Nonhygroscopic Aerosols Research Articles

Model of the Deposition of Aerosol Particles in the Respiratory Tract of the Rat. II. Hygroscopic Particle Deposition

Rats are frequently used to study the pharmacological and toxicological effects of inhaled aerosol particles. The deposition behavior of aerosol particles in airways is affected by their hygroscopic properties, which accordingly influence the results of such studies. A recently published nonhygroscopic aerosol particle deposition model for rat airways was extended with equations for hygroscopic particle growth in humid air and with a model to mimic the temperature and relative humidity conditions in the rat airways transformed from the upper human airways. As there are no experimental data available for hygroscopic deposition in rat lungs, several model assumptions were made for the humidity distribution in the upper rat airways. The total and regional deposition probability of salt particles in the diameter range 0.02 to 5 μm in rat lung was significantly changed by the hygroscopic properties. The maximum ratios of the total deposition of inhaled initially dry sodium chloride, cobalt chloride, and zinc sulfate particles compared with nonhygroscopic particles were 3.28, 2.44, and 2.13, respectively, and the minimum ratios 0.57, 0.63, and 0.70, respectively. The corresponding maximum (and minimum) ratios for the hygroscopic drugs histamine dihydrochloride, carbenicillin disodium, and atropine sulfate were 1.86 (0.65), 1.53 (0.70), and 1.35 (0.76), respectively. Total deposition was about 20% higher in human airways than in rat airways. The flow regime in the rat upper airways influenced total and regional deposition much less than it did in human airways. The hygroscopicity of salt and drug aerosol particles is an important factor in rat lung deposition.

Influence of Humidity on Clogging of Flat and Pleated HEPA Filters

The influence of humidity on changes to the pressure drop of flat and pleated HEPA filters clogged by polydisperse hygroscopic and non-hygroscopic aerosols has been studied. For flat filters, the results confirm the observations reported by Gupta et al. (1993) that with a hygroscopic aerosol at humidity below the deliquescent point, or with a non-hygroscopic aerosol, the particulate specific cake resistance decreases as relative humidity increases. For pleated filters as for flat filters, the results reveal that during the formation of the particulate cake, the increase in relative humidity leads to a decrease in the specific cake resistance. When the reduction in filtration area, specific to pleated filters, becomes large, the presence of humidity accelerates the filling of pleats causing a greater pressure drop for a same aerosol mass loading. With a hygroscopic aerosol at a humidity above its deliquescent point, the change in pressure drop through flat or pleated filters is not linear but characteristic of liquid aerosol filtration. The influence of humidity on the efficiency of pleated filters, measured by a soda fluorescein aerosol, has also been studied. For clean filters, the efficiency decreases with increasing relative humidity above 90%. For filters clogged with solid aerosol, change in efficiency versus collected surface mass reaches a maximum whose value depends on the relative humidity; when the aerosol is liquid, the efficiency decreases throughout the clogging.

Particle deposition in human respiratory system: Deposition of concentrated hygroscopic aerosols

In the nearly saturated human respiratory tract, the presence of water-soluble substances in the inhaled aerosols can cause change in the size distribution of the particles. This consequently alters the lung deposition profiles of the inhaled airborne particles. Similarly, the presence of high concentration of hygroscopic aerosols also affects the water vapor and temperature profiles in the respiratory tract. A model is presented to analyze these effects in human respiratory system. The model solves simultaneously the heat and mass transfer equations to determine the size evolution of respirable particles and gas-phase properties within human respiratory tract. First, the model predictions for nonhygroscopic aerosols are compared with experimental results. The model results are compared with experimental results of sodium chloride particles. The model reproduces the major features of the experimental data. The water vapor profile is significantly modified only when a high concentration of particles is present. The model is used to study the effect of equilibrium assumptions on particle deposition. Simulations show that an infinite dilution solution assumption to calculate the saturation equilibrium over droplet could induce errors in estimating particle growth. This error is significant in the case of particles of size greater than 1 μm and at number concentrations higher than 105/cm3.

