Production Of Condensation Nuclei Research Articles

Rapid cloud removal of dimethyl sulfide oxidation products limits SO2 and cloud condensation nuclei production in the marine atmosphere

Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The oxidation of DMS leads to the formation and growth of cloud condensation nuclei (CCN) with consequent effects on Earth's radiation balance and climate. The quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of existing aerosol particles and clouds. In the unpolluted marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory toward sulfur dioxide (SO2) and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that the irreversible loss of HPMTF to clouds in the marine boundary layer determines the HPMTF lifetime (τHPMTF < 2 h) and terminates DMS oxidation to SO2 When accounting for HPMTF cloud loss in a global chemical transport model, we show that SO2 production from DMS is reduced by 35% globally and near-surface (0 to 3 km) SO2 concentrations over the ocean are lowered by 24%. This large, previously unconsidered loss process for volatile sulfur accelerates the timescale for the conversion of DMS to sulfate while limiting new particle formation in the marine atmosphere and changing the dynamics of aerosol growth. This loss process potentially reduces the spatial scale over which DMS emissions contribute to aerosol production and growth and weakens the link between DMS emission and marine CCN production with subsequent implications for cloud formation, radiative forcing, and climate.

Linking Meteorology, Turbulence, and Air Chemistry in the Amazon Rain Forest

Abstract We describe the salient features of a field study whose goals are to quantify the vertical distribution of plant-emitted hydrocarbons and their contribution to aerosol and cloud condensation nuclei production above a central Amazonian rain forest. Using observing systems deployed on a 50-m meteorological tower, complemented with tethered balloon deployments, the vertical distribution of hydrocarbons and aerosols was determined under different boundary layer thermodynamic states. The rain forest emits sufficient reactive hydrocarbons, such as isoprene and monoterpenes, to provide precursors of secondary organic aerosols and cloud condensation nuclei. Mesoscale convective systems transport ozone from the middle troposphere, enriching the atmospheric boundary layer as well as the forest canopy and surface layer. Through multiple chemical transformations, the ozone-enriched atmospheric surface layer can oxidize rain forest–emitted hydrocarbons. One conclusion derived from the field studies is that the rain forest produces the necessary chemical species and in sufficient amounts to undergo oxidation and generate aerosols that subsequently activate into cloud condensation nuclei.

Submicron aerosols at thirteen diversified sites in China: size distribution, new particle formation and corresponding contribution to cloud condensation nuclei production

Abstract. Understanding the particle number size distributions in diversified atmospheric environments is important in order to design mitigation strategies related to submicron particles and their effects on regional air quality, haze and human health. In this study, we conducted 15 different field measurement campaigns between 2007 and 2011 at 13 individual sites in China, including five urban sites, four regional sites, three coastal/background sites and one ship cruise measurement along eastern coastline of China. Size resolved particles were measured in the 15–600 nm size range. The median particle number concentrations (PNCs) were found to vary in the range of 1.1−2.2 × 104 cm−3 at urban sites, 0.8−1.5 × 104 cm−3 at regional sites, 0.4−0.6 × 104 cm−3 at coastal/background sites, and 0.5 × 104 cm−3 during cruise measurement. Peak diameters at each of these sites varied greatly from 24 to 115 nm. Particles in the 15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm (accumulation mode) range showed different characteristics at each sites, indicating the features of primary emissions and secondary formation in these diversified atmospheric environments. Diurnal variations show a build-up of accumulation mode particles belt at regional sites, suggesting the contribution of regional secondary aerosol pollution. Frequencies of new particle formation (NPF) events were much higher at urban and regional sites than at coastal sites and during cruise measurement. The average growth rates (GRs) of nucleation mode particles were 8.0–10.9 nm h−1 at urban sites, 7.4–13.6 nm h−1 at regional sites and 2.8–7.5 nm h−1 at coastal sites and during cruise measurement. The high gaseous precursors and strong oxidation at urban and regional sites not only favored the formation of particles, but also accelerated the growth rate of the nucleation mode particles. No significant difference in condensation sink (CS) during NPF days were observed among different site types, suggesting that the NPF events in background areas were more influenced by the pollutant transport. In addition, average contributions of NPF events to potential cloud condensation nuclei (CCN) at 0.2% super-saturation in the afternoon of all sampling days were calculated as 11% and 6% at urban sites and regional sites, respectively. On the other hand, NPF events at coastal sites and during cruise measurement had little impact on potential production of CCN. This study provides a large data set of particle size distribution in diversified atmosphere of China, improving our general understanding of emission, secondary formation, new particle formation and corresponding CCN activity of submicron aerosols in Chinese environments.

