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Identification of the determinants of efficient aerosol delivery and the specific challenges of aerosol delivery to infants and children can facilitate a systematic approach to optimize aerosol delivery to this population. There are inherent anatomical, physiologic, pathophysiologic, and technical limitations of aerosol efficiency in infants and young children. Nevertheless, one can enhance aerosol efficiency through application of sound principles of aerosol delivery and by exerting control over factors that are amenable to intervention. Improvements in aerosol formulations and delivery systems are being made that will enhance efficiency, decrease risk, and reduce waste and cost. Attention to aerosol particle size (1-3 microm mass median aerodynamic diameter and geometric standard deviation < 2 microm), and the concentration of this respirable particle fraction produced by an aerosol system may enhance delivery through endotracheal tubes and to the lower respiratory tract in infants and children with low V(T) and low inspiratory rates. Attention to the choice of delivery system and to details of proper MDI technique (shaking, priming, immediate actuation, and avoiding multiple actuations prior to inhalation), choice of the aerosol spacer and patient interface (type of face mask, endotracheal tube, mouthpiece), spacer cleaning, and consideration of the medicine to be aerosolized (solution or suspension, viscosity) permit adjustment of the aerosol regimen to optimize delivery. All the patient-related, system-related, and operator-dependent considerations combined can greatly impact aerosol delivery efficacy and improve therapeutic response. Therefore, education and motivation of medical personnel, parents and caregivers, and patients regarding factors that influence aerosol efficiency and teaching of proper technique must be prioritized in order to improve aerosol delivery. Aerosol therapy to all patients, especially infants and young children, would be well served if we had a clear understanding of the efficiency and functional differences among the various drugs and devices. These are substantive issues with daily therapeutic impact that have received increasingly outspoken concern over the past decade by aerosol scientists and clinicians. These issues must be given due attention by drug and device manufacturers as well as by regulatory agencies. The medication, the device, and the conditions under which they are tested must be considered together and studied as thoroughly as the medications themselves with respect to total output and particle size distribution. As noted by Bisgaard, medication dose recommendations are useless unless the device and technique used are specified. Medication dose recommendation could be facilitated by setting equivalent standards for generic and brand-name medications and devices. In addition, standardization of in vitro models with better replicas of infants' and children's anatomy (oropharynx, upper airways), and better in vitro lung models, plus utilization of realistic breathing patterns of infants and children will improve in vitro prediction of the in vivo dose delivered to lower airways. This would greatly facilitate selection of delivery systems under specific circumstances for infants and children of various ages). Safety profile, therapeutic efficacy, and efficiency of aerosolized medications delivered to infants and children need to be rigorously studied. This is particularly true for medications with potentially great benefit but possible adverse effects, such as inhaled glucocorticoid therapy in extremely premature infants. Common sense, ethics, and due respect for the same high standard of approval requirements of adults and older children should motivate further research in understanding and improving aerosol delivery in infants and young children.
A small aerosol chamber was developed for testing and delivery of aerosols of immunologically important proteins to the respiratory tracts of rodents. The chamber was designed to accommodate the small aerosol volumes produced by metered-dose propellant-driven aerosol canisters. Metered bursts of protein aerosols released into the chamber could be sampled for their particle sizes or used to expose the noses of up to six mice to the aerosols. The chamber consisted of a polyethylene tank with two removable plexiglass end plates. One end plate accommodated the propellant-driven, metered-dose, aerosol vial. The other end of the tank was fitted with a plate accepting aerosol sampling devices or a plate containing mouse restrainers. Uniform concentrations of aerosolized proteins were obtained at different positions in the chamber when sampled for particles of respirable size. Respirable-sized protein particles produced by propellant-driven aerosols ranged from 5 to 50% of total aerosolized protein. Propellant-driven aerosols of proteins released in the chamber produced aerosol particles equivalent to 15-26 micrograms of total protein exposure to the respiratory tract of each mouse. The chamber permitted aerosol releases without risk of operator exposure. This aerosol chamber will permit the testing of protein aerosols for their immunologic consequences to the respiratory tract. Potential proteins for testing in this device include immunizing vaccine antigens, immunomodulating cytokine proteins, and passive antibody aerosol therapies against respiratory infections.
