Size Distribution Of Atmospheric Particles Research Articles

Particle size distribution of polycyclic aromatic hydrocarbons in the ambient air of a traffic intersection

Abstract Atmospheric particle and PAH (Polycyclic Aromatic Hydrocarbons) mass size distributions in both a traffic intersection and a rural site were measured with two MOUDIs (Micro‐orifice Uniform Deposit Impactors) and a NRI (Noll Rotary Impactor) from June 1994 to June 1995 in southern Taiwan. In the ambient air of the traffic intersection, both the total PAHs and total particle mass were found to be with unimodal size distributions, while at the rural site, they were found to be with bimodal size distributions. Twelve PAHs were found to have a significant bimodal‐distribution: Nap, AcPy, Flu, PA, Ant, FL, CYC, BaA, BkF, DBA, BbC and BghiP. The remaining PAHs (Acp, Pyr, CHR, BbF, BeP, BaP, PER, IND, and COR) had a unimodal or unimodal‐like distribution. In the ambient air of the traffic intersection, the cumulative fraction of total PAHs in the particle size range below 1,2.5, 10 and 25 μm, in sequence, were 50.9%, 74.2%, 90.8% and 95.9%, respectively, while those values at the rural site, in sequence, were 38.3%, 56.4%, 85.7% and 94.0%, respectively. The Traffic/Rural ratio of BaP varied between 7.07 and 17.6 and averaged 11.2 in the fine particle mode; it varied between 5.32 and 16.9 and averaged 10.6 in the coarse particle mode. The high concentration of carcinogenic PAHs in the ambient air of the traffic intersection is a strong potential factor for inducing a high rate of lung cancer. The MMDo of total PAHs and total particle mass in the ambient air of the traffic intersection were 0.943 and 3.59 μm, respectively. However, these two values at the rural site were 1.67 and 2.03 μm, respectively. These results revealed that there was a larger amount of smaller particulates in the ambient air of the traffic intersection. Smaller particulates have more specific area and therefore allow more PAH mass to be adsorbed on them.

Influence of Submicron Particles on Hydrophobic Organic Contaminants in Precipitation. 2. Scavenging of Polycyclic Aromatic Hydrocarbons by Rain

In the second of two papers documenting the importance of submicron particles in controlling the concentrations and distributions of organic contaminants in precipitation, we examine the percipitation scavenging of polycyclic aromatic hydrocarbons (PAHs) as a function of the size distribution of atmospheric particles. We argue that particle scavenging rather than gas scavenging is the dominant removal mechanism for PAHs from the atmosphere by precipitation and that previously reported PAH gas scavenging ratios were overestimated due to the presence of submicron particles in the operationally defined dissolved phase of precipitation samples. In a series of five storms in the Chesapeake Bay region during summer 1992, dimensionless PAH scavenging ratios for submicron particles range from 10 4 to 10 5 , while those for larger particles (>0.5 μm) range from 10 5 to 10 6 . In contrast, gas scavenging ratios, as predicted from temperature-corrected Henry's law constants, range from 10 to 500. The particle scavenging ratios of PAHs associated with large and small particles are similar to those measured for a variety of inorganic species and with those predicted for incloud scavenging of trace atmospheric species. Relative standard deviations of PAH particle scavenging ratios measured during the five storms are nearly 100%, suggesting that precipitation scavenging mechanisms are highly variable among the storms. This variability should be considered when using gas and particle scavenging ratios to model wet depositional fluxes of organic contaminants from the atmosphere.

Influence of gas to particle conversion on the modal size distribution of atmospheric particles

Influence of gas to particle conversion on the modal size distribution of atmospheric particles

CN, CCN and particle size in Southern Ocean air at Cape Grim

Seasonal changes in atmospheric particle size distribution are derived by combining light-scatter particle size spectrometry with particle sizes derived from cloud condensation nucleus (CCN) concentration and sub-micrometre aerosol composition measurements. The distributions obtained are similar to others obtained in the clean marine boundary layer, using different techniques. They show a division of the aerosol “accumulation” mode into two branches, one largely associated with the CCN population and the other with the condensation nucleus (CN) population. A third, and larger, mode which is attributed to seasalt is also observed. Time series of CN and CCN concentrations at Cape Grim are presented and shown to have opposite trends over the past decade. The trend for CN is an increase of around 1.2% per year whilst CCN have decreased at about 3% per year. These trends are shown to be not seasonally uniform, with different dependences for CN and CCN. Finally, existing and possible future global CN and CCN measuring networks are discussed.

