Submicron Atmospheric Particles Research Articles

Seasonal charge distributions of submicron atmospheric particles in Yokohama, Japan

Charge distribution measurements are required to understand the spatiotemporal distribution of the number concentrations of submicron atmospheric particles that affect radiative forcing and particle deposition in human airways. The number concentrations of non-charged and charged particles within the 0.3–0.5 μm diameter (D) range were measured at Keio University in Yokohama, Japan, from June 2022 to January 2023 by combining a parallel-pate particle separator and optical particle counters to investigate critical parameters controlling the charging state of submicron atmospheric particles. The measurement uncertainties in the average charge number per particle (pave) and the standard deviation (1σ), derived from the charge distribution of the submicron particles, were within 15%. The monthly median values of 1σ increased in summer and decreased in winter and correlated with the water vapor amount and wind speed. The 1σ values in summer and winter, derived from the seasonally averaged charge distributions of particles, were close to those from the theoretically calculated charge distribution of particles within 0.387–0.5 μm D range and with D = 0.3 μm, respectively, suggesting that the observed particle charge distributions approached the stationary charge distribution for the effective D. In summer, the frequent transport of water molecules and ions from the Pacific Ocean causes efficient collisions between multiple ions and submicron particles with a larger effective D, which may expand the charge distribution of particles. The polarity ratio, the concentration of positively charged particles relative to that of negatively charged particles, was almost unity, indicating the well-balanced charge polarity of the submicron atmospheric particles. The polarity ratio and pave changed significantly during lightning events, indicating that the atmospheric particle charge balance broke. Our findings show that the charge distribution of submicron atmospheric particles can be partly controlled by meteorological parameters (e.g., absolute humidity) and the microphysical properties of the particles.

Novel Single-Particle Analytical Technique for Submicron Atmospheric Aerosols: Combined Use of Dark-Field Scattering and Surface-Enhanced Raman Spectroscopy.

Raman microspectrometry (RMS) is a useful single particle analysis method that can provide information on the mixing states, molecular species, and chemical functional groups of individual aerosol particles, which are difficult to determine by bulk analysis techniques. On the other hand, drawbacks, such as low Raman cross-section, spatial resolution (∼1 μm), and optical diffraction limit, make the analysis of atmospheric particles in the submicron size range difficult using conventional RMS. This study developed a new strategy to detect individual submicron-size atmospheric particles by combining dark-field (DF) microscopy and surface-enhanced Raman spectroscopy (SERS). The DF technique overcomes optical spatial diffraction limit by contrast enhancement, allowing the visualization of submicron particles. SERS facilitates spectroscopic characterization (obtaining information on molecular fingerprints and mixing states) of trace amounts of analyte by increasing the Raman scattering cross-section at the hot spot. SERS-active silver substrates sputter-coated on a Si wafer efficiently provided a clear background in the dark-field image and uniform hot spots over a large area, which were suitable for single-particle analysis. Various functional groups in individual particles and their heterogeneous mixing states were investigated, demonstrating the potential of this method to provide improved information on submicron atmospheric particles of femtogram-level masses. DF-SERS may elucidate the detailed physicochemical characteristics of individual submicron particles, providing new information on the formation mechanisms and fates of atmospheric particles.

Long-Term Characterization of Submicron Atmospheric Particles in an Urban Background Site in Southern Italy

Continuous measurements of particle number size distributions in the size range from 10 nm to 800 nm were performed from 2015 to 2019 at the ECO Environmental-Climate Observatory of Lecce (Global Atmosphere Watch Programme/Aerosol, Clouds and Trace Gases Research Infrastructure (GAW/ACTRIS) regional station). The main objectives of this work were to investigate the daily, weekly and seasonal trends of particle number concentrations and their dependence on meteorological parameters gathering information on potential sources. The highest total number concentrations were observed during autumn-winter with average values nearly twice as high as in summer. More than 52% of total particle number concentration consisted of Aitken mode (20 nm < particle diameter (Dp) < 100 nm) particles followed by accumulation (100 nm < Dp < 800 nm) and nucleation (10 nm < Dp < 20 nm) modes representing, respectively, 27% and 21% of particles. The total number concentration was usually significantly higher during workdays than during weekends/holidays in all years, showing a trend likely correlated with local traffic activities. The number concentration of each particle mode showed a characteristic daily variation that was different in cold and warm seasons. The highest concentrations of the Aitken and accumulation particle mode were observed in the morning and the late evening, during typical rush hour traffic times, highlighting that the two-particle size ranges are related, although there was significant variation in the number concentrations. The peak in the number concentrations of the nucleation mode observed in the midday of spring and summer can be attributed to the intensive formation of new particles from gaseous precursors. Based on Pearson coefficients between particle number concentrations and meteorological parameters, temperature, and wind speed had significant negative relationships with the Aitken and accumulation particle number concentrations, whereas relative humidity was positively correlated. No significant correlations were found for the nucleation particle number concentrations.

