Residential Wood Combustion in Germany: A Twin-Site Study of Local Village Contributions to Particulate Pollutants and Their Potential Health Effects

Residential wood combustion contributing to airborne particulate matter (PM10) was studied for 1 year at two sites in the village of Melpitz. Significant excess pollution was observed at the Melpitz center compared to that at the TROPOS research station Melpitz reference site, situated only 700 m away. Local concentration increments at the village site for the combustion PM constituents organic carbon, elemental carbon, levoglucosan, and benzo[a]pyrene were determined under appropriate wind directions, and their winter mean values were 0.7 μg m-3, 0.3 μg m-3, 0.1 μg m-3, and 0.4 ng m-3, representing relative increases over the regional background concentration of 24, 70, 61, and 107%, respectively. Yearly, weekly, and diurnal profiles of village increments suggest residential heating as the dominant source of this excess pollution, mainly originating from wood combustion. Receptor modeling using positive matrix factorization quantified 4.5 μg m-3 wood combustion PM at the village site, representing an increment of 1.9 μg m-3 and an increase of ∼75% over the 2.6 μg m-3 regional background wood combustion PM. This increment varied with season, temperature, and boundary layer height and reached daily mean values of 4-6 μg m-3 during unfavorable meteorological conditions. Potential health effects were estimated and resulted in an all-cause mortality from short-term exposure to wood combustion PM of 2.1 cases per 100,000 inhabitants and year for areas with similar wood smoke levels as observed in Melpitz. The excess cancer risk from the concentrations of polycyclic aromatic hydrocarbons was 6.4 per 100,000. For both health metrics, the very local contributions from the village itself were about 40-50%, indicating a strong potential for mitigation through local-scale policies. A compilation of literature data demonstrates wood combustion to represent a major source of PM pollution in Germany, with average winter-time contributions of 10-20%. The present study quantifies the negative impacts of heating with wood in rural residential areas, where the continuous monitoring of air quality is typically lacking. Further regulation of this PM source is warranted in order to protect human health.

The variability of mass concentrations and source apportionment analysis of equivalent black carbon across urban Europe

This study analyzed the variability of equivalent black carbon (eBC) mass concentrations and their sources in urban Europe to provide insights into the use of eBC as an advanced air quality (AQ) parameter for AQ standards. This study compiled eBC mass concentration datasets covering the period between 2006 and 2022 from 50 measurement stations, including 23 urban background (UB), 18 traffic (TR), 7 suburban (SUB), and 2 regional background (RB) sites. The results highlighted the need for the harmonization of eBC measurements to allow for direct comparisons between eBC mass concentrations measured across urban Europe. The eBC mass concentrations exhibited a decreasing trend as follows: TR > UB > SUB > RB. Furthermore, a clear decreasing trend in eBC concentrations was observed in the UB sites moving from Southern to Northern Europe. The eBC mass concentrations exhibited significant spatiotemporal heterogeneity, including marked differences in eBC mass concentration and variable contributions of pollution sources to bulk eBC between different cities. Seasonal patterns in eBC concentrations were also evident, with higher winter concentrations observed in a large proportion of cities, especially at UB and SUB sites. The contribution of eBC from fossil fuel combustion, mostly traffic (eBCT) was higher than that of residential and commercial sources (eBCRC) in all European sites studied. Nevertheless, eBCRC still had a substantial contribution to total eBC mass concentrations at a majority of the sites. eBC trend analysis revealed decreasing trends for eBCT over the last decade, while eBCRC remained relatively constant or even increased slightly in some cities.

Size-segregated particle number concentrations and respiratory emergency room visits in Beijing, China

BACKGROUND

The link between concentrations of particulate matter (PM) and respiratory morbidity has been investigated in numerous studies.

OBJECTIVES

The aim of this study was to analyze the role of different particle size fractions with respect to respiratory health in Beijing, China.

METHODS

Data on particle size distributions from 3 nm to 1 µm; PM10 (PM ≤ 10 µm), nitrogen dioxide (NO(2)), and sulfur dioxide concentrations; and meteorologic variables were collected daily from March 2004 to December 2006. Concurrently, daily counts of emergency room visits (ERV) for respiratory diseases were obtained from the Peking University Third Hospital. We estimated pollutant effects in single- and two-pollutant generalized additive models, controlling for meteorologic and other time-varying covariates. Time-delayed associations were estimated using polynomial distributed lag, cumulative effects, and single lag models.