A generator for the production of radiolabelled ultrafine carbonaceous particles for deposition and clearance studies in the respiratory tract

A generator for the production of radiolabelled ultrafine carbonaceous particles for inhalation and clearance studies is described. A Technegas generator in combination with 99 m Tc labelling is a device used in clinical routine to investigate the ventilation of the human lung. However, under standard operating conditions the Technegas generator does not provide ultrafine particles with a stable radiolabel. The removal of saline from the Tc-eluate by an ion exchange column yielded low leaching rates of the radiolabel from the particles of below 4% within 24 h (12% under standard conditions) and guaranteed non-hygroscopic aerosol properties. Short burning times (2 s; standard 15 s) and immediate dilution of the generated aerosol into a conductive bag yielded stable ultrafine particles in the size range between 40 and 100 nm count median diameter (standard 200 nm), with a geometric standard deviation of 1.6. We adapted the generator to a bolus inhalation system, allowing regional aerosol deposition into different lung regions and appropriate clearance studies. In addition the particles can be labelled by 111 In instead of 99 m Tc, extending the investigation time of clearance studies from 1 day to some weeks.

Effect of surfactant deficiency and surfactant replacement on airway patency in the piglet lung

We investigated the effect of surfactant deficiency on airway patency and the effectiveness of surfactant replacement as either an instilled liquid bolus, a non-hygroscopic aerosol or a hygroscopic aerosol. Small airway patency was assessed in isolated piglet lungs by passing a continuous flow of gas though a cannulated airway. Occlusion was assessed by measuring increases in pressure in the cannula that resulted from airway obstruction. In surfactant-deficient conditions the amount of airway closure increased approximately three-fold. However, administration of exogenous surfactant as an instilled liquid bolus, non-hygroscopic aerosol or a hygroscopic aerosol decreased airway closure such that it was statistically similar to that recorded prior to induction of surfactant deficiency, although the instilled and hygroscopic aerosol surfactant both appeared superior to the non-hygroscopic aerosol. These experiments showed that pulmonary surfactant does have a role in maintaining airway patency and that airway closure induced by surfactant deficiency could be reduced by administration of surfactant in any of the aforementioned forms.

Integration of size distributions and size-resolved hygroscopicity measured during the Houston Supersite for compositional categorization of the aerosol

Measurements of aerosol size distributions and hygroscopicity were combined to infer the size-resolved composition of the ambient aerosol during the Houston Supersite campaign from June through October, 2001. The 3000+ distributions used in this analysis were measured at the Aldine site north and typically downwind of the greater Houston metropolitan area. Size distributions spanning the diameter range from 0.025 to 0.700 μm, and hygroscopic behavior at eight logarithmically spaced dry diameters from 0.025 to 0.344 μm were analyzed. At smaller dry sizes, the aerosol hygroscopic growth factor distributions were typically monomodal and peaked at or near a growth factor of 1.0, indicating predominantly non-hygroscopic aerosols. Particles larger than ∼0.100 μm exhibited bimodal growth patterns, with increasing importance of the hygroscopic mode with increasing dry particle size. Hygroscopic growth distributions were used to partition the aerosol into pure insoluble, mixed insoluble, mixed soluble, and pure soluble categories. This categorization scheme was used to analyze in detail four multi-day episodes. During two of these episodes new particle formation events were observed daily. The recently formed particles were only sparingly hygroscopic, suggesting they were composed primarily of insoluble material. To contrast these periods during which pronounced diurnal variability was observed, a third period was chosen because the aerosol concentration and composition varied little. The fourth period analyzed spanned the passage of a cold front, which had a pronounced influence on the aerosol distributions.

Modeling Particle Deposition in Extrathoracic Airways

The extrathoracic (ET) airways filter, warm, and humidify the inspired air and provide olfactory function. These multiple functions are reflected in its complex anatomy and physiology. The ET airways form the first line of defense against inhaled pollutants, both gaseous as well as particulate. To accurately assess the risk posed by inhaled particulate matter to the lung, it is essential to understand the filtering efficiency of the ET airways. In this paper computational fluid dynamics is used to simulate the airflow patterns and the thermodynamics of the ET airways. We detail the procedure to develop a computer reconstruction of the ET airways and the computer model to simulate the flow variable. Using this information we compute the particle trajectories, for both hygroscopic and nonhygroscopic aerosols, and use this data to evaluate the particle deposition pattern in the ET airways. The model predicts high relative humidity conditions in the ET airways. The model also shows that the high relative humi...