Flash Freeze Flow Tube to Vitrify Aerosol Particles at Fixed Relative Humidity Values.

Development of methods to measure the phase transitions and physical properties of submicron atmospheric aerosol particles is needed to better model these systems. In this paper, we present a method to flash freeze submicron particles to measure phase transitions as a function of relative humidity (RH). Particles are equilibrated at a fixed RH, vitrified in a temperature-controlled flow tube, and imaged with cryogenic transmission electron microscopy (cryo-TEM). We demonstrate the use of the technique for measuring the efflorescence relative humidity (ERH) of potassium sulfate and potassium chloride aerosol as well as the separation RH (SRH) for a multicomponent organic/inorganic system that undergoes liquid-liquid phase separation (LLPS). The location of phase transitions can shift between the micrometer and nanometer size regimes, and particles in a given population may have a range of RH over which a phase transition occurs. This technique addresses these requirements by allowing for characterization of the phase transitions for individual particles in a population on the submicron scale.

Speciation of arsenic: a case study of PM1 in Zabrze

The aim of the study was to determine ambient concentrations of soluble, inorganic form of As ((As(III) and As(V)) in submicron atmospheric particles (PM1) in one of the most polluted region of Europe (Upper Silesia, Poland). Quantitative analyses of soluble As, soluble As (III) and As (V) after chromatographic separation and total As in digested PM1 samples were performed on the Elan 6100 DRC-e ICP-MS spectrometer. Results of analysis of the 15 randomly selected daily samples of PM1 from summer to winter season were presented. We showed that As(V) is dominating soluble, inorganic form of As in ambient air of selected city in Upper Silesia (Zabrze). Ambient concentrations of As(III) and As(V) as well as their mass percentages in water-soluble and total As changed seasonally. In winter season, when emissions from coal combustion prevailed, ambient concentration of soluble As(V) was about three times higher than in summer and accounted for 55% of total As. Ambient mass of As(III) was about 3.7% of the total As mass. During summer, when the sources of As may be more differentiated (industry, traffic, secondary emission from some surfaces, e.g., soils, roads, farmlands and dumps), soluble As(V) accounted for 23% of total As while soluble As(III) 6.7%.

Highly size-resolved characterization of water-soluble inorganic ions in submicron atmospheric particles

Up to date, few attentions have been given to the special characterization of water-soluble inorganic ions (WSIs) in the submicron atmospheric particles. In this study, to implement a highly size-resolved characterization of WSIs in the submicron atmospheric particles, ten sets of size-segregated submicron atmospheric particles were collected in Hangzhou (China) from November to December 2015, with cut-off diameters of 0.060, 0.108, 0.170, 0.260, 0.400, 0.650, and 1.000 μm. The particulate WSIs, including Cl−, NO3−, SO42−, Na+, NH4+, K+, and Ca2+ were analyzed by ion chromatography, and their mode distributions and potential sources were assessed. It was found that the particulate WSIs constituted a substantial part (40.4~70.9%) in each fraction of submicron particles, of which the secondary inorganic ions (SO42−, NO3−, and NH4+) were the dominant species. The sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) were increased when the submicron particles became coarser, indicating the enhanced secondary formation processes of SO42− and NO3− in the coarser submicron particles, thus resulting in the higher fractional contribution of secondary inorganic aerosols in the coarser submicron atmospheric particles. The correlation coefficients between K+ and Cl−, NO3−, and SO42− were 0.9293 (P = 0.002), 0.9702 (P < 0.001), and 0.9723 (P < 0.001), suggesting their dominant contribution from the biomass burning. Furthermore, it was found that PM0.4–1 (aerodynamic diameter of 0.400–1.000 μm) was a substantial part (66.6%) of submicron atmospheric particles. Compared to PM0.4 (aerodynamic diameter ≤ 0.400 μm), the concentration of WSIs in PM0.4–1 was prominently higher, and the secondary formation processes of SO42− and NO3− in PM0.4–1 were significantly enhanced.

