Atmospheric Cloud Condensation Nuclei Research Articles

Modifications on the coastal atmospheric sulfur and cloud condensation nuclei along the Eastern China seas by shipping fuel transition

Marine fuel combustion from shipping releases SO2 and forms sulfate particles, which may alter low cloud characteristics. A series of strategies were implemented to control the sulfur content of ship fuel oil from 2018 to 2020, offering insights into the effects of the ship fuel oil transition on sulfur-related pollutants and the consequent cloud condensation nuclei (CCN) in the atmosphere. Compared to 2018 in the southeast China waters, shipping SO2 emission decreased by 78 % in 2020, resulting in a 76 % reduction in ship-related total sulfur concentration, and a decrease of 54 % in CCN number concentration under supersaturation 0.2 % (CCN0.2) contributed by shipping. The response of CCN0.2 to ship-related sulfate modification is more pronounced in relatively clean environments than polluted environments, highlighting the uneven changes in coastal CCN along the Eastern China Sea induced by the ship fuel policies. CCN can trigger the formation of cloud droplets, 2020 fuel regulation may have and will reduce the cooling radiative forcing effect with strong spatial heterogeneity. The study provides insights into the variations in coastal atmospheric sulfur-related pollutants and CCN in uneven response to changes in ship fuel oil, prompting the need for further comprehensive assessments of the climate effects resulting from potential shifts in ship fuel use in the future.

Role of gas–molecular cluster–aerosol dynamics in atmospheric new-particle formation

New-particle formation from vapors through molecular cluster formation is a central process affecting atmospheric aerosol and cloud condensation nuclei numbers, and a significant source of uncertainty in assessments of aerosol radiative forcing. While advances in experimental and computational methods provide improved assessments of particle formation rates from different species, the standard approach to implement these data in aerosol models rests on highly simplifying assumptions concerning gas–cluster–aerosol dynamics. To quantify the effects of the simplifications, we develop an open-source tool for explicitly simulating the dynamics of the complete particle size spectrum from vapor molecules and molecular clusters to larger aerosols for multi-compound new-particle formation. We demonstrate that the simplified treatment is a reasonable approximation for particle formation from weakly clustering chemical compounds, but results in overprediction of particle numbers and of the contribution of new-particle formation to cloud condensation nuclei for strongly clustering, low-concentration trace gases. The new explicit approach circumvents these issues, thus enabling robust model–measurement comparisons, improved assessment of the importance of different particle formation agents, and construction of optimal simplifications for large-scale models.

Atmospheric Sulfuric Acid Dimer Formation in a Polluted Environment.

New particle formation (NPF) contributes significantly to atmospheric particle number concentrations and cloud condensation nuclei (CCN). In sulfur-rich environments, field measurements have shown that sulfuric acid dimer formation is likely the critical step in NPF. We investigated the dimer formation process based upon the measured sulfuric acid monomer and dimer concentrations, along with previously reported amine concentrations in a sulfur-rich atmosphere (Atlanta, USA). The average sulfuric acid concentration was in the range of 1.7 × 107–1.4 × 108 cm−3 and the corresponding neutral dimer concentrations were 4.1 × 105–5.0 × 106 cm−3 and 2.6 × 105–2.7 × 106 cm−3 after sub-collision and collision ion-induced clustering (IIC) corrections, respectively. Two previously proposed acid–base mechanisms (namely AA and AB) were employed to respectively estimate the evaporation rates of the dimers and the acid–amine complexes. The results show evaporation rates of 0.1–1.3 s−1 for the dimers based on the simultaneously measured average concentrations of the total amines, much higher than those (1.2–13.1 s−1) for the acid–amine complexes. This indicates that the mechanism for dimer formation is likely AA through the formation of more volatile dimers in the initial step of the cluster formation.

