Formation Of Cloud Condensation Nuclei Research Articles

Mathematical derivation and physical interpretation of particle size-resolved activation ratio based on particle hygroscopicity distribution: Application on global characterization of CCN activity

Size-resolved particle activation ratio (SPAR), the size-dependent ability of aerosol particles to form cloud condensation nuclei (CCN), is generally parameterized by a formula with sigmoidal shape with three key parameters. However, our understanding about the intrinsic relationship between the sigmoidal shape function and aerosol hygroscopicity distribution remains incomplete. In this study, the relationship between SPAR and particle hygroscopicity distribution is mathematically derived and relationships between key parameters for SPAR and particle hygroscopicity distribution are manifested, making it clear for the physical understanding of key CCN spectral characteristics. On the basis of the mathematically derived SPAR parameterization, a simplified method to calculate SPAR parameters (including maximum activation fraction (MAF), critical diameter and its heterogeneity of CCN-active particles) based on hygroscopicity distribution data is proposed. This simplified method is applied to Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) field measurement datasets around the world for the meta-analysis of regional and seasonal characteristics of CCN activity. It was found that, for CCN-active particles in polluted regions, the MAF can reach lower values, and the variations of both hygroscopicity and its heterogeneity can be larger, compared with those in clean regions. In summer, the MAF and the hygroscopicity of CCN can reach higher values than those in winter. In addition, the variations of SPAR parameters among different campaigns are large and thus measurements of CCN Counter or HTDMA are needed to specify the SPAR parameters at a specific site during a specific period. The bulk CCN activity at different SSs are also calculated based on the calculated SPAR by considering the measured particle number size distribution. The mathematical derivation and physical interpretation of SPAR parameterization in this study can further the understanding of CCN activity based on particle hygroscopicity distribution. The proposed simplified method to calculate SPAR parameters based on HTDMA measurements allows meta-analysis of SPAR parameters and helps expand the CCN activity datasets around the world.

Large contribution of organics to condensational growth and formation of cloud condensation nuclei (CCN) in the remote marine boundary layer

Abstract. Marine low clouds strongly influence global climate, and their radiative effects are particularly susceptible to the concentration of cloud condensation nuclei (CCN). One major source of CCN is the condensational growth of pre-CCN particles, and sulfate has long been considered the major condensing species in the remote marine boundary layer. While some studies have suggested that secondary organic species can contribute to particle growth, its importance remains unclear. Here we present the first long-term observational evidence that organics play an important role in particle growth over remote oceans. To the contrary of traditional thinking, sulfate dominated condensational growth for only a small (∼18 %) fraction of the 62 observed growth events, even fewer than the organic-dominated events (24 %). During most (58 %) growth events, the major condensing species included both organics and sulfate. Potential precursors of the secondary organics are volatile organic compounds from ocean biological activities and those produced by the air–sea interfacial oxidation. Our results indicate that the condensation of secondary organics contributes strongly to the growth of pre-CCN particles and thereby the CCN population over remote oceans.

Thermochemical Properties of Menthol and Terpineol

The work continues the project of physicochemical characterization of terpenic substances that are present in plants and after emission to the atmosphere play an important role in the formation of cloud condensation nuclei. Two substances, which are solid at room temperature, were studied in this work, namely both enantiomers of menthol and (–)- $$\upalpha$$ -terpineol. Temperatures and enthalpies of fusion were measured, isobaric heat capacities were measured in the temperature range 326.15–348.15 K and vapor pressures were measured in the temperature range 400–430 K. The experimental values were compared with predictions by COSMO-RS. Modern nonstatistical algorithms based on mathematical gnostics were used for data analysis.

