Ambient particle-concentrating systems

Figure 3 Schematic diagram of the ambient particle concentrating system used to conduct animal exposures. The RH/T probe measures relative humidity and temperature. Specific honeycomb denuders can be used to remove varying gaseous aerosol components (14,15). (From Ref 14.)...

Urban aerosols are complicated systems composed of material from many different sources. Achieving cost-effective air particle reductions in airsheds not meeting national ambient air quality standards requires identification of major aerosol sources and quantitative determination of their contribution to particle concentrations. Quantitative source Impact assesment, however, requires either calculation of a source s impact from fundamental meteorological principles using source oriented dispersion models, or resolving source contributions with receptor models based on the measurement of characteristic chemical and physical aerosol features. Q)... 

Fresh ambient particulate POM sampled near a freeway was also exposed in this passive system for 3 h in the dark to 200 ppb of 03 in air at 1% RH. Concentrations of specific PAHs determined in the ambient particles and their percent reacted were similar for samples collected on both kinds of filters (glass fiber and TIGF). Again, under passive exposure conditions to approximately ambient levels of 03, BaP and BaA were found to be significantly more reactive than BeP. 

Public concern for the hazards of particle suspensions in the indoor and outdoor environment has produced regulations limiting particle concentrations and exposure levels. In the workplace, dust hazards are constrained by total mass concentration as well as concentration of specific toxic chemicals. In the ambient air, protection is stipulated in terms of total mass concentration of suspended particles andcertain chemical species, namely, lead and sulfate. Recently, measures of exposure have begun to distinguish between fine particles less than 2.5 fxm and coarse particles between 2.5 and 10 fxm. This separation relates to the ability of particles to penetrate the human respiratory system, and to different sources of fine and coarse particles. 

Concentrated ambient particle system (CAPS) is a new technology that has been developed to allow ambient particles to be concentrated in real time by factors of 25 or more (Sioutas et al. 1995). CAPS chambers are typically smaller in size (3-5 m in volume) and mimic the ambient conditions in a particular geographical area. Variations in particulate composition between cities can affect the impact of the findings (Mills et al. 2008). Furthermore, exposure concentrations can vary from day to day depending on ambient levels of PM from which the air is taken, as well as the concentrating factor of the instrument used. Exposure concentrations in CAPS can range from relatively low levels to concentrations much higher (23-311 pg/m ) than those commonly found in polluted cities (USEPA 2004). 

Jerrett M, Newbold KB, Burnett RT et al (2007) Geographies of uncertainty in the health benefits of air quality improvements. Stoch Environ Res Risk Assess 21 511-522 Kodavanti UP, Schladweiler MC, Ledbetter AD et al (2005) Consistent pulmonary and systemic responses from inhalation of fine concentrated ambient particles roles of rat strains used and physicochemical properties. Environ Health Perspect 113(11) 1561-1568 Kuenzli N, Jerrett M, Mack WJ et al (2005) Ambient air pollution and atherosclerosis in Los Angeles. Environ Health Perspect 113 201-206... 

Mobile phase A mixture of acetonitrile, methanol, and 0.01 M tetramethylammonium [18] perchlorate in 0.1% aqueous trifluoroacetic acid (40 5 55, v/v/v), at a constant flow rate of 1.0 ml/min at ambient temperature. Chromatographic system Separation was accomphshed on an ODS-AQ column 5 cm X 4.0 mm I.D., 3 pm particle size similar separation could be achieved on a 5 cm X 4.6 mm, 3 pm ODS-2 column. The detector was operated at a wavelength of 205 run. Standard curves were hnear (r > 0.9998) over the concentration range 0.01 15 pg/ml with both inter- and intraday coefficients of variation typically less than 5%... 

Although respiratory protective devices and protective clothing fabrics are generally considered to provide adequate protection for exposures to fine-sized particulates, it is unclear whether these are effective barriers for nanoparticulates, defined as particulates with particle sizes <100 nm. Unfortunately, the currently available methodologies utilized in industrial hygiene practices to measure particle exposures also may not be sufficiently sensitive to measure occupational or ambient aerosol concentrations, whether in terms of particle mass, particle numbers or surface area. Therefore, it will be critical to develop a sensitive system to assess the barrier effectiveness or permeation of protective clothing fabrics, filters and respirators. 

Previous particle exposure studies have not used real ambient particles to investigate particle toxicity or develop dose-response relationships. Our laboratory has developed and evaluated a technique that can be used to separate and concentrate respirable particles from ambient air before their delivery to an inhalation exposure system (14,15). With this approach, particles are airborne throughout the... 

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

Emulsion Solvent Evaporation The basic concept of the emulsion solvent evaporation technique producing nanoparticles is very straightforward. The particles are formed as an emulsion of a polymer-surfactant mixture and dispersed in an organic solvent. The solvent is then evaporated to leave behind the individual emulsion droplets which form stable free nanoparticles [203], This method is far easier and more preferable over methods such as spray drying and homogenization and operates under ambient conditions and mild emulsification conditions. The size and composition of the final particles are affected by variables such as phase ratio of the emulsion system, organic solvent composition, emulsion concentration, apparatus used, and properties of the polymer [204],... 

Equation (29) shows that the rate of fuel consumption in a diffusion-controlled system is inversely proportional to the radius of the fuel particle. Hence, below some critical particle size, other conditions being constant, the rate of mass (oxygen) transfer will become faster than the rate of the surface chemical reacdon. When this condition prevails, the kinetic rate controls the mass consumption rate of the fuel and the concentration of the oxidant close to the surface does not differ appreciably from its bulk (ambient) concentration. If the fuel particle is porous, the essential assumption is always that the chemical rate is fast enough to render the particle impervious to the oxygen concentration. 

We come now to one of the principal difficulties in the field of aerosol measurements, namely, the determination of chemical composition. The difficulties stem from a number of factors. Aerosols formed under uncontrolled circumstances such as many industrial emissions or the ambient aerosol are often multicomponent. Compo.sitlons differ significantly from particle to particle an individual particle may be a highly concentrated solution droplet containing insoluble matter such as chains of soot particles. The size composition probability density function (Chapter I) can be used to characterize the chemicals and size properties of such systems (but not their morphology). 

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