Fine Particle Sulfate Research Articles

Effects of Surface Wetness on the Evolution and Vertical Transport of Submicron Particles

Abstract Simulations have been carried out with a numerical model describing air chemistry, aerosol microphysics, and turbulent mixing, in order to study the behavior of fine sulfate particles in the atmospheric surface layer over wet surfaces. Achievement of local equilibrium of sulfuric acid vapor between the gas phase and particles is rapid and can overpower turbulent mixing in controlling local particle size distributions. Numerical results clearly indicate that in regions of relative humidifies lower than about 80% the large submicron particles increase in number at the expense of concentrations of smaller particles. Simulations that incorporate turbulent mixing and surface dry deposition above wet surfaces show rapid change of vertical flux with height and tend to product downward fluxes for particles larger than 0.1 μm in radius and upward fluxes for particles smaller than about 0.05 μm in radius. This tendency has been seen in fluxes measured by eddy correlation at heights of several meters above ...

Composition and origin of summertime air pollutants at Deep Creek Lake, Maryland

A 1 month intensive summertime field study conducted in rural western Maryland resulted in a comprehensive set of fine particle, gaseous and meteorological data. Sulfur in the assumed form of ammonium sulfate accounted for 67% of the average fine particle mass and had a very high correlation with fine particle mass ( r=0.99). Other measured species, includiqg carbon and nitrate, made only minor contributions to the fine mass. Peak sulfate concentrations, averaged over 6-h intervals, exceeded 50 μg m −3. Nitric acid concentrations showed strong daytime maxima and on a 24 h basis were about four times those of fine particle nitrate. Sulfur in the gas phase (SO 2) constituted more than half of the total sulfur, indicating that the sampling site was being influenced by local sources. Fine particle selenium was well correlated with fine particle sulfur ( r=0.70). The ratio of fine particle sulfur to selenium was 2800, characteristic of a rural site downwind of coal-burning areas. Mixed-layer back trajectories were used to identify possible source regions for the measured parameters. Wind frequency-normalized concentrations of parameters associated with coal-burning (S, Se, SO 2 and mass) were highest for back trajectories arriving at Deep Creek Lake from the west-northwest. Use of Rahn and Lowenthal regional signatures showed an overwhelming dominance by the Lower Midwest region, and a surprisingly weak impact by the Upper Midwest region, at the site.

Effect of ambient humidity on dichotomous sampler coarse/fine ratios

Atmospheric aerosols were measured in August 1983 on Allegheny Mountain and Laurel Hill in southwestern Pennsylvania. Ambient humidity was observed to influence the coarse to fine particle ratios as determined by dichotomous samplers. This influence is evident in the particle mass and in its component chemical species. The sampling run with the most pronounced mass shift resulted in an apparent loss of 50 % of the fine mass and 66 % of the fine particle sulfur to the coarse fraction. The magnitude of the mass shift appears to be related to the length of time that the aerosol was in a saturated environment and also to the original dry particle size. These observations have serious implications for receptor modeling with dichotomous sampler data whenever only the fine particles are considered.

Relationships between direction of wind flow and fine particle sulfur concentrations within and upwind of St Louis, MO

The relationships are considered between monthly and quarterly means of the fine particle sulfur (S) concentrations and wind flow direction, period of day and season of the year. The measurements used are those obtained at selected urban and at rural monitoring stations in the St Louis area during the Regional Air Pollution Study in 1975, 1976 and 1977. Higher mean fine particle S concentrations are observed with wind flows from the E compared to the W and from the NE and SE quadrants compared to the NW quadrant. Substantially higher fine particle S concentrations are obtained with wind flows from the E compared to the W even when conditions are selected so that the values of temperature, solar radiation intensity and wind speed are within the same restricted ranges. A consistent increase in the fine particle S concentrations occurs through the late morning and afternoon with decrease in the evening and especially in the early morning during spring and summer months with wind flows from the E. The contributions are estimated for local scale and regional scale processes to the observed fine particle S concentrations. Local scale processes include those involving atmospheric formation and primary emissions each contribute 0.6−1.0 and 0.6 μg m −3 of the fine particle S. Regional scale processes account for the greater part of the observed concentrations especially when the wind flows are from the SE or SW. Regional scale episodes involving passage of warm high pressure systems to the E of St Louis with accumulation of precursors made especially significant contributions to formation of fine particle S. The atmospheric gas phase and liquid phase chemical reactions contributing to the formation of fine particle S are discussed. Emphasis is placed on the effects of chemistry on the seasonal variations in concentrations of fine particle S.

