Atmospheric Environment (v.39, #19)
List for forthcoming papers (III-IV).
Editorial board (i).
Hydrocarbon observations and ozone production rates in Western Houston during the Texas 2000 Air Quality Study by Carl M. Berkowitz; Chester W. Spicer; Paul V. Doskey (3383-3396).
Measurements of total non-methane hydrocarbon in whole air canisters collected from the top of a skyscraper on the western edge of Houston, Texas are summarized with an emphasis on samples collected during the passage of plumes of O3 and the associated rapid increase in the mixing ratio of this species. The back-trajectories associated with these events showed a pronounced deceleration of air parcels over central and western Houston and were not necessarily associated with direct passage over the petrochemical plants located in the heavily industrialized eastern part of Houston. As a result of the time these air parcels spent over the central and western parts of Houston, their VOC mix and associated chemical production rates were expected to differ from similar observations made over eastern Houston from aircraft sampling at low altitudes. Although periods of high O3 in the western part of the city were closely associated with light alkenes, these same observations show isoprene to make a significant contribution to the total VOC reactivity in the early afternoon (the start of peak photochemical activity) in contrast to observations made east of our sampling site that found the reactivity to be dominated by anthropogenic species. By initializing a 0-dimensional chemical kinetic model with observations made at the Williams Tower, we find that the ozone production efficiency scaled linearly to the ratio of total hydrocarbons and NO x , with an average OPE of 7.2, ranging from 2.3 to 16.9; these values are smaller than those reported in eastern Houston, suggesting a strong gradient in photochemical productivity across the city.
Keywords: Ozone; Ozone production efficiency; Houston; Box-model; Hydrocarbons; Williams Tower; Texas 2000 Air Quality Study;
The chemistry of precipitation and its relation to aerosol in Beijing by Aohan Tang; Guoshun Zhuang; Ying Wang; Hui Yuan; Yele Sun (3397-3406).
Fifty-three rain events throughout the entire year of 2003 were collected in Beijing and the concentration of 15 major ions with the pH of the rainwater were analyzed. The close correlations of the acidity in rainwater with the concentrations of aerosol and gases in the air were observed and elaborated. The scavenging of the pollutants from the air directly affects the pH and composition of the rainwater. The major ions in rainwater in Beijing were SO4 2−, NO3 −, Cl−, NH4 +, Ca2+, Mg2+, K+, and F−. The alkaline cations, NH4 + and Ca2+, acted as acid neutralizers and buffered the acidity of rain. The temporal variation of those major pollution ions in rainwater was similar to that of the air pollution. The concentrations of SO4 2−, NO3 −, and NH4 + have increased for the last two decades and likely indicated that the air pollution has become more and more serious in Beijing since the 1980s. The ratio of the concentration of SO4 2− to NO3 − observed in 2003 was much lower than that in 1981, indicating that the air pollution resulting from the traffic emission, NO x , has been more significant. A remarkably positive correlation between pH and Ca2+ concentration illustrates that Ca2+ generally from mineral aerosols plays an important role in buffering rainwater acidity in Beijing and in northern China at all times. The concentrations of SO4 2− and NO3 −, the predominant acid anions in rain, was much higher in Beijing than other cities, suggesting that the anthropogenic air pollution in Beijing has been a much more serious problem than other places.
Keywords: Rainwater; Precipitation; pH; Acid rain; Aerosol; Buffer; Scavenging;
Multi-plume aerosol dynamics and transport model for urban scale particle pollution by Matthias Ketzel; Ruwim Berkowicz (3407-3420).
The Multi-plume Aerosol dynamics and Transport (MAT) model has been developed to study the dynamics of the particle size distribution in urban environments. The MAT model uses a novel multi-plume scheme for vertical dispersion and routines of the aerodynamics models AERO3. It treats the processes: emission from a near ground source, dilution with background air, deposition, coagulation and condensation. The employed plume approach is computationally efficient compared to grid models and is therefore suitable for calculating longer time series.The treatment of the different processes in the model was validated against analytical solutions and literature data and later the full model was applied to a field data set from the Copenhagen area. The range of changes in particle concentration including all processes compared to an inert treatment of particles lies between 13% and 23% of loss in total number concentration and 2% loss and 8% gain for the total volume concentration. This agrees well with measurements in Copenhagen that indicated total number concentration (ToN) losses in the range of 15–30% between kerbside and urban rooftop level. The model also reproduces the shift of the maximum in the size distribution to slightly larger diameters between street and urban rooftop level.Because of the uncertainties in the parameters describing the different processes and their similar influence on the particle size distribution, it is possible to obtain similar results with different parameter combinations. More research and model validation is needed to narrow the range of possible input parameters and model assumptions for this type of modelling.