Multimedia partitioning of particle-bound organics

A spatial-multimedia-compartmental approach to modeling the partitioning and intermedia fluxes of particle-bound and volatile organics in the environment was developed with emphasis on a detailed description of intermedia transport processes associated with the gaseous, dissolved, and particle phases. Based on this approach a spatial-multimedia-compartmental model (COSMCM) of chemical transport and fate was developed. The COSMCM is composed of eight compartments, namely, air—gaseous phase, air—particulate phase, water, suspended solids (in water), biota (in water), sediment, soil, and vegetation. The COSMCM includes detailed modules of rain scavenging of gaseous and particle-bound chemicals, dry deposition, wind erosion and resuspension of soil, rain infiltration, surface runoff, and resuspension and deposition of sediment particles. In addition, the COSMCM accounts for the dependency of atmosphere/soil and atmosphere/water intermedia transport on particle size and the dynamic changes in the atmospheric particle size distribution. Test cases with benzo(a)pyrene and pyrene distributions in the Los Angeles region revealed that the current approach is of sufficient accuracy and flexibility for estimating pollutant fluxes and multimedia partitioning.

Modelling urban and regional aerosols—I. model development

The partial differential equation that describes the size and composition distribution of atmospheric particles is stated. The equation describes the processes that may influence the particulate size and composition, namely emissions, deposition, advection, turbulent, diffusion, condensation, evaporation, coagulation, nucleation, settling and heterogeneous chemical reactions. Each term in the equation is analysed to estimate its influence on the overall distributions under typical urban conditions. Numerical methods are developed to solve the equation in conjunction with an Eulerian gas-phase model.

Correlation of the atmospheric extinction coefficient with the concentration of particulate matter for measurements in a polluted urban area

Measurements of the volume extinction coefficient employing a Laser transmission path through the atmospheric boundary layer of the city of Leipzig are presented. Working conditions of a long path measurement and the calibration are discussed. To compare the extinction coefficient with other atmospheric quantities the influence of relative humidity on the extinction coefficient is eliminated by a humidity correction. The humidity corrected extinction coefficient is shown to be a measure of atmospheric loading. Based on changes of concentration of aerosol particles the results of measurements are classified in terms of heating or non-heating period and in terms of different air masses. For the empirical relation between the humidity corrected extinction coefficient and the concentration of particulate matter the specific extinction is introduced. With the help of this quantity conclusions are drawn about the shape of the size distribution of atmospheric particles.

A comparison of dry deposition modeled from size distribution data and measured with a smooth surface for total particle mass, lead and calcium in Chicago

For 11 sampling periods, atmospheric particle and elemental (Pb, Ca) mass size distributions (0.1–100 μm diameter) were measured with a Noll Rotary Impactor (NRI) and cascade impactor in Chicago, Illinois. The NRI and cascade impactor measurements were continuous; there was no displacement in the bimodal size distributions. Lead, a primarily anthropogenic element, tended to be associated with the fine-particle mode (< 2.5 μmdiameter); Ca, a primarily crustal element, was associated with the coarse particle mode (< 2.5 μmdiameter). Atmospheric dry deposition fluxes were simultaneously measured with a specially designed and constructed smooth surface pointed into the wind. A particle dry deposition velocity model was used in conjunction with the measured sized distributions to calculate dry deposition fluxes, which were then compared to the measured fluxes. The method, which combined a 12-step flux calculation with the particle dry deposition velocity model, agreed with the measured flux data to within a factor of two. The modeled cumulative fluxes show that fine particles are responsible for only a small fraction of the dry deposition flux. The per cent of the modeled flux due to particles less than 2.5 μm was 0.06, 0.5 and 0.06% for particle mass, Pb and Ca, respectively. The results indicate that atmospheric dry deposition is dominated by coarse particles due to their high deposition velocities.

Diurnal variations of the mobility spectrum of ions and size distribution of fine aerosols in the atmosphere

Measurements of mobility spectra of atmospheric ions with mobility between 3.37 × 10−4 and 6.91 × 10−8 m2/(V s), have been made at a height of 1 m above ground at different times of day at Pune (18° 32′ N, 73° 51′ E, 559 m above msl), India. Measurements made for a period of two days only are presented here. Observations demonstrate the presence of all three groups of ions: small, intermediate and large, each having a distinct peak in mobility at all times of day. Diurnal variations of the mobility spectrum show that ion concentrations in all the mobility ranges increase during nighttime and attain their maximum values in the early morning hours. Mobility spectra at these early morning hours suggest the possibility of the presence of ions of mobility even larger than that of 3.37 × 10−4 m2/(V s). Size distribution of atmospheric aerosol particles in the radius range of 0.0023 &gt; r &gt; 0.03 μm, as computed from the mobility spectra, are bimodal in shape throughout the day on either of the two days. One peak that occurs in the nuclei mode, is always observed at 0.003μm, while the position of the other peak which occurs in accumulation mode, changes between 0.01 and 0.03 μm, at different times of the day. The peak in accumulation mode occurs at larger radius when the peak in nuclei mode is higher. Diurnal variation of the concentration of particles ( 0.03 &gt; r &gt; 0.0063 μm) in accumulation mode exhibits single periodicity with a peak in the early morning and that of particles (0.002 &lt; r ≤ 0.0063 μm) in the nuclei mode exhibits double periodicity with the first peak in the afternoon and the second in the early morning. The observations suggest that high concentrations of particles in the nuclei mode at Pune may be due to photochemical activity in the afternoon and to the presence of decay products of radon and the aerosol particles formed by the radiolytic process in the early morning.