Particle shape and internal inhomogeneity effects on the optical properties of tropospheric aerosols of relevance to climate forcing

Direct climate forcing by atmospheric aerosols is a strong function of the aerosol scattering coefficient, single‐scatter albedo, and upscatter fraction. Recent estimates of forcing assume that atmospheric particles are homogeneous spheres. In this paper we attempt to quantify the uncertainty associated with this assumption. We have developed a model, NEPH3, which calculates all the optical properties relevant to direct forcing. The model is tested against measured scattering coefficients from Barbados, assuming that the aerosol particles are homogeneous spheres, stratified spheres, and spheroids. The correlation coefficient of model predictions with measurements is 0.98, for the April 5 to May 3 period, while it is 0.86 for the low dust period of April 14 to May 3. The model indicates that the scattering and extinction coefficients and as a result, the single‐scatter albedo are insensitive to the shape and the structure of the particles throughout the measurement period. On the other hand, our calculations show that volume equivalent spherical‐nonspherical differences in the backscatter fraction can be large, especially in cases of nonhygroscopic (dust) aerosol, or when the relative humidity is low enough so that the particles are dry. The shape of the particles seems to be important in upscatter fraction calculations too, especially for small solar zenith angles and super‐micron‐sized particles. Therefore for the size distributions measured in this study, the assumption that atmospheric aerosols are homogeneous spheres may introduce errors as high as 300% in direct forcing estimations, especially when the Sun is increasingly close to the zenith.

Vertical distribution of aerosol particles and CCN in clear air around the British Isles

We present vertical profiles of aerosol particles and cloud condensation nuclei (CCN) obtained during four flights around the British Isles under different synoptic situations and in different seasons. The calculated net downward radiative flux was reduced significantly by the presence of an aerosol layer close to the surface, especially for the two very polluted days. The heating rates in the aerosol layer increased by between a factor of 2 and more than an order of magnitude. Particle and CCN concentrations after air mass passage over the U.K. increased by about a factor of 2, the changes in the spectra being due to increases in the concentration of particles smaller than 0.2 μm in radius and to decreases in the concentration of large particles (5–11)μm). The changes in aerosol size distributions after air mass passage over land resulted in changes in microphysical and radiative characteristics of the clouds that developed. There is evidence that non-hygroscopic aerosol particles account for up to 50% of the aerosol particle number concentration during two heavily polluted flights.

Feasibility of Using Multiwavelength Lidar Measurements to Measure Cloud Condensation Nuclei

Abstract This paper addresses the feasibility of using mulliwavelength lidar measurements to differentiate both qualitatively and quantitatively between the relative concentrations of hygroscopic and nonhygroscopic aerosol particles. The proposed technique utilizes the fact that hygroscopic particles undergo a size increase and refractive-index change with increasing relative humidity and that different wavelengths respond to these changes in different ways. The lidar wavelengths considered are 0.289, 0.355, 0.532, 0.694, 1.064, and 2.02 µm and the 9–11.5-µm range. It is shown that under certain conditions, a judicious choice of lidar wavelengths can provide a differential backscatter, sufficient to provide information on the size and percentage number concentration of the hygroscopic aerosol and, consequently, cloud condensation nuclei concentration. The presence of a mode of coarse particles (median radius greater than 0.3 µm) produces ambiguous results and limits application of the technique to regions...

Uncertainty and sensitivity analysis of fog formation rates calculated with the containment code FIPLOC-M

An uncertainty and sensitivity analysis was performed on the fog formation rate for non-hygroscopic aerosols calculated with the multi-compartment containment code FIPLOC-M for a VANAM experiment. The uncertainty was found to be moderate. Main contributors were uncertain parameters mainly used in the modelling of the heat and mass transfer onto walls. The ranking of these parameters changed with the conditions in the test. The analysis provided information for minor code improvements and necessary future work to reduce the uncertainty associated with the steam source specification.

Predicted Deposition of Nonhygroscopic Aerosols in the Human Lung as a Function of Subject Age

A predictive aerosol deposition model, which has been validated by comparison with experimental data from adult test subjects, is used to study particle deposition patterns within the developing human lung. Here, an age-dependent lung morphology is presented in which the growth of bronchial airway dimensions is described by the measurements of Phalen et al. (1985), and the number and sizes of pulmonary airways are derived from Dunnill (1962). Total, and compartmental tracheobronchial and pulmonary deposition fractions are calculated for different breathing patterns, from sedentary to maximal activity, and particle sizes ranging over three orders of magnitude. The influences of human subject age and physical activity levels upon regional aerosol deposition within the developing lung are complex; systematic patterns, however, can be identified which are consistent with the effects of linear airway dimensions and particle flow characteristics upon effective particle deposition mechanisms.