PURPOSE: Gd-DTPA aerosol ventilation MR imaging was obtained using a modified aerosol delivery system with an aerosol reservoir to non-invasively assess regional lung ventilation in dogs. MATERIAL AND METHODS: Seven anesthetized, spontaneously breathing normal dogs inhaled 200 mmol Gd/l Gd-DTPA aerosol produced by an ultrasonic nebulizer, using an open-circuit aerosol delivery system with or without an aerosol reservoir. Fast gradient-echo MR images were sequentially acquired with an interval time of 1 min for 25 min before and after aerosol inhalation. The aerosol study was also performed using the aerosol delivery system with an aerosol reservoir in the same 7 dogs after airway obstruction with a balloon catheter, and in another 7 dogs after pulmonary arterial embolization with enbucrilate. An i.v. Gd-DTPA-enhanced dynamic MR study after i.v. bolus injection of a 0.1 mmol/kg dose of Gd-DTPA was combined to assess regional lung perfusion. Lung enhancement effect was evaluated by time-signal intensity curves and the subtracted ventilation- and perfusion-weighted images. RESULTS: With or without the aerosol reservoir, the normal dog lungs were gradually and gravity-dependently enhanced with time after aerosol inhalation. The use of the aerosol reservoir, however, showed significantly greater lung enhancement without a significant increase in breathing rate and with minimal reduction in PaO2 of less than 5 mm Hg in these animals. The enhancement effect of i.v. injection of Gd-DTPA at pulmonary arterial perfusion phase was significantly greater compared to that of Gd-DTPA aerosol throughout the normal lungs, and the subtracted ventilation-weighted and perfusion-weighted images showed homogeneous but gravity-dependent aerosol deposition and perfusion. These images clearly defined the regionally matched perfusion-ventilation deficits in the lung regions distal to bronchial obstruction in all the airway obstruction dogs, and the regionally mismatched perfusion-ventilation in the embolized regions of all the pulmonary arterial embolization animals. CONCLUSION: Gd-based aerosol can non-invasively image regional lung ventilation in spontaneously breathing animals, using an adequate aerosol delivery system. The combined use of Gd-DTPA perfusion MR imaging may be acceptable for defining regionally impaired lung function associated with acute airway obstruction and pulmonary arterial embolization.
Several factors interact in influencing aerosol deposition during mechanical ventilation. Among these factors, the artificial airway is a significant barrier for aerosol deposition. Earlier studies overemphasized the impediments created by the artificial airway to aerosol delivery, because the aerosol generator was placed adjacent to the endotracheal tube or was connected to it. When the aerosol generator is placed away from the endotracheal tube, the fraction that deposits within the tube is reduced and greater aerosol deposition occurs in the lungs. The type of aerosol generator used and the ventilator settings have a greater effect than the size of the tube on the amount of aerosol that deposits in the artificial airway. To minimize aerosol loss within artificial airways, an endotracheal tube of the appropriate size should be selected. "Priming" the tube with a few doses of aerosol before use decreases the electrostatic charge on its walls and may reduce aerosol deposition within the tube. Similarly, using a spacer with the MDI, and placement of the combination in the inspiratory limb at a distance of at least 15 cm from the endotracheal tube reduces aerosol loss within the endotracheal tube. Use of nebulizers that produce submicronic aerosols, and placing them closer to the ventilator instead of closer to the patient also decreases aerosol impaction in the artificial airway. Use of a low inspiratory flow (30-60 L/min in adults), higher duty cycle (> 0.3), and helium-oxygen mixture instead of air or oxygen are other measures to reduce aerosol loss in the airway and thereby improve aerosol delivery to the lower respiratory tract of mechanically ventilated patients.