Bimodal distribution of sulfuric acid aerosols in the upper haze of Venus

Observations by the SPICAV/SOIR instruments aboard Venus Express have revealed that the upper haze (UH) of Venus, between 70 and 90km, is variable on the order of days and that it is populated by two particle modes. We use a one-dimensional microphysics and vertical transport model based on the Community Aerosol and Radiation Model for Atmospheres to evaluate whether interaction of upwelled cloud particles and sulfuric acid particles nucleated in situ on meteoric dust are able to generate the two observed modes, and whether their observed variability are due in part to the action of vertical transient winds at the cloud tops. Nucleation of photochemically produced sulfuric acid onto polysulfur condensation nuclei generates mode 1 cloud droplets, which then diffuse upwards into the UH. Droplets generated in the UH from nucleation of sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles and therefore cannot reproduce the observed bimodal size distribution. By comparison, the mass transport enabled by transient winds at the cloud tops, possibly caused by sustained subsolar cloud top convection, are able to generate a bimodal size distribution in a time scale consistent with Venus Express observations. Below the altitude where the cloud particles are generated, sedimentation and vigorous convection causes the formation of large mode 2 and mode 3 particles in the middle and lower clouds. Evaporation of the particles below the clouds causes a local sulfuric acid vapor maximum that results in upwelling of sulfuric acid back into the clouds. In the case where the polysulfur condensation nuclei are small and their production rate is high, coagulation of small droplets onto larger droplets in the middle cloud may set up an oscillation in the size modes of the particles such that precipitation of sulfuric acid “rain” may be possible immediately below the clouds once every few Earth months. Reduction of the polysulfur condensation nuclei production rate destroys this oscillation and reduces the mode 1 particle abundance in the middle cloud by two orders of magnitude. However, it better reproduces the sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets as constrained by fits to UV reflectivity data. In general we find satisfactory agreement between our nominal and transient wind results and observations from Pioneer Venus, Venus Express, and Magellan, though improvements could be made by incorporating sulfur microphysics.

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.

Determination of cloud condensation nuclei production from measured new particle formation events

A semi‐analytical expression has been developed that accurately models the population dynamics of an aerosol growing from the detection limit (3 nm) to a characteristic CCN size (100 nm), quantifying the contributions of size and time‐dependent source and sink terms such as coagulation of smaller particles and scavenging by the pre‐existing aerosol. These model inputs were calculated from measured aerosol size distributions and growth rates acquired during intensive measurement campaigns in Boulder, CO, Atlanta, GA, and Tecamac, Mexico. Twenty CCN formation events from these campaigns were used to test the validity of this model. Measured growth rates ranged from 3–22 nm/h. The modeled and measured CCN production probabilities agreed well with each other, ranging from 1–20%. The pre‐existing CCN number concentration increased on average by a factor of 3.8 as a result of new particle formation.