RESULTS

Associations of respiratory ERV with NO(2) concentrations and 100-1,000 nm particle number or surface area concentrations were of similar magnitude-that is, approximately 5% increase in respiratory ERV with an interquartile range increase in air pollution concentration. In general, particles < 50 nm were not positively associated with ERV, whereas particles 50-100 nm were adversely associated with respiratory ERV, both being fractions of ultrafine particles. Effect estimates from two-pollutant models were most consistent for NO(2).

CONCLUSIONS

Present levels of air pollution in Beijing were adversely associated with respiratory ERV. NO(2) concentrations seemed to be a better surrogate for evaluating overall respiratory health effects of ambient air pollution than PM(10) or particle number concentrations in Beijing.

Indoor and outdoor submicrometer particles: exposure and epidemiologic relevance ("the 3 indoor Ls")

Airborne particles represent a very important pollutant with respect to healthy housing conditions. The snag is that in lack of indoor data epidemiological studies focusing on submicron and ultrafine (<100 nm in diameter) particles are usually forced to use outdoor particle concentrations only. On the other hand it is known that people spend most of their time indoors. The aim of this paper is therefore to give a short comprehensive overview of the indoor/outdoor problem with regard to submicron and ultrafine particles, investigating how indoor particle size distributions correlate with outdoor concentrations in the absence of significant indoor sources. In the absence of a major indoor source, total indoor particle number concentrations were always lower than outdoor concentrations. The highest ratios between indoor and outdoor concentrations tend to correlate with lower rather than higher total outdoor particle number concentrations. Concentration ratios depend on particle size. Time lags of the correlation coefficients between the concentrations of indoor and outdoor particles of different diameters have been determined to assess the time the particles need to enter the indoor site through closed modern-type windows. Typical lag times of 0.5-3 h between somewhat smaller indoor particles and somewhat larger outdoor particles have been observed. To assess the resulting particle burden for humans, a suitably weighted average emphasizing indoor aerosol particles must be used. To classify the health effects of particles of different diameters, different decreases of particle number concentrations depending on the particle sizes must be taken into account if indoor concentrations cannot be measured and outdoor concentrations are used in place of indoor measurements. In urban areas, ultrafine particles originate primarily from rapidly increasing traffic, which is the dominating source at many urban sites. The influence of traffic on outdoor and indoor concentrations is therefore of special interest.

Relationship between different size classes of particulate matter and meteorology in three European cities

Evidence on the correlation between particle mass and (ultrafine) particle number concentrations is limited. Winter- and spring-time measurements of urban background air pollution were performed in Amsterdam (The Netherlands), Erfurt (Germany) and Helsinki (Finland), within the framework of the EU funded ULTRA study. Daily average concentrations of ambient particulate matter with a 50% cut off of 2.5 microm (PM2.5), total particle number concentrations and particle number concentrations in different size classes were collected at fixed monitoring sites. The aim of this paper is to assess differences in particle concentrations in several size classes across cities, the correlation between different particle fractions and to assess the differential impact of meteorological factors on their concentrations. The medians of ultrafine particle number concentrations were similar across the three cities (range 15.1 x 10(3)-18.3 x 10(3) counts cm(-3)). Within the ultrafine particle fraction, the sub fraction (10-30 nm) made a higher contribution to particle number concentrations in Erfurt than in Helsinki and Amsterdam. Larger differences across the cities were found for PM2.5(range 11-17 microg m(-3)). PM2.5 and ultrafine particle concentrations were weakly (Amsterdam, Helsinki) to moderately (Erfurt) correlated. The inconsistent correlation for PM2.5 and ultrafine particle concentrations between the three cities was partly explained by the larger impact of more local sources from the city on ultrafine particle concentrations than on PM2.5, suggesting that the upwind or downwind location of the measuring site in regard to potential particle sources has to be considered. Also, relationship with wind direction and meteorological data differed, suggesting that particle number and particle mass are two separate indicators of airborne particulate matter. Both decreased with increasing wind speed, but ultrafine particle number counts consistently decreased with increasing relative humidity, whereas PM2.5 increased with increasing barometric pressure. Within the ultrafine particle mode, nucleation mode (10-30 nm) and Aitken mode (30-100 nm) had distinctly different relationships with accumulation mode particles and weather conditions. Since the composition of these particle fractions also differs, it is of interest to test in future epidemiological studies whether they have different health effects.