Characterization of PAHs in size-fractionated submicron atmospheric particles and their association with the intracellular oxidative stress

The submicron atmospheric particulate matters (PMs), consisting of 7 size-resolved fractions, were collected by two Dekati low pressure impactors from December 2015 to January 2016 in Hangzhou, China. The chemical analysis revealed the higher accumulation efficiency of polycyclic aromatic hydrocarbons (PAHs) in the finer submicron PMs, and 77.0% of particulate PAHs in PM1 were associated with PM0.4. Moreover, the BaP equivalent concentrations (BaPeq) were evaluated for size-fractionated submicron PMs, indicating that 77.2% of carcinogenicity of particulate PAHs in PM1 were associated with PM0.4. In the cytotoxic tests, a significant size-dependent decrease of glutathione (GSH) level was observed in the PMs-exposed human pulmonary epithelial cells (A549), demonstrating the greater intracellular oxidative stress induced by the finer submicron PMs. The results also suggested that 82.4% of PM1-induced oxidative stress were associated with PM0.4, and the intracellular oxidative stress was significantly correlated with the particulate PAHs. Therefore, besides PM10, PM2.5 and PM1, special attentions should be given to PM0.4 as well.

Broad spectrum analysis of polar and apolar organic compounds in submicron atmospheric particles

A method for the quantitative analysis of organic compounds on submicron particulate matter (PM1) collected on quartz filters was developed. The compounds analyzed encompassed C22–C35 alkanes, polycyclic aromatic hydrocarbons (PAHs), quinones, levoglucosan, cis-pinonic acid and short chain dicarboxylic acids such as malonic, succinic, glutaric, adipic, suberic, azelaic, malic and phthalic acids. The method included extraction with a pressure liquid extraction system, sample filtration though glass fibre filter, fractionation by high performance liquid chromatography and subsequent analysis by gas chromatography coupled to mass spectrometry. The study of the extraction efficiency of different solvent mixtures showed that DCM:MeOH 1:1 was the one providing the highest recoveries for all compounds. Extraction temperatures of 100°C provided better results than 60°C or 80°C. This method provided comparable extraction efficiency and qualitative and quantitative data to those involving Soxhlet extraction. Method recoveries for alkanes, most PAH, quinones and polar compounds calculated from spiked real samples were 52–72%, 78–101%, 50–62% and 76–104%, respectively, reproducibilities were 2–28%, 7–29%, 10–27% and 5–28%, respectively, limits of quantification were 0.01–0.1ng/m3, 0.01–0.27ng/m3, 0.04ng/m3 and 0.32–2.8ng/m3, respectively, which affords the quantification of a broad number of primary and secondary organic constituents of submicron aerosols.

Submicron particle characteristics of atmospheres in a long highway tunnel.

This study used a scanning mobility particle sizer (SMPS) to measure and categorize submicron atmospheric particles in the 14-737-nm size range for ambient and urban roadside air and for air in the Hsuehshan Tunnel (12.9 km), Taiwan. Principal component analysis, traffic flow, and particle size distributions were used to identify the emission characteristics of light-duty vehicles (LDV) with the SMPS data. In the Hsuehshan Tunnel, the particle size from the majority of emissions discharged by LDV is approximately 20-60 nm, and the maximum particle number can reach up to 2.5 × 10(5). In contrast, submicron particle size distribution for urban roadsides is mostly 14-200 nm, and the maximum particle number is approximately 4 × 10(4) with the particle number for most particle sizes being below 1,200. The submicron particle size distribution at the ambient air station was unimodal with a mode sizes at 30-50 nm with the maximum particle number of 3,000.

Hygroscopicity, CCN and volatility properties of submicron atmospheric aerosol in a boreal forest environment during the summer of 2010

Abstract. A Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) was applied to study the hygroscopicity and volatility properties of submicron atmospheric aerosol particles in a boreal forest environment in Hyytiälä, Finland during the summer of 2010. Aitken and accumulation mode internally mixed particles (50 nm, 75 nm and 110 nm in diameter) were investigated. Hygroscopicity was found to increase with particle size. The relative mass fraction of organics and SO42- is probably the major contributor to the fluctuation of the hygroscopicity for all particle sizes. The Cloud Condensation Nuclei Counter (CCNC)-derived hygroscopicity parameter κ was observed to be slightly higher than κ calculated from VH-TDMA data under sub-saturated conditions, potential reasons for this behavior are discussed shortly. Also, the size-resolved volatility properties of particles were investigated. Upon heating, more small particles evaporated compared to large particles. There was a significant amount of aerosol volume (non-volatile material) left, even at heating temperatures of 280 °C. Using size resolved volatility-hygroscopicity analysis, we concluded that there was always hygroscopic material remaining in the particles at different heating temperatures, even at 280 °C. This indicates that the observed non-volatile aerosol material did not consist solely of black carbon.