This review of ultralow-volume (ULV) ground aerosols for adult mosquito control includes discussion on application volume, aerosol generators, droplet size, meteorology, swath, dispersal speed, assay methods, insecticide efficacy, and nontarget effects. It summarizes the efficacy of ULV insecticidal aerosols against many important pest and disease-bearing species of mosquitoes in a wide range of locations and habitats in the United States and in some countries of Asia and the Americas. Fourteen conclusions were drawn from the review. 1) ULV ground aerosol applications of insecticide are as efficacious against adult mosquitoes as high- or low-volume aerosols. 2) ULV aerosols with an optimum droplet size spectrum can be produced by several types of nozzles including vortex, pneumatic, and rotary. Droplet size of a particular insecticide formulation is dependent primarily on nozzle air pressure or rotation speed and secondarily on insecticide flow rate. 3) Label flow rates of insecticide for ULV aerosol application can be delivered accurately during routine operations with speed-correlated metering systems within a calibrated speed range, usually not exceeding 20 mph. 4) The most economical and convenient method of droplet size determination for ULV aerosols of insecticide is the waved-slide technique. 5) The efficacy of ULV ground aerosols against adult mosquitoes is related to droplet size because it governs air transport and impingement. The optimum droplet size for mosquito adulticiding is 8-15 microns volume median diameter (VMD) on the basis of laboratory wind-tunnel tests and field research with caged mosquitoes. 6) In general, ULV aerosols should be applied following sunset when mosquitoes are active and meteorological conditions are favorable for achieving maximum levels of control. Application can be made during daytime hours when conditions permit, but rates may have to be increased. The critical meteorological factors are wind velocity and direction, temperature, and atmospheric stability and turbulence. 7) Maximum effective swaths are obtained with aerosols in the optimum VMD range during favorable meteorological conditions in open to moderately open terrain. The insecticide dosage must be increased in proportion to increased swath to maintain the same level of mosquito control. 8) Dispersal speed within a range of 2.5-20 mph is not a factor affecting efficacy if insecticide rate and optimum droplet size are maintained. 9) The results of caged mosquito assays are comparable with reductions in free-flying natural populations. 10) The field efficacies of mosquito adulticides applied as ULV ground aerosols are predictable from the results of laboratory wind-tunnel tests. 11) Results of field tests in open to moderately open terrain during favorable meteorological conditions indicated that ULV insecticidal aerosol application rates producing 90% or more control of Anopheles, Culex, and Psorophora spp. are below or approximately equal to maximum United States Environmental Protection Agency label rates. Against some Aedes spp., some pyrethroid insecticides must be synergized to produce 90% control at label rates. 12) Results of field tests in residential areas with moderate to dense vegetation and in citrus groves or other densely wooded areas showed that insecticide rates of ULV ground aerosols must be increased 2-3-fold to obtain 90% or more control of adult mosquitoes. However, the maximum rates on some insecticide labels would have to be increased to allow higher application rates. 13) Applications of ULV ground aerosols of insecticide in accordance with label directions following sunset do not pose a serious threat to humans, nontarget beneficial animals, or automotive paints. 14) Some aerosol generators operated at high RPM levels exceed the OSHA 8-h hearing hazard criteria of 90 dBA and may require hearing protectors for operators.
Eleven diurnal aerosol visible light absorption and scattering patterns were obtained from measurements done with an aethalometer and an integrating nephelometer during 28 February-10 March 1997 at two different sites in the Mexico City basin. Both measurement sites, the Merced site affected by regional and urban-scale aerosol and the Pedregal site dominated by regional-scale aerosol, showed a variety of diurnal light absorption and scattering patterns. For the majority of the 11 studied days, the highest absorption peaks appeared in the early morning, 07.00-09.30 h while those of scattering appeared later, 09.30-11.00 h. The earlier absorption peaks could be attributed to the elevated elemental carbon vehicular emissions during the heavy traffic hours whereas the later scattering peaks could be attributed to secondary aerosols formed photochemically in the atmosphere. During the period examined, the Pedregal site exhibited on the average a lower aerosol scattering and a higher aerosol absorption contribution to the total aerosol visible light extinction and a better visibility than that of the Merced site. Hence, the impact of aerosol absorption on the visibility degradation due to aerosols was greater at the less hazy Pedregal site. The overall 11-day aerosol visibility average of 20.9 km found at La Merced site, was only 9.4 km lower than that of 30.3 km found at the Pedregal site. This small aerosol visibility difference, of the order of the standard deviation, led to the conclusion that besides the regional-scale aerosol impact, the urban-scale aerosol impact on aerosol visible light extinction is very similar at La Merced and Pedregal sites.