Deposition of 0.02–0.2 <italic>μ</italic>m Particles in the Human Respiratory Tract: Effects of Variations in Respiratory Pattern

Abstract Experimental studies which quantify deposition of particles smaller than 0.5 μ m diameter are few, and there is a paucity of experimental data clarifying deposition fraction (DF) for particles in the ultrafine (less than 0.1 μ m) size range. We have measured the DF for 5 size fractions (0.024–0.24 μ m) of a non-hygroscopic heterodisperse aerosol in the human respiratory tract. The aerosol was inhaled during steady state breathing from a chamber by normal male volunteers. Aerosol size distribution and concentration in inhaled and exhaled air were measured using an electrical aerosol analyzer. Initial studies were performed using a controlled respiratory pattern of 1 litre tidal volume (TV) at 12 breaths per minute, and a flow pattern modified from a recording of natural breathing. In subsequent studies, a fixed flow pattern was devised to facilitate study of the variations in TV and inspiratory pause (IP). Using the fixed flow pattern, a pause time of 0s, and TV of 1, the mean DF ranged from 0.49 for the 0.024 μ m particle to 0.12 for the 0.24 μ m particle, and from 0.68 to 0.32 when the IP was 2.5s. For the 2 litre TV, mean DF ranged from 0.63 for the 0.024 μ m particle to 0.36 for the 0.24 μ m particle. DF in the initial studies resembled DF measured with the fixed flow, 1 TV, 2.5s IP. This is because residence time for these two patterns was similar. The data demonstrate that deposition increases as particle size falls below 0.1 μ m, and increases with increasing tidal volume and increasing inspiratory pause time. The observations agree with and validate predictions of earlier mathematical deposition models.

Airway deposition of hygroscopic heterodispersed aerosols: results of a computer calculation.

A new computer model is developed and used to calculate the deposition of inhaled heterodispersed hygroscopic aerosols for mouth breathing in a Weibel symmetric bronchial tree. The model was first validated by obtaining good agreement with recent experimental and theoretical data on regional and total airway deposition of monodispersed and heterodispersed nonhygroscopic aerosols. The model was then used to obtain predictions of regional and total deposition of heterodispersed hygroscopic aerosol particles (droplets of NaCl solutions). Parameters that were varied in the hygroscopic calculations include initial droplet NaCl concentration, time of inspiration and expiration, volume of aerosol inspired, period of breath holding, and initial inhaled lognormal aerosol mass median diameter and geometric standard deviation. Results of the computer calculations show that increasing heterodispersity tends to flatten and broaden regional deposition curves when fraction of inhaled mass deposited is plotted vs. inhaled mass median aerodynamic particle diameter. Hygroscopicity is shown to increase tracheobronchial and pulmonary airway deposition with hypertonic NaCl solution aerosols showing increases over isotonic and nonhygroscopic aerosols of up to 200%.

Influence of atmospheric pollutants on cloud microphysics and rainfall

For investigating the physical reasons for the observed increase in rainfall, field observational programmes have been undertaken in the upwind and downwind of industrial complexes of the Bombay region. During these programmes, surface observations of trace gases ( SO2 and NO x ), giant size hygroscopic and nonhygroscopic aerosols and rain water samples have been made in the years 1972, 1973 and 1974. Aircraft observations of trace gases (SO2 and NH3), giant size aerosols, cloud condensation nuclei as well as of cloud liquid water content, cloud droplet spectra and temperature have been made on limited days during August 1974. Results of the analysis of the surface and aircraft observations have indicated that the chemical, thermal and microphysical condi­tions of clouds are markedly different in the upwind and downwind regions of the industrial complexes in the Bombay region. It is hypothesised that observed increase in rainfall in the region following the industrialisation is due to the differences in the chemical and physical conditions in the downwind clouds.

Ambient Sulfate Aerosol Deposition in Man: Modeling the Influence of Hygroscopicity

Atmospheric sulfate aerosols [H2SO4, (NH4)2SO4, and NH4HSO4] are of international concern because of their global prevalence and potential irritant or toxic effects on humans. To assess hazards following inhalation exposure, the total dose delivered to the human respiratory tract and its regional distribution must be determined. The mass median aerodynamic diameter of the inhaled aerosol will influence the sites of deposition in the respiratory tract. Atmospheric sulfate aerosols are hygroscopic and will have changing particle sizes and densities as they absorb water vapor in the humid environment of the human respiratory tract. Experimental and theoretical data that describe particle size as a function of temperature and relative humidity were used in computer subroutines of an aerosol deposition model in order to calculate the dose dispersion of H2SO4, (NH4)2SO4, and NH4HSO4 aerosols in man. Different temperature and relative humidity environments that approximately correspond to nasal and oral breathing were studied. The predicted deposition patterns are very different from those of nonhygroscopic aerosols with identical inhaled mass median aerodynamic diameter values.