Molecular characterization of carbonyl compounds in atmospheric fine particulate matters (PM2.5) in Beijing by derivatization with Girard's reagent T combined with positive-ion ESI Orbitrap MS

Carbonyl compounds in aerosols endanger human health, affect atmospheric light absorption and cloud condensation nuclei activity, and are important precursors of secondary organic aerosols, but their composition is poorly understood. In the present study, we developed a new analytical method to characterize carbonyl compounds in PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) by chemical derivatization with Girard's reagent T combined with positive-ion ESI high resolution-mass spectrometry (HR-MS). Girard's reagent T selectively labels carbonyl compounds, and HR-MS provides accurate elemental composition of derivatives. This method realized the comprehensive molecular characterization of carbonyl compounds in PM2.5. Thousands of carbonyl formulas (2330) were identified, including aliphatic carbonyls and a series of aromatic carbonyls. This method was further applied to the quantification of carbonyl compounds in PM2.5 samples collected in summer and winter from 2016 to 2017. In winter, carbonyl compounds had the highest contribution to organic matter (10%) and PM2.5 (4%), respectively, and the concentration of carbonyls showed obvious seasonal variation characteristics: 2.04 μg/m3 in winter and 0.35 μg/m3 in summer. The detailed characterization of the molecular composition of carbonyl compounds in PM2.5 provides basic data for further evaluating its impact on the climate effect of organic aerosols.

Improved prediction of dimethyl sulfide (DMS) distributions in the northeast subarctic Pacific using machine-learning algorithms

Abstract. Dimethyl sulfide (DMS) is a volatile biogenic gas with the potential to influence regional climate as a source of atmospheric aerosols and cloud condensation nuclei (CCN). The complexity of the oceanic DMS cycle presents a challenge in accurately predicting sea surface concentrations and sea–air fluxes of this gas. In this study, we applied machine-learning methods to model the distribution of DMS in the northeast subarctic Pacific (NESAP), a global DMS hot spot. Using nearly two decades of ship-based DMS observations, combined with satellite-derived oceanographic data, we constructed ensembles of 1000 machine-learning models using two techniques: random forest regression (RFR) and artificial neural networks (ANN). Our models dramatically improve upon existing statistical DMS models, capturing up to 62 % of observed DMS variability in the NESAP and demonstrating notable regional patterns that are associated with mesoscale oceanographic variability. In particular, our results indicate a strong coherence between DMS concentrations, sea surface nitrate (SSN) concentrations, photosynthetically active radiation (PAR), and sea surface height anomalies (SSHA), suggesting that NESAP DMS cycling is primarily influenced by heterogenous nutrient availability, light-dependent processes and physical mixing. Based on our model output, we derive summertime, sea–air flux estimates of 1.16 ± 1.22 Tg S in the NESAP. Our work demonstrates a new approach to capturing spatial and temporal patterns in DMS variability, which is likely applicable to other oceanic regions.

Further analysis of CCN data at a mid-Antarctica Peninsula field site

Observations of very low atmospheric cloud condensation nuclei occurred about 10% of the daytime sampling periods at Palmer Station during February 1994. These measurements were not only observed following typical nuclei reducing weather events or phenomena. We do advocate the need and worthiness for a more comprehensive study to assess the frequency of low nuclei concentrations. The comprehensive study would include concurrent CCN activity spectra, individual nuclei or aerosol morphology and corresponding chemical composition, meteorology, atmospheric chemistry, and radiation measurements made simultaneously at least at Palmer. The study will contribute to the understanding of such very low nuclei event occurrence, to a more quantified assessment of their climatic relevance for this region, and to the development of a more viable aerosol measurement system. A suggested functional definition for a viable aerosol measurement system is provided.

Hygroscopic property of inorganic salts in atmospheric aerosols measured with physisorption analyzer

Hygroscopicity is capable of significantly affecting atmospheric visibility, radiative forcing, and cloud condensation nuclei process. Herein, a physisorption analyzer was adopted to determine the hygroscopicity of inorganic salt particles in atmospheric aerosols (e.g., NaNO3, NaClO4, MgSO4, K3PO4, K2HPO4, and KH2PO4) at 298 K. By regulating the ambient relative humidity (RH), qualitative and quantitative information of the mentioned particles in humidifying and dehumidifying cycles was acquired. The deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) were measured, and supersaturation was observed and recorded during the dehumidification process. The water-to-salt molar ratios (WSR) of the mentioned inorganic salts depending on RH were determined, and the hygroscopic results of NaNO3 and NaClO4 particles were well consistent with the results achieved with other methods or by theoretical prediction. This study fitted WSR-to-RH equations suitable for NaNO3, NaClO4, MgSO4, K3PO4, and K2HPO4 particles. The adsorption heats for monolayer water molecules in the mentioned inorganic salt particles are calculated. The present study lays a solid foundation for gaining insights into the effects of RH on atmospheric aerosols.