An understanding of the scaling laws governing aerosol sampler performance leads to new options for testing aerosol samplers at small scale in a small laboratory wind tunnel. Two methods are described in this paper. The first involves an extension of what is referred to as the "conventional" approach, in which scaled aerosol sampler systems are tested in a small wind tunnel while exposed to relatively monodisperse aerosols. Such aerosols are collected by test and reference samplers respectively and assessed gravimetrically. The new studies were carried out for a modified, low flowrate version of the IOM personal inhalable aerosol sampler. It was shown that such experiments can be carried out with a very high level of repeatability, and this supported the general validity of the aerosol sampler scaling laws. The second method involves a novel testing system and protocol for evaluating the performances of aerosol samplers. Here, scaled aerosol samplers of interest are exposed to polydisperse aerosols, again in a small wind tunnel. In this instance, the sampled particles are counted and sized using a direct-reading aerodynamic particle sizer (the APS). A prototype automated aerosol sampler testing system based on this approach was built and evaluated in preliminary experiments to determine the performance of another modified version of the IOM personal inhalable aerosol sampler. The design of the new test system accounts for the complex fluid mechanical coupling that occurs near the sampler inlet involving the transition between the external flow outside the sampler and the internal airflow inside the sampler, leading in turn to uncontrolled particle losses. The problem was overcome by the insertion of porous plastic foam plugs. where the penetration characteristics are well understood, into the entries of both the test and the reference samplers. Preliminary experiments with this new system also supported the general validity of the aerosol sampler scaling laws. In addition, they demonstrated high potential that this approach may be applied in a standardised aerosol testing method and protocol.
We used an in vitro model system to examine the sites of deposition of aqueous therapeutic aerosols administered through 3-mm, 6-mm, and 9-mm endotracheal tubes (commonly used in infants, children, and adults) at clinically relevant inspiratory flow rates. Aerosol was delivered to the endotracheal tube via a "T" piece and a 90 degree elbow. Aerosol exiting the endotracheal tube passed through an appropriately sized Plexiglas model of the trachea and mainstem bronchi, and then into an 80-liter bag. Aerosol deposited in the "T" and elbow, endotracheal tube, large airway model, and collection bag was quantitated separately using 0.1% uranine as a tracer. Study of a conventional aerosol typical of those in common clinical use (aerodynamic mass median diameter = 3.95 microns) showed that most of the aerosol delivered into each endotracheal tube was deposited before leaving the mainstem bronchi. Substitution of an alternative nebulizer that produced a much smaller aerosol particle size (aerodynamic mass median diameter = 0.54 micron) dramatically decreased aerosol deposition in the "T" and elbow, endotracheal tube, and large airway model, and increased the quantity of aerosol penetrating beyond the mainstem bronchi up to ninefold. The mass median particle diameter of the conventional aerosol was reduced during endotracheal tube and large airway passage by poorly defined aerodynamic mechanisms that selectively removed larger particles. The smaller submicron aerosol was not similarly affected. Thus, conventional therapeutic aerosols appear to penetrate poorly through endotracheal tubes. Use of smaller particle size aerosols in treatment of intubated patients may be an effective way to circumvent this problem.
Since the late 1970s, there has been considerable discussion about describing human aerosol exposure in terms of a scientific criterion based on the efficiency with which particles are inhaled through the nose and/or mouth during breathing. As international agreement on the quantitative form of this criterion has emerged, progress is quickening towards workplace and environment aerosol standards in which the current 'total aerosol' approach will be replaced by one based on 'inhalability'. Wind tunnel investigations of a range of personal samplers currently used in workplaces for sampling 'total' aerosol have shown that many of these are not adequate for collecting the inhalable fraction. Such experimental evidence is supported by considerations of the physical sampling characteristics of the various samplers. Studies have been conducted to investigate workers' exposures to 'total' and inhalable aerosol in the workplaces of several industries in several countries, using side-by-side sampling in which participating workers wear two samplers, one for 'total' aerosol and the other for inhalable aerosol. The results from the several hundred sample pairs taken so far show that the level of exposure based on inhalable aerosol consistently exceeds that for 'total' aerosol. The observed ratios between the inhalable and 'total' aerosol exposures range from 1.2 to > 3, tending to be greater for workplaces where the aerosol is expected to be coarser. Such results may be used to assess the impact on industry of new limit values based on inhalable aerosol. It is clear that measured levels of exposure will tend to rise, so that there will be generally increased proportions of exposure measurements where levels will come close to, or exceed, current exposure limits. Those proportions may be greater still if new, lower limit values for 'total' aerosol currently under consideration for some substances are implemented. This paper examines these issues by reference to examples of exposure data taken from a range of industries and proposes options for how such information might influence the setting of future occupational exposure limits.