Ion balances of size-resolved tropospheric aerosol samples: implications for the acidity and atmospheric processing of aerosols

A large set of size-resolved aerosol samples was inspected with regard to their ion balance to shed light on how the aerosol acidity changes with particle size in the lower troposphere and what implications this might have for the atmospheric processing of aerosols. Quite different behaviour between the remote and more polluted environments could be observed. At the remote sites, practically the whole accumulation mode had cation-to-anion ratios clearly below unity, indicating that these particles were quite acidic. The supermicron size range was considerably less acidic and may in some cases have been close to neutral or even alkaline. An interesting feature common to the remote sites was a clear jump in the cation-to-anion ratio when going from the accumulation to the Aitken mode. The most likely reason for this was cloud processing which, via in-cloud sulphate production, makes the smallest accumulation-mode particles more acidic than the non-activated Aitken-mode particles. A direct consequence of the less acidic nature of the Aitken mode is that it can take up semi-volatile, water-soluble gases much easier than the accumulation mode. This feature may have significant implications for atmospheric cloud condensation nuclei production in remote environments. In rural and urban locations, the cation-to-anion ratio was close to unity over most of the accumulation mode, but increased significantly when going to either larger or smaller particle sizes. The high cation-to-anion ratios in the supermicron size range were ascribed to carbonate associated with mineral dust. The ubiquitous presence of carbonate in these particles indicates that they were neutral or alkaline, making them good sites for heterogeneous reactions involving acidic trace gases. The high cation-to-anion ratios in the Aitken mode suggest that these particles contained some water-soluble anions not detected by our chemical analysis. This is worth keeping in mind when investigating the hygroscopic properties or potential health effects of ultrafine particles in polluted environments.

Relative roles of secondary sulfate and organics in atmospheric cloud condensation nuclei production

Atmospheric production of cloud condensation nuclei (CCN) becomes increasingly important when going to rural or more remote locations. A preliminary investigation on the relative roles of two of the most important compound classes contributing to atmospheric CCN production, sulfate and secondary organic matter, was performed. The investigation was made using a Lagrangian air parcel model that simulates the time evolution of a particle population within a marine or a continental boundary layer. Model simulations demonstrated that for a system containing small (&lt;40–50 nm diameter) primary or secondary particles, production of new CCN can be thought of as a two‐step process: (1) condensational growth of very small particles to a so‐called “potential activation zone,” in which these particles can be activated to cloud droplets at high supersaturations associated with strong updrafts, and (2) growth of particles from the “potential activation zone” to sizes where they form droplets at more typical cloud supersaturations. Since the exact location and width of the “potential activation zone” depend on both cloud physics and the chemical properties of the smallest particles able to act as CCN, the border between these two steps is not very sharp under real atmospheric conditions. According to the simulations, the first step of the above steps relies heavily on the presence of nonvolatile organic vapors, with their required gas phase source rate being of the order 0.1–0.5 μg m−3 d−1 or greater. Sulfuric acid formed in the gas phase can give significant contribution under very specific conditions only. While condensational growth associated with secondary organics may also be involved in the second step, in‐cloud sulfate production associated with strong updrafts appears to be the most effective way to move particles from the “potential activation zone” to larger sizes. In general, the second step was shown to depend on the amount of hygroscopic material transported to particles in the “potential activation zone,” on the variability of the cloud supersaturation between successive cloud events and on the amount of SO2 available for in‐cloud oxidation.

Secondary organics and atmospheric cloud condensation nuclei production

The influence of secondary organics on atmospheric cloud condensation nuclei (CCN) production was investigated using a zero‐dimensional box model that simulates the production of secondary organics in the gas phase, the transportation of these organics from gas to the particulate phase, and the resulting growth of the particles. Model simulations demonstrated that the growth of nanometer‐size nuclei to a CCN size requires the presence of organics of extremely low volatility. These “nonvolatile” organics need to have saturation vapors pressures of the order of 0.01–0.1 parts per trillion or lower and, in order to induce sufficient nuclei growth, must have gas phase production rates of the order of 0.3–1 μg m−3 d−1 under conditions typical for continental background areas. As the nuclei grow in size, they start to uptake volatile organics more efficiently. As a result, organic matter in both the nuclei grown into a CCN size and in the preexisting accumulation mode particles is expected to be dominated by “low‐volatile” organics rather than organics that actually are responsible for the nuclei growth. The modeling results suggest that the monoterpene oxidation products identified so far in field or laboratory experiments, although important contributors to secondary particulate matter, are unlikely to be the ones that grow nuclei to a CCN size. In field experiments, positive identification of organics producing new CCN would require information on the chemical composition of particles smaller than about 0.1 μm in diameter, which is the size range where nonvolatile organics are likely to be enriched compared with other secondary or primary organics. Since the gas phase production rate of nonvolatile organics needs not to be very large in order to induce significant nuclei growth, more attention should also be paid to reaction products that have minor yields in smog chamber experiments.