Ambient sulfate aerosol deposition in man: modeling the influence of hygroscopicity.

Atmospheric sulfate aerosols [H2SO4, (NH4)2SO4, and NH4HSO4] are of international concern because of their global prevalence and potential irritant or toxic effects on humans. To assess hazards following inhalation exposure, the total dose delivered to the human respiratory tract and its regional distribution must be determined. The mass median aerodynamic diameter of the inhaled aerosol will influence the sites of deposition in the respiratory tract. Atmospheric sulfate aerosols are hygroscopic and will have changing particle sizes and densities as they absorb water vapor in the humid environment of the human respiratory tract. Experimental and theoretical data that describe particle size as a function of temperature and relative humidity were used in computer subroutines of an aerosol deposition model in order to calculate the dose dispersion of H2SO4, (NH4)2SO4, and NH4HSO4 aerosols in man. Different temperature and relative humidity environments that approximately correspond to nasal and oral breathing were studied. The predicted deposition patterns are very different from those of nonhygroscopic aerosols with identical inhaled mass median aerodynamic diameter values.

Quantitative deposition of ultrafine stable particles in the human respiratory tract.

Theoretical models of particle deposition in the respiratory tract predict high fractional deposition for particles of less than 0.1 micron, but there are few confirming experimental data for those predictions. We have measured the deposition fraction of a nonhygroscopic aerosol in the human respiratory tract. The aerosol had a count mean diameter of 0.044 micron SD of 1.93, as measured with an electrical aerosol analyzer, and was produced from a 0.01% solution of bis(2-ethylhexyl) sebacate using a condensation generator. Subjects inhaled the aerosol using a controlled respiratory pattern of 1 liter tidal volume, 12/min. Deposition was calculated as the difference in concentration between inhaled and exhaled aerosol of five size fractions corrected for system deposition and dead-space constants. Three deposition studies were done on each of five normal male volunteers. Means (+/- SE) for the five size fractions were 0.024 micron, 0.71 +/- 0.06; 0.043 micron, 0.62 +/- 0.06; 0.075 micron, 0.53 +/- 0.05; 0.13 micron, 0.44 +/- 0.04; and 0.24 micron, 0.37 +/- 0.06. These data demonstrate that deposition of inhaled particles in the 0.024- to 0.24-micron size range is high and increases with decreasing size. These observations agree with and validate predictions of mathematical models.

Deposition of sulfuric acid mist in the respiratory tracts of guinea pigs and rats.

Radiolabeled sulfuric acid mists in the size range of 0.4-1.2 micron mass median aerodynamic diameter (MMAD) were generated at 20 and 80% relative humidity at concentrations from 1.3 to 20 micrograms/l. Guinea pigs and rats were exposed to these aerosols by the nose-only route for short periods (30 s) and were quickly sacrificed and dissected. The regional respiratory-tract deposition patterns were measured. The results indicate that regional deposition fraction is positively correlated with droplet size of the sulfuric acid but is not correlated with atmospheric concentration or relative humidity over the ranges of the parameters studied. A comparison of the data obtained in these studies with those from earlier studies indicates that the deposition of sulfuric acid in the respiratory tract of rats is greater than for nonhygroscopic aerosols having similar MMADs. This may be due to the growth of the droplets in the high humidity of the respiratory tract.

The deposition of hygroscopic phosphoric acid aerosols in ciliated airways of man

The hygroscopic growth of phosphoric acid aerosol (D c > 0.5 μm) within the human tracheobronchial tree is modeled to investigate changes in deposition characteristics when compared to nonhygroscopic aerosols of identical preinspired size. Phosphoric acid particles are assumed to grow in a stepwise fashion to 99% relative humidity (RH) within conducting airways of the lung, having initially reached equilibrium at 90% RH (T = 37 °C) in the trachea. Deposition efficiencies for growth and no growth are calculated from theoretical equations for inertial impaction, sedimentation and diffusion. The results show that neglecting the growth of an inhaled phosphoric acid aerosol may result in underestimation of the total deliverable dose by a factor of as much as 600–700%. Significant differences in regional deposition sites for hygroscopic or nonhygroscopic aerosols are predicted. Increased deposition efficiencies imply that measured physical properties (respirable fraction, aerodynamic diameter) of aerosols alone are not sufficient to assess deposition characteristics within the lung: hygroscopic growth must also be considered.