Keywords: Aerosol dynamics modelling; Particle size distribution; Plume model; Traffic source; Urban dispersion;
Nitrous oxide emission from the burning of agricultural residue by Mitsuteru Ogawa; Naohiro Yoshida (3421-3429).
The intramolecular distribution of stable isotopes in nitrous oxide from biomass burning plumes was measured for analysis of nitrous oxide behavior. Biomass burning experiments carried out for collecting the burning plumes used a grate-type test furnace. Dried rice straw was used as the biomass material for burning. Nitrous oxide was formed mainly in the flaming stage. The isotopomer ratios of the end-member of the burning were estimated, assuming simple mixing with background air. The nitrous oxide in the burning plume was depleted in 15N relative to the nitrogen compounds bound in the rice straw, but was rather similar relative to atmospheric nitrogen, and was slightly enriched in 18O relative to atmospheric oxygen. The central nitrogen atom was slightly heavier than the end-positioned atom. The kinetic isotope effects in nitrous oxide during the thermal decomposition and hydrogen reduction were evaluated at 1273 K. Assuming that a part of the nitrous oxide formed in the flame region was thermally destroyed or reduced, the behavior of nitrous oxide during biomass burning was analyzed on the basis of the isotopomer signatures and the kinetic isotope effects during the destruction reaction. The δ 15 N of the central nitrogen in nitrous oxide before destruction in the flame region was almost equivalent to that of the end-positioned nitrogen. The extent of the destruction reaction was quantitatively evaluated and small. This suggests that the nitrous oxide formed in the flames diffused quickly and is quenched by the surrounding air.
Keywords: Biomass burning; Nitrous oxide; Intramolecular distribution of isotopes; Isotopic fractionation; Agricultural residue;
Chemical evolution of an isolated power plant plume during the TexAQS 2000 study by Stephen R. Springston; Lawrence I. Kleinman; Frederick Brechtel; Yin-Nan Lee; Linda J. Nunnermacker; Jian Wang (3431-3443).
Stack emissions from a coal-burning power plant were measured during a research flight of the DOE G-1 during the Texas Air Quality Study (TexAQS 2000) on 10 September 2000. Clean upstream air and an isolated location allowed the plume to be unambiguously sampled during 12 successive downwind transects to a distance of 63 km—corresponding to a processing time of 4.6 h. The chemical transformation rates of sulfur and nitrogen primary pollutants into aerosol SO 4 2 - and HNO 3 yield independent values of OH concentration (8.0 and 11 × 10 6 cm - 3 , respectively) that are consistent within experimental uncertainty and qualitatively agree with constrained steady-state (CSS) box model calculations. Ozone production efficiency increases with plume age as expected. Primary aerosol emissions with D p > 5 μ m were sampled near the stack. As the plume ages, aerosol size distributions adjusted for dilution show constant number concentrations of aerosols D p > 10 nm and a marked increase in accumulation-mode particles ( D p > 0.1 μ m) as gas-to-particle-conversion causes smaller particles to grow.
Keywords: Power-plant plume; Texas 2000 Air Quality Study; Aerosol growth; Airborne measurements;
Analyzing a database of residential air leakage in the United States by Wanyu R. Chan; William W. Nazaroff; Phillip N. Price; Michael D. Sohn; Ashok J. Gadgil (3445-3455).
We analyzed more than 70,000 air leakage measurements in houses across the United States to relate leakage area—the effective size of all penetrations of the building shell—to readily available building characteristics such as building size, year built, geographic region, and various construction characteristics. After adjusting for the lack of statistical representativeness of the data, we found that the distribution of leakage area normalized by floor area is approximately lognormal. Based on a classification tree analysis, year built and floor area are the two most significant predictors of leakage area: older and smaller houses tend to have higher normalized leakage areas than newer and larger ones. Multivariate regressions of normalized leakage are presented with respect to these two factors for three house classifications: low-income households, energy program houses, and conventional houses. We demonstrate a method of applying the regression model to housing characteristics from the American Housing Survey to derive a leakage-area distribution for all single-family houses in the US. The air exchange rates implied by these estimates agree reasonably well with published measurements.
