Efficacy and safety of direct oral anticoagulants in older adults with atrial fibrillation: a prospective single-centre cohort study.

INTRODUCTION: Direct oral anticoagulants (DOACs) are underused in the elderly, regardless the evidence in their favour in this population. METHODS: We prospectively enrolled anticoagulant-naïve patients aged ≥ 75 years who started treatment with DOACs for atrial fibrillation (AF) and stratified them in older adults (aged 75-84 years) and extremely older adults (≥ 85 years). Thrombotic and hemorrhagic events were evaluated for 12 months follow-up. RESULTS: We enrolled 518 consecutive patients. They were mostly aged 75-84 years (299 patients; 57.7%) vs. ≥ 85 years (219 patients; 42.3%). Extremely older adults showed higher incidence of all the endpoints (systemic cardioembolism [HR 3.25 (95% CI 1.71-6.18)], major bleeding [HR 2.75 (95% CI 1.77-4.27)], and clinically relevant non-major bleeding [HR 2.13 (95% CI 1.17-3.92)]) vs. older adults during the first year after starting anticoagulation. In patients aged ≥ 85 years, no difference in the aforementioned endpoints was found between those receiving on-label vs. off-label DOACs. In the extremely older adults, chronic kidney disease, polypharmacy, use of antipsychotics, and DOAC discontinuation correlated with higher rates of thrombotic events, whereas a history of bleeding, Charlson Index ≥ 6, use of reduced DOAC dose, absence of a caregiver, use of non-steroidal anti-inflammatory drugs (NSAIDs), and HAS-BLED score ≥ 3 were associated with major bleedings. CONCLUSIONS: Naïve patients aged ≥ 85 who started a DOAC for AF are at higher risk of thrombotic and bleeding events compared to those aged 75-84 years in the first year of therapy. History of bleeding, HAS-BLED score ≥ 3 and use of NSAIDs are associated with higher rates of major bleeding.

Midlatitude Ozone Depletion and Air Quality Impacts from Industrial Halogen Emissions in the Great Salt Lake Basin.

We report aircraft observations of extreme levels of HCl and the dihalogens Cl2, Br2, and BrCl in an industrial plume near the Great Salt Lake, Utah. Complete depletion of O3 was observed concurrently with halogen enhancements as a direct result of photochemically produced halogen radicals. Observed fluxes for Cl2, HCl, and NOx agreed with facility-reported emissions inventories. Bromine emissions are not required to be reported in the inventory, but are estimated as 173 Mg year-1 Br2 and 949 Mg year-1 BrCl, representing a major uncounted oxidant source. A zero-dimensional photochemical box model reproduced the observed O3 depletions and demonstrated that bromine radical cycling was principally responsible for the rapid O3 depletion. Inclusion of observed halogen emissions in both the box model and a 3D chemical model showed significant increases in oxidants and particulate matter (PM2.5) in the populated regions of the Great Salt Lake Basin, where winter PM2.5 is among the most severe air quality issues in the U.S. The model shows regional PM2.5 increases of 10%-25% attributable to this single industrial halogen source, demonstrating the impact of underreported industrial bromine emissions on oxidation sources and air quality within a major urban area of the western U.S.

Orthostatic hypotension and night-time dipper patterns in geriatric outpatients.

Orthostatic hypotension (OH) and blood pressure circadian dysfunctions are common in older adults and may be related to aging-related autonomic nervous system deficits. This study aimed to evaluate the relationship between orthostatic and nocturnal blood pressure changes in geriatric outpatients. This cross-sectional study was carried out with 425 Italian individuals aged ≥65 years (mean age 75.8 ± 7.1 years) who attended a hypertension outpatient clinic from January 2013 to January 2020. Each patient underwent orthostatic testing and noninvasive 24-h blood pressure monitoring (ABPM). OH was detected in 38.1% of patients, and these individuals were more likely to have abnormal circadian blood pressure patterns (reverse and nondipper) than those without OH (61.7% vs. 51.7%; p = 0.045). In linear regression, after adjusting for potential confounders, orthostatic and nocturnal changes in systolic blood pressure were inversely associated (ß = -0.63, 95% CI [-0.95; -0.32]; p < 0.001). This association was stronger in patients ≥80 years. OH is highly prevalent in older patients and is associated with altered nocturnal blood pressure profiles, especially in the oldest old. Because both OH and altered blood pressure patterns are associated with elevated cardiovascular risk and mortality, our study suggests that elderly patients with OH should undergo noninvasive 24-h blood pressure monitoring.

Novel Analysis to Quantify Plume Crosswind Heterogeneity Applied to Biomass Burning Smoke.