Number size distribution of insolubleatmospheric aerosol particles in fog/cloud-water

AbstractThe design and the efficiency — curve of a newly developed fog/cloud-water sampler (rotating arm collector)is discussed. Fog/cloud-water samples were taken during Oct./Nov. 1990 on the mountain ‘Kleiner Feldberg’/Taunus, FRG. The number size distribution of the insoluble atmospheric aerosol particles in water is determined in the size range 0.025μm < r p < 10.0μm . The size distribution of activated aerosol particles in air is derived from this distribution. Comparison of the spectrum of the activated aerosol particles with the total distribution of aerosol particles in air (measured during the same campaign, but in the size range 0.008μm < r p < 0.45μm ) indicates, that in the size range r p > 0.06μm the major part of atmospheric aerosol particles becomes activated during fog/clouds. The variations of the size distribution in fog/cloud-water during an event is low.

Concentration and size distribution of atmospheric particulate matter at a coastal site on the Baltic Sea

During a period of 13 months (from March 1986 to March 1987) the size distribution and concentration of atmospheric particles in the size range from 0.05 to 25 μm were measured on the western coast of the Baltic Sea. The average particle concentration for the period was 65 μgm −3. The fine particle fraction (0.05–0.4 μm) was 70% of the total concentration. The highest concentrations were usually recorded for southeasterly to southwesterly winds. Wet removal processes play an important role in explaining the variation of particle concentration and size distribution.

Development of a dry deposition model for atmospheric coarse particles

Atmospheric inertial deposition of coarse particles has been quantified by the evaluation of particle dry deposition flux data collected simultaneously on the top and bottom surfaces of a smooth plate with a sharp leading edge that was pointed into the wind by a wind vane. The deposited particles were weighed and counted. The airborne concentration of coarse particles was measured with a Rotary Impactor. Deposition velocity was determined by dividing the mass flux (plate) by the airborne concentration (Rotary Impactor). The deposition velocity was considered to be due to gravitational settling ( V ST ) and inertial deposition ( V I ). Deposition to the upper plate surface ( V dU ) was given by: V dU = V ST + V I , while deposition to the lower plate surface ( V dL ) was given by: V dL = − V ST + V I . The inertial deposition velocity was defined as: V I = \\ ̄ ge AU ∗ , where \\ ̄ ge A is the particle effective inertial coefficient and U ∗ is friction velocity. Based on these equations, \\ ̄ ge A was evaluated as a function of particle size as: \\ ̄ ge A = 1.12e −30.36/d n , where d a is the particle aerodynamic diameter (μm). The correlation coefficient was 0.92, \\ ̄ ge A varied from 0.1 to 1.0 for particles between 5 and 100 μm diameter. The particle dry deposition fluxes obtained for the top and bottom surfaces of the plate were extended to the free atmosphere. A particle flux ratio ( F R ) was defined as: F R = V dL V dU . The mass median aerodynamic diameter MMD a for the atmospheric coarse particle size distribution correlated closely with the geometric mean values of ( F R ). The flux ratio was also related to the shape of the coarse particle mass distribution. The flux ratio was less than 0.1 for particles smaller than 3 μm diameter and did not increase significantly with wind speed. This corresponded to a minimum in the coarse particle mass distribution that was present for particles smaller than 3 μm diameter. The flux ratio was also small for particles larger than 50 μm diameter but increased rapidly with wind speed. This indicated that larger particles could remain suspended under high wind speed conditions. The measured mass distributions for atmospheric coarse particles showed an increase in larger particles with an increase in wind speed. This was in accordance with the increase in the particle flux ratio.

Influence of refractive index and particle size interval on mie calculated backscatter and extinction

Abstract Comparing lidar-derived backscatter coefficients with those inferred from simultaneously measured particle size distributions, discrepancies were observed. To understand the origin of these discrepancies, a systematic study was undertaken on the influence of the complex index of refraction on the extinction and backscatter coefficients calculated from atmospheric particle size distributions. Also effects due to consideration of a limited size interval were investigated. The backscatter coefficients change by two to three orders of magnitude when either the real or the imaginary part of the refractive index is varied. Extinction coefficients are, however, much less sensitive to these variations. The results also have a bearing on the evaluation of lidar signals in an inhomogeneous atmosphere.