Arctic and Antarctic Sea Ice Mean State in the Community Earth System Model Version 2 and the Influence of Atmospheric Chemistry

AbstractArctic and Antarctic sea ice has undergone significant and rapid change with the changing climate. Here, we present preindustrial and historical results from the newly released Community Earth System Model Version 2 (CESM2) to assess the Arctic and Antarctic sea ice. Two configurations of the CESM2 are available that differ only in their atmospheric model top and the inclusion of comprehensive atmospheric chemistry, including prognostic aerosols. The CESM2 configuration with comprehensive atmospheric chemistry has significantly thicker Arctic sea ice year‐round and better captures decreasing trends in sea ice extent and volume over the satellite period. In the Antarctic, both CESM configurations have similar mean state ice extent and volume, but the ice extent trends are opposite to satellite observations. We find that differences in the Arctic sea ice between CESM2 configurations are the result of differences in liquid clouds. Over the Arctic, the CESM2 configuration without prognostic aerosol formation has fewer aerosols to form cloud condensation nuclei, leading to thinner liquid clouds. As a result, the sea ice receives much more shortwave radiation early in the melt season, driving a stronger ice albedo feedback and leading to additional sea ice loss and significantly thinner ice year‐round. The aerosols necessary for the Arctic liquid cloud formation are produced from different precursor emissions and transported to the Arctic. Thus, the main reason sea ice differs in the Arctic is the transport of cloud‐impacting aerosols into the region, while the Antarctic remains relatively pristine from extrapolar aerosol transport.

Size-dependent influence of NOx on the growth rates of organic aerosol particles.

Atmospheric new-particle formation (NPF) affects climate by contributing to a large fraction of the cloud condensation nuclei (CCN). Highly oxygenated organic molecules (HOMs) drive the early particle growth and therefore substantially influence the survival of newly formed particles to CCN. Nitrogen oxide (NOx) is known to suppress the NPF driven by HOMs, but the underlying mechanism remains largely unclear. Here, we examine the response of particle growth to the changes of HOM formation caused by NOx. We show that NOx suppresses particle growth in general, but the suppression is rather nonuniform and size dependent, which can be quantitatively explained by the shifted HOM volatility after adding NOx. By illustrating how NOx affects the early growth of new particles, a critical step of CCN formation, our results help provide a refined assessment of the potential climatic effects caused by the diverse changes of NOx level in forest regions around the globe.

Liquid-Liquid Phase Separation in Supermicrometer and Submicrometer Aerosol Particles.

ConspectusThe interactions of aerosol particles with light and clouds are among the most uncertain aspects of anthropogenic climate forcings. The effects of aerosol particles on climate depend on their optical properties, heterogeneous chemistry, water uptake behavior, and ice nucleation activity. These properties in turn depend on aerosol physics and chemistry including composition, size, shape, internal structure (morphology), and phase state. The greatest numbers of particles are found at small, submicrometer sizes, and the properties of aerosol particles can differ on the nanoscale compared with measurements of bulk materials. As a result, our focus has been on characterizing the phase transitions of aerosol particles in both supermicrometer and submicrometer particles. The phase transition of particular interest for us has been liquid-liquid phase separation (LLPS), which occurs when components of a solution phase separate due to a difference in solubilities. For example, organic compounds can have limited solubility in salt solutions especially as the water content decreases, increasing the concentration of the salt solution, and causing phase separation between organic-rich and inorganic-rich phases. To characterize the systems of interest, we primarily use optical microscopy for supermicrometer particles and cryogenic-transmission microscopy for submicrometer particles.This Account details our main results to date for the phase transitions of supermicrometer particles and the morphology of submicrometer aerosol. We have found that the relative humidity (RH) at which LLPS occurs (separation RH; SRH) is highly sensitive to the composition of the particles. For supermicrometer particles, SRH decreases as the pH is lowered to atmospherically relevant values. SRH also decreases when non-phase-separating organic compounds are added to the particles. For submicrometer particles, a size dependence of morphology is observed in systems that undergo LLPS in supermicrometer particles. In the limit of slow drying rates, particles <30 nm are homogeneous and larger particles are phase-separated. This size dependence of aerosol morphology arises because small particles cannot overcome the activation barrier needed to form a new phase when phase separation occurs by a nucleation and growth mechanism. The inhibition of LLPS in small particles is observed for mixtures of ammonium sulfate with single organic compounds as well as complex organics like α-pinene secondary organic matter. The morphology of particles affects activation diameters for the formation of cloud condensation nuclei. These results more generally have implications for aerosol properties that affect the climate system. In addition, LLPS is also widely studied in materials and biological chemistry, and our results could potentially translate to implications for these fields.