The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation

The activation of aerosol particles into cloud droplets in the Earth’s atmosphere is both a key process for the climate budget and a main source of uncertainty. Its investigation is facing major experimental challenges, as no technique can measure the main driving parameters, the Raoult’s term and surface tension, σ, for sub-micron atmospheric particles. In addition, the surfactant fraction of atmospheric aerosols could not be isolated until recently. Here we present the first dynamic investigation of the total surfactant fraction of atmospheric aerosols, evidencing adsorption barriers that limit their gradient (partitioning) in particles and should enhance their cloud-forming efficiency compared with current models. The results also show that the equilibration time of surfactants in sub-micron atmospheric particles should be beyond the detection of most on-line instruments. Such instrumental and theoretical shortcomings would be consistent with atmospheric and laboratory observations and could have limited the understanding of cloud activation until now.

Long-term volatility measurements of submicron atmospheric aerosol in Hyytiälä, Finland

Abstract. The volatility of submicron atmospheric aerosol particles was investigated at a boreal forest site in Hyytiälä, Finland from January 2008 to May 2010. These long-term observations allowed for studying the seasonal behavior of aerosol evaporation with a special focus on compounds that remained in the aerosol phase at 280 °C. The temperature-response of evaporation was also studied by heating the aerosol sample step-wise to six temperatures ranging from 80 °C to 280 °C. The mass fraction remaining after heating (MFR) was determined from the measured particle number size distributions before and after heating assuming a constant particle density (1.6 g cm−3). On average 19% of the total aerosol mass remained in the particulate phase at 280 °C. The particles evaporated less at low ambient temperatures during winter as compared with the warmer months. Black carbon (BC) fraction of aerosol mass correlated positively with the MFR at 280 °C, but could not explain it completely: most of the time a notable fraction of this non-volatile residual was something other than BC. Using additional information on ambient meteorological conditions and results from an Aerodyne aerosol mass spectrometer (AMS), the chemical composition of MFR at 280 °C and its seasonal behavior was further examined. Correlation analysis with ambient temperature and mass fractions of polycyclic aromatic hydrocarbons (PAHs) indicated that MFR at 280 °C is probably affected by anthropogenic emissions. On the other hand, results from the AMS analysis suggested that there may be very low-volatile organics, possibly organonitrates, in the non-volatile (at 280 °C) fraction of aerosol mass.

Images reveal that atmospheric particles can undergo liquid–liquid phase separations

A large fraction of submicron atmospheric aerosol particles contains both organic material and inorganic salts. As the relative humidity cycles in the atmosphere and the water content of the particles correspondingly changes, these mixed particles can undergo a range of phase transitions, possibly including liquid-liquid phase separation. If liquid-liquid phase separation occurs, the gas-particle partitioning of atmospheric semivolatile organic compounds, the scattering and absorption of solar radiation, and the reactive uptake of gas species on atmospheric particles may be affected, with important implications for climate predictions. The actual occurrence of liquid-liquid phase separation within individual atmospheric particles has been considered uncertain, in large part because of the absence of observations for real-world samples. Here, using optical and fluorescence microscopy, we present images that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions. These results reveal that atmospheric particles can undergo liquid-liquid phase separations. To explore the implications of these findings, we carried out simulations of the Atlanta urban environment and found that liquid-liquid phase separation can result in increased concentrations of gas-phase NO(3) and N(2)O(5) due to decreased particle uptake of N(2)O(5).

Arctic organic aerosol measurements show particles from mixed combustion in spring haze and from frost flowers in winter

