Dimethyl sulfide (DMS; CH3SCH3) from marine phytoplankton is a notable source of atmospheric sulfur1. Its oxidation products include sulfuric acid (SA; H2SO4) and methanesulfonic acid (MSA; CH3SO3H), which has a higher yield than SA below 10 °C (ref. 2). Although SA is known to drive the formation of new particles3, which may subsequently grow and act as cloud condensation nuclei (CCN), the role of MSA remains unclear4. Here, in experiments performed under atmospheric conditions at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we show that MSA nucleates together with ammonia (NH3) below -10 °C, at rates comparable with SA-NH3. Moreover, MSA and SA nucleate synergistically below -10 °C, forming multi-acid molecular clusters with NH3. Even at ultralow NH3 levels, MSA drives particle growth at or near the kinetic limit below 9 °C and above 40% relative humidity (RH). Because MSA and SA generally coexist at similar concentrations in cool marine regions, our findings indicate that nucleation rates may be accelerated up to tenfold and growth rates up to twofold compared with SA-NH3 alone. Our global model simulations indicate that MSA can enhance CCN concentrations, especially in polar regions. We propose that MSA might be an important driver of biogenic particles in cool, pristine marine regions of both the present-day and pre-industrial atmospheres and yet is unaccounted for in global climate models5.

Abstract. Laboratory experiments addressing complex phenomena such as atmospheric new-particle formation and growth typically involve numerous instruments measuring a range of key coupled variables. In addition to independent calibration, the combined dataset provides not just constraints on the parameters of interest but also on the critical instrument calibrations. Here we find good agreement between production and loss rates of sulfuric acid (H2SO4) in an experiment performed at the CERN CLOUD chamber involving oxidation of sulfur dioxide (SO2) in the presence of ammonia (NH3) at 58 % relative humidity, driving new-particle formation and growth of particles by H2SO4 + NH3 nucleation initiated by O3 photolysis via several light sources. This closure requires consistency across numerous parameters, including: the particle number and size distribution; their condensation sink for H2SO4; the particle growth rates; the concentration of H2SO4; and the nucleation coefficients for both neutral and ion-induced pathways. Our study shows that accurate agreement can be achieved between production and loss of condensable vapors in laboratory chambers under atmospheric conditions, with accuracy ultimately tied to particle number measurement (i.e. a condensation particle counter). This, in turn implies parameters such as the H2SO4 concentration and particle size distributions can be determined to a comparable precision.

This paper explores the possibility of using machine learning methods for analyzing observations from the “Solntse-Terahertz” scientific equipment, developed at the Lebedev Physical Institute for installation on the Russian segment of the ISS. The scientific equipment consists of eight detectors, with target frequencies ranging from 0.4 to 12.0 THz. One of the primary goals of the experiment is to study solar flares whose spectra in this range often have a U-shaped form. The primary focus in determining the spectral parameters is on identifying spectral indices of the decaying and rising parts of the spectrum, as well as the position of the turnover point. The algorithms were trained using model data on the intensity of radiation passing through optical paths of the instrument. The data was obtained by numerical integration methods. The analysis has shown that the Stacking algorithm demonstrates the highest accuracy in determining the spectral parameters and can be integrated into the data processing system for future experiment on the ISS, enabling the automatic preliminary restoration of solar flare spectrum parameters.

We present a "diagonal" Volatility Basis Set (dVBS) comparing gas-phase concentrations of oxygenated organic molecules (OOM) to their condensed-phase mass fractions. This permits closure of vapor concentrations with particle composition constrained by particle growth rates, allowing the contributions of quasi non-volatile condensation, equilibrium partitioning, and reactive uptake to be separated. The dVBS accommodates both equilibrium and dynamical (growth) conditions. Growth implies an association between gas and particle concentrations governed by a "condensation line" that is set by the particle growth rate, which fixes the total (excess) concentration of condensible vapors. The condensation line defines an infeasible region of high particle mass fraction and low gas concentration; under steady-state growth conditions, compounds cannot appear in this infeasible region without being formed by condensed-phase chemistry. We test the dVBS with observations from the CLOUD experiment at CERN using data from a FIGAERO I- Chemical Ionization Mass Spectrometer measuring vapors directly and particle composition via temperature programmed desorption from a filter. A dVBS analysis finds that data from an α-pinene + O3 run at 243 K are consistent with volatility driven condensation forming the large majority of particle mass, with no compounds clearly within the infeasible region.

Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the 'Cosmics Leaving Outdoor Droplets' chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products' saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.