Biogenic volatile organic compounds (BVOCs) reactivity related to new particle formation (NPF) over the Landes forest

Abstract Atmospheric particles play a major role in both air quality and climate change. Formation of secondary particles in the atmosphere has been observed over many different environments and is believed to provide up to half of the atmospheric cloud condensation nuclei (CCN) at a global scale. However, high uncertainties are still remaining in the description of mechanisms involved in new particle formation (NPF). Especially, more evidences of the implication of biogenic volatile organic compounds (BVOCs) in NPF from field studies are still needed. To investigate this question, two field campaigns have been set up during July 2014 and July 2015, in the French Landes forest (south west of France). Summer 2015 was characterized by a strong hydric stress, whereas summer 2014 was rainy. In 2015, frequent nocturnal NPF was observed, reaching a frequency of occurrence of ~55% of the nights, while only one event was observed in 2014. In July 2015, monoterpene mixing ratios (dominated by α- and β-pinene) were higher, mostly due to high ambient temperatures and drought. A focus was made on the 2015 field campaign, where NPF was mostly observed. The mean diurnal variation of the ratio between α- and β-pinene mixing ratios highlighted in-canopy reactivity of monoterpenes with ozone in the early night. This hypothesis was reinforced by the increasing gas phase levels of pinonaldehyde and nopinone, the main first-generation products arising from α- and β-pinene ozonolysis, at night, before NPF started. It strongly suggests that monoterpene oxidation further generated very-low volatility gases involved in NPF. This finding is also supported by the high concentrations of the SOA traditional biogenic tracers, e.g. pinic and pinonic acids, quantified in the particulate phase. The role of BVOCs in NPF is thus highlighted, as well as the importance of nighttime NPF.

Molecular identification of organic vapors driving atmospheric nanoparticle growth

Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50 nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.

Subpollen particles as atmospheric cloud condensation nuclei

Bioparticles represent a significant fraction of the total atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of micrometers (plant pollen, vegetation residues) and like other atmospheric aerosol particles, the degree of involvement of bioaerosols in atmospheric processes largely de- pends on their hygroscopic and cloud condensation nuclei properties. In this paper the ability of the pine, birch and rape subpollen particles to act as cloud condensation nuclei are considered. Submicron particles were obtained by aqueous extraction of biological material from pollen grains and subsequent solidification of the atomized liquid droplets. The parameters of cloud activation are determined in the size range of 20-270 nm in the range of water vapor supersaturations 0.1-1.1%. Based on experimental results, the hygroscopicity parameter, characterizing the effect of the chemical composition of the subparticles on their con- densation properties, is determined. The range of the hygroscopic parameter changes was 0.12-0.13. In general, the results of measurements showed that the condensation activity of the subpollen particles is comparable with the condensation activity of secondary organic aerosols and weakly depends on the type of the primary pollen.

Subpollen Particles as Atmospheric Cloud Condensation Nuclei

Bioparticles constitute a significant fraction of atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of micrometers (plant pollen and vegetation residues). Like other atmospheric aerosol particles, the degree of involvement of bioaerosols in atmospheric processes largely depends on their hygroscopic and condensation properties. This paper studies the ability of subpollen particles of pine, birch, and rape to serve as cloud condensation nuclei. Secondary particles are obtained by the aqueous extraction of biological material from pollen grains and the subsequent solidification of atomized liquid droplets. The parameters of cloud activation are determined in the size range of 20–270 nm and water-vapor supersaturations of 0.1–1.1%. Measurement data were used to determine the hygroscopicity parameter that characterizes the effect of the chemical composition of subparticles on their condensation properties. The hygroscopic parameter varies in the range from 0.12 to 0.13. In general, the results of measurements have shown that the condensation activity of subpollen particles is comparable with the condensation activity of secondary organic aerosols and depends weakly on the type of primary pollen.

