability and favorable photochemical conditions such as increased solar irradiance played a role in initiating particle formation over the reef. These findings provide evidence that the GBR ecosystem can influence local aerosol formation processes, with implications for regional cloud formation and climate feedbacks in marine ecosystems.

Coral reefs are among the most biologically important ecosystems on Earth and are highly sensitive to climate change. The Great Barrier Reef (GBR) is the largest coral reef system globally, yet the extent to which it contributes to local atmospheric particle loading remains poorly understood. Here, we present a case study focusing on particle formation processes observed during a six-week measurement campaign at Heron Island on the GBR. Our results show that when air masses spent considerable time over the reef itself, we observed a number of new particle formation events. These events were preceded by an increase in dimethylsulfoxide (DMSO) concentrations and led to increased sulfate and ammonium in the resulting particle population. Importantly, DMSO concentrations were not higher during event days in comparison to other days, suggesting that both precursor availability and favorable photochemical conditions such as increased solar irradiance played a role in initiating particle formation over the reef. These findings provide evidence that the GBR ecosystem can influence local aerosol formation processes, with implications for regional cloud formation and climate feedbacks in marine ecosystems.

Knowledge of ground-level ozone (O₃) formation in the Southern Hemisphere is limited due to the lack of long-term in situ O₃ observations. Here, we analyzed the ground-based measurement data of O₃, formaldehyde (HCHO), nitrogen dioxide (NO₂), and benzene, toluene, and xylene (BTX) collected from 2011 to 2020 at two sites in eastern Australia, namely, Memorial Park and Springwood. Only HCHO at Memorial Park showed a statistically significant upward trend (0.19 ppb yr^-1). Compared with the sea-influenced air masses, the land-influenced air masses were observed to enhance all pollutant concentrations at two sites. According to the site-specific sensitivity of the O₃ to the HCHO-to-NO₂ ratio (FNR), the daytime formation of the O₃ at two sites was mainly in the volatile organic compound (VOC)-limited regime. When the long-term variability of NO₂ was weak, HCHO, particularly from primary emissions indicated by BTX, was observed to predominantly control the monthly FNR at each site over time. Our work underscores the importance of long-term in situ measurements in interpreting ground-level O₃ formation and potentially informs future O₃ studies in other areas in the Southern Hemisphere.

The Italian Po Valley is one of the most polluted regions in Europe. During winter, meteorological conditions favor long and dense fogs, which strongly affect visibility and human health. In spring, the frequency of nighttime fogs reduces while daytime new particle formation events become more common. This transition is likely caused by a reduction in particulate matter (PM _2.5 ), leading to a decrease in the relevant condensation sink. The physics and chemistry of fog and aerosol have been studied at the San Pietro Capofiume site since the 1980s, but the detailed processes driving the observed trends are not fully understood. Hence, during winter and spring 2021/22, the Fog and Aerosol Interaction Research Italy (FAIRARI) campaign was carried out, using a wide spectrum of approaches, including in situ measurements, outdoor chamber experiments, and remote sensing. Atmospheric constituents and their properties were measured ranging from gas molecules and molecular clusters to fog droplets. One unique aspect of this study is the direct measurement of the aerosol composition inside and outside of fog, showing a slightly greater dominance of organic compounds in the interstitial compared to the droplet phase. Satellite observations of fog provided a spatial context and agreed well with in situ measurements of droplet size. They were complemented with in situ chamber experiments, providing insights into oxidative processes and revealing a large secondary organic aerosol-forming potential of ambient air upon chemical aging. The oxidative potential of aerosol and fog water inferred the impact of aerosol–fog interactions on particle toxicity. Significance Statement: Aerosol and fog influence our climate and can have adverse effects on human health and visibility. Through anthropogenic emissions, such as from industry or transport, humans can influence the physical and chemical properties of fog and aerosol. The FAIRARI campaign investigated the formation of aerosols and aerosol–fog interactions in the Italian Po Valley, one of the most polluted regions in Europe. State-of-the-art experimental methods revealed the details of aerosols and fogs from the molecular level to the droplet scale. We observed a clear transition from winter to spring, with fog-dominated periods followed by an intensified secondary aerosol formation period. Organic and nitrate compounds dominated the composition of aerosol and fog residuals. The results will contribute to various aerosol–fog interaction modeling activities.

