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Remarkable perturbations in the stratospheric abundances of chlorine species and ozone were observed over Southern Hemisphere mid-latitudes following the 2020 Australian wildfires 1 , 2 . These changes in atmospheric chemical composition suggest that wildfire aerosols affect stratospheric chlorine and ozone depletion chemistry. Here we propose that wildfire aerosol containing a mixture of oxidized organics and sulfate 3 – 7 increases hydrochloric acid solubility 8 – 11 and associated heterogeneous reaction rates, activating reactive chlorine species and enhancing ozone loss rates at relatively warm stratospheric temperatures. We test our hypothesis by comparing atmospheric observations to model simulations that include the proposed mechanism. Modelled changes in 2020 hydrochloric acid, chlorine nitrate and hypochlorous acid abundances are in good agreement with observations 1 , 2 . Our results indicate that wildfire aerosol chemistry, although not accounting for the record duration of the 2020 Antarctic ozone hole, does yield an increase in its area and a 3–5% depletion of southern mid-latitude total column ozone. These findings increase concern 2 , 12 , 13 that more frequent and intense wildfires could delay ozone recovery in a warming world. Comparison of model simulations with atmospheric observations from the Southern Hemisphere mid-latitudes following the 2020 Australian wildfires shows that the wildfire aerosol composition promotes stratospheric chlorine and ozone depletion chemistry.

Purpose To compare in vivo the total and regional pulmonary deposition of aerosol particles generated by a new system combining a vibrating-mesh nebulizer with a specific valved holding chamber and constant-output jet nebulizer connected to a corrugated tube. Methods Cross-over study comparing aerosol delivery to the lungs using two nebulizers in 6 healthy male subjects: a vibrating-mesh nebulizer combined with a valved holding chamber (Aerogen Ultra®, Aerogen Ltd., Galway, Ireland) and a jet nebulizer connected to a corrugated tube (Opti-Mist Plus Nebulizer®, ConvaTec, Bridgewater, NJ). Nebulizers were filled with diethylenetriaminepentaacetic acid labelled with technetium-99 m ( 99m Tc-DTPA, 2 mCi/4 mL). Pulmonary deposition of 99m Tc-DTPA was measured by single-photon emission computed tomography combined with a low dose CT-scan (SPECT-CT). Results Pulmonary aerosol deposition from SPECT-CT analysis was six times increased with the vibrating-mesh nebulizer as compared to the jet nebulizer (34.1 ± 6.0% versus 5.2 ± 1.1%, p  < 0.001). However, aerosol penetration expressed as the three-dimensional normalized ratio of the outer and the inner regions of the lungs was similar between both nebulizers. Conclusions This study demonstrated the high superiority of the new system combining a vibrating-mesh nebulizer with a valved holding chamber to deliver nebulized particles into the lungs as comparted to a constant-output jet nebulizer with a corrugated tube.

Influenza A viruses are believed to spread between humans through contact, large respiratory droplets and small particle droplet nuclei (aerosols), but the relative importance of each of these modes of transmission is unclear. Volunteer studies suggest that infections via aerosol transmission may have a higher risk of febrile illness. Here we apply a mathematical model to data from randomized controlled trials of hand hygiene and surgical face masks in Hong Kong and Bangkok households. In these particular environments, inferences on the relative importance of modes of transmission are facilitated by information on the timing of secondary infections and apparent differences in clinical presentation of secondary infections resulting from aerosol transmission. We find that aerosol transmission accounts for approximately half of all transmission events. This implies that measures to reduce transmission by contact or large droplets may not be sufficient to control influenza A virus transmission in households. Influenza A viruses spread through contact, large and small respiratory droplets (aerosols), but the relative importance of these modes of transmission is unclear. Cowling et al . model data from community trials of face masks and hand hygiene and find that aerosol transmission accounts for half of influenza occurrences.

Purpose The design development of a small, hand held, battery operated, breath actuated inhaler as a drug/device platform for inhaled insulin posed a number of technical challenges. Our goal was to optimize lung deposition and distribution with aerosol generators producing 3–6 μm particle size distribution. Methods In silico modeling with computational fluid dynamics (CFD) and in vitro testing of device components were assessed using an Alberta idealized adult airway (Copley, UK) to optimize mouthpiece and aerosol path design for dose delivered distal to the trachea. Human factors use testing was designed to determine the ability to perform inspiratory manuevers with LED guidance within target flow limits. In vivo testing with healthy normal subjects of radiolabeled aerosol compared 2 breathing patterns for lung deposition efficiency, distribution, and subject preference. Results CFD demonstrated that flows ≤5 L/min and ≥15 L/min reduced the delivery efficiencg. Prototypes tested with inspiratory flow of 10 L/min provided up to 70% of dose delivered distal to the model throat with aerosols of 3 to 6 μm. Users guided by LED were able to inhale for 8–24 s with 5 s breath hold. Lung dose >70% with peripheral to central ratios >2.0 were achieved, with subject preference for the longer inspiratory time with breath hold. Conclusion The device design phase integration led to a novel design and inspiratory pattern with greater levels of peripheral deposition than previously reported with commercial inhalers. The rationale and process of the application of these methods are described with implications for use in future device development.

