A new atmospherically relevant oxidant of sulphur dioxide.

Atmospheric oxidation is a key phenomenon that connects atmospheric chemistry with globally challenging environmental issues, such as climate change, stratospheric ozone loss, acidification of soils and water, and health effects of air quality. Ozone, the hydroxyl radical and the nitrate radical are generally considered to be the dominant oxidants that initiate the removal of trace gases, including pollutants, from the atmosphere. Here we present atmospheric observations from a boreal forest region in Finland, supported by laboratory experiments and theoretical considerations, that allow us to identify another compound, probably a stabilized Criegee intermediate (a carbonyl oxide with two free-radical sites) or its derivative, which has a significant capacity to oxidize sulphur dioxide and potentially other trace gases. This compound probably enhances the reactivity of the atmosphere, particularly with regard to the production of sulphuric acid, and consequently atmospheric aerosol formation. Our findings suggest that this new atmospherically relevant oxidation route is important relative to oxidation by the hydroxyl radical, at least at moderate concentrations of that radical. We also find that the oxidation chemistry of this compound seems to be tightly linked to the presence of alkenes of biogenic origin.

Atmospheric gas-to-particle conversion: why NPF events are observed in megacities?

In terms of the global aerosol particle number load, atmospheric new particle formation (NPF) dominates over primary emissions. The key for quantifying the importance of atmospheric NPF is to understand how gas-to-particle conversion (GTP) takes place at sizes below a few nanometers in particle diameter in different environments, and how this nano-GTP affects the survival of small clusters into larger sizes. The survival probability of growing clusters is tied closely to the competition between their growth and scavenging by pre-existing aerosol particles, and the key parameter in this respect is the ratio between the condensation sink (CS) and the cluster growth rate (GR). Here we define their ratio as a dimensionless survival parameter, P, as P = (CS/10-4 s-1)/(GR/nm h-1). Theoretical arguments and observations in clean and moderately-polluted conditions indicate that P needs to be smaller than about 50 for a notable NPF to take place. However, the existing literature shows that in China, NPF occurs frequently in megacities such as in Beijing, Nanjing and Shanghai, and our analysis shows that the calculated values of P are even larger than 200 in these cases. By combining direct observations and conceptual modelling, we explore the variability of the survival parameter P in different environments and probe the reasons for NPF occurrence under highly-polluted conditions.

Chemistry of atmospheric nucleation: on the recent advances on precursor characterization and atmospheric cluster composition in connection with atmospheric new particle formation.

The recent development in measurement techniques and theoretical understanding has enabled us to study atmospheric vapor, cluster and nanoparticle concentrations, dynamics, and their connection to atmospheric nucleation. Here we present a summary of the chemistry of atmospheric clustering, growing nanoparticles, and their precursors. In this work, we focus particularly on atmospheric gas-to-particle conversion and recent progress in its understanding.

Problematic situations related to social media use and competencies to prevent them: results of a Delphi study.

A three-round Delphi method was used to study the problematic situations that adolescents may encounter when using the social media, and the competencies needed to address these situations. A panel of Finnish experts (N = 22) provided an open-ended list of problematic situations and competencies in 2020-2021. These were then evaluated and ranked according to their significance. The experts provided an information-rich list of both problematic situations and competencies. Finally, 16 problematic situations and 19 competencies were ranked in order of importance by the experts. The most important problematic situations were direct and indirect cyberbullying and sexual harassment. The most important competencies were the ability to act responsibly, knowing what kinds of activity are prohibited, and knowing whom to contact on exposure to cyberbullying or harassment. The findings can be used in developing policies, recommendations, and solutions aimed at counteracting the harmful effects of social media on wellbeing during adolescence.

Heterogeneous nucleation in multi-component vapor on a partially wettable charged conducting particle. I. Formulation of general equations: electrical surface and line excess quantities.

Thermodynamics is applied to formulate general equations for internal energies and grand potential for a system consisting of a dielectric liquid nucleus of a new phase on a charged insoluble conducting sphere within a uniform macroscopic one- or multicomponent mother phase. The currently available model for ion-induced nucleation assumes complete spherical symmetry of the system, implying that the seed ion is immediately surrounded by the condensing liquid from all sides. We take a step further and treat more realistic geometries, where a cap-shaped liquid cluster forms on the surface of the seed particle. To take into account spontaneous polarization of surface layer molecules we introduce the electrical surface and line excess quantities.

Heterogeneous nucleation in multi-component vapor on a partially wettable charged conducting particle. II. The generalized Laplace, Gibbs-Kelvin, and Young equations and application to nucleation.