Aerosol–photolysis interaction reduces particulate matter during wintertime haze events

Aerosol-radiation interaction (ARI) plays a significant role in the accumulation of fine particulate matter (PM2.5) by stabilizing the planetary boundary layer and thus deteriorating air quality during haze events. However, modification of photolysis by aerosol scattering or absorbing solar radiation (aerosol-photolysis interaction or API) alters the atmospheric oxidizing capacity, decreases the rate of secondary aerosol formation, and ultimately alleviates the ARI effect on PM2.5 pollution. Therefore, the synergetic effect of both ARI and API can either aggravate or even mitigate PM2.5 pollution. To test the effect, a fully coupled Weather Research and Forecasting (WRF)-Chem model has been used to simulate a heavy haze episode in North China Plain. Our results show that ARI contributes to a 7.8% increase in near-surface PM2.5 However, API suppresses secondary aerosol formation, and the combination of ARI and API results in only 4.8% net increase of PM2.5 Additionally, API increases the solar radiation reaching the surface and perturbs aerosol nucleation and activation to form cloud condensation nuclei, influencing aerosol-cloud interaction. The results suggest that API reduces PM2.5 pollution during haze events, but adds uncertainties in climate prediction.

Bacteria as Cloud Condensation Nuclei (CCN) in the Atmosphere

Bacteria activation and cloud condensation nuclei (CCN) formation have been studied in the atmosphere using the classical theory of heterogeneous nucleation. Simulations were performed for the binary system of sulfuric acid/water using laboratory-determined contact angles. Realistic model simulations were performed at different atmospheric heights for a set of 140 different bacteria. Model simulations showed that bacteria activation is a potentially favorable process in the atmosphere which may be enhanced at lower temperatures. CCN formation from bacteria nuclei is dependent on ambient atmospheric conditions (temperature, relative humidity), bacteria size, and sulfuric acid concentration. Furthermore, a critical parameter for the determination of bacteria activation is the value of the intermolecular potential between the bacteria’s surface and the critical cluster formed at their surface. In the classical nucleation theory, this is parameterized with the contact angle between substrate and critical cluster. Therefore, the dataset of laboratory values for the contact angle of water on different bacteria substrates needs to be enriched for realistic simulations of bacteria activation in the atmosphere.

New Particle Formation in the Atmosphere: From Molecular Clusters to Global Climate

AbstractNew particle formation (NPF) represents the first step in the complex processes leading to formation of cloud condensation nuclei. Newly formed nanoparticles affect human health, air quality, weather, and climate. This review provides a brief history, synthesizes recent significant progresses, and outlines the challenges and future directions for research relevant to NPF. New developments include the emergence of state‐of‐the‐art instruments that measure prenucleation clusters and newly nucleated nanoparticles down to about 1 nm; systematic laboratory studies of multicomponent nucleation systems, including collaborative experiments conducted in the Cosmics Leaving Outdoor Droplets chamber at CERN; observations of NPF in different types of forests, extremely polluted urban locations, coastal sites, polar regions, and high‐elevation sites; and improved nucleation theories and parameterizations to account for NPF in atmospheric models. The challenges include the lack of understanding of the fundamental chemical mechanisms responsible for aerosol nucleation and growth under diverse environments, the effects of SO2 and NOx on NPF, and the contribution of anthropogenic organic compounds to NPF. It is also critical to develop instruments that can detect chemical composition of particles from 3 to 20 nm and improve parameterizations to represent NPF over a wide range of atmospheric conditions of chemical precursor, temperature, and humidity.