Co-condensation of nitric acid and ammonia vapors to form ammonium nitrate transforms from a fully semi-volatile behavior when it is relatively warm (273 K and above, typical of the seasonal planetary boundary layer) into effectively non-volatile and irreversible uptake for the limiting vapor when it is cold (well below 273 K, typical of the upper troposphere and occasionally the wintertime boundary layer). This causes the system to switch in character from the one governed by semi-volatile equilibrium (how it is usually portrayed) to the one governed by irreversible reactive uptake to even the smallest particles. Uptake involves an activation diameter, which can be as small as 1 nm for typical vapor concentrations, and subsequent growth rates can be very high, exceeding 1000 nm h-1. In addition to this somewhat surprising behavior, the system provides an exemplary case for semi-volatile reactive uptake within the context of volatility and saturation ratios.

The article briefly describes the goals and tasks of the planned “Sun–Terahertz” space experiment on board the Russian segment of the ISS. The experiment was aimed at studying radiation from the Sun in the unexplored terahertz range at frequencies of 1012–1013 Hz and obtaining new data on the terahertz radiation of the Sun, solar active regions, and solar flares. The scientific equipment being developed is a set of eight detectors sensitive to radiation of various frequencies: 0.4, 0.7, 1.0, 3.0, 5.0, 7.0, 10.0, and 12.0 THz. The main components of the electronics unit of the scientific equipment are considered: amplifiers, optical-chopper drivers, the power board, and the electronics board. The accuracy of signal measurements using an ADC on the electronics board was calculated, and the sensitivity of the scientific equipment was assessed.

The study of precipitation of high-energy electrons from the magnetosphere into the Earth’s atmosphere is important for studying the physical mechanisms of electron acceleration during interplanetary disturbances in near-Earth space, the processes of formation of trapped electron fluxes in the magnetosphere and their subsequent precipitation into the atmosphere. In addition, the precipitating electrons affect the spacecraft operation and often lead to significant destruction of mesospheric ozone, etc. Since 1957, the Dolgoprudny Scientific Station of the Lebedev Physical Institute has been conducting continuous measurements of cosmic ray fluxes at altitudes of 0–30 km in the atmosphere of polar latitudes (Murmansk oblast, Antarctica) and at middle latitude (Moscow oblast). During this time, almost 600 cases of electron precipitation were recorded, mainly from the Earth’s outer radiation belt near its polar boundary due to measurement in Murmansk oblast. At the same time, several cases of electron precipitation were recorded at mid-latitude (Moscow oblast) and at the Mirny station in Antarctica, in particular, in 2022–2023. The paper discusses interplanetary and geomagnetic conditions during these events. Analysis of measurement data in the stratosphere made it possible to establish the absorption spectra of secondary bremsstrahlung photons and, on their basis, using the method we developed, to determine the primary energy spectra of precipitating magnetospheric electrons.

The future space experiment «Sun-Terahertz» is aimed at studying the Sun in the unexplored terahertz range, obtaining new data on the terahertz radiation of the Sun, solar active regions and solar flares. The scientific equipment being developed is a set of eight detectors sensitive to radiation of various frequencies in the range 0.4–12.0 THz. The Golay cell optoacoustic receiver was used as a sensitive element of the detectors. This paper examines the problem of changing the sensitivity of receivers of this type when their own temperature changes (temperature effect). Using a test bench based on a single-channel model of scientific equipment and a black body simulator, the linear section of the temperature dependence of the receiver was determined. A method for compensating the temperature effect of optoacoustic converters Golay cell has been developed and the results of its testing on a test bench are presented. This technique will be useful in the development of scientific equipment based on Golay cells, the operation of which is expected under conditions of temperature changes in the surrounding space.

Isoprene affects new particle formation rates in environments and experiments also containing monoterpenes. For the most part, isoprene reduces particle formation rates, but the reason is debated. It is proposed that due to its fast reaction with OH, isoprene may compete with larger monoterpenes for oxidants. However, by forming a large amount of peroxy-radicals (RO2), isoprene may also interfere with the formation of the nucleating species compared to a purely monoterpene system. We explore the RO2 cross reactions between monoterpene and isoprene oxidation products using the radical Volatility Basis Set (radical-VBS), a simplified reaction mechanism, comparing with observations from the CLOUD experiment at CERN. We find that isoprene interferes with covalently bound C20 dimers formed in the pure monoterpene system and consequently reduces the yields of the lowest volatility (Ultra Low Volatility Organic Carbon, ULVOC) VBS products. This in turn reduces nucleation rates, while having less of an effect on subsequent growth rates.

The article presents a brief description of the main scientific objectives of the Solntse–Terahertz project. As part of this project, the Lebedev Physical Institute is manufacturing scientific equipment for installation on the Russian segment of the International Space Station. The optical system of each of the eight scientific equipment’s radiation receivers consists of a system of mirrors, an optical chopper, low-pass and bandpass filters. Spectral characteristics were obtained for each element of this system. When calibrating the device, a source—a black-body simulator (BBS)—is used, and, therefore, using numerical integration methods, the intensity of radiation from the BBS that passes through the filter system was calculated. To estimate the characteristic signal from the quiet Sun, the radiation intensity passing through the filter system was calculated using numerical integration methods using the standard ASTM E-490 solar spectrum.