Submicron atmospheric aerosol particles were collected between 1 March 2008 and 1 March 2009 at Barrow, Alaska, to characterize the organic mass (OM) in the Arctic aerosol. Organic functional group concentrations and trace metals were measured with FTIR on submicron particles collected on Teflon filters. The OM varied from 0.07 μg m−3 in summer to 0.43 μg m−3 in winter, and 0.35 μg m−3 in spring, showing a transition in OM composition between spring and winter. Most of the OM in spring could be attributed to anthropogenic sources, consisting primarily of alkane and carboxylic acid functional groups and correlated to elemental tracers of industrial pollution, biomass burning, and shipping emissions. PMF analysis associated OM with two factors, a Mixed Combustion factor (MCF) and an Ocean‐derived factor (ODF). Back trajectory analysis revealed that the highest fractions of the MCF were associated with air masses that had originated from northeastern Asia and the shipping lanes south of the Bering Straits. The ODF consisted of organic hydroxyl groups and correlated with organic and inorganic seawater components. The ODF accounted for more than 55% of OM in winter when the sampled air masses originated along the coastal and lake regions of the Northwest Territories of Canada. Frost flowers with organic‐salt coatings that arise by brine rejection during sea ice formation may account for this large source of carbohydrate‐like OM during the ice‐covered winter season. While the anthropogenic sources contributed more than 0.3 μg m−3 of the springtime haze OM, ocean‐derived particles provided comparable OM sources in winter.

Carbohydrate-like composition of submicron atmospheric particles and their production from ocean bubble bursting

Oceans cover over two-thirds of the Earth's surface, and the particles emitted to the atmosphere by waves breaking on sea surfaces provide an important contribution to the planetary albedo. During the International Chemistry Experiment in the Arctic LOwer Troposphere (ICEALOT) cruise on the R/V Knorr in March and April of 2008, organic mass accounted for 15-47% of the submicron particle mass in the air masses sampled over the North Atlantic and Arctic Oceans. A majority of this organic component (0.1-0.4 microm(-3)) consisted of organic hydroxyl (including polyol and other alcohol) groups characteristic of saccharides, similar to biogenic carbohydrates found in seawater. The large fraction of organic hydroxyl groups measured during ICEALOT in submicron atmospheric aerosol exceeded those measured in most previous campaigns but were similar to particles in marine air masses in the open ocean (Southeast Pacific Ocean) and coastal sites at northern Alaska (Barrow) and northeastern North America (Appledore Island and Chebogue Point). The ocean-derived organic hydroxyl mass concentration during ICEALOT correlated strongly to submicron Na concentration and wind speed. The observed submicron particle ratios of marine organic mass to Na were enriched by factors of approximately 10(2)-approximately 10(3) over reported sea surface organic to Na ratios, suggesting that the surface-controlled process of film bursting is influenced by the dissolved organic components present in the sea surface microlayer. Both marine organic components and Na increased with increasing number mean diameter of the accumulation mode, suggesting a possible link between organic components in the ocean surface and aerosol-cloud interactions.

Mass spectral characterization of submicron biogenic organic particles in the Amazon Basin

Submicron atmospheric particles in the Amazon Basin were characterized by a high‐resolution aerosol mass spectrometer during the wet season of 2008. Patterns in the mass spectra closely resembled those of secondary‐organic‐aerosol (SOA) particles formed in environmental chambers from biogenic precursor gases. In contrast, mass spectral indicators of primary biological aerosol particles (PBAPs) were insignificant, suggesting that PBAPs contributed negligibly to the submicron fraction of particles during the period of study. For 40% of the measurement periods, the mass spectra indicate that in‐Basin biogenic SOA production was the dominant source of the submicron mass fraction, contrasted to other periods (30%) during which out‐of‐Basin organic‐carbon sources were significant on top of the baseline in‐Basin processes. The in‐Basin periods had an average organic‐particle loading of 0.6 μg m−3 and an average elemental oxygen‐to‐carbon (O:C) ratio of 0.42, compared to 0.9 μg m−3 and 0.49, respectively, during periods of out‐of‐Basin influence. On the basis of the data, we conclude that most of the organic material composing submicron particles over the Basin derived from biogenic SOA production, a finding that is consistent with microscopy observations made in a concurrent study. This source was augmented during some periods by aged organic material delivered by long‐range transport.

Characterization of organic ambient aerosol during MIRAGE 2006 on three platforms

Abstract. Submicron atmospheric aerosol particles were collected during the Megacity Initiative: Local and Global Research Observation (MILAGRO) in March 2006 at three platforms located in the Mexico City urban area (at the Mexico City Atmospheric Monitoring System building – SIMAT), at about 60 km south-east of the metropolitan area (Altzomoni in the Cortes Pass), and on board the NCAR C130 aircraft. Organic functional group and elemental composition were measured by FTIR and XRF. The average organic mass (OM) concentration, calculated as the sum of organic functional group concentrations, was 9.9 μg m−3 at SIMAT, 6.6 μg m−3 at Altzomoni, and 5.7 μg m−3 on the C130. Aliphatic saturated C-C-H and carboxylic acid COOH groups dominated OM (more than 60%) at the ground sites. On the C130, a non-acid carbonyl C=O, carboxylic acid COOH, and amine NH2 groups were observed in concentrations above detection limit only outside the Mexico City basin. From the elemental composition of SIMAT samples, we estimated the upper bound of average contribution of biomass burning to the organic carbon (OC) as 33–39%. The average OM/OC ratio was 1.8 at SIMAT, 2.0 at Altzomoni, and 1.6–1.8 on the C130. On the aircraft, higher OM/OC ratios were measured outside of the Mexico City basin, north of the urban area, along the city outflow direction. The average carboxylic acid to aliphatic saturated ratio at SIMAT reflected a local increase of oxidized functional group concentration in aged particles.