LOW-MOLECULAR-WEIGHT DICARBOXYLIC ACIDS IN AN URBAN AND RURAL ATMOSPHERE

Chemistry of oxalic, malonic, and succinic acid was studied at the two sites representing the urban and rural conditions, and at a site intermediate between these two. The investigation was based on the particle collection with a virtual impactor and a Berner low-pressure impactor. Concentrations of the three diacids displayed large seasonal amplitudes with low values in winter. Suggestive of common sources or atmospheric formation processes, the correlation between oxalic and malonic acid concentrations was high. Both the local traffic and secondary production in the long-range transported air masses seemed to be the important sources for these two acids. Contrary to oxalic and malonic acid, no enrichment at the urban site compared with the rural site was observed for succinic acid. The seasonal cycle of this acid resembled that of methanesulfonic acid. The most likely sources for succinic acid in our samples was the secondary production in the long-range transported air, with potentially significant contribution coming from biogenic sources. The three diacids had quite different distributions over the particulate phase. Oxalic acid had a dominant accumulation mode, a clear Aitken mode at sizes below about 0.15 μm of particle diameter, and modes corresponding to the sea-salt and crustal particle size ranges. Most of the malonic acid was associated with sea-salt particles, even though in a few samples an accumulation mode was also present. Succinic acid was distributed between the accumulation and the sea-salt particle modes, in addition to which it frequently had quite a pronounced Aitken mode. Oxalic and succinic acids are among the organics that may contribute to the atmospheric cloud condensation nuclei production. Oxalic and malonic acid, and to a smaller extent succinic acid, participate in reactions occurring in sea-salt particles.

Dimethylsulfide, aerosols, and condensation nuclei over the tropical northeastern Atlantic Ocean

Concentration of dimethylsuifide (DMS) in seawater, concentrations of DMS and sulfur dioxide (SO2) in the atmosphere, concentrations of methanesulfonate (MSA) and non‐sea‐salt sulfate (nss‐SO42−) in size‐segregated aerosols, and number concentration of condensation nuclei (CN) were measured during September and October 1991 in the northern tropical Atlantic Ocean in order to assess the role of DMS in CN production over this oceanic area. Radon‐222 activity and aerosol ionic composition were used to distinguish air masses with oceanic, continental, and/or polluted characters. No obvious covariation appeared between DMS and its oxidation products (SO2, H2SO4, and MSA) over the whole period of the experiment. However, the division of data into subsets according to continental tracer information allowed us to show that SO2 and nss‐SO4 concentrations correlated with DMS concentration in unpolluted air masses. MSA and nss‐SO42− were found to be mainly concentrated in particles with diameters &lt; of 0.6 μm. Daily mean nss‐SO42− in the &lt;0.6‐μm‐diameter range and CN concentration were correlated (R = 0.91, n = 17, P &lt; 0.001), which suggests that H2SO4 is an important CN precursor. Atmospheric DMS and CN number daily mean concentrations also correlated (R = 0.82, n = 21, P &lt; 0.001). However, the CN population was strongly influenced by continental inputs less than 500 km downwind of Africa, whereas DMS seemed to be able to affect the CN number concentration at about 1500 km from this continent.