Keywords: Air leakage; Blower door; Fan pressurization measurements; Infiltration;
Exposure assessment and modeling of particulate matter for asthmatic children using personal nephelometers by Chang-Fu Wu; Ralph J. Delfino; Joshua N. Floro; Penelope J.E. Quintana; Behzad S. Samimi; Michael T. Kleinman; Ryan W. Allen; L.-J. Sally Liu (3457-3469).
It has been shown that acute exposures to particulate matter (PM) may exacerbate asthma in children. However, most epidemiological studies have relied on time-integrated PM measurements taken at a centrally located stationary monitoring sites. In this article, we characterized children's short-term personal exposures to PM2.5 (PM with aerodynamic diameters <2.5 μm) and separated them into ambient and nonambient components. The personal DataRAM without a size-selective inlet was used to estimate real-time PM2.5 concentrations on 20 asthmatic children, inside and outside of their residences, and at a central site. The personal and indoor pDRs were operated passively, while the home outdoor and central site instruments were operated actively. The subjects received 29.2% of their exposures at school, even though they only spent 16.4% of their time there. More precise personal clouds were estimated for the home-indoor and home-outdoor microenvironments where PM concentrations were measured. The personal cloud increased with increasing activity levels and was higher during outdoor activities than during indoor activities. We built models to predict personal PM exposures based on either microenvironmental or central-site PM2.5 measurements, and evaluated the modeled exposures against the actual personal measurements. A multiple regression model with central site PM concentration as the main predictor had a better prediction power ( R 2 = 0.41 ) than a three-microenvironmental model ( R 2 = 0.11 ). We further constructed a source-specific exposure model utilizing the time-space-activity information and the particle infiltration efficiencies (mean=0.72±0.15) calculated from a recursive mass balance model. It was estimated that the mean hourly personal exposures resulting from ambient, indoor-generated, and personal activity PM2.5 were 11.1, 5.5, and 10.0 μg/m3, respectively, when the modeling error was minimized. The high PM2.5 exposure to personal activities reported in our study is likely due to children's more active lifestyle as compared with older adult subjects in previous studies.
Keywords: Pm2.5; Personal cloud; Infiltration efficiency; Spatial model; Exposure model;
Seasonal variations of aerosol over Dona Paula, a coastal site on the west coast of India by T. Suresh; Elgar Desa (3471-3480).
We report here the observations of the aerosol studies carried-out for three years (2000–2002) at Dona-Paula, Goa (15.456°N, 73.801°E), a coastal site on the west coast of India. Aerosol optical depths were measured using a five channel sunphotometer with wavelengths at 440, 500, 675, 870 and 936 nm. The site enjoys a tropical climate and is under the influence of the strong southwest or summer monsoon and weak northeast or winter monsoon. Being a coastal station land-sea breeze play an important role in the variations of the aerosol loading over the site and their transport to the Arabian Sea. The mean aerosol optical thicknesses (AOT) at 500 and 870 nm are 0.46 (±0.15) and 0.23 (±0.097), respectively, while the Angstrom exponent is 1.31 (±0.347). The aerosol properties over the site showed a distinct seasonal variations, with high values of AOT observed during summer, with mean values of 0.48 (±0.15) and 0.26 (±0.09) at 500 and 870 nm, respectively, while during the winter relatively low values were observed, with mean value of 0.41 (±0.14) and 0.19 (±0.09) at 500 and 870 nm, respectively. The values of Angstrom exponents observed at the site suggest that the aerosol comprise mostly of the small size particles, with relatively larger particles being observed during summer than winter. An anti-correlation is observed between the inter-annual variations in the aerosol loading and the rainfall over Goa. Aerosol properties show diurnal variations, with comparatively lower values of AOT being observed in the evening. These diurnal variations are within a limit of 10% of the average values observed for the day. Seasonal patterns in the diurnal variations of aerosol optical depths have been observed. Considering the effect of the meteorological parameters over the aerosol, it is observed that the AOT is positively correlated with water vapor column, however the wind is found to aid in the reduction of aerosol load over Goa. It can be inferred from the weak negative correlation between AOT and Angstrom exponent that the contribution of large size particles in increasing the aerosol load was marginal. The aerosol optical depth derived from SeaWiFS at 865 nm was found to agree well with the measured values at 870 nm. However, the Angstrom exponent values from SeaWiFS at 510 nm were found to be underestimated.