Elemental composition and sources of fine and ultrafine ambient particles in Erfurt, Germany

We present the first results of a source apportionment for the urban aerosol in Erfurt, Germany, for the period 1995-1998. The analysis is based on data of particle number concentrations (0.01-2.5 microm; mean 1.8 x 10(4) cm(-3), continuous), the concentration of the ambient gases SO(2), NO, NO(2) and CO (continuous), particle mass less than 2.5 microm (PM(2.5)) and less than 10 microm (PM(10)) (Harvard Impactor sampling, mean PM(2.5) 26.3 micro/m(3), mean PM(10) 38.2 microg/m(3)) and the size fractionated concentrations of 19 elements (impactor sampling 0.05-1.62 microm, PIXE analysis). We determined: (a) the correlations between (i) the 1- and 24-h average concentrations of the gaseous pollutants and the particle number as well as the particle mass concentration and (ii) between the 24-h elemental concentrations; (b) Crustal Enrichment Factors for the PIXE elements using Si as reference element; and (c) the diurnal pattern of the measured pollutants on weekdays and on weekends. The highly correlated PIXE elements Si, Al, Ti and Ca having low enrichment factors were identified as soil elements. The strong correlation of particle number concentrations with NO, which is considered to be typically emitted by traffic, and the striking similarity of their diurnal variation suggest that a sizable fraction of the particle number concentration is associated with emission from vehicles. Besides NO and particle number concentrations other pollutants such as NO(2), CO as well as the elements Zn and Cu were strongly correlated and appear to reflect motor vehicle traffic. Sulfur could be a tracer for coal combustion, however, it was not correlated with any of the quoted elements. Highly correlated elements V and Ni have similar enrichment factors and are considered as tracers for oil combustion.

Increased asthma medication use in association with ambient fine and ultrafine particles

The association between particulate air pollution and asthma medication use and symptoms was assessed in a panel study of 53 adult asthmatics in Erfurt, Germany in winter 1996/1997. Number concentrations of ultrafine particles, 0.01-0.1 microm in diameter (NC(0.01-0.1), mean 17,300 x cm(-3), and mass concentrations of fine particles 0.01-2.5 microm in diameter (MC(0.01-2.5)), mean 30.3 microg x m(-3), were measured concurrently. They were not highly correlated (r=0.45). The associations between ambient particle concentrations and the prevalence of inhaled beta2-agonist, corticosteroid use and asthma symptoms, were analysed separately with logistic regression models, adjusting for trend, temperature, weekend, holidays, and first order autocorrelation of the error. Cumulative exposures over 14 days of ultrafine and fine particles were associated with corticosteroid use. Beta2-agonist use was associated with 5-day mean NC(0.01-0.1) and MC(0.01-2.5). The prevalence of asthma symptoms was associated with ambient particle concentrations. The results suggest that reported asthma medication use and symptoms increase in association with particulate air pollution and gaseous pollutants such as nitrogen dioxide.

PM25 measurements in ambient aerosol: comparison between Harvard impactor (HI) and the tapered element oscillating microbalance (TEOM) system

A comparison, based on the regression of 32 daily mean PM25 aerosol loadings determined by a tapered element oscillating microbalance (TEOM) and by a Harvard impactor (HI), is reported for the ambient aerosol of Erfurt (Germany). The PM2.5 concentrations measured by the TEOM were systematically lower then those obtained by the HI. The ratio of the means TEOM/HI was 0.74 and the regression equation is TEOM = 0.69 x HI + 0.071. This result is consistent with reports elsewhere suggesting that semi-volatile aerosol material is lost from the heated sample filter on the TEOM. To verify this assertion, a heating system was developed for the HI which was able to keep the HI sample filter at 50+/-1 degrees C. After the implementation of this heating system, no systematically differences were observed between the TEOM and the heated HI system. The ratio of means was 1.06 and the regression equation TEOM = 1.10 x HI - 0.668. Because the measured levels of ammonium nitrate were very low in Erfurt, we concluded that other compounds like semi-volatile organics were responsible for the loss of particulate material at 50 degrees C.

