Growth Of Aerosol Particles Research Articles

Chemical deposition on aerosol particles

Problems on the growth of aerosol particles in chemical deposition with allowance for the influence of a buffer (impurity) gas have been investigated theoretically.

Hygroscopic properties of aerosol particles over the central Arctic Ocean during summer

The hygroscopic properties of submicrometer aerosol particles in the Arctic summer marine boundary layer (MBL) were observed on board the icebreaker Oden during the Arctic Ocean Expedition 1996 (AOE‐96). The measurements were performed between July 15 and August 25 1996 and covered the region between longitudes 16°‐147°E and latitudes 70°‐87.5°N, mostly over melting pack ice. The hygroscopic tandem differential mobility analyzer (H‐TDMA) was used to determine the hygroscopic diameter growth of aerosol particles at four dry diameters (15, 35, 50, and 165 nm) and three relative humidities (50%, 70%, and 90% RH). The hygroscopic behavior of the aerosol particles over the pack ice showed large temporal variations, in contrast to previous observations in marine boundary layers over warmer oceans. These variations were mostly due to the high degree of vertical atmospheric stratification often observed over the pack ice. However, when comparing the average diameter growth factors of the more hygroscopic particle group, representing an aged aerosol with growth factors between 1.4–1.9 at 90% RH and present in 81–86% of all cases, the agreement between the measurements over the Arctic and the warmer oceans was very good and depended on the average wind speed. The average diameter growth factors of the more hygroscopic particles as a function of relative humidity were modeled empirically by power law expressions. The concentration of cloud condensation nuclei (CCN) estimated from aerosol number size distribution and hygroscopic growth data correlated well with direct measurements but overpredicted the CCN concentrations by about 30%. In 43 cases when the sampled air mass had undergone processing in Arctic Ocean MBL clouds, the minimum CCN diameter was estimated to be 76±15 nm, corresponding to effective water vapor supersaturations of 0.28±0.08%.

NUCLEATION CONTROLLED FORMATION AND GROWTH OF AEROSOL PARTICLES

NUCLEATION CONTROLLED FORMATION AND GROWTH OF AEROSOL PARTICLES

Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR)

Aerosol formation and subsequent particle growth in ambient air have been frequently observed at a boreal forest site (SMEAR II station) in Southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest) has focused on: (a) determination of formation mechanisms of aerosol particles in the boreal forest site; (b) verification of emissions of secondary organic aerosols from the boreal forest site; and (c) quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. The approach of the project was to combine the continuous measurements with a number of intensive field studies. These field studies were organised in three periods, two of which were during the most intense particle production season and one during a non-event season. Although the exact formation route for 3 nm particles remains unclear, the results can be summarised as follows: Nucleation was always connected to Arctic or Polar air advecting over the site, giving conditions for a stable nocturnal boundary layer followed by a rapid formation and growth of a turbulent convective mixed layer closely followed by formation of new particles. The nucleation seems to occur in the mixed layer or entrainment zone. However two more prerequisites seem to be necessary. A certain threshold of high enough sulphuric acid and ammonia concentrations is probably needed as the number of newly formed particles was correlated with the product of the sulphuric acid production and the ammonia concentrations. No such correlation was found with the oxidation products of terpenes. The condensation sink, i.e., effective particle area, is probably of importance as no nucleation was observed at high values of the condensation sink. From measurement of the hygroscopic properties of the nucleation particles it was found that inorganic compounds and hygroscopic organic compounds contributed both to the particle growth during daytime while at night time organic compounds dominated. Emissions rates for several gaseous compounds was determined. Using four independent ways to estimate the amount of the condensable vapour needed for observed growth of aerosol particles we get an estimate of 2–10×107 vapour molecules cm−3. The estimations for source rate give 7.5–11×104 cm−3 s−1. These results lead to the following conclusions: The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia). After nucleation, growth into observable sizes (~3 nm) is required before new particles appear. The major part of this growth is probably due to condensation of organic vapours. However, there is lack of direct proof of this phenomenon because the composition of 1–5 nm size particles is extremely difficult to determine using the present state-of-art instrumentation.

Nonsingular self-preserving regimes of coagulation-condensation process.

Growth of disperse particles is considered assuming that the preexisting disperse particles coagulate and grow simultaneously by condensing a low volatile substance (vapor, in what follows) whose concentration is permanently refreshed by a spatially uniform and constant in time source. The kinetics of the condensation-coagulation process is studied under the assumption that the condensation rate and coagulation kernels are homogeneous functions of the particle masses. The power exponents characterizing these functions define the asymptotic self-preserving regimes of the particle growth. Four such regimes are detected: (i) the mass of the disperse phase consumes all vapor and grows linearly with time, while the vapor concentration grows (or even drops) with time as its power s<1; (ii) the mass of the disperse phase grows slower than a linear function of time, while the vapor concentration grows asymptotically as time; (iii) the mass of disperse phase remains finite; and (iv) both, the mass of disperse phase and the vapor concentration grow linearly with time. For all above regimes the equations are derived defining the shape of the asymptotic mass distribution. The latter is shown to depend on a combination of the particle mass and time. The theory is illustrated by two exactly soluble models, and numerical results for the condensation-coagulation growth of aerosol particles in free molecular regime.

Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols.

Aerosols affect the Earth's temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon--soot--that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed) or incorporated within them (internally mixed), or a black-carbon core could be surrounded by a well mixed shell. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2 in terms of direct forcing.

Influence of surface phenomena on the growth of aerosol particles in a buffer (admixture) gas

The influence of a buffer (admixture) gas on the deposition of molecules of a vapor on particles of an aerosol system is investigated.

Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR)

Aerosol formation and subsequent particle growth in ambient air have been frequently observed at a boreal forest site (SMEAR II station) in Southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest) has focused on: (a) determination of formation mechanisms of aerosol particles in the boreal forest site; (b) verification of emissions of secondary organic aerosols from the boreal forest site; and (c) quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. The approach of the project was to combine the continuous measurements with a number of intensive field studies. These field studies were organised in three periods, two of which were during the most intense particle production season and one during a non-event season. Although the exact formation route for 3 nm particles remains unclear, the results can be summarised as follows: Nucleation was always connected to Arctic or Polar air advecting over the site, giving conditions for a stable nocturnal boundary layer followed by a rapid formation and growth of a turbulent convective mixed layer closely followed by formation of new particles. The nucleation seems to occur in the mixed layer or entrainment zone. However two more prerequisites seem to be necessary. A certain threshold of high enough sulphuric acid and ammonia concentrations is probably needed as the number of newly formed particles was correlated with the product of the sulphuric acid production and the ammonia concentrations. No such correlation was found with the oxidation products of terpenes. The condensation sink, i.e., effective particle area, is probably of importance as no nucleation was observed at high values of the condensation sink. From measurement of the hygroscopic properties of the nucleation particles it was found that inorganic compounds and hygroscopic organic compounds contributed both to the particle growth during daytime while at night time organic compounds dominated. Emissions rates for several gaseous compounds was determined. Using four independent ways to estimate the amount of the condensable vapour needed for observed growth of aerosol particles we get an estimate of 2–10×107 vapour molecules cm−3. The estimations for source rate give 7.5–11×104 cm−3 s−1. These results lead to the following conclusions: The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia). After nucleation, growth into observable sizes (~3 nm) is required before new particles appear. The major part of this growth is probably due to condensation of organic vapours. However, there is lack of direct proof of this phenomenon because the composition of 1–5 nm size particles is extremely difficult to determine using the present state-of-art instrumentation.

Nucleation burst in a coagulating system

The source-enhanced formation and growth of disperse particles is considered assuming the particles born by nucleation grow then by coagulation and condensation of a low volatile vapor onto their surfaces. After formulating the basic equations governing the particle-formation-growth process a realistic process is considered: nucleation-coagulation growth of aerosol particles in a free molecular regime. The kinetics of this process is studied under the assumption that the particle mass spectrum has a log-normal form whose parameters are expressed in terms of three moments of particle mass distribution: particle number concentration, and the moments of the orders 1/3 and 2/3. These three moments together with condensable vapor concentration are shown to meet a set of four first-order nonlinear differential equations that contain a small parameter: relative vapor concentration spent to the disperse particle production. This parameter, however, does not permit a direct application of the perturbation theory: only after two consequent rescalings it becomes possible to remove the small parameter and describe the particle-formation-growth process in terms of universal functions, depending on a specially defined nondimensional group playing the role of time. It is shown that the particle-formation-growth process can be naturally separated into two stages: (i) formation by nucleation and condensational growth of particles, and (ii) growth of formed particles by coagulation and condensation. Each stage is described by its own set of universal functions which are found from the solution of respective differential equations. The asymptotic stage of the process is shown to be described by a self-preserving distribution depending only on two moments: particle number concentration and the moment of particle-mass distribution of the order of 2/3.