Densities, Vapor Pressures, and Surface Tensions of Selected Terpenes

The knowledge of physico-chemical properties of terpenes and terpenoids are necessary for understanding of formation of cloud condensation nuclei. In this work properties of $$\upalpha$$ -pinene and $$\upbeta$$ -pinene, namely liquid densities, saturated vapor pressure, surface tension and interfacial tension in mixtures with water were measured in the temperature range between 300 and 370 K. Saturated vapor pressures were also modelled by COSMO-RS and compared both with our mesurements and literature values measured at lower temperatures. A modern nonstatistical technique based on mathematical gnostics was used for data analysis.

Biogenic Aerosol in the Arctic from Eight Years of MSA Data from Ny Ålesund (Svalbard Islands) and Thule (Greenland)

In remote marine areas, biogenic productivity and atmospheric particulate are coupled through dimethylsulfide (DMS) emission by phytoplankton. Once in the atmosphere, the gaseous DMS is oxidized to produce H2SO4 and methanesulfonic acid (MSA); both species can affect the formation of cloud condensation nuclei. This study analyses eight years of biogenic aerosol evolution and variability at two Arctic sites: Thule (76.5° N, 68.8° W) and Ny Ålesund (78.9° N, 11.9° E). Sea ice plays a key role in determining the MSA concentration in polar regions. At the beginning of the melting season, in April, up to June, the biogenic aerosol concentration appears inversely correlated with sea ice extent and area, and positively correlated with the extent of the ice-free area in the marginal ice zone (IF-MIZ). The upper ocean stratification induced by sea ice melting might have a role in these correlations, since the springtime formation of this surface layer regulates the accumulation of phytoplankton and nutrients, allowing the DMS to escape from the sea to the atmosphere. The multiyear analysis reveals a progressive decrease in MSA concentration in May at Thule and an increase in July August at Ny Ålesund. Therefore, while the MSA seasonal evolution is mainly related with the sea ice retreat in April, May, and June, the IF-MIZ extent appears as the main factor affecting the longer-term behavior of MSA.

Simultaneous and Synergic Production of Bioavailable Iron and Reactive Iodine Species in Ice.

The bioavailable iron is essential for all living organisms, and the dissolution of iron oxide contained in dust and soil is one of the major sources of bioavailable iron in nature. Iodine in the polar atmosphere is related to ozone depletion, mercury oxidation, and cloud condensation nuclei formation. Here we show that the chemical reaction between iron oxides and iodide (I-) is markedly accelerated to produce bioavailable iron (Fe(II)aq) and tri-iodide (I3-: evaporable in the form of I2) in frozen solution (both with and without light irradiation), while it is negligible in aqueous phase. The freeze-enhanced production of Fe(II)aq and tri-iodide is ascribed to the freeze concentration of iron oxides, iodides, and protons in the ice grain boundaries. The outdoor experiments carried out in midlatitude during a winter day (Pohang, Korea: 36°0' N, 129°19' E) and in an Antarctic environment (King George Island: 62°13' S 58°47' W) also showed the enhanced generation of Fe(II)aq and tri-iodide in ice. This study proposes a previously unknown abiotic mechanism and source of bioavailable iron and active iodine species in the polar environment. The pulse input of bioavailable iron and reactive iodine when ice melts may influence the oceanic primary production and CCN formation.

Structure-Function Analysis Indicates that an Active-Site Water Molecule Participates in Dimethylsulfoniopropionate Cleavage by DddK.