Air quality in postunification Erfurt, East Germany: associating changes in pollutant concentrations with changes in emissions

The unification of East and West Germany in 1990 resulted in sharp decreases in emissions of major air pollutants. This change in air quality has provided an opportunity for a natural experiment to evaluate the health impacts of air pollution. We evaluated airborne particle size distribution and gaseous co-pollutant data collected in Erfurt, Germany, throughout the 1990s and assessed the extent to which the observed changes are associated with changes in the two major emission sources: coal burning for power production and residential heating, and motor vehicles. Continuous data for sulfur dioxide, total suspended particulates (TSP), nitric oxide, carbon monoxide, and meteorologic parameters were available for 1990-1999, and size-selective particle number and mass concentration measurements were made during winters of 1991 and 1998. We used hourly profiles of pollutants and linear regression analyses, stratified by year, weekday/weekend, and hour, using NO and SO(2) as markers of traffic- and heating-related combustion sources, respectively, to study the patterns of various particle size fractions. Supplementary data on traffic and heating-related sources were gathered to support hypotheses linking these sources with observed changes in ambient air pollution levels. Substantially decreased (19-91%) concentrations were observed for all pollutants, with the exception of particles in the 0.01-0.03 microm size range (representing the smallest ultrafine particles that were measured). The number concentration for these particles increased by 115% between 1991 and 1998. The ratio of these ultrafine particles to TSP also increased by more than 500%, indicating a dramatic change in the size distribution of airborne particles. Analysis of hourly concentration patterns indicated that in 1991, concentrations of SO(2) and larger particle sizes were related to residential heating with coal. These peaks were no longer evident in 1998 due to decreases in coal consumption and consequent decreased emissions of SO(2) and larger particles. These decreases in coal combustion and the decreased concentrations of SO(2) and particles of larger size classes may have led to decreased particle scavenging and may be partially responsible for the observed increases in ultrafine particles. Traffic-related changes, such as increased numbers of trucks and increased use of diesel vehicles in Erfurt, were also associated with increased number concentrations of ultrafine particles. Morning particle peaks of all sizes were associated with NO and CO (markers for traffic) in both the 1991 and 1998 periods. There were significant differences in the ultrafine particle levels for morning hours between 1991 and 1998, suggesting that traffic was the cause of this increase.

Daily mortality and fine and ultrafine particles in Erfurt, Germany part I: role of particle number and particle mass

Increases in morbidity and mortality have been observed consistently and coherently in association with ambient air pollution. A number of studies on short-term effects have identified ambient particles as a major pollutant in urban air. This study, conducted in Erfurt, Germany, investigated the association of mortality not only with ambient particles but also with gaseous pollutants and indicators of sources. Part I of this study concentrates on particles. Data were collected prospectively over a 3.5-year period from September 1995 to December 1998. Death certificates were obtained from the local authorities and aggregated to daily time series of total counts and counts for subgroups. In addition to standard data for particle mass with diameters < or = 2.5 microm (PM2.5)* or < or = 10 microm (PM10) from impactors, a mobile aerosol spectrometer (MAS) was used to obtain size-specific number and mass concentration data in six size classes between 0.01 microm and 2.5 microm. Particles smaller than 0.1 microm were labeled ultrafine particles (three size classes), and particles between 0.1 and 2.5 microm were termed fine particles (three size classes). Concentrations of the gases sulfur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide (CO) were also measured. The daily average total number concentration was 18,000 particles/cm3 with 88% of particles below 0.1 pm and 58% below 0.03 microm in diameter. The average mass concentration (PM2.5) was 26 microg/m3; of this, 75% of particles were between 0.1 and 0.5 microm in diameter. Other average concentrations were 38 microg/m3 for PM10, 17 microg/m3 for SO2, 36 microg/m3 for NO2, and 600 microg/m3 for CO. Ambient air pollution demonstrated a strong seasonality with maximum concentrations in winter. Across the study period, fine particle mass decreased, whereas ultrafine particle number was unchanged. The proportion of ultrafine particles below 0.03 microm diameter increased compared with the proportion of other particles. During the study, concentrations of SO2 and CO also decreased, whereas the concentration of NO2 remained unchanged. The data were analyzed using Poisson regression techniques with generalized additive modeling (GAM) to allow nonparametric adjustment for the confounders. Both the best single-day lag and the overall association of multiple days fitted by a polynomial distributed lag model were used to assess the lag structure between air pollution and death. Mortality increased in association with level of ambient air pollution after adjustment for season, influenza epidemics, day of week, and weather. In the sensitivity analyses, the results proved stable against changes of the confounder model. We saw comparable associations for ultrafine and fine particles in a distributed lag model where the contribution of the previous 4 to 5 days was considered. Furthermore, the data suggest a somewhat more delayed association of ultrafine particles than of fine particles if single-day lags are considered. The associations tended to be stronger in winter than in summer and at ages below 70 years compared to ages above 70 years. Analysis of the prevalent diseases mentioned on death certificates revealed that the overall association for respiratory diseases was slightly stronger than for cardiovascular diseases. In two-pollutant models, associations of ultrafine and fine particles seemed to be largely independent of each other, and the risk was enhanced if both were considered at the same time. Furthermore, when the associations were summed for the six size classes between 0.01 and 2.5 microm, the overall association was clearly stronger than the associations of the individual size classes alone. Associations were observed for SO2, NO2, and CO with mortality despite low concentrations of these gases. These associations disappeared in two-pollutant models for NO2 and CO, but they remained stable for SO2. The persistence of the SO2 effect was interpreted as artifact, however, because the SO2 concentration was much below levels at which effects are usually expected. Furthermore, the results for SO2 were inconsistent with those from earlier studies conducted in Erfurt. We conclude that both fine particles (represented by particle mass) and ultrafine particles (represented by particle number) showed independent effects on mortality at ambient concentrations. Comparable associations for gaseous pollutants were interpreted as artifacts of collinearity with particles from the same sources.