Direct measurement of new particle formation based on tethered airship around the top of the planetary boundary layer in eastern China

New particle formation (NPF) is one main source of atmospheric aerosols and plays an important role in global climate by contributing up to two thirds of the atmospheric cloud condensation nuclei. Numerous studies on characteristics and mechanisms of near-surface NPF have been conducted in last decades. However, the characteristics of NPF around the top of the planetary boundary layer (PBL) remains unclear due to the limitations of vertical measurements. In this study, a tethered airship onboard with advanced particle instruments was deployed for directly measurement of the NPF exactly above and under the top of the PBL in the Yangtze River Delta (YRD) of eastern China in December 2017. Coupled with the real time ground Lidar observation, we successfully conducted measurement of aerosol size distribution, chemical components of aerosol and gas pollutants with 100 m above/under the top of the PBL. Despite not being observed within the PBL during the flight and at three ground sites in YRD, NPF event with the growth rate of 3.8 nm/h was detected above the PBL. High oxidizing capacity, enough condensable vapors and low condensation sink above the PBL favor the onset of NPF. Model simulation and the aerosol chemical composition result indicate the important role of gaseous sulfuric acid in NPF and its subsequent growth in the upper atmosphere. Our study highlights the potential mechanism of NPF above the PBL and the need of direct vertical measurements to better understand NPF in the atmosphere and its climate effect.

Anthropogenic pollution elevates the peak height of new particle formation from planetary boundary layer to lower free troposphere

AbstractNew particle formation (NPF) and subsequent growth are primary sources of atmospheric aerosol particles and cloud condensation nuclei. Previous studies have been conducted in relatively clean environments; investigation of NPF events over highly polluted megacities is still lacking. Here we show, based on a recent yearlong aircraft campaign conducted over Beijing, China, from April 2011 to June 2012, that NPF occurrence peaks in the lower free troposphere (LT), instead of planetary boundary layer (PBL), as most previous studies have found and that the distance of NPF peak to PBL top increases with increasing aerosol loading. Further analysis reveals that increased aerosols suppress NPF in PBL, but enhance NPF in LT due to a complex chain of aerosol‐radiation‐photochemistry interactions that affect both NPF sources and sinks. These findings shed new light on our understanding of NPF occurrence, NPF vertical distribution, and thus their effects on atmospheric photochemistry, clouds, and climate.

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 1: Aerosol size distribution, hygroscopicity, and new model parametrizations for CCN prediction

Abstract. Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation (S = 0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172 nm at S = 0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit = 0.14 ± 0.03), higher values for the accumulation mode (κAcc = 0.22 ± 0.05), and an overall mean value of κmean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.

Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications

Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.

Pollen as atmospheric cloud condensation nuclei

AbstractAnemophilous (wind‐dispersed) pollen grains are emitted in large quantities by vegetation in the midlatitudes for reproduction. Pollen grains are coarse particles (5–150 µm) that can rupture when wet to form submicron subpollen particles (SPP) that may have a climatic role. Laboratory CCN experiments of six fresh pollen samples show that SPP activate as CCN at a range of sizes, requiring supersaturations from 0.81 (± 0.07)% for 50 nm particles, 0.26 (± 0.03)% for 100 nm particles, and 0.12 (± 0.00)% for 200 nm particles. Compositional analyses indicate that SPP contain carbohydrates and proteins. The SPP contribution to global CCN is uncertain but could be important depending on pollen concentrations outside the surface layer and the number of SPP generated from a single pollen grain. The production of hygroscopic SPP from pollen represents a novel, biologically driven cloud formation pathway that may influence cloud optical properties and lifetimes, thereby influencing climate.

Aircraft measurements of the vertical distribution and activation property of aerosol particles over the Loess Plateau in China

For the first time, comprehensive aircraft measurements of atmospheric aerosols and cloud condensation nuclei (CCN) were made over the Loess Plateau in Shanxi, China. Data from six flights in July and August 2013 were analyzed. Fine aerosols were predominant over the region. On the one hazy day, the fraction of fine particles in the total aerosol load was the greatest. Aerosol number concentration decreased exponentially with altitude. Inversion layers caused low-level aerosol accumulation zones. The mean aerosol particle size increased with altitude, and the larger particles were mainly found above 2km. Aerosol number size distributions at different height ranges showed two or three peaks. The aerosol number size distribution from 0.01μm to 20μm can be fitted with three log-normal distribution functions. The number concentration of CCN (NCCN) decreased with altitude. NCCN was linearly related to the CN concentration (NCN). The fraction of CCN to CN (fCCN/CN) at 0.3% SS was half of that at 0.4% SS. The fCCN/CN on the hazy day was lower than on the clear days. Vertical profiles of fCCN/CN and the effective diameter (ED) were similar, although the fCCN/CN increased with altitude.

