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PubMed2006

A mathematical approach to selective scavenging of the different classes of typical atmospheric aerosols by rainout and health impact.

In this work, initially a general mathematical framework for wet deposition processes is developed and followed by an in-depth discussion of the scavenging of material below cloud due to rain. These processes are then integrated into an overall framework focussing mainly on precipitation scavenging by rain. This work studies the scavenging efficiencies of aerosol particles within a given rain regime as a function of time by below-cloud scavenging. The health impact of aerosol before and after rain is also considered by comparing the respirable dust fractions. The well-known equations of below-cloud scavenging are applied to eight different classes of atmospheric aerosols (marine background (MB), clean continental background (CCB), average background (AB), background and aged urban plume (BAUP), background and local sources (BLS), urban average (UA), urban and freeway (UF) and central power plant (CCP)) in two precipitation regimes (drizzle and heavy rain) with one drop size distribution (DSD). From this study it is inferred that respirable dust is scavenged with relative ease by rainout. Compared with the volume of respirable aerosol average urban environment (UA) before rain roughly 5.2% remains after 18 hours of drizzle and 4% after 18 hours of heavy rain. Over a long timescale, the results show that heavy rain is more efficient than drizzle in particle scavenging.

Aerosols↗
PubMed2000

Characterization of an aerosol chamber for human exposures to endotoxin.

The objective of this study was to develop and characterize an exposure chamber in which human subjects could be exposed to low dust concentrations carrying an endotoxin coating. An exposure chamber, dust dispersion method, and endotoxin characterization technique were developed for inhalation exposures. A 6.27 m3 exposure chamber was designed and constructed from cinder block, glass windows, and Plexiglas. Using an acetone adhesion process, Enterobacter agglomerans were adsorbed onto respirable cellulose particles to create the endotoxin aerosol. The size distribution of the endotoxin-treated particles was verified using light microscopy and cascade impactors. A dry powder dust generator was refined to consistently disperse small quantities of the aerosol into the chamber to maintain dust concentrations at approximately 250 micrograms/m3. Dust levels during the chamber exposures were monitored using a portable continuous aerosol monitor (PCAM). During initial exposure runs, PCAM monitoring stations were positioned at different locations within a 0.5-meter matrix to document mixing patterns. Total dust and cascade impactor samples were collected throughout each exposure period to characterize the chamber operating system and insure the mean airborne dust concentration fulfilled target levels. A one-factor analysis of variance at the 95 percent confidence interval illustrated that there was not a statistically significant difference in the mean dust concentration throughout the exposure runs compared to the individual runs. Together the consistency of the total dust filters, endotoxin concentrations, and aerosol-monitoring instrument were adequate to allow use of the chamber for experimental studies involving human volunteers.

Aerosols↗
PubMed2003

A comparison of the sampling efficiencies of a range of atmosphere samplers when collecting polymeric diphenylmethane di-isocyanate (MDI) aerosols.

Polymeric diphenylmethane di-isocyanate (PMDI) is a precursor or an intermediate in the manufacture of pure MDI and is used in many industrial applications. Potential health effects of diisocyanates are generally considered to include irritation and respiratory sensitization, dictating the need for low occupational hygiene standards and robust hygiene monitoring methods. A wide range of methods has been developed or adopted for this purpose but questions concerning their ability to accurately sample MDI aerosols in the occupational environment have often been raised. In order to provide such information, studies have been conducted to compare several MDI sampling systems: the Institute of Occupational Medicine (IOM) 25-mm open-faced inhalable dust sampler; the 13-mm Millipore Swinnex Cassette sampler; the 37-mm open-face Millipore cassette; the midget-impinger, the glass tube containing glass wool, and two direct reading paper tape monitors. The program was comprised of two phases, the first being a preliminary comparison of the collection efficiencies of the IOM, 13 mm and midget-impinger at a range of orientations to air flow, aerosol particle sizes, and sampling flow rates, using inert polyethylene glycol aerosols. The second phase compared all samplers operating according to each manufacturer's recommendations and sampling PMDI aerosols at a range of particle sizes and concentrations. All studies were conducted in a wind tunnel. All filter methods performed well in atmospheres containing small particles except impingers that required a filter backup. In general, the variability of all the samplers was high for larger particle size ranges. Direct reading monitors showed low efficiencies.

Aerosols↗
PubMed1991

Indoor and outdoor concentrations of inorganic acidic aerosols and gases.