Respiratory effects are associated with the number of ultrafine particles

The association between fine and ultrafine particles and respiratory health was studied in adults with a history of asthma in Erfurt, Eastern Germany. Twenty-seven nonsmoking asthmatics recorded their peak expiratory flow (PEF) and respiratory symptoms daily. The size distribution of ambient particles in the range of 0.01 to 2.5 microm was determined with an aerosol spectrometer during the winter season 1991-1992. Most of the particles (73%) were in the ultrafine fraction (smaller than 0.1 microm in diameter), whereas most of the mass (82%) was attributable to particles in the size range of 0.1 to 0.5 microm. Because these two fractions did not have similar time courses (correlation coefficient r = 0.51), a comparison of their health effects was possible. Both fractions were associated with a decrease of PEF and an increase in cough and feeling ill during the day. Health effects of the 5-d mean of the number of ultrafine particles were larger than those of the mass of the fine particles. In addition, the effects of the number of the ultrafine particles on PEF were stronger than those of particulate matter smaller than 10 microm (PM10). Therefore, the present study suggests that the size distribution of ambient particles helps to elucidate the properties of ambient aerosols responsible for health effects.

Aerosol bolus dispersion and effective airway diameters in mildly asthmatic children

The contribution of aerosol techniques, the estimation of aerosol bolus dispersion and effective airway dimensions, to the clinical diagnosis of paediatric asthma was studied. In 47 children, aged 11 +/- 2 yrs, with mild asthma (forced expiratory volume in one second (FEV1) 83 +/- 9% of forced vital capacity (FVC)) effective airway diameters were derived from the recovery of inhaled 1 micron sebacate droplets. Intrapulmonary dispersion of inhaled boluses of 0.4 micron droplets was studied, by characterizing the concentration distributions of droplets in the exhaled air by their standard deviation and skewness. Effective airway diameters increased in asthmatic subjects with increasing body size, and did not differ from those obtained in 16 healthy children of similar age and height. Standard deviation and skewness of particle boluses exhaled from shallow lung depths were higher in the asthmatic children than the healthy children (e.g. standard deviation 91 +/- 17 ml vs 79 +/- 15 ml, skewness 0.38 +/- 0.16 vs 0.23 +/- 0.16, respectively, for boluses in 140 ml lung depth). The sensitivity and specificity of bolus dispersion to detect alterations in lung function was comparable to that of FEV1/FVC, the most sensitive conventional lung function parameter in the present study. There was no correlation between body height or lung function and bolus parameters. We conclude that aerosol measurements do not provide an obvious benefit for the clinical diagnosis of mild paediatric asthma, but bolus dispersion supplies additional information on alterations in convective gas transport in the diseased lung.

Aerosol bolus dispersion and effective airway diameters in mildly asthmatic children

The contribution of aerosol techniques, the estimation of aerosol bolus dispersion and effective airway dimensions, to the clinical diagnosis of paediatric asthma was studied. In 47 children, aged 11 +/- 2 yrs, with mild asthma (forced expiratory volume in one second (FEV1) 83 +/- 9% of forced vital capacity (FVC)) effective airway diameters were derived from the recovery of inhaled 1 micron sebacate droplets. Intrapulmonary dispersion of inhaled boluses of 0.4 micron droplets was studied, by characterizing the concentration distributions of droplets in the exhaled air by their standard deviation and skewness. Effective airway diameters increased in asthmatic subjects with increasing body size, and did not differ from those obtained in 16 healthy children of similar age and height. Standard deviation and skewness of particle boluses exhaled from shallow lung depths were higher in the asthmatic children than the healthy children (e.g. standard deviation 91 +/- 17 ml vs 79 +/- 15 ml, skewness 0.38 +/- 0.16 vs 0.23 +/- 0.16, respectively, for boluses in 140 ml lung depth). The sensitivity and specificity of bolus dispersion to detect alterations in lung function was comparable to that of FEV1/FVC, the most sensitive conventional lung function parameter in the present study. There was no correlation between body height or lung function and bolus parameters. We conclude that aerosol measurements do not provide an obvious benefit for the clinical diagnosis of mild paediatric asthma, but bolus dispersion supplies additional information on alterations in convective gas transport in the diseased lung.