The osmolyte dimethylsulfoniopropionate (DMSP) is produced in petagram quantities in marine environments and has important roles in global sulfur and carbon cycling. Many marine microorganisms catabolize DMSP via DMSP lyases, generating the climate-active gas dimethyl sulfide (DMS). DMS oxidation products participate in forming cloud condensation nuclei and, thus, may influence weather and climate. SAR11 bacteria are the most abundant marine heterotrophic bacteria; many of them contain the DMSP lyase DddK, and their dddK transcripts are relatively abundant in seawater. In a recently described catalytic mechanism for DddK, Tyr64 is predicted to act as the catalytic base initiating the β-elimination reaction of DMSP. Tyr64 was proposed to be deprotonated by coordination to the metal cofactor or its neighboring His96. To further probe this mechanism, we purified and characterized the DddK protein from Pelagibacter ubique strain HTCC1062 and determined the crystal structures of wild-type DddK and its Y64A and Y122A mutants (bearing a change of Y to A at position 64 or 122, respectively), where the Y122A mutant is complexed with DMSP. The structural and mutational analyses largely support the catalytic role of Tyr64, but not the method of its deprotonation. Our data indicate that an active water molecule in the active site of DddK plays an important role in the deprotonation of Tyr64 and that this is far more likely than coordination to the metal or His96. Sequence alignment and phylogenetic analysis suggest that the proposed catalytic mechanism of DddK has universal significance. Our results provide new mechanistic insights into DddK and enrich our understanding of DMS generation by SAR11 bacteria.IMPORTANCE The climate-active gas dimethyl sulfide (DMS) plays an important role in global sulfur cycling and atmospheric chemistry. DMS is mainly produced through the bacterial cleavage of marine dimethylsulfoniopropionate (DMSP). When released into the atmosphere from the oceans, DMS can be photochemically oxidized into DMSO or sulfate aerosols, which form cloud condensation nuclei that influence the reflectivity of clouds and, thereby, global temperature. SAR11 bacteria are the most abundant marine heterotrophic bacteria, and many of them contain DMSP lyase DddK to cleave DMSP, generating DMS. In this study, based on structural analyses and mutational assays, we revealed the catalytic mechanism of DddK, which has universal significance in SAR11 bacteria. This study provides new insights into the catalytic mechanism of DddK, leading to a better understanding of how SAR11 bacteria generate DMS.

Size distribution and chemical composition of primary particles emitted during open biomass burning processes: Impacts on cloud condensation nuclei activation

As a major source of fine particles, open biomass burning can affect climate and the hydrological cycle via the formation of cloud condensation nuclei (CCN) and their deposition. This study investigated the effect of aerosol size and chemical composition (water-soluble compounds, elemental carbon, and organic carbon) on CCN activation during the complete combustion of six commonly used crop (rice, wheat, corn, soybean, and cotton) and leaf residues in a simulation chamber developed for this study. Geometric mean diameters (GMD) of emitted primary particles ranged from 68 to 130 nm and water-soluble compound (WSC) content ranged from 33 to 50%. Although GMDs and WSCs possessed similar temporal tendencies during the combustion process, their average values were dependent on the type of biomass. Number concentration ratios of CCN and particle (CCN/CN) ranged from 1.4–2.1% and 5.8–8.3% at supersaturations of 0.2% and 1.0%, respectively. The CCN/CN value increased during the combustion process when the GMD and WSC content increased. Correlation coefficients for GMD and CCN activation ranged from 0.62 to 0.93, while correlations for WSC and CCN activation ranged from 0.33 to 0.95. Soybean biomass had the highest correlations for both GMD and WSC with CCN activation at various supersaturations. These results suggest that the size and chemical composition of biomass aerosols are important in CCN formation, while the aerosol size has a higher impact.

Vertical Characterization and Source Apportionment of Water-Soluble Organic Aerosol with High-resolution Aerosol Mass Spectrometry in Beijing, China

Water-soluble organic aerosol (WSOA) constitutes a large fraction of organic aerosol (OA) and plays an important role in affecting aerosol hygroscopicity and cloud condensation nuclei formation. Here, we characterized WSOA in fine particles that were collected at ground level and at 260 m on a meteorological tower in Beijing in winter using offline aerosol mass spectrometry (AMS) and compared them with the simultaneous real-time online AMS measurements. Our results showed large increases in WSOA from nonheating season to heating season by 43% and 53% at ground level and at 260 m, respectively. WSOA was highly oxidized in winter with a higher oxygen-to-carbon ratio (O/C = 0.69) at 260 m than at ground level (0.63). On average, WSOA contributed 47% and 52% to the total OA at ground level and at 260 m, respectively. Positive matrix factorization analysis further showed that primary OA was the dominant source of WSOA (52–61%) with coal combustion (CCOA) and biomass burning OA (BBOA) being two major contributo...