Annular denuder-filter pack sampling systems were used to make indoor and outdoor measurements of aerosol strong H+, SO4(2-), NH4+, NO3- and NO2-, and the gaseous pollutants SO2, HNO3, HONO and NH3 during summer and winter periods in Boston, Massachusetts. Outdoor levels of SO2, HNO3, H+ and SO4(2-) exceeded their indoor concentrations during both seasons. Winter indoor/outdoor ratios were lower than during the summer, probably due to lower air exchange rates during the winter period. During both monitoring periods, indoor/outdoor ratios of aerosol strong H+ were 40-50 percent of the indoor/outdoor SO4(2-) ratio. Since aerosol strong acidity is typically associated with SO4(2-), this finding is indicative of neutralization of the acidic aerosol by the higher indoor NH3 levels. Geometric mean indoor/outdoor NH3 ratios of 3.5 and 23 respectively were measured for the summer and winter sampling periods. For HONO, NH3, NH4+ and NO2-, indoor concentrations were significantly higher than ambient levels. Indoor levels of NO3- were slightly less than outdoor concentrations.

Acids↗
PubMed2000

Estimates of particle hygroscopicity during the Southeastern Aerosol and Visibility Study.

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects.

Aerosols↗
PubMed2001

Chemical characterization of emissions from vegetable oil processing and their contribution to aerosol mass using the organic molecular markers approach.

The organic fraction of aerosol emitted from a vegetable oil processing plant was studied to investigate the contribution of emissions to ambient particles in the surrounding area. Solvent-soluble particulate organic compounds emitted from the plant accounted for 10% of total suspended particles. This percentage was lower in the receptor sites (less than 6% of total aerosol mass). Nonpolar, moderate polar, polar, and acidic compounds were detected in both emitted and ambient aerosol samples. The processing and combustion of olive pits yielded a source with strong biogenic characteristics, such as the high values of the carbon preference index (CPI) for all compound classes. Polycyclic aromatic hydrocarbons (PAHs) detected in emissions were associated with both olive pits and diesel combustion. The chromatographic profile of dimethylphenanthrenes (DMPs) was characteristic of olive pit combustion. Organic aerosols collected in two receptor sites provided a different pattern. The significant contribution of vehicular emissions was identified by CPI values (approximately 1) of n-alkanes and the presence of the unresolved complex mixture (UCM). In addition, PAH concentration diagnostic ratios indicated that emissions from catalyst and noncatalyst automobiles and heavy trucks were significant. The strong even-to-odd predominance of n-alkanols, n-alkanoic acids, and their salts indicated the contribution of a source with biogenic characteristics. However, the profile of DMPs at receptor sites was similar to that observed for diesel particulates. These differences indicated that the contribution of vegetable oil processing emissions to the atmosphere was negligible.

Aerosols↗
PubMed2002

Secondary organic aerosol formation from the irradiation of simulated automobile exhaust.

A laboratory study was conducted to evaluate the potential for secondary organic aerosol formation from emissions from automotive exhaust. The goal was to determine to what extent photochemical oxidation products of these hydrocarbons contribute to secondary organic aerosol (SOA) and how well their formation is described by recently developed models for SOA formation. The quality of a surrogate was tested by comparing its reactivity with that from irradiations of authentic automobile exhaust. Experiments for secondary particle formation using the surrogate were conducted in a fixed volume reactor operated in a dynamic mode. The mass concentration of the aerosol was determined from measurements of organic carbon collected on quartz filters and was corrected for the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. A functional group analysis of the aerosol made by Fourier transform infrared (FTIR) spectroscopy indicated

Aerosols↗
PubMed2003

Hygroscopic organic aerosols during BRAVO?

The hygroscopic properties of the organic fraction of aerosols are poorly understood. The ability of organic aerosols to absorb water as a function of relative humidity (RH) was examined using data collected during the 1999 Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). (On average, organics accounted for 22% of fine particulate matter with an aerodynamic diameter less than 2.5 microm (PM2.5) mass). Hourly RH exceeded 80% only 3.5% of the time and averaged 44%. BRAVO aerosol chemical composition and dry particle size distributions were used to estimate PM2.5 light scattering (Bsp) at low and high ambient RH. Liquid water growth associated with inorganic species was sufficient to account for measured Bsp for RH between 70 and 95%.

Adsorption↗
PubMed2004

Chemical composition of post-harvest biomass burning aerosols in Gwangju, Korea.