FOREIGN AEROSOL IN NUCLEATING VAPOUR

Condensational growth of foreign aerosol particles in the presence of a spacially uniform source of condensable vapour is considered assuming the latter to be able to produce new particles by nucleation. These newly born particles, in turn, grow by condensation and coagulate depositing simultaneously onto the foreign particles surfaces. A model of this process is proposed. Two new approximations are introduced allowing for a simple description of free molecular and transition regimes of the condensational process in terms of the generalised moments of the foreign particle size distribution, with no assumptions being done on the shape of the latter. The behaviour of the nucleation mode is considered within a lognormal theory that describes the evolution of the size spectrum in terms of a lognormal distribution with time-dependent parameters (the total mass, number concentration and the width of the distribution). The set of six ordinary first-order differential equations is formulated for the time dependencies of the vapour concentration, mass and number concentrations of the nucleation mode, the width of the lognormal distribution of the nucleation mode and two generalised moments of the foreign particle size distributions. Final results are presented as the products of nondimensional functions by the dimensional carriers expressed in terms of the external parameters: the number concentration of foreign aerosol N f0 and the vapour source productivity I. Numerical calculations are performed for normal atmospheric conditions in rural areas (the source prodictivity does not exceed 10 7 molecules cm −3 and the concentration of foreign particles is less than 10 3 particles cm −3 ) and assuming that the nonbarrier nucleation (dimers are stable) produces the particles of nucleation mode. The time dependencies of all values of interest are plotted and discussed in view of the correspondence of the model to the atmospheric reality. Only one nondimensional group γ∝ I/ N f0 2 governs the dynamics of the particle formation–growth process. It is shown that the maximal number concentration of newly born particles decreases in increasing the number concentration of foreign particles. This dependence displays an unexpected discontinuity (a first-order phase transition): at a critical value of the governing parameter the intensity of the nucleation burst changes by about two decimal orders.

Upper tropospheric SO2 conversion into sulfuric acid aerosols and cloud condensation nuclei

We have investigated the potential of upper tropospheric cloud condensation nuclei (CCN) formation from sulfur dioxide. This process involves three steps including SO2 conversion to gaseous sulfuric acid (GSA), homogeneous bimolecular nucleation of GSA and water vapor leading to new aerosol particles, and new aerosol particle growth via mutual coagulation and GSA‐H2O condensation. Our investigation includes both measurements of SO2 and GSA as well as model calculations of SO2 conversion to new aerosol particles in the presence of preexisting aerosols which act as a competing sink for GSA. The model reproduces the measured abundance ratio GSA‐SO2 reasonably well. Furthermore, the model predicts that efficient upper tropospheric CCN formation from SO2 may, in fact, occur under certain plausible conditions. These conditions are explored utilizing the factor FCCN, defined as a ratio of the source and sink terms of gaseous sulfuric acid. In particular, a threshold FCCN value for efficient CCN formation is calculated with the model.

Condensational Growth of Fine Aerosol Particles to Increase Precipitation Efficiency

As the environmental problems grow, the regulation of the pollutants emitted from power plants increases. Most of the pollutants in particle phase are removed by particle removal facilities, but fine particles between 0.1 micron and I micron in diameter have a low removal efficiency compared to particles in other size ranges. Therefore the present concern has concentrated on the removal of those fine particles. The purpose of this study is to grow fine particles by condensation to the range larger than I micron. Theoretically the general dynamic equation is solved with an assumption that the particle size follows a log-normal distribution to calculate the temporal behavior of the size distribution. Experiments have been carried out to compare the results with the theoretical predictions. Particles grown by condensation are sampled by impactors and observed with SEM photographs

Variation characteristics of atmospheric aerosol optical depths and visibility in North China during 1980–1994

Using a method developed by Qiu (Qiu, J., 1998. A method to determine atmospheric aerosol optical depth using total direct solar radiation. J. Atmos. Sci. 55, 734–758), 0.75 μm aerosol optical depths at five meteorological observatories in north China during 1980–1994 are retrieved from global direct solar radiation, and variation characteristics of the depths and visibility are analyzed. These observatories are located in the cities of Wulumuqi, Geermu, Harbin, Beijing and Zhengzhou. It is found that during 1980–1994 the aerosol optical depths show an increasing trend at all five sites. During winter the trend is stronger. In winter at Beijing and Wulumuqi, the depth increased by a factor of about two in 15 years. Pollution caused due to the burning of fossil fuel is the main cause of the change. In spring at Geermu the depth is larger and its increase is the quickest among the four seasons, mainly due to desert dust events. The Pinatubo volcanic eruption in 1991 had a significant influence on the aerosol optical depth. The yearly averaged depths over five sites in 1992 after the eruption increased by 0.068 to 0.212, compared to those in 1990, while from 1992 to 1994 they generally show a decreasing trend. In some cities such as Zhengzhou and Geermu, both visibility and optical depth show an increasing trend during 1980–1994, a possible reason for this is that the aerosol particle vertical distribution shifts up in the troposphere. At Geermu, Harbin, Beijing and Zhengzhou, optical depths in summer are larger, which may be because of the growth of aerosol particles growing in the moist summer. Apart from Geermu, at the other four sites visibility in winter is smaller, especially at Wulumuqi and Harbin. At Harbin, visibility in summer is about twice larger than that in winter, but the difference between depths is small, implying the turbid lower troposphere in winter and the larger extinction coefficient in the upper troposphere during summer.