Urban Cloud Condensation Nuclei Spectral Flux

The cloud condensation nuclei (CCN) spectral flux and the condensation nuclei (CN) flux from an urban area are determined from in situ aircraft measurements at Denver, Colorado. The concentration differences between upwind and downwind cross sections at several altitudes are used to estimate anthropogenic fluxes. The CCN and CN production rate estimates are consistently three times larger than a similar 1966 study by Squires, also at Denver. On a per capita basis, the present measurements are only a factor of 2 higher. This is probably within the seasonal and day-to-day variability and/or may be result of somewhat different measurement techniques. The instantaneous CCN spectra produced flux estimates over the range of critical supersaturation Sc of 0.04%–0.9%. Some of the estimated particle production rates for Denver are 1 × 1018 s−1 for CN, 1.7 × 1017 s−1 for CCN at 0.9% Sc, 1.16 × 1017 s−1 for CCN at 0.5% Sc, 3 × 1015 s−1 for CCN at 0.1% Sc, and 5 × 1014 s−1 for CCN at 0.04% Sc.

Production of condensation nuclei in clean air by nucleation of H 2SO 4

High concentrations (e.g. 10 4–10 5 cm −3) of condensation nuclei are occasionally observed in the polar regions or over the central oceans in air that has been free of passage over continental surfaces for many days. The particles are relatively fresh, being no more than a few days old, as otherwise interparticle coagulation would lower the concentration well below that observed. We show a plausible scheme through which the particles (assumed to be droplets of H 2SO 4) may be produced from the acid vapor phase through the process of homogeneous nucleation, and develop (approximate) analytic expressions to estimate the particle production. A large fraction of pre-existing aerosol, however, must first be scavenged, as they would otherwise serve as surfaces of condensation and inhibit the nucleation. We conclude that the production of substantial (> 10 3 cm −3) numbers of new particles can take place only in humid pre-cleaned air mass systems.

Marine condensation nucleus generation inferred from whitecap simulation tank results

The condensation nuclei (CN) produced during a set of experiments in the Whitecap Simultation Tank at University College, Galway, were measured with a TSI 3020 nucleus counter. The total number of CN produced per breaking wave event was 3.5 ± 0.5 × 107 for a seawater temperature near 15°C. The CN production per unit area of whitecap (108 m−2) and the previously observed whitecap time decay constant of ∼3.5 s implies a whitecap CN flux Fw of ∼2.8 + 0.9 × 107 m−2 s−1. This can be combined with the whitecap coverage W versus 10 m wind speed U relation of E. C. Monahan and I. O'Muircheartaigh (1980), W(U) = 3.84 × 10−6 U3.41, to estimate the general oceanic CN flux F0 = WFW. For U = 10 m s−1, this relation gives W = 1%, and thus F0 is ∼2.8 × 105 m−2 s−1. Using the same Whitecap Simulation Tank and a PMS classical aerosol spectrometer, E. C. Monahan et al. (1982) determined that the whitecap flux Fw of giant particles (radii &gt; 1 μm at relative humidity = 80%) was ∼2 × 106 m−2S−1. Clearly, most of the CN produced by this whitecap simulation are of submicron size, and this was also the case in the model breaking wave experiments of R. J. Cipriano et al. (1983). Both laboratory whitecap simulations suggest that the ocean contributes significantly to the CN and cloud condensation nuclei populations of the marine atmospheric boundary layer far from land.

Radiolytic condensation nuclei in aerosol neutralizers

Abstract Production of condensation nuclei in nuclei-free air in two commercially available aerosol neutralizers was tested. No nuclei formation was found for the neutralizer using a beta source at any of the flow rates used. The concentration of nuclei produced in the neutralizer using an alpha source varied with the airflow. Nuclei formation could be prevented by utilizing a high flow rate through the neutralizer or trace quantities of an efficient radical scavenger such as methanol.

Condensation nuclei production from sulfur dioxide photooxidation in air

The suggestion tht hydrated HSO/sub 3/ radicals can condense directly to produce sulfate particulates is examined. In particular the experiments of Leifer et al. are analyzed. It is concluded that the anomalously high rates of nucleation observed in these experiments is an artifact of the condensation nuclei counter method of detection-additional nuclei being produced in the counter itself. Other corroborating evidence in favor of the conventional condensation mechanism is presented. 1 figure.