Based on the results of a previous paper [M. Noppel, H. Vehkamäki, P. M. Winkler, M. Kulmala, and P. E. Wagner, J. Chem. Phys. 139, 134107 (2013)], we derive a thermodynamically consistent expression for reversible or minimal work needed to form a dielectric liquid nucleus of a new phase on a charged insoluble conducting sphere within a uniform macroscopic one- or multicomponent mother phase. The currently available model for ion-induced nucleation assumes complete spherical symmetry of the system, implying that the seed ion is immediately surrounded by the condensing liquid from all sides. We take a step further and treat more realistic geometries, where a cap-shaped liquid cluster forms on the surface of the seed particle. We derive the equilibrium conditions for such a cluster. The equalities of chemical potentials of each species between the nucleus and the vapor represent the conditions of chemical equilibrium. The generalized Young equation that relates contact angle with surface tensions, surface excess polarizations, and line tension, also containing the electrical contribution from triple line excess polarization, expresses the condition of thermodynamic equilibrium at three-phase contact line. The generalized Laplace equation gives the condition of mechanical equilibrium at vapor-liquid dividing surface: it relates generalized pressures in neighboring bulk phases at an interface with surface tension, excess surface polarization, and dielectric displacements in neighboring phases with two principal radii of surface curvature and curvatures of equipotential surfaces in neighboring phases at that point. We also re-express the generalized Laplace equation as a partial differential equation, which, along with electrostatic Laplace equations for bulk phases, determines the shape of a nucleus. We derive expressions that are suitable for calculations of the size and composition of a critical nucleus (generalized version of the classical Kelvin-Thomson equation).

Observed coupling between air mass history, secondary growth of nucleation mode particles and aerosol pollution levels in Beijing.

Atmospheric aerosols have significant effects on the climate and on human health. New particle formation (NPF) is globally an important source of aerosols but its relevance especially towards aerosol mass loadings in highly polluted regions is still controversial. In addition, uncertainties remain regarding the processes leading to severe pollution episodes, concerning e.g. the role of atmospheric transport. In this study, we utilize air mass history analysis in combination with different fields related to the intensity of anthropogenic emissions in order to calculate air mass exposure to anthropogenic emissions (AME) prior to their arrival at Beijing, China. The AME is used as a semi-quantitative metric for describing the effect of air mass history on the potential for aerosol formation. We show that NPF events occur in clean air masses, described by low AME. However, increasing AME seems to be required for substantial growth of nucleation mode (diameter < 30 nm) particles, originating either from NPF or direct emissions, into larger mass-relevant sizes. This finding assists in establishing and understanding the connection between small nucleation mode particles, secondary aerosol formation and the development of pollution episodes. We further use the AME, in combination with basic meteorological variables, for developing a simple and easy-to-apply regression model to predict aerosol volume and mass concentrations. Since the model directly only accounts for changes in meteorological conditions, it can also be used to estimate the influence of emission changes on pollution levels. We apply the developed model to briefly investigate the effects of the COVID-19 lockdown on PM2.5 concentrations in Beijing. While no clear influence directly attributable to the lockdown measures is found, the results are in line with other studies utilizing more widely applied approaches.

OH reactivity measurements within a boreal forest: evidence for unknown reactive emissions.

Boreal forests emit large amounts of volatile organic compounds (VOCs) which react with the hydroxyl radical (OH) to influence regional ozone levels and form secondary organic aerosol. Using OH reactivity measurements within a boreal forest in Finland, we investigated the budget of reactive VOCs. OH reactivity was measured using the comparative reactivity method, whereas 30 individual VOCs were measured using proton transfer reaction mass spectrometry, thermal-desorption gas chromatography mass spectrometry, and liquid chromatography mass spectrometry, in August 2008. The measured OH reactivity ranged from below detection limit (3.5 s(-1)), to approximately 60 s(-1) in a single pollution event. The average OH reactivity was approximately 9 s(-1) and no diel variation was observed in the profiles. The measured OH sinks (approximately 30 species) accounted for only 50% of the total measured OH reactivity, implying unknown reactive VOCs within the forest. The five highest measured OH sinks were: monoterpenes (1 s(-1)), CO (0.7 s(-1)), isoprene (0.5 s(-1)), propanal and acetone (0.3 s(-1)), and methane (0.3 s(-1)). We suggest that models be constrained by direct OH reactivity measurements to accurately assess the impact of boreal forest emissions on regional atmospheric chemistry and climate.

A computational fluid dynamics approach to nucleation in the water-sulfuric acid system.