Compared to stratospheric SO2 injection for climate intervention, alumina particle injection could reduce stratospheric warming and associated adverse impacts. However, heterogeneous chemistry on alumina particles, especially chlorine activation via ClONO2+HCl→surfCl2+HNO3${\\text{ClONO}}_{2}+\\text{HCl}\\stackrel{\\text{surf}}{\\to }{\\text{Cl}}_{2}+{\\text{HNO}}_{3}$ , is poorly constrained under stratospheric conditions, such as low temperature and humidity. This study quantifies the uncertainty in modeling the ozone response to alumina injection. We show that extrapolating the limited experimental data for ClONO2 + HCl to stratospheric conditions leads to uncertainties in heterogeneous reaction rates of almost two orders of magnitude. Implementation of injection of 5 Mt/yr of particles with 240 nm radius in an aerosol‐chemistry‐climate model shows that resulting global total ozone depletions range between negligible and as large as 9%, that is more than twice the loss caused by chlorofluorocarbons, depending on assumptions on the degree of dissociation and interaction of the acids HCl, HNO3, and H2SO4 on the alumina surface. Plain Language Summary Global warming caused by increasing greenhouse gases could be temporarily reduced by introducing aerosol particles into the stratosphere. The most frequently studied approach to climate intervention uses H2SO4‐H2O aerosols, which, however, could result in undesirably strong warming of the stratosphere and significant ozone depletion. This might be improved by injecting solid particles, for example, made of aluminum oxide. However, here we show that the extremely limited availability of experimental studies on heterogeneous chemistry on alumina under the influence of stratospheric concentrations of HCl, HNO3, H2SO4, and H2O leads to large uncertainties in the impact of alumina injection on stratospheric ozone. In order to quantify these uncertainties, we integrated the currently available knowledge about the most important heterogeneous reaction ClONO2+HCl→surfCl2+HNO3${\\text{ClONO}}_{2}+\\text{HCl}\\stackrel{\\text{surf}}{\\to }{\\text{Cl}}_{2}+{\\text{HNO}}_{3}$into an aerosol‐chemistry‐climate model. We conclude that the uncertainty in the resulting heterogeneous reaction rate is more than two orders of magnitude depending on the partitioning of HCl, H2SO4, and HNO3 on the alumina surface. This could lead to global ozone column depletion ranging between almost negligible and up to 9%, which would be more than twice as much as the ozone loss caused by chlorofluorocarbons in the late 1990s. Key Points Heterogeneous chemistry on solid alumina particles is highly uncertain and depends strongly on the partitioning of acids onto the surface The reaction rate of ClONO2 with HCl on alumina particles is uncertain by up to two orders of magnitude under stratospheric conditions Injection of 5 Mt/yr of alumina particles could double global ozone reductions compared to chlorofluorocarbons in the late 1990s

Atmospheric aerosols formed by nucleation of vapors affect radiative forcing and therefore climate. However, the underlying mechanisms of nucleation remain unclear, particularly the involvement of organic compounds. Here, we present high-resolution mass spectra of ion clusters observed during new particle formation experiments performed at the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research. The experiments involved sulfuric acid vapor and different stabilizing species, including ammonia and dimethylamine, as well as oxidation products of pinanediol, a surrogate for organic vapors formed from monoterpenes. A striking resemblance is revealed between the mass spectra from the chamber experiments with oxidized organics and ambient data obtained during new particle formation events at the Hyytiälä boreal forest research station. We observe that large oxidized organic compounds, arising from the oxidation of monoterpenes, cluster directly with single sulfuric acid molecules and then form growing clusters of one to three sulfuric acid molecules plus one to four oxidized organics. Most of these organic compounds retain 10 carbon atoms, and some of them are remarkably highly oxidized (oxygen-to-carbon ratios up to 1.2). The average degree of oxygenation of the organic compounds decreases while the clusters are growing. Our measurements therefore connect oxidized organics directly, and in detail, with the very first steps of new particle formation and their growth between 1 and 2 nm in a controlled environment. Thus, they confirm that oxidized organics are involved in both the formation and growth of particles under ambient conditions.