Potential contribution of sulfate production in cumulus cloud droplets to ground level particle sulfur concentrations

The relationships have been examined between the presence or absence of cumulus clouds and 3rd quarter fine particle sulfur concentrations in St Louis. An association between the presence of cumulus clouds with SO 2 conversions in droplets and incrementally higher fine particle sulfur concentrations can be demonstrated. However, diurnal patterns of fine particle sulfur concentrations in the presence of cumulus clouds are not consistent with local contributions from sulfate formation in cumulus clouds. Morning fog often occurs on the same days on which cumulus clouds form later. Reactions of SO 2 in fog droplets appear to make a contribution, but do not account for the major part of the increments in fine particle sulfur concentrations associated with cumulus clouds. The variations in fine particle sulfur concentrations observed can be explained if a substantial part of the sulfate formed in cumulus is transported upwards from the planetary boundary layer into the lower free troposphere. Subsequent multiday regional scale horizontal transport with concurrent gradual vertical transport of sulfate down to the surface would be consistent with the observed results.

Relationships involving fine particle mass, fine particle sulfur and ozone during episodic periods at sites in and around St. Louis, Mo

The measurements during episodic periods in the St. Louis area in 1975 and 1976 of fine particle sulfur, fine particle mass and ozone are related. Such episodes are concentrated into time periods in the late spring and summer months. During such episodes, particle sulfur is the major constituent of the fine particle mass. The sum of the non-sulfur species in the fine particle mass do not show similar episodic patterns as the fine particle sulfur. Elevated concentrations of fine particle sulfur and of ozone usually occur together within the same episodic time periods. However, the day to day variations in fine particle sulfur and of ozone do differ somewhat within these time periods. Both fine particle sulfur and ozone show the influence of regional scale and local scale atmospheric photochemical processes on their formation during episodic time periods. Regional scale boundary layer processes frequently appear to contribute more to fine particle sulfur concentrations than to ozone formation. Local scale primary emissions also contribute to the ambient fine particle sulfur concentrations at core urban locations.

A quantitative assessment of source contributions to inhalable particulate matter pollution in metropolitan Boston

In this paper, source apportionment techniques are employed to identify and quantify the major particle pollution source classes affecting a monitoring site in metropolitan Boston, MA. A Principal Component Analysis (PCA) of paniculate elemental data allows the estimation of mass contributions for five fine mass panicle source classes (soil, motor vehicle, coal related, oil and salt aerosols), and six coarse panicle source classes (soil, motor vehicle, refuse incineration, residual oil, salt and sulfate aerosols). Also derived are the elemental characteristics of those source aerosols and their contributions to the total recorded elemental concentrations (i.e. an elemental mass balance). These are estimated by applying a new approach to apportioning mass among various PCA source components: the calculation of Absolute Principal Component Scores, and the subsequent regression of daily mass and elemental concentrations on these scores. One advantage of the PCA source apportionment approach developed is that it allows the estimation of mass and source particle characteristics for an unconventional source category: transported (coal combustion related) aerosols. This particle class is estimated to represent a major portion of the aerosol mass, averaging roughly 40 per cent of the fine mass and 25 per cent of the inhalable particle mass at the Watertown, MA site. About 45 per cent of the fine particle sulfur is ascribed to this one component, with only 20 per cent assigned to pollution from local sources. The composition of the coal related aerosol at this site is found to be quite different from particles measured in the stacks of coal-fired power plants. Sulfates were estimated to comprise a much larger percentage of the ambient coal related aerosol than has been measured in stacks, while crustal element percentages were much reduced. This is thought to be due to primary panicle deposition and secondary aerosol accretion experienced during transport. Overall, the results indicate that the application of further emission controls to local point sources of particles would have less influence on fine aerosol and sulfate concentrations than would the control of more distant emissions causing aerosols transported into the Boston vicinity.