Pure biogenic new particle formation (NPF) induced by highly oxygenated organic molecules (HOMs) could be an important mechanism for pre-industrial aerosol formation. However, it has not been unambiguously confirmed in the ambient due to the scarcity of truly pristine continental locations in the present-day atmosphere or the lack of chemical characterization of NPF precursors. Here, we report ambient observations of pure biogenic HOM-driven NPF over a peatland in southern Finland. Meteorological decoupling processes formed an “air pocket” (i.e., a very shallow surface layer) at night and favored NPF initiated entirely by biogenic HOM from this peatland, whose atmospheric environment closely resembles that of the pre-industrial era. Our study sheds light on pre-industrial aerosol formation, which represents the baseline for estimating the impact of present and future aerosol on climate, as well as on future NPF, the features of which may revert toward pre-industrial–like conditions due to air pollution mitigation.

New particle formation (NPF) is a major source of aerosol particles and cloud condensation nuclei in the troposphere, playing an important role in both air quality and climate. Frequent NPF events have been observed in heavily polluted urban environments, contributing to the aerosol number concentration by a significant amount. The Po Valley region in northern Italy has been characterized as a hotspot for high aerosol loadings and frequent NPF events in southern Europe. However, the mechanisms of NPF and growth in this region are not completely understood. In this study, we conducted a continuous 2-month measurement campaign with state-of-the-art instruments to elucidate the NPF and growth mechanisms in northern Italy. Our results demonstrate that frequent NPF events (66 % of all days during the measurement campaign) are primarily driven by abundant sulfuric acid (8.5×10 ⁶ cm ⁻³ ) and basic molecules in this area. In contrast, oxygenated organic molecules from the atmospheric oxidation of volatile organic compounds (VOCs) appear to play a minor role in the initial cluster formation but contribute significantly to the consecutive growth process. Regarding alkaline molecules, amines are insufficient to stabilize all sulfuric acid clusters in the Po Valley. Ion cluster measurements and kinetic models suggest that ammonia (10 ppb) must therefore also play a role in the nucleation process. Generally, the high formation rates of sub-2 nm particles (87 cm ⁻³ s ⁻¹ ) and nucleation-mode growth rates (5.1 nm h ⁻¹ ) as well as the relatively low condensational sink (8.9×10-3 s ⁻¹ ) will result in a high survival probability for newly formed particles, making NPF crucial for the springtime aerosol number budget. Our results also indicate that reducing key pollutants, such as SO ₂ , amine and NH ₃ , could help to substantially decrease the particle number concentrations in the Po Valley region.

Accurate measurement of the size distribution of sub-10 nm aerosol particles is still a challenge. Here we introduce a novel version of the Airmodus particle size magnifier (PSM 2.0), which is a condensation-particle-counter-based instrument with a sizing range of 1–12 nm. The extended size range compared to the earlier PSM version enables the direct detection of forming clusters and particles as well as the study of their growth processes without the challenges related to particle charging. It also gives an overlap between the activation size distribution measurements with the PSM and mobility size distribution measurements with conventional mobility particle sizers. We compared the performance of PSM 2.0 to that of a mobility particle size spectrometer, the original A10 particle size magnifier, and a Neutral cluster and Air Ion Spectrometer (NAIS) during field measurements. Also, calibration results were compared against the A10 instrument. The results show that PSM 2.0 is able to activate sub-2 nm clusters and that the concentration and size distribution between 2–12 nm compare well, especially with the NAIS.

New particle formation (NPF) is a major source of aerosol particles and cloud condensation nuclei in the troposphere, playing an important role in both air quality and climate. Frequent NPF events have been observed in heavily polluted urban environments, contributing to the aerosol number concentration by a significant amount. The Po Valley region in northern Italy has been characterized as a hotspot for high aerosol loadings and frequent NPF events in Southern Europe. However, the mechanisms of NPF and growth in this region are not completely understood. In this study, we conducted a continuous 2-month measurement campaign with state-of-the-art instruments to elucidate the NPF and the growth mechanisms in Northern Italy. Our results show that abundant sulfuric acid, ammonia and amines from agricultural activities may be the dominant components driving the frequent NPF events (66 % of all days during the measurement campaign) in this area. In contrast, organics seem to have a smaller role in cluster formation but contribute to the consecutive growth process. According to ion cluster measurements and kinetic model results, dimethylamine is not sufficient to stabilize all of the sulfuric acid during springtime in the Po Valley, suggesting that other amines and ammonia can also be involved. Generally, the high formation rates of sub-2 nm particles (87 cm⁻³ s⁻¹) and nucleation mode growth rates (5.1 nm h⁻¹) together with the relatively low condensational sink (8.9 × 10⁻³ s⁻¹) will result in a high survival probability of newly formed particles, making NPF crucial for the springtime aerosol number budget in the Po Valley region.