Spray painters are potentially exposed to aerosols containing hexavalent chromium [Cr(VI)] via inhalation of chromate-based paint sprays. Evaluating the particle size distribution of a paint spray aerosol, and the variables that may affect this distribution, is necessary to determine the site and degree of respiratory deposition and the damage that may result from inhaled Cr(VI)-containing paint particles. This study examined the effect of spray gun atomization pressure, aerosol generation source and aerosol aging on the size distribution of chromate-based paint overspray aerosols generated in a bench-scale paint spray booth. The study also determined the effect of particle bounce inside a Marple personal cascade impactor on measured size distributions of paint spray aerosols. Marple personal cascade impactors with a modified inlet were used for sample collection. The data indicated that paint particle bounce did not occur inside the cascade impactors sufficiently to affect size distribution when using uncoated stainless steel or PVC substrate sampling media. A decrease in paint aerosol mass median aerodynamic diameter (MMAD) from 8.2 to 7.0 mum was observed as gun atomization pressure increased from 6 to 10 psi. Overspray aerosols were sampled at two locations in the spray booth. A downstream sampling position simulated the exposure of a worker standing between the painted surface and exhaust, a situation encountered in booths with multiple workers. The measured mean MMAD was 7.2 mum. The distance between the painted surface and sampler was varied to sample oversprays of varying ages between 2.8 and 7.7 s. Age was not a significant factor for determining MMAD. Overspray was sampled at a 90 degrees position to simulate a worker standing in front of the surface being painted with air flowing to the worker's side, a common situation in field applications. The resulting overspray MMAD averaged 5.9 mum. Direct-spray aerosols were sampled at ages from 5.3 to 11.7 s. Overspray and direct-spray results indicated that most of the change in aerosol size distribution occurred between the time the paint aerosol impacted the painted surface and the time the overspray became 2.8 s old. The overall mean MMAD of overspray in the study was 6.4 mum and may have been underestimated due to sampling efficiency biases. If inhaled by a worker, the overspray aerosols evaluated in this study would mostly deposit in the head airways region of the respiratory tract. Paint overspray aerosols contained Cr primarily in the Cr(VI) state.
Oropharyngeal deposition and subsequent delivery of metered-dose inhaler (MDI) aerosols into the lung were measured with the actuator alone and with 4 different kinds of auxiliary devices; open-end straight tube, Aerochamber, Nebuhaler, and InspirEase. The total mass of dry aerosol discharged directly from the actuator, from the auxiliary devices, and through the oropharyngeal model was determined by collecting the aerosol on the absolute filter and weighing the filter. Aerosol depositions in the auxiliary devices and in the oropharynx as well as the amount of aerosol delivered past the oropharynx were determined as percentages of the total aerosol mass output from the actuator alone. Six different MDI aerosols, 3 bronchodilators, and 3 corticosteroids were used. With the actuator alone, oropharyngeal deposition ranged from 33 to 71% at an inspiratory flow rate of 0.33 L/s, depending on the type of MDI aerosols. Aerosol delivery into the lung was 29 to 67%. With the auxiliary devices, oropharyngeal deposition markedly decreased to the range below 6% regardless of the type of auxiliary device and aerosol. A major deposition (23 to 72%) occurred in the auxiliary devices except for Nebuhaler in which a much reduced deposition (8 to 18%) occurred. Aerosol delivery into the lung was in the range of 40 to 72% with the open-end tube, 26 to 62% with the Aerochamber, 34 to 60% with InspirEase, and 31 to 92% with Nebuhaler. Although a substantial increase in aerosol delivery (as much as 38%) was found with a large size Nebuhaler, the aerosol delivery with other smaller auxiliary devices used was comparable to those obtained without the auxiliary devices.
Aerosol growth by heterogeneous reactions of diverse carbonyls in the presence and absence of acidified seed aerosols was studied in a 4 m long flow reactor (2.5 cm i.d.) and a 2-m3 indoor Teflon film chamber under darkness. The acid catalytic effects on heterogeneous aerosol production were observed for diverse carbonyls in various ranges of humidities and compositions of seed inorganic aerosols. Particle population data measured by a scanning mobility particle sizer were used to calculate organic aerosol growth. To accountforthe aerosol growth contributed by heterogeneous reactions, the increase in organic aerosol mass was normalized bythe organic mass predicted by partitioning or the square of predicted organic mass. The carbonyl heterogeneous reactions were accelerated in the presence of acid catalysts (H2SO4), leading to higher aerosol yields than in their absence. The experimental data from aerosol yields in the flow reactorwere semiempirically fitted to the model parameters to predict the organic aerosol growth. The model parameters consist of environmental characteristics and molecular structure information of organic carbonyls. Basicity constants of carbonyls were used to describe the proton affinity of carbonyls for the acid catalysts. Particle environmental factors, such as humidity, temperature, and inorganic seed composition, were expressed by excess acidity and the parameters obtained from an inorganic thermodynamic model. A stepwise regression analysis of the aerosol growth model for the experimental data revealed that either the chemical structure information of carbonyls or characteristic environmental parameters are statistically significant in the prediction of organic aerosol growth. It was concluded thatthis model approach is applicable to predict secondary organic aerosol formation by heterogeneous reaction.