Semi-empirical parameterization of size-dependent atmospheric nanoparticle growth in continental environments

Abstract. The capability to accurately yet efficiently represent atmospheric nanoparticle growth by biogenic and anthropogenic secondary organics is a challenge for current atmospheric large-scale models. It is, however, crucial to predict nanoparticle growth accurately in order to reliably estimate the atmospheric cloud condensation nuclei (CCN) concentrations. In this work we introduce a simple semi-empirical parameterization for sub-20 nm particle growth that distributes secondary organics to the nanoparticles according to their size and is therefore able to reproduce particle growth observed in the atmosphere. The parameterization includes particle growth by sulfuric acid, secondary organics from monoterpene oxidation (SORGMT) and an additional condensable vapor of non-monoterpene organics ("background"). The performance of the proposed parameterization was investigated using ambient data on particle growth rates in three diameter ranges (1.5–3 nm, 3–7 nm and 7–20 nm). The growth rate data were acquired from particle/air ion number size distribution measurements at six continental sites over Europe. The longest time series of 7 yr (2003–2009) was obtained from a boreal forest site in Hyytiälä, Finland, while about one year of data (2008–2009) was used for the other stations. The extensive ambient measurements made it possible to test how well the parameterization captures the seasonal cycle observed in sub-20 nm particle growth and to determine the weighing factors for distributing the SORGMT for different sized particles as well as the background mass flux (concentration). Besides the monoterpene oxidation products, background organics with a concentration comparable to SORGMT, around 6 × 107 cm−3 (consistent with an additional global SOA yield of 100 Tg yr−1) was needed to reproduce the observed nanoparticle growth. Simulations with global models suggest that the "background" could be linked to secondary biogenic organics that are formed in the presence of anthropogenic pollution.

Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results

Abstract. This paper synthesizes the available scientific information connecting atmospheric nucleation with subsequent cloud condensation nuclei (CCN) formation. We review both observations and model studies related to this topic, and discuss the potential climatic implications. We conclude that CCN production associated with atmospheric nucleation is both frequent and widespread phenomenon in many types of continental boundary layers, and probably also over a large fraction of the free troposphere. The contribution of nucleation to the global CCN budget spans a relatively large uncertainty range, which, together with our poor understanding of aerosol-cloud interactions, results in major uncertainties in the radiative forcing by atmospheric aerosols. In order to better quantify the role of atmospheric nucleation in CCN formation and Earth System behavior, more information is needed on (i) the factors controlling atmospheric CCN production and (ii) the properties of both primary and secondary CCN and their interconnections. In future investigations, more emphasis should be put on combining field measurements with regional and large-scale model studies.

On the characterization of nanoparticles emitted from combustion sources related to understanding their effects on health and climate

This work describes the use of well-controlled laboratory flames to produce aerosols of organic carbon (OC) as model particles representative of the OC fraction of combustion-generated particulate matter emissions in fresh exhausts. Water–particle interactions are explored in two specific cases. In the first case, particles are exposed to saturated environments and come into direct contact with liquid water by bubbling flame samples through a column of water. This case is representative of particle–liquid interactions relevant to wet removal routes by particle interception by rain or fog droplets or in biological systems covered with biological fluids composed mostly of water. In the second case, the particles are exposed to sub-saturated vapors with H2O concentrations representative of cloud-forming atmospheres. The particles’ capacity to serve as atmospheric cloud condensation nuclei (CCN) by rapid growth to droplets was measured and compared to NaCl particles, which are highly soluble particles with well known activation diameters. The results show measureable interactions with water in highly saturated conditions. However, in sub-saturated environments, no growth by water condensation was observed, and fresh emissions of OC nanoparticles are not likely to act as CCN in atmospherically relevant humidity.