Measurement of laboratory and ambient aerosols with temperature and humidity controlled nephelometry

The relationships between fine particle light scattering extinction coefficient, relative humidity and temperature can be used to quantify sulfate mass concentration and composition for laboratory generated and ambient aerosols. This measurement involves the use of an integrating nephelometer as well as a system for controlling the temperature and relative humidity of the air directly upstream of the nephelometer. Recent improvements in the control of these variables has subsequently enhanced our ability to detect the presence of sulfate compounds in complex atmospheric mixtures. Measurements at two urban sites (Seattle, WA and Riverside, CA) indicate the presence of fine presence of fine particle sulfate compounds mixed with more volatile compounds. Measurements at a ‘background’ site (Ozette Lake, WA) indicate a mixture of acidic sulfate compounds with compounds that are less volatile than (NH 4) 2SO 4.

Source apportionment methods applied to the determination of the origin of ambient aerosols that affect visibility in forested areas

An aerosol characterization, visibility, and receptor modeling study was conducted in the Shenandoah Valley, VA between 14 July and 15 August 1980. The objectives of this study were to: (1) determine the origin of the ambient particles, (2) determine the major chemical species contributing to the light extinction coefficient, (3) evaluate analytical methods to characterize aerosols and (4) provide data for comparison with chemical composition of aerosols collected in the Great Smoky Mountains and in the Abastumani Mountains of Georgian Soviet Socialist Republic. The average sulfate concentrations measured in fine particles (<2.5μm) at these three locations were: 12.0μgm −3 at Great Smoky Mountains; 13.6 μg m −3 at Shenandoah Valley, and 4.6 μg m −3 at Abastumani Mountains; the fractions of sulfate in the fine particle mass concentrations at each site were 0.50,0.50 and 0.38, respectively. For the two studies in the United States, the fine particle sulfate during sulfate maxima was mostly in the form of ammonium acid sulfate. Factor analysis of the fine aerosol composition measured in the Shenandoah Valley yielded a persistent factor containing large loadings on mass, SO 2− 4, S, NH + 4, H +, Se and total nitrate (sum of particulate nitrate and nitric acid), which is characteristic of coal-fired sources. This factor analysis grouping along with additional emissions information suggests that coal-fired power plants are the principal source of sulfate and nitrate.

Physical and chemical indicators of urban visual air quality judgments

Key issues in the selection of physical/chemical measures of atmospheric properties as indicators of judgments of visual air quality are addressed. The relations between measures and judgments made over a variety of times, observation locations and atmospheric conditions are examined experimentally. Light scattering measured throughout the day at a site characterized by high aerosol concentrations was the single measure most strongly related to judgments of visual air quality. A combination of measures taken at a single site and/or other sites are somewhat better indicators of visual air quality than light scattering alone. Light extinction measured by a telephotometer is strongly related to midday visual air quality. The 4-h averaged fine particle sulfur and 12-h averaged fine particle S, sulfate, nitrate and ammonium are all strongly related to the corresponding mean visual air quality. Although these midday hourly and 4-h and 12-h average measures may be used to indicate trends in visual air quality, hourly measures taken throughout the day are required for monitoring diurnal patterns or worst case visual air quality. The application of the method and findings to understanding visual air quality in other urban areas is discussed.

Composition of aerosol particles collected at rural sites in the ohio river valley

Fine and coarse mode aerosol particles were collected for 16 months at three rural sites spanning a 600 km length of the Ohio River Valley. Particle mass and concentrations of 15 elements are reported as means, quarterly means and parameters of the frequency distributions. Results are also presented from analysis of two regional episodes: a high sulfur event and a forest fire. Fine particle mass and elemental composition are remarkably uniform from site to site. Sulfur is the predominant element in the fine particles, and shows a marked annual cycle. The mean ratio of potassium to silicon in the fine particles is 8 times the value found in crustal materials and in the coarse aerosol. Factor analysis of element concentrations indicates three clusters throughout the year: 1. (1) coarse particle crustal elements; 2. (2) fine particle sulfur and selenium and 3. (3) fine particle manganese, iron and zinc. A high temperature, crystalline alumino-silicate characteristic of combustion was identified in the aerosol particles.