ChemInform Abstract: NUCLEATION BY FREE RADICALS FROM THE PHOTOOXIDATION OF SULFUR DIOXIDE IN AIR

AbstractEine Neuanalyse von Literaturresultaten zum bedeutenden atmosphärischen Prozeß der Keimkondensation durch Photooxidation von SO2 zeigt, daß die Keimbildung nicht, wie bisher angenommen, durch Clusterbildung aus H2SO4‐ und H2O‐Molekülen erfolgt.

Nucleation by free radicals from the photooxidation of sulfur dioxide in air

Previously reported experimental results of the production of condensation nuclei by the photooxidation of SO/sub 2/ in air are reanalyzed on the basis that the principal photochemical reaction of SO/sub 2/ is SO/sub 2/ + OH + M ..-->.. HSO/sub 3/ + M. The ideas that gaseous H/sub 2/SO/sub 4/ is the end product of the reaction and that nuclei were formed from clusters of H/sub 2/SO/sub 4/ and H/sub 2/O molecules are shown to be probably incorrect on the basis of (1) comparison to nucleation rates expected from the theory of heteromolecular homogeneous nucleation and (2) calculations indicating that nucleation rates were kinetically controlled such that the nuclei formed contained only one or two sulfur-bearing entities. The nucleation phenomena are compatible with the idea that free radicals and the hydrated complex SO/sub 3/ . H/sub 2/O are nuclei precursors. We suggest a mechanism involving the formation and recombination of hydrated forms of HSO/sub 3/ and HSO/sub 5/ radicals to explain nucleation for conditions of relative humidity greater than about 5%. For lower relative humidities the reaction SO/sub 2/ + O + M ..-->.. SO/sub 3/ + M followed by the formation of a hydrated complex of SO/sub 3/ ismore » suggested as controlling nucleation. A model based on these mechanisms yields the results that nuclei consist of single molecules of H/sub 2/S/sub 2/O/sub 6/ or possibly H/sub 2/S/sub 2/O/sub 8/, plus their associated H/sub 2/O molecules, at high relative humidities (>5%) and that at low relative humidities the nuclei consist of single molecules of H/sub 2/SO/sub 4/, plus associated H/sub 2/O molecules. These mechanisms are used as a basis for suggesting a general explanation for the phenomenon of photoinduced nucleation. 50 references, 4 figures, 3 tables.« less

Formation of condensation nuclei by ions of given polarity and age

We have studied the production of condensation nuclei by ions of given polarity and age in mixtures of pure gas (O 2, N 2, Ar), H 2O (800 to 20,000 ppm) and SO 2 (1 ppm). When the ageing time of ions increases from 10 to 100 msec, and with constant concentration of water vapour, particle production goes through a maximum. If the ageing time is kept constant and the water concentration is varied, the same phenomenon is observed. When 100 ppm of NO is added to the mixture no further particles are produced so that it can be supposed that the reaction is due to the emission of free radicals. The mobility of ions is about 1.4 cm 2 V −1 sec −1. It can therefore be concluded that, in this case, we have H 2O-ion-impurity reactions with reaction times of about 50 msec.

Experiments on the formation of particles by chemical reactions in the dark and under influence of light.

Some experiments concerning the photochemical production of condensation nuclei are described. Preliminary measurements of filtered atomospheric air, initially free of particles yielded high concentrations of particles by reactions in the dark when the air was previously irradiated by sunlight. In further investigations a definite composition of pure gases was used. The formation of nitric acid particles from NO2 in pure nitrogen of different relative humidities in the dark and under influence of light was investigated. No particle formation was found which could be correlated to any production of nitric acid nuclei. Even within a spectral region in which photolysis of NO2 takes place no HNO3-nucleation could be found. The particles detected under certain conditions of irradiation originate from impurities in the walls of the reaction chamber. Particle growth in an irradiated mixture of N2 and NO2 with benzene is demonstrated and the mean radius of particles is calculated from measurement with a diffusion battery.