We present a novel method, the Gaussian observational model for edge to center heterogeneity (GOMECH), to quantify the horizontal chemical structure of plumes. GOMECH fits observations of short-lived emissions or products against a long-lived tracer (e.g., CO) to provide relative metrics for the plume width (wi/wCO) and center (bi/wCO). To validate GOMECH, we investigate OH and NO3 oxidation processes in smoke plumes sampled during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality, a 2019 wildfire smoke study). An analysis of 430 crosswind transects demonstrates that nitrous acid (HONO), a primary source of OH, is narrower than CO (wHONO/wCO = 0.73-0.84 ± 0.01) and maleic anhydride (an OH oxidation product) is enhanced on plume edges (wmaleicanhydride/wCO = 1.06-1.12 ± 0.01). By contrast, NO3 production [P(NO3)] occurs mainly at the plume center (wP(NO3)/wCO = 0.91-1.00 ± 0.01). Phenolic emissions, highly reactive to OH and NO3, are narrower than CO (wphenol/wCO = 0.96 ± 0.03, wcatechol/wCO = 0.91 ± 0.01, and wmethylcatechol/wCO = 0.84 ± 0.01), suggesting that plume edge phenolic losses are the greatest. Yet, nitrophenolic aerosol, their oxidation product, is the greatest at the plume center (wnitrophenolicaerosol/wCO = 0.95 ± 0.02). In a large plume case study, GOMECH suggests that nitrocatechol aerosol is most associated with P(NO3). Last, we corroborate GOMECH with a large eddy simulation model which suggests most (55%) of nitrocatechol is produced through NO3 in our case study.

Variability and Time of Day Dependence of Ozone Photochemistry in Western Wildfire Plumes.

Understanding the efficiency and variability of photochemical ozone (O3) production from western wildfire plumes is important to accurately estimate their influence on North American air quality. A set of photochemical measurements were made from the NOAA Twin Otter research aircraft as a part of the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) experiment. We use a zero-dimensional (0-D) box model to investigate the chemistry driving O3 production in modeled plumes. Modeled afternoon plumes reached a maximum O3 mixing ratio of 140 ± 50 ppbv (average ± standard deviation) within 20 ± 10 min of emission compared to 76 ± 12 ppbv in 60 ± 30 min in evening plumes. Afternoon and evening maximum O3 isopleths indicate that plumes were near their peak in NOx efficiency. A radical budget describes the NOx volatile - organic compound (VOC) sensitivities of these plumes. Afternoon plumes displayed a rapid transition from VOC-sensitive to NOx-sensitive chemistry, driven by HOx (=OH + HO2) production from photolysis of nitrous acid (HONO) (48 ± 20% of primary HOx) and formaldehyde (HCHO) (26 ± 9%) emitted directly from the fire. Evening plumes exhibit a slower transition from peak NOx efficiency to VOC-sensitive O3 production caused by a reduction in photolysis rates and fire emissions. HOx production in evening plumes is controlled by HONO photolysis (53 ± 7%), HCHO photolysis (18 ± 9%), and alkene ozonolysis (17 ± 9%).

Dehydroepiandrosterone sulfate and fall risk in older people: Sex differences in the Pro.V.A. longitudinal study.

BACKGROUND: The effect of dehydroepiandrosterone sulfate (DHEA-S) on fall risk in older age is still unclear, as is the effect of sex on any relationship between the two. Our aim was to evaluate the association between DHEA-S and the risk of falls and risk of recurrent falls in community-dwelling older men and women. METHODS: We included 1949 (781 M, 1168 F) older adults enrolled in the Progetto Veneto Anziani study. Baseline serum DHEA-S levels were analyzed by immunoassay. The number of falls reported in the year preceding the 4.4-year follow-up assessment was collected. The association between DHEA-S and falls was analyzed by multinomial logistic regression, adjusting for potential confounders and considering death as alternative outcome. RESULTS: After the follow-up, 548 (36.8%) individuals reported at least one fall in the previous year, and 214 (14.4%) reported ≥2 falls (recurrent falls). Each 1-standard deviation (SD) increase in log-transformed DHEA-S level reduced the odds of experiencing at least one fall by 9% (95%CI:0.88-0.95), and the risk of recurrent falls by 16% (95%CI:0.79-0.89). The highest DHEA-S tertile was 27% (95%CI:0.65-0.83) less likely to experience recurrent falls than the lowest tertile. The analyses, stratified by sex, suggested a strong association between DHEA-S and the fall risk for women (OR = 0.91; 95%CI:0.87-0.95 for at least one fall; OR = 0.83, 95%CI:0.78-0.89 for recurrent falls per each 1-SD increase in log-transformed DHEA-S); non-significant results were observed among men. CONCLUSIONS: Higher levels of DHEA-S are associated with a lower risk of falls and recurrent falls in older people, especially women.