Detection of early lung impairment with aerosol bolus dispersion

The broadening of inhaled aerosol boluses (aerosol bolus dispersion) during respiration provides a noninvasive measure of convective gas mixing in the lungs. In this study, the sensitivity and specificity of this technique for the diagnosis of early lung impairment due to cigarette smoking was evaluated. Two hundred and sixteen randomly selected subjects (126 smokers and 90 nonsmokers) were investigated with aerosol dispersion in comparison to conventional lung function tests. The cumulative cigarette consumption of the subjects was quantified by "pack-years" (PY). Smokers were classified into the following groups: 0 < PY < or = 10; 10 < PY < or = 20; 20 < PY < or = 30; and PY > 30. Forced expiratory volume in one second (FEV1), maximal expiratory flow at 25, 50 and 75% vital capacity (MEF25, MEF50 and MEF75) decreased significantly with increasing cigarette consumption. In comparison to nonsmokers, FEV1 was significantly reduced in smokers of 10 < PY < or = 30, and MEF75 was significantly reduced in smokers of PY > 20. Aerosol bolus dispersion increased with increasing PY. For all groups of smokers, even those with PY < 10, bolus dispersion was significantly increased in comparison to lifelong nonsmokers, indicating alterations in convective gas mixing in the lungs. Calculation of receiver operating characteristics for the lung function parameters under consideration showed that bolus dispersion has a higher sensitivity and specificity than conventional lung function parameters. Hence, the aerosol bolus dispersion test could be a promising epidemiological tool to study early abnormalities in intrapulmonary gas mixing due to environmental factors.

Accuracy and resolution power of aerosol-derived airway morphometry in a simple lung model

Aerosol-derived airway morphometry (ADAM) uses sedimentational deposition of monodisperse aerosol particles during breathhold to estimate intrapulmonary air-space dimensions. To determine the accuracy and resolution power of this technique a simple physical lung model comprised of uniform glass beads was investigated. Using the chordlength model, aerosol recovery from this porous medium was calculated by computer simulation of the geometrical structure of air-spaces between glass beads. The results of this calculation were then compared with experimental data: Calculated and measured air-space dimensions differ less than 2% for particles with diameters above about 1 micron. The measured air-space dimension can be described geometrically by the mean chordlength of the porous medium. To estimate the resolution power of ADAM, a defined change in air-space dimensions represented by a horizontal air slit was introduced into the porous medium. This air slit induces a marked increase of measured air-space dimensions. The volumetric width of this increase is the higher the deeper the slit is situated within the medium. Intercomparison of these data with the results of aerosol bolus dispersion measurements suggests that the resolution power of ADAM is decreased by the same mechanisms that increase dispersion of aerosol boluses, demonstrating the close relationship between both methods.

Aerosol bolus dispersion in the respiratory tract of children

To investigate mechanisms of intrapulmonary convective gas transport, aerosol bolus dispersion was measured in 16 healthy children aged 7-11 years. Subjects inhaled 50-mL aerosol boluses consisting of 0.4-micron droplets of di(2-ethylhexyl) sebacate suspended in air into volumetric lung depths between 95 and 540 mL. Bolus dispersion was quantified by volumetric bolus half-width and by volumetric standard deviation of particle concentrations. Bolus half-width increased from a mean of 160 mL to 360 mL with increasing lung depth, the regression being a power law with an average exponent of 0.48. Standard deviation increased from 68 to 136 mL with the 0.42th power of volumetric penetration. There was no correlation of bolus dispersion with age, body height, or lung function parameters, except for boluses penetrating very deep into the lung where dispersion was weakly related to lung volume. The results obtained in children did not differ from those found in an adult population in an earlier study. It was concluded that airway size per se does not have a strong influence on bolus dispersion. Rather, parameters of airway geometry may be among the dominating factors influencing the fate of inhaled particles.