Microbiology and Ecology of Methylated Amine Metabolism in Marine Ecosystems.

Methylated amines (MAs) are ubiquitous in marine ecosystems, found from surface seawaters to sediment pore waters. These volatile ammonium analogs play important roles in biogeochemical cycles of carbon and nitrogen in the marine water column. They also contribute to the release of climate-active gases, being precursors of the potent greenhouse gas methane through methanogenesis in coastal sediments. Very recently, it also became acknowledged that MAs are important precursors for new particle growth, hence forming cloud-condensation nuclei in the marine atmosphere. Microbial metabolism of MAs has been demonstrated in the marine ecosystems for both Archaea and Bacteria. In this chapter, we summarize the latest developments in analytical methods for quantifying MA concentrations in marine surface water and sediments. We discuss the metabolic pathways leading to the formation and degradation of MAs by marine microbes and the novel biochemistry and structural biology of the enzymes for MA transformation. Lastly, we highlight the need for future research toward a better understanding of the microbiology and ecology of oceanic MA cycles.

Climate Change Effects on Secondary Compounds of Forest Trees in the Northern Hemisphere.

Plant secondary compounds (PSCs), also called secondary metabolites, have high chemical and structural diversity and appear as non-volatile or volatile compounds. These compounds may have evolved to have specific physiological and ecological functions in the adaptation of plants to their growth environment. PSCs are produced by several metabolic pathways and many PSCs are specific for a few plant genera or families. In forest ecosystems, full-grown trees constitute the majority of plant biomass and are thus capable of producing significant amounts of PSCs. We summarize older literature and review recent progress in understanding the effects of abiotic and biotic factors on PSC production of forest trees and PSC behavior in forest ecosystems. The roles of different PSCs under stress and their important role in protecting plants against abiotic and biotic factors are also discussed. There was strong evidence that major climate change factors, CO2 and warming, have contradictory effects on the main PSC groups. CO2 increases phenolic compounds in foliage, but limits terpenoids in foliage and emissions. Warming decreases phenolic compounds in foliage but increases terpenoids in foliage and emissions. Other abiotic stresses have more variable effects. PSCs may help trees to adapt to a changing climate and to pressure from current and invasive pests and pathogens. Indirect adaptation comes via the effects of PSCs on soil chemistry and nutrient cycling, the formation of cloud condensation nuclei from tree volatiles and by CO2 sequestration into PSCs in the wood of living and dead forest trees.

Comprehensive analysis of particle growth rates from nucleation mode to cloud condensation nuclei in boreal forest

Abstract. Growth of aerosol particles to sizes at which they can act as cloud condensation nuclei (CCN) is a crucial factor in estimating the current and future impacts of aerosol–cloud–climate interactions. Growth rates (GRs) are typically determined for particles with diameters (dP) smaller than 40 nm immediately after a regional new particle formation (NPF) event. These growth rates are often taken as representatives for the particle growth to CCN sizes (dP &gt; 50–100 nm). In modelling frameworks, the concentration of the condensable vapours causing the growth is typically calculated with steady state assumptions, where the condensation sink (CS) is the only loss term for the vapours. Additionally, the growth to CCN sizes is represented with the condensation of extremely low-volatility vapours and gas–particle partitioning of semi-volatile vapours. Here, we use a novel automatic method to determine growth rates from below 10 nm to hundreds of nanometres from a 20-year-long particle size distribution (PSD) data set in boreal forest. With this method, we are able to detect growth rates also at times other than immediately after a NPF event. We show that the GR increases with an increasing oxidation rate of monoterpenes, which is closely coupled with the ambient temperature. Based on our analysis, the oxidation reactions of monoterpenes with ozone, hydroxyl radical and nitrate radical all are capable of producing vapours that contribute to the particle growth in the studied size ranges. We find that GR increases with particle diameter, resulting in up to 3-fold increases in GRs for particles with dP ∼ 100 nm in comparison to those with dP ∼ 10 nm. We use a single particle model to show that this increase in GR can be explained with aerosol-phase reactions, in which semi-volatile vapours form non-volatile dimers. Finally, our analysis reveals that the GR of particles with dP &lt; 100 nm is not limited by the condensation sink, even though the GR of larger particles is. Our findings suggest that in the boreal continental environment, the formation of CCN from NPF or sub-100 nm emissions is more effective than previously thought and that the formation of CCN is not as strongly self-limiting a process as the previous estimates have suggested.