Studies of aerosol particle deposition in the respiratory tract requires experimental inhalation of artificial model aerosols. The paper formulates some of the most important requirements for the properties of such aerosols. Several suitable fractions were prepared as part of a research project dealing with the use of microporous polymers for diagnostic purposes. 5 fractions of the polymer designated G-gel 60 with the particle size as stated by the manufacturer, ranging from 3 to 7 micron were evaluated using a 16-channel particle dispersity analyzer HIAC/ROYCO MT 3210 with the sensor 1200 and operated by a microprocessor, the equipment being coupled to an APPLE IIe computer. G-gel 60 particles introduced into the aerosol were characterized by the parameters CMAD, MMAD and sg both numerically and graphically. The measurement procedure was found to be very sensitive with respect to all fractions in evaluating the subtile differences between different lot numbers of the aerosol. G-gel 60 fractions characterized both numerically and graphically were compared with the known aerosols from paraffin oil and atmospheric air. The equipment MT 3210 enables prompt determination of the percentages of aerosol particles distribution by size class. The authors conclude that the procedure, both in its numerical and graphical versions, is particularly suitable for the diagnosis of aerosol particles deposition in the respiratory tract, offering a new application for HIAC/ROYCO in the field of medicine. In evaluating atmospheric aerosol in exhaled air, the number of particles was found to be below that in inhaled air, the difference being dependent on the choice of investigation methods. Percentual distribution of deposited particles following one minute ventilation proved to be at its maximum, as regards atmospheric aerosol, in the 0.30-0.50 micron range. The deposition curve was similar to already published curves, being characterized by an S-shaped pattern with maximum deposition in the greater size classes. An analysis of inhaled, exhaled and deposited aerosol suggested that deposited aerosol is more polydisperse and has particles of greater sizes than inhaled aerosol. Investigation of the effect of apnoe on deposition indicated that deposition increased as a function of apnoeic pause.
Aerosol delivered through metered-dose inhalers (MDI) offers a potentially convenient way to deliver bronchodilator agents and corticosteroids to the lungs of patients with asthma and COPD. Unfortunately, most patients are unable to coordinate satisfactorily their actuation with inhalation, a problem overcome by using auxiliary MDI aerosol delivery systems. Left to their own judgment, patients often inhale the aerosol with a high inspiratory flow rather than slowly to produce optimal aerosol deposition within the airways. This problem has been corrected by one of the auxiliary MDI aerosol delivery systems (InspirEase) through auditory, visual, and tactile feedback mechanisms. MDI devices release aerosol at a high jet velocity in large particle sizes, depositing most of the aerosol in the oropharynx which can lead to potential systemic absorption of adrenergic agonists with CNS and cardiovascular side effects, oral thrush, and suppression of adrenocortical activity. All the auxiliary MDI aerosol systems promote delivery of small aerosol particles and markedly diminish oropharyngeal impaction. Of all the systems, only InspirEase provides volume and flow feedback controls to ensure an optimal inhalation maneuver. Auxiliary MDI aerosol systems should always be used for aerosolized corticosteroid administration because they minimize oropharyngeal deposition and improve aerosol delivery efficiency.