The main objective of this study was to investigate the chemical characteristics of post-harvest biomass burning aerosols from field burning of barley straw in late spring and rice straw in late fall in rural areas of Korea. A 12-hr integrated intensive sampling of particulate matter (PM) with an aerodynamic diameter less than or equal to 10 microm (PM10) and PM with an aerodynamic diameter less than or equal to 2.5 microm (PM2.5) biomass burning aerosols had been conducted continuously in Gwangju, Korea, during two biomass burning periods: June 4--15, 2001, and October 8--November 14, 2002. The fine and coarse particles of biomass burning aerosols were analyzed for mass and ionic, elemental, and carbonaceous species. The average fine and coarse mass concentrations of biomass burning aerosols were, respectively, 129.6 and 24.2 microg/m3 in June 2001 and 47.1 and 33.2 microg/m3 in October--November 2002. An exceptionally high PM2.5 concentration of 157.8 microg/m3 was observed during biomass burning events under stagnant atmospheric conditions. In the fine mode, chlorine and potassium were unusually rich because of the high content of semi-arid vegetation. Both organic carbon (OC) and elemental carbon increased during the biomass burning periods, with the former exhibiting a higher abundance. PM from the open field burning of agricultural waste has an adverse impact on local air quality and regional climate.

Aerosols↗
PubMed2006

Light scattering from sea-salt aerosols at Interagency Monitoring of Protected Visual Environments (IMPROVE) sites.

A method is described to estimate light scattering (Bsp) by sea-salt aerosols at coastal locations in the Interagency Monitoring of Protected Visual Environments (IMPROVE) network. Dry mass scattering efficiencies for fine and coarse sea-salt particles were based on previously measured dry sea-salt size distributions. Enhancement of sea-salt particle scattering by hygroscopic growth was based on NaCl water activity data. Sea-salt aerosol mass at the IMPROVE site in the Virgin Islands (VIIS) was estimated from strontium (Sr) concentrations in IMPROVE aerosol samples. Estimated Bsp, including contributions from sea-salt mass based on Sr, agreed well with measured Bsp at the VIIS IMPROVE site. On average, sea salt accounted for 52% of estimated Bsp at this site. Sea-salt aerosol mass cannot be reliably estimated from Sr unless its crustal enrichment factor exceeds 10. Sodium (Na) concentrations are not accurately determined by X-ray fluorescence analysis in IMPROVE samples. It is recommended that Na be measured in the fine and coarse modes by a more appropriate method, such as atomic absorption spectroscopy or ion chromatography, to account for scattering by sea-salt particles at IMPROVE sites where such contributions may be significant.

Aerosols↗
PubMed1978

Respiratory response to iodine vapor alone and with sodium chloride aerosol.

Respiratory function measurements in guinea pigs were used to evaluate the irritant response to 1-h exposures to iodine vapor and the effect of 10 mg/m(3) submicrometer sodium chloride aerosol on this response. Iodine alone at 0.5 ppm produced no detectable response. Concentrations of 3-4 ppm increased resistance and decreased frequency and minute volume. The response appeared to be upper respiratory. At 7 ppm there was also a decrease in compliance, suggesting pulmonary effects. The response was potentiated by the sodium chloride aerosol. Increased resistance and decreased compliance and frequency were observed at 0.4 ppm. The changes at concentrations of 1-2 ppm were greater when the aerosol was present and included a decrease in compliance. The comparative effects of the sodium chloride aerosol on iodine, sulfur dioxide, and formaldehyde are discussed.

Aerosols↗
PubMed1979

Toxicity of 0.4- and 0.8-microm sulfuric acid aerosols in the guinea pig.

To determine mortality caused by inhaled sulfuric acid mist, groups of Hartley guinea pigs 2-3 mo old were exposed for 8 h to graded concentrations of aerosols of 0.4 or 0.8 microm mass median aerodynamic diameter. Relative humidity during exposures was maintained at 70-80%. Based on probit analysis, the concentration required to produce 50% mortality (LC50) for deaths to 21 d after exposure was 30 mg/m3 for the 0.8-microm aerosol. For the 0.4-microm aerosol, the LC50 was above 109 mg/m3, the highest concentration obtainable at that particle size. At both particle sizes, the animals either tended to develop severe dyspnea and die minutes (0.4 microm) or hours (0.8 microm) thereafter or appeared nearly unaffected. Lesions in animals that died as a results of 0.4-microm exposures were restricted to hyperinflation; animals that died as a result of 0.8-microm exposures also showed hemorrhage and transudation. No gross or histopathologic changes were observed in animals that appeared unaffected during exposure. Differences in total and/or regional respiratory tract deposition may account for the different responses to the two aerosols.