The link between biogenic volatile organic compounds in the atmosphere and their conversion to aerosol particles is unclear, but a direct reaction pathway is now described by which volatile organic compounds lead to low-volatility vapours that can then condense onto aerosol surfaces, producing secondary organic aerosol. From forest emission to aerosol Forests emit large quantities of volatile organic compounds to the atmosphere. The condensable oxidation products of volatile organic compounds emitted by forests can form secondary organic aerosols or SOAs that can affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. But our understanding of the link between biogenic volatile organic compounds and their conversion to aerosol particles remains limited. This study reveals that a direct reaction pathway can lead from volatile organic compounds to low-volatility vapours that can then condense onto aerosol surfaces producing secondary organic aerosol and can significantly enhance the formation and growth of aerosol particles over forested regions. Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol 1 , 2 , which is known to affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei 3 . The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours 4 , 5 , 6 , but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies 2 . We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere–aerosol–climate feedback mechanisms 6 , 7 , 8 , and the air quality and climate effects of biogenic emissions generally.

Pressurized metered dose inhalers (pMDI) are a vital therapy for the treatment of lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). In pMDI, the propellants used to deliver the drug to the lungs are hydrofluorocarbons (HFC). However, the current HFCs in use have large global warming potential (GWP). In order to reduce or eliminate the use of propellants with large global warming potential, efforts are underway within the pharmaceutical industry to transition to the use of low GWP propellants in pMDI, while maintaining their effectiveness in treating disease. The current switch from higher GWP propellants mirrors the switch from chlorofluorocarbon (CFC) propellants to HFCs undertaken in the 1990’s, which was driven by ozone depletion concerns. In this paper, the International Pharmaceutical Aerosol Consortium on Regulation and Science (IPAC-RS) discusses aspects of the switch to low GWP propellants from the perspective of materials compatibility of pMDI components with low GWP propellants. Leveraging the learnings and advances in pMDI component materials implemented following the switch from CFCs, industry is well positioned to make the change. This paper describes the utility of the low GWP propellants being developed for use in pMDI and the learnings from the previous transition that are being leveraged by industry. The current state of development will be described, including a review of available literature supporting the transition to low GWP propellants.

The presence of ice in clouds can influence cloud lifetime, precipitation and radiative properties; here, organic material at the sea–air interface, possibly associated with phytoplankton cell exudates, is shown to nucleate ice under conditions relevant for ice cloud formation in the atmospheric environment. Ice-forming 'biological' particles in the marine atmosphere The presence of ice in clouds can have an influence on cloud lifetime and radiative properties. It remains uncertain to what extent sea spray may act as ice nucleating particles that facilitate the formation of ice in clouds. This study finds that organic material at the sea–air interface, probably derived from phytoplankton cell exudates, nucleates ice under conditions relevant for ice cloud formation in the atmospheric environment. Model simulations suggest that marine organic material may be an important source of ice nucleating particles in remote marine environments such as the Southern Ocean. The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties 1 , 2 . The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles 1 , 2 . Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 . Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea–air interface or sea surface microlayer 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 . Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

Aerosol particles can form in the atmosphere by nucleation of highly oxidized biogenic vapours in the absence of sulfuric acid, with ions from Galactic cosmic rays increasing the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Aerosol particles can form in the atmosphere by nucleation of highly oxidized biogenic vapours in the absence of sulfuric acid, with ions from Galactic cosmic rays increasing the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Aerosol particle formation in clean air The effect of atmospheric aerosols on clouds and the radiative forcing of the climate system remains poorly understood. It is thought that nucleation of aerosol particles from atmospheric vapours rarely proceeds in the absence of sulfuric acid. Now two papers in this week’s Nature point to a previously unappreciated role for highly oxygenated molecules (HOMs) in promoting new particle formation and growth, essentially a mechanism that produces aerosols in the absence of pollution. Jasper Kirkby et al . show that aerosol particles can form as a result of ion-induced nucleation of HOMs in the absence of sulfuric acid under conditions relevant to the atmosphere in the CLOUD chamber at CERN. Jasmin Tröstl et al . examined the role of organic vapours in the initial growth of nucleated organic particles in the absence of sulfuric acid in the CERN CLOUD chamber under atmospheric conditions. They find that the organic vapours driving initial growth have extremely low volatilities. With increasing particle size, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility. Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood 1 . Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours 2 . It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere 3 , 4 , and that ions have a relatively minor role 5 . Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded 6 , 7 . Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.