This study presents a computational fluid dynamics modeling approach to investigate the nucleation in the water-sulfuric acid system in a flow tube. On the basis of an existing experimental setup (Brus, D.; Hyvärinen, A.-P.; Viisanen, Y.; Kulmala, M.; Lihavainen, H. Atmos. Chem. Phys. 2010, 10, 2631-2641), we first establish the effect of convection on the flow profile. We then proceed to simulate nucleation for relative humidities of 10, 30, and 50% and for sulfuric acid concentration between 10(9) to 3 x 10(10) cm(-3). We describe the nucleation zone in detail and determine how flow rate and relative humidity affect its characteristics. Experimental nucleation rates are compared to rates gained from classical binary and kinetic nucleation theory as well as cluster activation theory. For low RH values, kinetic theory yields the best agreement with experimental results while binary nucleation best reproduces the experimental nucleation behavior at 50% relative humidity. Particle growth is modeled for an example case at 50% relative humidity. The final simulated diameter is very close to the experimental result.

Stable sulphate clusters as a source of new atmospheric particles

The formation of new atmospheric particles with diameters of 3-10 nm has been observed at a variety of altitudes and locations. Such aerosol particles have the potential to grow into cloud condensation nuclei, thus affecting cloud formation as well as the global radiation budget. In some cases, the observed formation rates of new particles have been adequately explained by binary nucleation, involving water and sulphuric acid, but in certain locations--particularly those within the marine boundary layer and at continental sites--observed ambient nucleation rates exceed those predicted by the binary scheme. In these locations, ambient sulphuric acid (H2SO4) levels are typically lower than required for binary nucleation, but are sufficient for ternary nucleation (sulphuric acid-ammonia-water). Here we present results from an aerosol dynamics model with a ternary nucleation scheme which indicate that nucleation in the troposphere should be ubiquitous, and yield a reservoir of thermodynamically stable clusters 1-3 nm in size. We suggest that the growth of these clusters to a detectable size (> 3 nm particle diameter) is restricted by the availability of condensable vapour. Observations of atmospheric particle formation and growth from a continental and a coastal site support this hypothesis, indicating that a growth process including ternary nucleation is likely to be responsible for the formation of cloud condensation nuclei.

Re-evaluation of the pressure effect for nucleation in laminar flow diffusion chamber experiments with fluent and the fine particle model.

This study is an investigation of the effect of total pressure on homogeneous nucleation rates of n-butanol in helium and n-pentanol in helium and argon in a laminar flow diffusion chamber (LFDC). To verify earlier findings, experimental data was re-evaluated using the computational fluid dynamics (CFD) software FLUENT in combination with the fine particle model (FPM) for aerosol dynamics calculations. This approach has been introduced in an earlier paper [Herrmann, E.; Lihavainen, H.; Hyvarinen, A.-P.; Riipinen, I.; Wilck, M.; Stratmann, F.; Kulmala, M. J. Phys. Chem. A 2006, 110, 12448]. As a result of our evaluation, a flaw in the femtube2 code was found which had been used in the original data analysis [Hyvarinen, A.-P.; Brus, D.; Zdimal, V.; Smolik, J.; Kulmala, M.; Viisanen, Y.; Lihavainen, H. J. Chem. Phys. 2006, 124, 224304]. The FLUENT analysis yielded a weak positive pressure effect for the nucleation of n-butanol in helium at low nucleation temperatures (265-270 K). n-Pentanol in helium showed a positive pressure effect at all temperatures (265-290 K), while the effect for the nucleation of n-pentanol in argon was negative at high temperatures (280 and 285 K) and positive at lower nucleation temperatures (265 K). These findings support results gained with the corrected femtube2 model. In this study, we also carried out a detailed comparison of FLUENT and femtube2 modeling results, especially focusing on the calculation of temperature and saturation ratio at nucleation rate maximum (T(nuc) and S(nuc), respectively) in both models.

Urban air pollution, and asthma and COPD hospital emergency room visits.