The GesTIO protocol experience: safety of a standardized order set for subcutaneous insulin regimen in elderly hospitalized patients.

BACKGROUNDS: In non-critical hospitalized patients with diabetes mellitus, guidelines suggest subcutaneous insulin therapy with basal-bolus regimen, even in old and vulnerable inpatients. AIM: To evaluate safety, efficacy, and benefit on clinical management of the GesTIO protocol, a set of subcutaneous insulin administration rules, in old and vulnerable non-ICU inpatients. METHODS: Retrospective, observational study. Patients admitted to Geriatric Clinic of Padua were studied. 88 patients matched the inclusion criteria: type 2 diabetes or hospital-related hyperglycemia, ≥65 years, regular measurements of capillary glycemia, and basal-bolus subcutaneous insulin regimen managed by "GesTIO protocol" for five consecutive days. MAIN OUTCOME MEASURES: ratio of patients with blood glucose (BG) <3.9 mmol/l; number of BG per patient in target range (5-11.1 mmol/l); daily mean BG; and calls to physicians for adjusting insulin therapy. RESULTS: Mean age was 82 ± 7 years. 9.1% patients experienced mild hypoglycaemia, and no severe hypoglycaemia was reported. The median number of BG per patients in target range increased from 2.0 ± 2 to 3.0 ± 2 (p < 0.001). The daily mean BG decreased from 11.06 ± 3.03 to 9.64 ± 2.58 mmol/l (-12.8%, p < 0.005). The mean number of calls to physicians per patient decreased from 0.83 to 0.45 (p < 0.05). CONCLUSIONS: Treatment with GesTIO protocol allows a safe and effective treatment even in very old and vulnerable inpatients with a faster management insulin therapy.

Global atmospheric particle formation from CERN CLOUD measurements.

Fundamental questions remain about the origin of newly formed atmospheric aerosol particles because data from laboratory measurements have been insufficient to build global models. In contrast, gas-phase chemistry models have been based on laboratory kinetics measurements for decades. We built a global model of aerosol formation by using extensive laboratory measurements of rates of nucleation involving sulfuric acid, ammonia, ions, and organic compounds conducted in the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber. The simulations and a comparison with atmospheric observations show that nearly all nucleation throughout the present-day atmosphere involves ammonia or biogenic organic compounds, in addition to sulfuric acid. A considerable fraction of nucleation involves ions, but the relatively weak dependence on ion concentrations indicates that for the processes studied, variations in cosmic ray intensity do not appreciably affect climate through nucleation in the present-day atmosphere.

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation.

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol-cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20-100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by [Formula: see text] (27%) to [Formula: see text] Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes.

Molecular-scale evidence of aerosol particle formation via sequential addition of HIO3.

Homogeneous nucleation and subsequent cluster growth leads to the formation of new aerosol particles in the atmosphere. The nucleation of sulfuric acid and organic vapours is thought to be responsible for the formation of new particles over continents, whereas iodine oxide vapours have been implicated in particle formation over coastal regions. The molecular clustering pathways that are involved in atmospheric particle formation have been elucidated in controlled laboratory studies of chemically simple systems, but direct molecular-level observations of nucleation in atmospheric field conditions that involve sulfuric acid, organic or iodine oxide vapours have yet to be reported. Here we present field data from Mace Head, Ireland, and supporting data from northern Greenland and Queen Maud Land, Antarctica, that enable us to identify the molecular steps involved in new particle formation in an iodine-rich, coastal atmospheric environment. We find that the formation and initial growth process is almost exclusively driven by iodine oxoacids and iodine oxide vapours, with average oxygen-to-iodine ratios of 2.4 found in the clusters. On the basis of this high ratio, together with the high concentrations of iodic acid (HIO3) observed, we suggest that cluster formation primarily proceeds by sequential addition of HIO3, followed by intracluster restructuring to I2O5 and recycling of water either in the atmosphere or on dehydration. Our study provides ambient atmospheric molecular-level observations of nucleation, supporting the previously suggested role of iodine-containing species in the formation of new aerosol particles, and identifies the key nucleating compound.

Effect of restoring sinus rhythm in hypertensive patients with atrial fibrillation undergoing electrical cardioversion.