Soluble aerosols are measured at Guangdong and Hainan Provinces of southern China. The measured chemical composition of aerosols includes F-, Cl-, NO3-, SO4=, Na+, NH4+, K+, Ca2+, and Mg2+. The locations of measurements include a mega city (Guangzhou), a medium city along the coastline (Haiko), a small city along the coastline (Shanya), and a remote island site in the South China Sea (Yongxing island). The results reveal that aerosols in this region are complex and heterogeneous. Sulfate aerosol (SO4=) has the highest concentrations in Guangzhou (approximately 41% of total soluble aerosol mass), suggesting that anthropogenic activities (e.g., coal burning) play important roles in controlling aerosol concentrations in Guangzhou. By contrast, the concentrations of chlorine (Cl-) and sodium (Na+) are higher in Yongxing than in Guangzhou, indicating that the sea salt is the dominant aerosol in this marine environment site. In the medium (Haiko) and small (Shanya) city sites, the effects of anthropogenic and marine activities on aerosols fall in between the values in the mega city and the remote island site. The measured ratio of Cl-/Na+ shows that the ratio is less than 1.16 in all observation sites. The ratio in the Guangzhou city, the Haiko city, the Shanya city, and the Yongxing island is 0.52, 0.91, 0.24, and 0.53, respectively, indicating that significantly heterogeneous chemical reactions occur on sea salt particles. Unlike those in Europe and North America, there are high concentrations of calcium (Ca+) in all observation sites. The percentage of calcium mass to the measured total soluble aerosols mass is 21, 32, 34, and 30 at Guangzhou, Haiko, Sanya, and Yongxing, respectively. The calculations show that calcium plays an important role in neutralizing aerosols. The calculated "cation/anion" (summation operator[ion+]/summation operator[ion-]) ratio is 2.5, 2.5, 3.2, and 2.1, at Guangzhou, Haiko, Shanya, and Yongxing, respectively. The high "cation/anion" ratios suggest that SO4=, NO3-, and Cl- are neutralized, and the aerosols as a whole (internally mixed), appear to be in an alkaline mode in this region. However, without taking into account for calcium, the calculated "cation/anion" ratio reduces to 1.2, 0.98, 1.3, and 0.8 at Guangzhou, Haiko, Sanya, and Yongxing, respectively. The property of aerosols switches from an alkaline mode to an acidity mode at the Haiko and Yongxing sites.
Organic aerosol formation during the atmospheric oxidation of toluene was investigated using smog chamber systems. Toluene oxidation was initiated by the UV irradiation of either toluene/air/NOx or toluene/air/CH3ONO/NO mixtures. Aerosol formation was monitored using scanning mobility particle sizers and toluene loss was monitored by in-situ FTIR spectroscopy or GC-FID techniques. The experimental results show that the reaction of OH radicals, NO3 radicals and/or ozone with the first generation products of toluene oxidation are sources of organic aerosol during the atmospheric oxidation of toluene. The aerosol results fall into two groups, aerosol formed in the absence and presence of ozone. An analytical expression for aerosol formation is developed and values are obtained for the yield of the aerosol species. In the absence of ozone the aerosol yield, defined as aerosol formed per unit toluene consumed once a threshold for aerosol formation has been exceeded, is 0.075 +/- 0.004. In the presence of ozone the aerosol yield is 0.108 +/- 0.004. This work provides experimental evidence and a simple theory confirming the formation of aerosol from secondary reactions.
The partitioning behavior of a set of diverse SOCs on two and three component mixtures of aerosols from different sources was studied using smog chamber experimental data. A set of SOCs of different compound types was introduced into a system containing a mixture of aerosols from two or more sources. Gas and particle samples were taken using a filter-filter-denuder sampling system, and a partitioning coefficient Kp was estimated using Kp = Cp/(CgTSP). Particle size distributions were measured using a differential mobility analyzer and a light scattering detector. Gas and particle samples were analyzed using GCMS. The aerosol composition in the chamber was tracked chemically using a combination of signature compounds and the organic matter mass fraction (f(om)) of the individual aerosol sources. The physical nature of the aerosol mixture in the chamber was determined using particle size distributions, and an aggregate Kp was estimated from theoretically calculated Kp on the individual sources. Model fits for Kp showed that when the mixture involved primary sources of aerosol, the aggregate Kp of the mixture could be successfully modeled as an external mixture of the Kp on the individual aerosols. There were significant differences observed for some SOCs between modeling the system as an external and as an internal mixture. However, when one of the aerosol sources was secondary, the aggregate model Kp required incorporation of the secondary aerosol products on the preexisting aerosol for adequate model fits. Modeling such a system as an external mixture grossly overpredicted the Kp of alkanes in the mixture. Indirect evidence of heterogeneous, acid-catalyzed reactions in the particle phase was also seen, leading to a significant increase in the polarity of the resulting aerosol mix and a resulting decrease in the observed Kp of alkanes in the chamber. The model was partly consistent with this decrease but could not completely explain the reduction in Kp because of insufficient knowledge of the secondary organic aerosol composition.