The Morphology and Size Distribution of Atmospheric Particles Deposited on Foliage and Inert Surfaces

Particles deposited on leaves and inert surfaces during dry periods were examined with scanning electron microscopy to determine their morphologies and size distributions. Deposited particles were classified into two general types: spherical fly ash particles released during the burning of fossil fuels, and nonspherical particles (primarily soil material) consisting of both organic and mineral matter. Size distribution data indicated that deposited particle mass was dominated by particles larger than 10 microns in diameter, despite the fact that nearly 40 percent of the over 3800 particles analyzed were less than 2 microns in diameter. Our observations lend support to the hypothesis that a small fraction of the airborne particle population is responsible for an unproportionally large fraction of the dry-deposited particle mass and that particle sedimentation may be an important dry deposition process.

An estimation of present and projected diesel particle evolution over Chigago

The impact of a potential increase in vehicular diesel emissions on atmospheric particle concentrations and size distributions in a large urban area (Chigago) is investigated numerically, for idealized meteorological conditions. Results indicate that the projected increase in diesel emissions would affect mainly the concentrations of particles with diameters smaller than 1 μm; larger particles would not be affected significantly. The particle concentrations in the accumulation mode (diameter near 0.2 μm) would be increased by about a factor of ten, while the concentration of particles of the Aitken nuclei mode (diameter near 0.02 μm) would be reduced significantly. The area in which the annual average air quality particulate standard is exceeded is quite small for the reference case based on emissions in 1983, but would increase to cover almost the entire urban area for the projected increase in diesel emissions in 2000.

Measurement of atmospheric particle size distribution during sand/duststorm in Riyadh, Saudi Arabia

This paper presents new results of measuring and analyzing atmospheric sand/dust particles during storms. Particles are collected at various heights in Riyadh, Saudi Arabia, a typical arid inland city. It is found that most of the particle size distributions can be described by a lognormal or normal distribution depending on the storm condition and height. The average diameter of sand/dust particles decreases with the increase of height according to a power law.

Atmospheric IR propagation

The state-of-the-art of IR atmospheric propagation modelling — important to both scientific and practical applications of IR radiation—is reviewed, based mainly on experimental work performed at the FfO. The main improvements of transmission models rely on the results of measurements, analysis and modelling of aerosol and other atmospheric particle size distributions (0.15 μm ⪷ dia ⪷ 12 mm) over land and sea, performed in the context of long-range transmission experiments and lidar probings. Remaining problem areas will be identified and discussed, e.g. continuum absorption and fog window. The modelling of turbulence-induced fluctuations of amplitude and phase is of increasing interest as related to IR atmospheric windows and relevant laser lines. Recent experimental results on phase fluctuations are discussed, especially in relation to attempts to derive a better modelling of atmospheric microturbulence ( C n).

Data inversion for cascade impactors: Fitting sums of log-normal distributions

The processing of data from cascade impactors is discussed and the effects of non-ideal response characteristics on impactor measurements are shown. Since atmospheric particle size distributions may contain two or three modes, the sparse data from an impactor cannot give detailed information about the shape of individual peaks. Thus a shape must be assumed, and it is suggested that a log-normal form is appropriate. A procedure is described which fits sums of log-normal distributions to impactor data, taking account of the detailed response functions. This procedure has been tested with simulated data including random errors, where it is found to reproduce the input distributions satisfactorily, and with actual atmospheric data.

On the concentration and size distribution of atmospheric sulfate particles under rural conditions

On the concentration and size distribution of atmospheric sulfate particles under rural conditions

Determination of the Ground Albedo and the Index of Absorption of Atmospheric Particulates by Remote Sensing. Part I: Theory

A statistical technique is developed for inferring the optimum values of the ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates. The procedure compares measurements of the ratio of the hemispheric diffuse to directly transmitted solar flux density at the earth’s surface with radiative transfer computations of the same as suggested by Herman el al. (1975). A detailed study is presented which shows the extent to which the ratio of diffuse to direct solar radiation is sensitive to many of the radiative transfer parameters. Results indicate that the optical depth and size distribution of atmospheric aerosol particles are the two parameters which uniquely specify the radiation field to the point where ground albedo and index of absorption can be inferred. Varying the real part of the complex refractive index of atmospheric particulates as well as their vertical distribution is found to have a negligible effect on the diffuse-direct ratio. The statistical procedure utilizes a semi-analytic gradient search method from least-squares theory and includes a detailed error analysis.