Advancing global aerosol simulations with size-segregated anthropogenic particle number emissions

Abstract. Climate models are important tools that are used for generating climate change projections, in which aerosol–climate interactions are one of the main sources of uncertainties. In order to quantify aerosol–radiation and aerosol–cloud interactions, detailed input of anthropogenic aerosol number emissions is necessary. However, the anthropogenic aerosol number emissions are usually converted from the corresponding mass emissions in pre-compiled emission inventories through a very simplistic method depending uniquely on chemical composition, particle size and density, which are defined for a few, very wide main source sectors. In this work, the anthropogenic particle number emissions converted from the AeroCom mass in the ECHAM-HAM climate model were replaced with the recently formulated number emissions from the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model. In the GAINS model the emission number size distributions vary, for example, with respect to the fuel and technology. Special attention was paid to accumulation mode particles (particle diameter dp &gt; 100 nm) because of (i) their capability of acting as cloud condensation nuclei (CCN), thus forming cloud droplets and affecting Earth's radiation budget, and (ii) their dominant role in forming the coagulation sink and thus limiting the concentration of sub-100 nm particles. In addition, the estimates of anthropogenic CCN formation, and thus the forcing from aerosol–climate interactions, are expected to be affected. Analysis of global particle number concentrations and size distributions reveals that GAINS implementation increases CCN concentration compared with AeroCom, with regional enhancement factors reaching values as high as 10. A comparison between modeled and observed concentrations shows that the increase in number concentration for accumulation mode particles agrees well with measurements, but it leads to a consistent underestimation of both nucleation mode and Aitken mode (dp &lt; 100 nm) particle number concentrations. This suggests that revisions are needed in the new particle formation and growth schemes currently applied in global modeling frameworks.

Investigation of ultrahigh-performance liquid chromatography/travelling-wave ion mobility/time-of-flight mass spectrometry for fast profiling of fatty acids in the high Arctic sea surface microlayer.

Fatty acids are enriched in the ocean surface microlayer (SML) and have as a consequence been detected worldwide in sea spray aerosols. In searching for a relationship between the properties of the atmospheric aerosol and its ability to form cloud condensation nuclei and to promote cloud droplet formation over remote marine areas, the role of surface active fatty acids sourced from the SML is of interest to be investigated. Here we present a fast method for profiling of major fatty acids in SML samples collected in the high Arctic (89°N, 1°W) in the summer of 2001. Ultrahigh-performance liquid chromatography (UHPLC)/travelling-wave ion mobility spectrometry (TWIMS)/time-of-flight (TOF) mass spectrometry (MS) for profiling was evaluated and compared with UHPLC/TOFMS. Except for evaporation and centrifugation, no sample preparation was necessary prior to the analysis. TOFMS data on accurate mass, isotopic ratios and fragmentation patterns enabled identification of the fatty acids. The TWIMS dimension added to the selectivity by extensive reduction of the noise level and the entire UHPLC/TWIMS/TOFMS method provided a fast profiling of the acids, ranging from C8 to C24 . Hexadecanoic and octadecanoic acids were shown to yield the highest signals among the FAs detected in a high Arctic SML sample, followed by the unsaturated octadecenoic and octadecadienoic acids. The predominance of signal from even-numbered carbon chains indicates a mainly biogenic origin of the detected FAs. This study presents a fast alternative method for screening and profiling of FAs, which has the advantage of not requiring any complicated sample preparation, thus limiting the loss of analytes. Almost no manual handling, together with the very small sample volumes needed, is certainly beneficial for the determination of trace amounts and should open up the field of applications to also include atmospheric aerosol and fog.