Iodine oxoacids are recognised for their significant contribution to the formation of new particles in marine and polar atmospheres. Nevertheless, to incorporate the iodine oxoacid nucleation mechanism into global simulations, it is essential to comprehend how this mechanism varies under various atmospheric conditions. In this study, we combined measurements from the CLOUD (Cosmic Leaving OUtdoor Droplets) chamber at CERN and simulations with a kinetic model to investigate the impact of temperature, ionisation, and humidity on iodine oxoacid nucleation. Our findings reveal that ion-induced particle formation rates remain largely unaffected by changes in temperature. However, neutral particle formation rates experience a significant increase when the temperature drops from +10 degrees C to -10 degrees C. Running the kinetic model with varying ionisation rates demonstrates that the particle formation rate only increases with a higher ionisation rate when the iodic acid concentration exceeds 1.5 x 107 cm-3, a concentration rarely reached in pristine marine atmospheres. Consequently, our simulations suggest that, despite higher ionisation rates, the charged cluster nucleation pathway of iodic acid is unlikely to be enhanced in the upper troposphere by higher ionisation rates. Instead, the neutral nucleation channel is likely to be the dominant channel in that region. Notably, the iodine oxoacid nucleation mechanism remains unaffected by changes in relative humidity from 2% to 80%. However, under unrealistically dry conditions (below 0.008% RH at +10 degrees C), iodine oxides (I2O4 and I2O5) significantly enhance formation rates. Therefore, we conclude that iodine oxoacid nucleation is the dominant nucleation mechanism for iodine nucleation in the marine and polar boundary layer atmosphere. Raising the ionisation rate (IR) increases the ion concentration, but also amplifies ion losses due to ion-ion recombination, consequently diminishing the formation rate of charged clusters at low HIO3 concentrations.

Currently, the complete chemical characterization of nanoparticles (< 100 nm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization have been recently developed to better detect and infer more accurately the sources and fates of sub-100 nm particles, but a detailed comparison of different approaches is missing. Here we report on the chemical composition of secondary organic aerosol (SOA) nanoparticles from experimental studies of α-pinene ozonolysis at −50, −30, and −10 ∘C and intercompare the results measured by different techniques. The experiments were performed at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). The chemical composition was measured simultaneously by four different techniques: (1) thermal desorption–differential mobility analyzer (TD–DMA) coupled to a NO3- chemical ionization–atmospheric-pressure-interface–time-of-flight (CI–APi–TOF) mass spectrometer, (2) filter inlet for gases and aerosols (FIGAERO) coupled to an I− high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS), (3) extractive electrospray Na+ ionization time-of-flight mass spectrometer (EESI-TOF), and (4) offline analysis of filters (FILTER) using ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS). Intercomparison was performed by contrasting the observed chemical composition as a function of oxidation state and carbon number, by estimating the volatility and comparing the fraction of volatility classes, and by comparing the thermal desorption behavior (for the thermal desorption techniques: TD–DMA and FIGAERO) and performing positive matrix factorization (PMF) analysis for the thermograms. We found that the methods generally agree on the most important compounds that are found in the nanoparticles. However, they do see different parts of the organic spectrum. We suggest potential explanations for these differences: thermal decomposition, aging, sampling artifacts, etc. We applied PMF analysis and found insights of thermal decomposition in the TD–DMA and the FIGAERO.

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (H2SO4), stabilized by ammonia (NH3). However, in marine and polar regions, NH3 is generally low, and H2SO4 is frequently found together with iodine oxoacids [HIOx, i.e., iodic acid (HIO3) and iodous acid (HIO2)]. In experiments performed with the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we investigated the interplay of H2SO4 and HIOx during atmospheric particle nucleation. We found that HIOx greatly enhances H2SO4(-NH3) nucleation through two different interactions. First, HIO3 strongly binds with H2SO4 in charged clusters so they drive particle nucleation synergistically. Second, HIO2 substitutes for NH3, forming strongly bound H2SO4-HIO2 acid-base pairs in molecular clusters. Global observations imply that HIOx is enhancing H2SO4(-NH3) nucleation rates 10- to 10,000-fold in marine and polar regions.