Light-induced evaporation and condensation growth of aerosol particles

We analyze the possibility of resonant optical radiation inducing evaporation and condensation growth of aerosol particles suspended in a vapor-gas mixture. The molecules of the vapor absorb radiation selectively as to velocity. We examine the Knudsen regime, in which the particle radius is much smaller than the mean free path of the molecules.

Hygroscopic growth of aerosol particles in the southern atlantic ocean and indian ocean

Hygroscopic growth of aerosol particles in the southern atlantic ocean and indian ocean

Particle growth in chemical deposition from the gas phase

The effect of the physicochemical processes occurring in an evaporator and a reactor on the growth of aerosol particles is investigated.

Extended monodisperse aerosol modelling for fusion power plant containments

It is found for conditions relative to fusion safety studies that there is a range of initial aerosol masses (up to ≈ 1000 kg) within which the aerosol particle growth dynamics are dominated by Brownian agglomeration. Above this range, the dominant growth mechanism is gravitational agglomeration. Previously, monodisperse aerosol modelling has been reported (W.E. Han, 19th Symposium on Fusion Teechnology, Lisbon, Portugal, 15–20 September, 1996) which enables the accurate prediction of aerosol behaviour up to initial masses of ≈ 1000 kg. Here monodisperse modelling is extended to deal with initial aerosol masses above 1000 kg, enabling the prediction of aerosol transport and the release to the environment in the gravitationally dominated agglomeration regime for hypothetical accidents involving mobilised radionuclides. It is shown that increasing the initial aerosol mass in the Brownian dominated agglomeration regime results in increased release to the environment. However, increases in initial mass in the gravitationally dominated regime soon lead to a maximum in release to the environment; as a result, further increases in initial mass produce smaller releases to the environment.

Stochastic models for coagulation of aerosol particles in intermittent turbulent flows

A stochastic model for solving Smoluchovski equation with random parameters governing coagulation of particles in a turbulent flow is presented. We analyze the influence of intermittency on the growth of aerosol particles.

Hygroscopic growth of aerosol particles in the marine boundary layer over the Pacific and Southern Oceans during the First Aerosol Characterization Experiment (ACE 1)

The hygroscopic properties of submicrometer aerosol particles were studied with a Hygroscopic Tandem Differential Mobility Analyzer (H‐TDMA) in the remote marine tropospheric boundary layer (MBL) over the Pacific and Southern Oceans in connection with the southern hemisphere marine First Aerosol Characterization Experiment (ACE 1) in October–December 1995. The H‐TDMA was placed on board the ship R/V NOAA Discoverer and measured the hygroscopic diameter growth of individual aerosol particles when taken from a dry state to a relative humidity (RH) of 89–90%. Measurements were performed for the particles with dry diameters of 35, 50, 75, and 150 (or 165) nm. The natural aerosol present in the remote MBL largely consists of two types, a sea‐salt component and a non‐sea‐salt (nss) sulfate component. Since their hygroscopic behavior is significantly different, the H‐TDMA could clearly distinguish between these two types and thus make in situ measurements of the mixing state of the MBL aerosol. During the ACE 1 intensive campaign in the Southern Ocean south of Australia, the hygroscopic diameter growth factors at RH = 90% for the nss‐sulfate aerosol particles were 1.62, 1.66, and 1.78 at dry particle diameters of 35, 50, and 150 nm, respectively, and for time periods with remote marine air masses. These values exceed those normally found in continental polluted environments. The growth factors for the externally mixed sea‐salt particles were even higher (2.12 and 2.14 for 50 and 150 nm). The corresponding values for the Pacific Ocean (at RH = 89%) for the nss‐sulfate particles were 1.56, 1.59, 1.61, and 1.63 for 35, 50, 75, and 165 nm. Particle deliquescence and RH hysteresis between RH = 68–90% was only observed in air masses north of the South Pacific Gyre, and then only for the Aitken mode particles (particle diameters ∼20–80 nm). The occurrence of externally mixed sea‐salt particles could be linked to conditions with high wind speeds in connection with frontal passages or low pressure systems. Nevertheless, the number of externally mixed 150 nm sea‐salt particles was found to be poorly correlated with local wind speed, probably due to a rather long life‐time of these submicrometer particles. Particles with hygroscopic growth factors significantly less than those of the nsssulfate particles (denoted less hygroscopic particles) were only present during periods with anthropogenic influence.

Deposition of a Substance From a Gas Mixture on Aerosol Particles

An investigation of the kinetics of the growth of aerosol particles in heat-stimulated chemical deposition of a substance in the system of gas mixture—aerosol particles is made.