BACKGROUND: There is little previous information of the effects of size fractioned particulate air pollution and source specific fine particles (PM(2.5); <2.5 microm) on asthma and chronic obstructive pulmonary disease (COPD) among children, adults and the elderly. OBJECTIVES: To determine the effects of daily variation in levels of different particle size fractions and gaseous pollutants on asthma and COPD by age group. METHODS: Levels of particulate air pollution, NO(2) and CO were measured from 1998 to 2004 at central outdoor monitoring sites in Helsinki, Finland. Associations between daily pollution levels and hospital emergency room visits were evaluated for asthma (ICD10: J45+J46) in children <15 years old, and for asthma and COPD (ICD10: J41+J44) in adults (15-64 years) and the elderly (>or=65 years). RESULTS: Three to 5 day lagged increases in asthma visits were found among children in association with nucleation (<0.03 microm), Aitken (0.03-0.1 microm) and accumulation (0.1-0.29 microm) mode particles, gaseous pollutants and traffic related PM(2.5) (7.8% (95% CI 3.5 to 12.3) for 1.1 microg/m(3) increase in traffic related PM(2.5) at lag 4). Pooled asthma-COPD visits among the elderly were associated with lag 0 of PM(2.5), coarse particles, gaseous pollutants and long range transported and traffic related PM(2.5) (3.9% (95% CI 0.28 to 7.7) at lag 0). Only accumulation mode and coarse particles were associated with asthma and COPD among adults. CONCLUSIONS: Among children, traffic related PM(2.5) had delayed effects, whereas among the elderly, several types of particles had effects that were more immediate. These findings suggest that the mechanisms of the respiratory effects of air pollution, and responsible pollutants, differ by age group.

Determination of isoprene and alpha-/beta-pinene oxidation products in boreal forest aerosols from Hyytiälä, Finland: diel variations and possible link with particle formation events.

Biogenic volatile organic compounds (VOCs), such as isoprene and alpha-/beta-pinene, are photo-oxidized in the atmosphere to non-volatile species resulting in secondary organic aerosol (SOA). The goal of this study was to examine time trends and diel variations of oxidation products of isoprene and alpha-/beta-pinene in order to investigate whether they are linked with meteorological parameters or trace gases. Separate day-night aerosol samples (PM(1)) were collected in a Scots pine dominated forest in southern Finland during 28 July-11 August 2005 and analyzed with gas chromatography/mass spectrometry (GC/MS). In addition, inorganic trace gases (SO(2), CO, NO(x), and O(3)), meteorological parameters, and the particle number concentration were monitored. The median total concentration of terpenoic acids (i.e., pinic acid, norpinic acid, and two novel compounds, 3-hydroxyglutaric acid and 2-hydroxy-4-isopropyladipic acid) was 65 ng m(-3), while that of isoprene oxidation products (i.e., 2-methyltetrols and C(5) alkene triols) was 17.2 ng m(-3). The 2-methyltetrols exhibited day/night variations with maxima during day-time, while alpha-/beta-pinene oxidation products did not show any diel variation. The sampling period was marked by a relatively high condensation sink, caused by pre-existing aerosol particles, and no nucleation events. In general, the concentration trends of the SOA compounds reflected those of the inorganic trace gases, meteorological parameters, and condensation sink. Both the isoprene and alpha-/beta-pinene SOA products were strongly influenced by SO(2), which is consistent with earlier reports that acidity plays a role in SOA formation. The results support previous proposals that oxygenated VOCs contribute to particle growth processes above boreal forest.

Ion-induced sulfuric acid-ammonia nucleation drives particle formation in coastal Antarctica.

Formation of new aerosol particles from trace gases is a major source of cloud condensation nuclei (CCN) in the global atmosphere, with potentially large effects on cloud optical properties and Earth's radiative balance. Controlled laboratory experiments have resolved, in detail, the different nucleation pathways likely responsible for atmospheric new particle formation, yet very little is known from field studies about the molecular steps and compounds involved in different regions of the atmosphere. The scarcity of primary particle sources makes secondary aerosol formation particularly important in the Antarctic atmosphere. Here, we report on the observation of ion-induced nucleation of sulfuric acid and ammonia-a process experimentally investigated by the CERN CLOUD experiment-as a major source of secondary aerosol particles over coastal Antarctica. We further show that measured high sulfuric acid concentrations, exceeding 107 molecules cm-3, are sufficient to explain the observed new particle growth rates. Our findings show that ion-induced nucleation is the dominant particle formation mechanism, implying that galactic cosmic radiation plays a key role in new particle formation in the pristine Antarctic atmosphere.

Impact on short-lived climate forcers increases projected warming due to deforestation.

The climate impact of deforestation depends on the relative strength of several biogeochemical and biogeophysical effects. In addition to affecting the exchange of carbon dioxide (CO2) and moisture with the atmosphere and surface albedo, vegetation emits biogenic volatile organic compounds (BVOCs) that alter the formation of short-lived climate forcers (SLCFs), which include aerosol, ozone and methane. Here we show that a scenario of complete global deforestation results in a net positive radiative forcing (RF; 0.12 W m-2) from SLCFs, with the negative RF from decreases in ozone and methane concentrations partially offsetting the positive aerosol RF. Combining RFs due to CO2, surface albedo and SLCFs suggests that global deforestation could cause 0.8 K warming after 100 years, with SLCFs contributing 8% of the effect. However, deforestation as projected by the RCP8.5 scenario leads to zero net RF from SLCF, primarily due to nonlinearities in the aerosol indirect effect.