Size dependence of in situ pH in submicron atmospheric particles in Hong Kong

Some studies have reported that small submicron atmospheric particles are more acidic than large submicron particles; other studies demonstrated a reversed trend. In this study, the size dependence of in situ pH in submicron particles in Hong Kong was investigated. The equivalent ratios of [NH 4 +] measured to [SO 4 2−] measured in submicron particles were found to be generally less than unity and size dependent, suggesting the possibility of incomplete gas–aerosol equilibrium. The Aerosol Inorganic Model-II (AIM-II) model using measured ionic compositions with the gas–aerosol partitioning disabled was used to estimate the in situ pH in different sized particles. The estimated in situ pH of different sized submicron atmospheric particles was between −2.5 and 1.5 and it generally decreases with increasing submicron particle size. At such low in situ pH, the estimated HSO 4 − equivalent concentrations were 3.2 times (on average) of those of H + in different sized particles. The trends of the size dependence of the [NH 4 +] measured to [SO 4 2−] measured ratio and pH under different regimes of relative humidity are discussed.

Interaction between SO 2 and submicron atmospheric particles

In the atmosphere, oxidation of sulfur dioxide (SO 2) to sulfate may occur in the gas phase, in cloud or fog droplets, or in the aerosol phase on the surface or inside aerosol particles. While aerosol phase reactions have been studied in the case of supermicron sea-salt and crustal particles, very few investigations regarding submicron particles are available. In this paper, the importance of aerosol phase sulfate production to the dynamics of submicron particle populations was examined. The investigation was based on model simulations and theoretical evaluations regarding potential SO 2 oxidation reactions. None of the relatively well-quantified aqueous phase reactions was rapid enough to make small nuclei grow to cloud condensation nuclei (CCN) size within the particle lifetime in the lower troposphere. This is consistent with the few observations showing that the smallest atmospheric particles are enriched in organics rather than sulfate. The amount of submicron particulate matter could be enhanced significantly by certain aerosol phase reactions, but this is likely to require a particle population having a pH close to 7. Aerosol phase reactions could partly explain the apparently too low SO 2-to-sulfate conversion rates predicted by several chemical transport models over polluted regions. In addition to the bulk aerosol phase, SO 2-to-sulfate conversion might involve physical adsorption of SO 2 or a compound reacting with it by the particle surface, or it could take place in a liquid surface layer that usually covers atmospheric particles. Reactions involving physical adsorption seem to have negligible influence on the dynamics of submicron atmospheric particle populations. Aerosol phase reactions worth future investigation are those occurring in particle surface layers and those occurring in cloud interstitial particles.

A study of the ability of pure secondary organic aerosol to act as cloud condensation nuclei

Submicron atmospheric particles that serve as cloud condensation nuclei (CCN) at low super-saturations are important for quantifying the effect of aerosols on cloud properties and global climate. In this study, we investigate experimentally the ability of model submicron aerosols consisting of pure organic species to become CCN at typical atmospheric supersaturations. The CCN activity of glutaric acid, adipic acid and dyoctylphthalate (DOP) aerosols was determined by producing a nearly monodisperse distribution of submicron particles and comparing total CCN concentrations to total number concentrations. The measurements were performed using a Tandem Differential Mobility Analyzer in combination with a cloud condensation nuclei counter at supersaturations of 0.30 and 1.0%. The uncertainty in the measurements was determined by using NaCl and (NH 4) 2SO 4 aerosols; the results indicated that activation diameters could be measured within an error of ± 16%. Adipic acid and glutaric acid aerosols served as CCN at both supersaturations and their behavior is in fair agreement with Köhler theory. On the other hand, DOP aerosol as large as 0.15 μm in diameter, did not become activated, even at supersaturations as high as 1.2%. These results indicate that the CCN activity of hygroscopic organic aerosols may be comparable to that of some inorganic aerosols.