INTRODUCTION: Little is known about the effects of atrial fibrillation (AF) on blood pressure (BP) levels in hypertensive patients. Some studies suggest a role for rhythm control in managing such patients' BP, but the improvement observed in cardiac performance after restoring sinus rhythm (SR) may coincide with an increase in BP. The aim of this study was to apply ambulatory BP monitoring to analyze BP changes in hypertensive patients after electrical cardioversion for persistent AF. METHODS AND RESULTS: The study included 54 hypertensive patients with persistent AF. Ambulatory BP monitoring was performed on the day before electrical cardioversion and again about a month later under conditions of stable medical treatment.Patients with a SR at follow-up (n=34) had significantly higher 24-h, night-time (P<0.05), and daytime (P=0.074) systolic BP, and significantly lower 24-h, daytime (P<0.05), and night-time (P=0.078) DBP. The number of patients with nocturnal dipping decreased from 20 to 14 and the number of those with reverse dipping increased from 1 to 7. Patients with recurrent AF at follow-up (n=20) showed no significant BP changes, except for a decrease in the mean night-time DBP. CONCLUSION: Restoring SR in hypertensive patients with AF led to a significant increase in their systolic BP (especially at night) and a decrease in their DBP. Hypertensive patients with AF should consequently undergo ambulatory BP monitoring after electrical cardioversion for the purpose of adjusting their antihypertensive treatment.

Ion-induced nucleation of pure biogenic particles.

Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere, and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. 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.

The role of low-volatility organic compounds in initial particle growth in the atmosphere.

About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer. Although recent studies predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory), has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10(-4.5) micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10(-4.5) to 10(-0.5) micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.

The effect of acid-base clustering and ions on the growth of atmospheric nano-particles.

The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.

Comparison of the SAWNUC model with CLOUD measurements of sulphuric acid-water nucleation.

Binary nucleation of sulphuric acid-water particles is expected to be an important process in the free troposphere at low temperatures. SAWNUC (Sulphuric Acid Water Nucleation) is a model of binary nucleation that is based on laboratory measurements of the binding energies of sulphuric acid and water in charged and neutral clusters. Predictions of SAWNUC are compared for the first time comprehensively with experimental binary nucleation data from the CLOUD chamber at European Organization for Nuclear Research. The experimental measurements span a temperature range of 208-292 K, sulphuric acid concentrations from 1·106 to 1·109 cm-3, and distinguish between ion-induced and neutral nucleation. Good agreement, within a factor of 5, is found between the experimental and modeled formation rates for ion-induced nucleation at 278 K and below and for neutral nucleation at 208 and 223 K. Differences at warm temperatures are attributed to ammonia contamination which was indicated by the presence of ammonia-sulphuric acid clusters, detected by an Atmospheric Pressure Interface Time of Flight (APi-TOF) mass spectrometer. APi-TOF measurements of the sulphuric acid ion cluster distributions ( (H2SO4)i·HSO4- with i = 0, 1, ..., 10) show qualitative agreement with the SAWNUC ion cluster distributions. Remaining differences between the measured and modeled distributions are most likely due to fragmentation in the APi-TOF. The CLOUD results are in good agreement with previously measured cluster binding energies and show the SAWNUC model to be a good representation of ion-induced and neutral binary nucleation of sulphuric acid-water clusters in the middle and upper troposphere.

Reliability of Oscillometric Blood Pressure Monitoring in Atrial Fibrillation Patients Admitted for Electric Cardioversion.

The reliability of automated oscillometric blood pressure (BP) monitors in atrial fibrillation (AF) has been poorly investigated, only comparing different patients with AF and sinus rhythm (SR), and is a method influenced by individual characteristics. This study compared the reliability of the oscillometric device A&D TM-2430 (A&D Company, Tokyo, Japan) with that of a mercury sphygmomanometer in AF patients whose SR was restored after electric cardioversion (ECV). Three consecutive BP measurements were obtained on the day before and about 30 days after ECV in stable treatment conditions. Of the 100 patients studied, 63 reported an SR at follow-up, with a significant increase in systolic BP and a significant decrease in diastolic BP according to both devices. There were no significant differences between the systolic and diastolic biases before and after ECV using Bland Altman analysis (P > .05 each). The oscillometric device analyzed, using three repeated measurements, is reliable in measuring BP in AF patients.

Insight into acid-base nucleation experiments by comparison of the chemical composition of positive, negative, and neutral clusters.

We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid-base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster-cluster collision.

Neutral molecular cluster formation of sulfuric acid-dimethylamine observed in real time under atmospheric conditions.

For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus.

Oxidation products of biogenic emissions contribute to nucleation of atmospheric particles.

Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity and variability of the atmosphere has hindered elucidation of the fundamental mechanism of new-particle formation from gaseous precursors. We show, in experiments performed with the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid and oxidized organic vapors at atmospheric concentrations reproduce particle nucleation rates observed in the lower atmosphere. The experiments reveal a nucleation mechanism involving the formation of clusters containing sulfuric acid and oxidized organic molecules from the very first step. Inclusion of this mechanism in a global aerosol model yields a photochemically and biologically driven seasonal cycle of particle concentrations in the continental boundary layer, in good agreement with observations.

Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere.

Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.