In-situ, rapid response measurement of H 2SO 4/(NH 4) 2SO 4 aerosols in urban Houston: A comparison with rural Virginia

We report measurements taken in Houston, Texas of the chemical composition and degree of hydration of haze particles and compare these results with previously reported measurements taken in rural Virginia. Our in-situ, real time measurements are based on detecting changes in particle light scattering extinction with changes in relative humidity and air temperature. With these methods we can determine fine particle mass and sulfate mass concentrations, and sulfate to ammonium ion molar ratio. In Houston, fine particle sulfate averaged 42 % of fine particle mass and the composition in terms of ammonium to sulfate molar ratio ranged from 0.5 to 2 with strong diurnal variation. The particles were most acid during the period 1500 to 2000 and neutral during 0200 to 0900. About 1 3 of the time the particles were droplets supersaturated in terms of salt content. In Virginia, the particles were on average more acidic and contained more water than those in Houston, but the particles were never observed to be supersaturated solution droplets. The difference in the hygroscopic behavior of the particles at the two sites is consistent with differences in both particle chemistry and ambient relative humidity.

In situ rapid-response measurement of sulfuric acid/ammonium sulfate aerosols in rural Virginia

Measurements of the chemical composition and degree of hydration of haze particles in rural Virginia during the summer of 1980 are reported. A new system of instruments, based on detecting relative changes in particle size by measurement of optical scattering, was used to determine with 5-min time resolution the fine particle sulfate mass concentration and NH/sub 4//sup +//SO/sub 4//sup 2 -/ molar ratio. We found sulfate and ammonium ions to average 58% of the mass of particles smaller than 1 ..mu..m. The particle composition in terms of the NH/sub 2//sup +//SO/sub 4//sup 2 -/ molar ratio ranged from 0.5 to 2 with strong diurnal variation. The particles were most acidic at 1500 EDT and least acidic in the period 0600-0900 EDT. The ratio of scattering at ambient RH to that at 35% RH depended only on relative humidity and not on particle chemical composition or increasing vs. decreasing relative humidity. The water contained in ambient aerosol particles was more strongly associated with sulfate and ammonium ions than with the remainder of fine particle mass; these two ions and their associated water caused about 70% of optical scattering.

Origins of aerosol sulfur size distributions in the Los Angeles basin

Low pressure impactor measurements show two distinct types of fine particle sulfur size distributions in Los Angeles, California. These two types of aerosol sulfur have mass median diameters of 0.54 ± 0.07μm and 0.20 ± 0.02 μm, respectively. Factors which may account for the two distribution types, including effects of relative humidity, coagulation, fogs and formation mechanisms, are discussed. Calculations show the 0.5 μm sulfur is consistent with chemical reactions in the aerosol phase, whereas the 0.2 μm sulfur results from homogeneous gas phase SO 2 oxidation. While the growth of the total aerosol volume distribution is not too sensitive to the mechanism, the chemical species distribution strongly depends on the growth law, and can be used to establish its form.

Intercomparison of concentration results from fine particle sulfur monitors

A one week intercomparison study was carried out to evaluate the ability of selected analytical instruments to measure fine paniculate sulfur concentrations. The instruments compared included five modified flame photometric detection systems and an automated dichotomous sampler that was coupled to an on-line, wavelength dispersive X-ray fluorescence analyzer tuned to measure sulfur on fine particle filters. All instruments were connected to a common duct. Concentrations were obtained in periods ranging from 1 to 30 min, but data were reported and intercompared on an hourly basis. Paniculate sulfur concentrations varied from 1 to 9 μg m −3. Results at all concentration levels from four of the six systems agreed to better than ± 5 % throughout the study; while all six agreed within ± 25 % of their composite-mean concentration values at the higher concentrations measured. Linear regression between the composite means and each sampler system's data set showed that the standard estimate of errors ranged from 0.2 to 0.6μgm −3, correlation coefficients from 0.979 to 0.994, and slopes ranged from 0.88 to 1.22. Sulfate concentrations were also determined every 6 h from the fine particle stage of another dichotomous sampler. They were 26 % lower than expected relative to the aerosol sulfur concentrations; thus it appears that either the aerosol sulfur was not entirely in sulfate form, or sulfate was not completely extractable by conventional procedures.