Aerosols↗
PubMed1980

Study of bisulfite and metabisulfite aerosol generation systems.

Sulfur (IV) aerosols may be generated only as the fully neutralized sulfite by nebulization techniques. Attempts to generate bisulfite and metabisulfite aerosols result in the production of sulfite aerosols and large amounts of SO2. Previous toxicologic studies on metabisulfite and bisulfite aerosols apparently documented the effects of high concentrations of gaseous SO2.

Aerosols↗
PubMed1981

Characterization of the aerosol in turkey rearing confinements.

A study was conducted to characterize the aerosol found in turkey rearing confinements, to study biological response to inhalation of the aerosol, and to evaluate a water spray, dust suppression system in one confinement as compared to a control barn. A significant reduction in aerosol concentration in the "sprayed" barn was inferred by many environmental and biological sampling parameters. Similarity of physical and biological factors in both study populations, with the exception of the dust suppression system, implied that a mortality rate increase of 1.74 of control versus "sprayed" barn was directly related to aerosol concentration.

Aerosols↗
PubMed1984

A double isotope method for characterizing hygroscopic selenious acid aerosols used in inhalation exposures.

Methods of generating and characterizing selenious acid aerosols for use in deposition and toxicity studies are described. Selenious acid aerosols were nebulized and heat treated at varied temperatures. Because selenious acid is hygroscopic, a solution containing 3H2O and 75Se was nebulized to determine the water content in selenium aerosols after generation. The stable aerosol was a hydrate of selenious acid, H2SeO3 X 1/2 H2O, at New Mexico ambient relative humidity (ca. 20%). The mass median aerodynamic diameter of the collected droplets was 0.6 micron with a geometric standard deviation of 1.3.

Aerosols↗
PubMed1987

Personal size-separating impactor for sampling microbiological aerosols.

A commercially-available personal impactor was altered to sample viable microorganisms onto a semisolid, moist, gelatin medium rather than onto a stainless steel or filter surface. The Marple personal cascade impactor is an eight-stage sampler with predicted cut-offs of 20, 15, 10, 6, 3.5, 2, 1, and 0.61 microns for stages one to eight, at a flow rate of 2 L/min. The possibility was examined that using trays containing a small amount of gelatin medium in place of the thin, flat filters of the original design would alter the impactor's performance. A polydisperse aerosol of di-2-ethylhexyl phthalate (DEHP or DOP) was sampled directly into an aerodynamic particle sizer and through a stage of the personal impactor. The aerosol particles penetrating the tested stage were sized and counted, and the counts compared with those in the total aerosol. With a Mylar medium filter as the collecting substrate, the measured particle cut-offs (D50) for stages four to seven were 5.2, 3.4, 1.4, and 1.0 microns. With a tray containing gelatin as the collecting substrate, the D50 were 5.9, 4.0, 1.6, and 1.0 microns. The size separation of the personal sampler for ambient bacterial and fungal aerosols compared well with that of the Andersen microbiological impactor. The use of a moist collecting surface, compared to a dry surface, can be expected to enhance recovery of viable airborne microorganisms sensitive to dehydration.

Aerosols↗
PubMed1990

Aerosols and protective clothing.

A complex test method for evaluating protective apparel in aerosol hazard conditions has been developed and examined under laboratory conditions. The effectiveness of the barrier or "collection efficiency" of aerosol protective apparel (APA) depends upon its structural properties such as porosity, thickness, and permeability as well as on its hydrodynamic properties, i.e., pressure drop. Aerosol generating systems and methods of measuring penetration and evaluating data are described. A method of testing protective apparel materials using a standard asbestos aerosol then is described and discussed in detail.

Aerosols↗
PubMed1991

Pulmonary effects of sulfur oxides on the surface of copper oxide aerosol.

The authors have developed a system that generates copper oxide aerosol similar to the primary emissions from smelters. The surface of the ultrafine copper oxide aerosol is coated with a layer of sulfur oxides consisting of sulfate, S(VI), and sulfite, S(IV). Guinea pigs were exposed to this sulfur oxide layered copper oxide aerosol, and pulmonary mechanical functions were measured by using the Amdur-Mead method. The concentration of sulfur oxides on the aerosol was determined by using a flame photometric detector system. Although sulfuric acid was not found in this system, S(IV) at concentrations as low as 0.36 mumol/m3 delivered as a surface layer caused prolonged changes in pulmonary mechanical functions.

Aerosols↗