Novel insights on new particle formation derived from a pan-european observing system.

The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (<~1 nm), followed by growth into quasi-stable aerosol particles a few nanometres (~1-10 nm) and larger (>~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future.

Production of neutral molecular clusters by controlled neutralization of mobility standards.

Measuring aerosols and molecular clusters below the 3 nm size limit is essential to increase our understanding of new particle formation. Instruments for the detection of sub-3 nm aerosols and clusters exist and need to be carefully calibrated and characterized. So far calibrations and laboratory tests have been carried out using mainly electrically charged aerosols, as they are easier to handle experimentally. However, the charging state of the cluster is an important variable to take into account. Furthermore, instrument characterization performed with charged aerosols could be biased, preventing a correct interpretation of data when electrically neutral sub-3 nm aerosols are involved. This article presents the first steps to generate electrically neutral molecular clusters as standards for calibration. We show two methods: One based on the neutralization of well-known molecular clusters (mobility standards) by ions generated in a switchable aerosol neutralizer. The second is based on the controlled neutralization of mobility standards with mobility standards of opposite polarity in a recombination cell. We highlight the challenges of these two techniques and, where possible, point out solutions. In addition, we give an outlook on the next steps toward generating well-defined neutral molecular clusters with a known chemical composition and concentration. Published with license by American Association for Aerosol Research.

Associations of traffic related air pollutants with hospitalisation for first acute myocardial infarction: the HEAPSS study.

BACKGROUND: Acute myocardial infarction (AMI) is the leading cause of death attributed to cardiovascular diseases. An association between traffic related air pollution and AMI has been suggested, but the evidence is still limited. OBJECTIVES: To evaluate in a multicentre study association between hospitalisation for first AMI and daily levels of traffic related air pollution. METHODS: The authors collected data on first AMI hospitalisations in five European cities. AMI registers were available in Augsburg and Barcelona; hospital discharge registers (HDRs) were used in Helsinki, Rome and Stockholm. NO2, CO, PM10 (particles <10 microm), and O3 were measured at central monitoring sites. Particle number concentration (PNC), a proxy for ultrafine particles (<0.1 microm), was measured for a year in each centre, and then modelled retrospectively for the whole study period. Generalised additive models were used for statistical analyses. Age and 28 day fatality and season were considered as potential effect modifiers in the three HDR centres. RESULTS: Nearly 27,000 cases of first AMI were recorded. There was a suggestion of an association of the same day CO and PNC levels with AMI: RR = 1.005 (95% CI 1.000 to 1.010) per 0.2 mg/m3 and RR = 1.005 (95% CI 0.996 to 1.015) per 10000 particles/cm3, respectively. However, associations were only observed in the three cities with HDR, where power for city-specific analyses was higher. The authors observed in these cities the most consistent associations among fatal cases aged <75 years: RR at 1 day lag for CO = 1.021 (95% CI 1.000 to 1.048) per 0.2 mg/m3, for PNC = 1.058 (95% CI 1.012 to 1.107) per 10000 particles/cm3, and for NO2 = 1.032 (95% CI 0.998 to 1.066) per 8 microg/m3. Effects of air pollution were more pronounced during the warm than the cold season. CONCLUSIONS: The authors found support for the hypothesis that exposure to traffic related air pollution increases the risk of AMI. Most consistent associations were observed among fatal cases aged <75 years and in the warm season.

Enhanced air pollution via aerosol-boundary layer feedback in China.

Severe air pollution episodes have been frequent in China during the recent years. While high emissions are the primary reason for increasing pollutant concentrations, the ultimate cause for the most severe pollution episodes has remained unclear. Here we show that a high concentration of particulate matter (PM) will enhance the stability of an urban boundary layer, which in turn decreases the boundary layer height and consequently cause further increases in PM concentrations. We estimate the strength of this positive feedback mechanism by combining a new theoretical framework with ambient observations. We show that the feedback remains moderate at fine PM concentrations lower than about 200 µg m(-3), but that it becomes increasingly effective at higher PM loadings resulting from the combined effect of high surface PM emissions and massive secondary PM production within the boundary layer. Our analysis explains why air pollution episodes are particularly serious and severe in megacities and during the days when synoptic weather conditions stay constant.

New particle formation in the free troposphere: A question of chemistry and timing.

New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid-ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.