Seawater and nonseawater aerosol components in the marine atmosphere of Samoa

Two multi‐element aerosol components and a third fine particle sulfur component have been identified in the marine atmosphere of Samoa based on elemental composition, time variation, and particle size distribution characteristics. On the basis of Pixe (proton induced X ray emission) analyses of 34 cascade impactor samples (17 simultaneous pairs), each of six particle size fractions, collected at 50 m height, July 16 to September 20, 1976, the components are (1) Cl, Br, K, and Sr in &gt;0.5 μm aerodynamic diameter particles, Ca in 0.5–4 μm particles, and S in &gt;1 μm particles, in proportions resembling, but not identical to, seawater composition; (2) a nonseawater component in &gt;4 μm particles, consisting of 80% of the Ca and median weight ratios for excess Ca/Zn = 3.4, Cu/Zn = 0.11, Ti/Pb = 1.0, Ti/Zn = 0.06, and Fe/Zn = 0.24; (3) S in &lt;1 μm particles with a geometric mean concentration of 63(1.15) ng/m3, comparable to coarse mode S concentrations and similar to values found elsewhere in the southern hemisphere. A wind speed bias against sampling &gt;4 μm particles during prevailing 1–15 m/s winds was evaluated for K, Cl, and S, indicating zero wind speed &gt;4 μm concentrations for component (1) to be on the average 2.0 times greater than measured. Differences in processes for transfer of the elements through the sea surface to jet and film drops may account for the observations.

PIXE analysis of aerosol samples collected over the atlantic ocean from a sailboat

Size-fractionated aerosol samples, collected over the Atlantic Ocean, were analyzed for up to 20 elements by PIXE. Using a sailboat as sampling platform, duplicate samples were taken for two-day periods by means of battery operated 6-stage cascade impactors, positioned about 8 m above the sea surface. In the PIXE analysis of the fine particle stages (stages 3 to 5) a 5 times smaller beam size was used than for stages 1 and 2. This led to significant improvement in the detection limits for the former stages. The results from the duplicate impactor samples were normally in good agreement, indicating that the combined uncertainty of sampling and PIXE analysis was of the order of 20%. The precision of the PIXE analysis alone was investigated by rebombarding some samples six months after the first analysis. The trends with time of the fine particle sulfur and the coarse particle iron concentrations are discussed in some detail.

Composition of size-fractionated aerosol in Charleston, West Virginia

Atmospheric aerosols were collected for 21 days in summer 1976 at Charleston, West Virginia, using five dichotomous virtual impactor samplers simultaneously. The samplers fractionated the aerosol into two aerodynamic size ranges, a fine (< 3.5 μm) and a coarse (> 3.5 μm) fraction. Physical and chemical composition of the aerosol in each size range was measured by filter weighing (total mass), proton induced gamma-ray analysis (carbon, nitrogen, and sulfur), X-ray fluorescence (elements heavier than magnesium), ion chromatography (sulfate, nitrate and sodium), and ion selective electrode (ammonium). Fine particle sulfur was found to be in the form of sulfate. Less than 1% of fine nitrogen was in the form of nitrate; more than 99% was present as ammonium ion. The high correlation between fine sulfur and nitrogen ( r = 0.92) and fine sulfate and ammonium ( r = 0.98) and the presence of sulfate and ammonium in the stoichiometric ratio for ammonium sulfate strongly suggest that ammonium sulfate was the main chemical form of fine sulfur and nitrogen. A detailed mass composition was determined for each particle size range, identifying 69 and 60% of the fine and coarse mass, respectively. Ammonium sulfate was the largest single chemical component (411%) of the fine aerosol mass. Carbon was also a large component of both fine and coarse particle mass constituting 16 and 12% respectively. Factor analysis indicated that four factors were sufficient to satisfactorily represent the variance of 26 measured parameters. The factors are characteristic of crustal material, ammonium sulfate, automotive emissions, and an unidentified anthropogenic source or set of sources.

Aerosol characterization for sulfur oxide health effects assessment

The mean concentrations of sulfur in six particle size fractions, from <0.25 μm to >4μm aerodynamic dia, have been determined in Florida during July–August and December, 1976 sampling seasons. A trend of decreasing concentration along the length of Florida, at ten sites from Pensacola to Miami, is found for sulfur in the fine particle mode, <2 μm dia, but not for >2 μm coarse mode sulfur. The trend is most regular for 0.5–1 μm particles, and urban concentrations show no consistent departure from the nonurban trend in this size range. Smaller and larger particle concentrations are more locally variable. The trends are interpreted in terms of a flow of continental air, containing a pollution-derived fine particle sulfur component, into Florida during northerly wind regimes and of less polluted maritime air with southerly flow. The magnitude of the apparent decrease in average concentration from north to south is dependent on the mix of air flow regimes at various locations in the state during the sample collection periods. The qualitative finding of the decreasing trend, however, may be typical in Florida over much of the year and may be useful for designing epidemiological studies of the relation between fine particle sulfur and public health.