Biogenic vapors form new particles in the atmosphere, affecting global climate. The contributions of monoterpenes and isoprene to new particle formation (NPF) have been extensively studied. However, sesquiterpenes have received little attention despite a potentially important role due to their high molecular weight. Via chamber experiments performed under atmospheric conditions, we report biogenic NPF resulting from the oxidation of pure mixtures of β-caryophyllene, α-pinene, and isoprene, which produces oxygenated compounds over a wide range of volatilities. We find that a class of vapors termed ultralow-volatility organic compounds (ULVOCs) are highly efficient nucleators and quantitatively determine NPF efficiency. When compared with a mixture of isoprene and monoterpene alone, adding only 2% sesquiterpene increases the ULVOC yield and doubles the formation rate. Thus, sesquiterpene emissions need to be included in assessments of global aerosol concentrations in pristine climates where biogenic NPF is expected to be a major source of cloud condensation nuclei.

The results of a study of energetic electron precipitation from the Earth’s outer radiation belt into the atmosphere during weak geomagnetic storm on February 1–5, 2015 are presented. The work was carried out on the basis of experimental data on electron fluxes with energies >0.1, >0.3, and >2 MeV obtained from Meteor-M2 polar satellite. For a comparative analysis of the electron fluxes of the outer radiation belt, precipitating and trapped, Van Allen Probes data were used. It is shown that the strongest precipitation are observed during the main phase of the storm and in the beginning of the recovery phase, when prolonged intense substorm activity occurs. In spite of significant precipitation in the wide L-MLT area as was found in [6], decrease in the flux of trapped electrons at the belt maximum during the main phase of the storm was not observed. Moreover, during the late recovery phase, the flux of electrons with E > 2 MeV increased, while that with E > 0.1 and E > 0.3 MeV did not change.

Aerosol particles have an important role in Earth's radiation balance and climate, both directly and indirectly through aerosol-cloud interactions. Most aerosol particles in the atmosphere are weakly charged, affecting both their collision rates with ions and neutral molecules, as well as the rates by which they are scavenged by other aerosol particles and cloud droplets. The rate coefficients between ions and aerosol particles are important since they determine the growth rates and lifetimes of ions and charged aerosol particles, and so they may influence cloud microphysics, dynamics, and aerosol processing. However, despite their importance, very few experimental measurements exist of charged aerosol collision rates under atmospheric conditions, where galactic cosmic rays in the lower troposphere give rise to ion pair concentrations of around 1000 cm(-3). Here we present measurements in the CERN CLOUD chamber of the rate coefficients between ions and small (< 10 nm) aerosol particles containing up to 9 elementary charges, e. We find the rate coefficient of a singly charged ion with an oppositely charged particle increases from 2.0 (0.4-4.4) x 10(-6) cm(3) s(-1) to 30.6 (24.9-45.1) x 10(-6) cm(3) s(-1) for particles with charges of 1 to 9 e, respectively, where the parentheses indicate the +/- 1 sigma uncertainty interval. Our measurements are compatible with theoretical predictions and show excellent agreement with the model of Gatti and Kortshagen (2008).

The paper briefly describes the goals and objectives of the planned space experiment "Sun - Terahertz" aboard the Russian Segment of the ISS. The experiment is aimed at studying solar radiation in the unexplored terahertz range at frequencies of 1012…1013 Hz, obtaining new data on terahertz radiation from the sun, solar active regions and solar flares. The main components of the optical path of scientific equipment are considered. With the help of the Blackbody Simulator and the Single-Channel Model, the detectors of scientific equipment were calibrated, the influence of the quality of the optical surface of the telescope mirrors on the detector signal amplitude in the terahertz range was studied, and a preliminary assessment of the detector sensitivity was carried out.

Information about the energetic electron precipitation (EEP) from the radiation belt into the atmosphere is important for assessing the ozone variability and dynamics of the middle atmosphere during magnetospheric and geomagnetic disturbances. The accurate values of energetic electron fluxes depending on their energy range are one of the most important problems for calculating atmospheric ionization rates, which, in turn, are taken into account for estimating ozone depletion in chemistry–climate models. Despite the importance of these processes for the high latitudes of middle atmosphere, precipitation of energetic electrons is still insufficiently studied. In order to better understand EEP and related processes in the atmosphere, it is important to have many realistic observations of EEP in order to correctly characterize their spectra. Invading the atmosphere, precipitating energetic electrons, in the range from tens of keV to relativistic energies of more than 1 MeV, generate bremsstrahlung, which penetrates into the stratosphere and is recorded by detectors on balloons. However, these observations can be made only when the balloon is at stratospheric heights. Near-Earth satellites, such as the polar-orbiting operational environmental satellites (POES), are constantly registering precipitating electrons in the loss cone, but are moving too fast in space. Based on a comparison of the results of EEP measurements on balloons and onboard POES satellites in 2003, we propose a criterion that makes it possible to constantly monitor EEP ionization at stratospheric heights using observations on POES satellites.