Keywords: Goa; India; Asia; Aerosol; Coastal aerosol; Atmospheric turbidity; Diurnal variation;
The commuters’ exposure to volatile chemicals and carcinogenic risk in Mexico City by Naohide Shiohara; Adrián A. Fernández-Bremauntz; Salvador Blanco Jiménez; Yukio Yanagisawa (3481-3489).
The commuters’ exposure levels to volatile organic compounds were investigated in the following public transport modes: private car, microbus, bus, and metro along three commuting routes in the Metropolitan Area of Mexico City. The target chemicals were benzene, toluene, ethylbenzene, m/p-xylene, and formaldehyde. Integrated samples were taken while traveling during the morning rush hour (weekdays 7:00–9:00 a.m.) for six consecutive weeks in June and July, 2002. Scheffe test showed that the average concentrations of all chemicals inside cars and microbuses were statistically higher than in metro trains ( P < 0.05 ). For non-formaldehyde chemicals, the average levels inside automobiles were significantly higher than in metro trains and buses ( P < 0.05 ). The exposure level of formaldehyde in the microbus was much higher than those in the car, bus, and metro ( P < 0.05 ). On the other hand, there were no differences in the exposure levels among transport routes. These findings suggest that for commuting trips of comparable durations, car and microbus passengers are exposed to higher levels of volatile organic compounds than bus and metro commuters. These findings are consistent with previous studies looking at exposure of commuters to carbon monoxide. The lifetime carcinogenic risk from commuting by car was 2.0×10−5–3.1×10−5, that by microbus was 3.1×10−5–4.0×10−5, that by bus was 2.0×10−5–2.7×10−5, and that by metro was 1.3×10−5–1.7×10−5 in Mexico City.
Keywords: Personal exposure; Commuting; Benzene; Formaldehyde; Lifetime cancer risk; Potential carcinogenic incidences;
Polycyclic aromatic hydrocarbons in residential air of ten Chicago area homes: Concentrations and influencing factors by An Li; Todd M. Schoonover; Qimeng Zou; Felice Norlock; Lorraine M. Conroy; Peter A. Scheff; Richard A. Wadden (3491-3501).
Indoor and outdoor air samples at 10 non-smoker homes in the Chicago area were concurrently collected once per month for a 14-month period starting June 2000. During each sampling event, temperature, humidity, CO2, and CO were recorded. Questionnaires were used to register household activities. For each sample, 16 polycyclic aromatic hydrocarbons (PAHs) were measured using gas chromatograph and mass spectrometer (GC/MS). The total concentration of the 16 PAHs (ΣPAHs) ranged from 13 to 2454 ng m−3 in the indoor air and from 13 to 1865 ng m−3 in the outdoor air. In most cases, the concentrations were found to be log-normally distributed. The sum of PAHs with molecular mass ⩽202 (ΣLight-PAHs, excluding naphthalene and anthracene) were found to behave differently than the sum of those with molecular mass ⩾228 (ΣHeavy-PAHs). Variations among seasons were significant for indoor ΣLight-PAHs, and temperature was found to positively correlate with indoor ΣLight-PAHs for nine of the 10 homes. For ΣHeavy-PAHs, the outdoor concentrations were found to be significantly higher in the fall and winter seasons than in the summer. The correlations of indoor and outdoor concentrations appear to be weak for light PAHs, but reasonably strong for heavy PAHs. The medians of indoor-to-outdoor ratio (I/O) are less than or very close to 1 for all PAHs except anthracene. The indoor concentrations of ΣPAHs tend to be higher as the age of the houses increases, and the surrounding industrial pollution was found to have impact on outdoor ΣHeavy-PAHs. For light PAHs indoors, comparison among homes indicates that the impact of house characteristics and indoor activities tends to be greater than the influence of the penetrating outdoor air.
Keywords: PAHs; Indoor air; Residential homes; Urban environment; Indoor to outdoor ratio;
Evaluation of levels, sources and distribution of airborne trace metals in seven districts of the Baixada Fluminense, Rio de Janeiro, Brazil by Simone Lorena Quiterio; Célia Regina Sousa; Graciela Arbilla; Viviane Escaleira (3503-3512).
The main goal of this work is to assess the concentrations of total suspended particles (TSP) and airborne particulate trace metals in seven districts of the Baixada Fluminense, a region of the Metropolitan area of Rio de Janeiro, where the pollution sources are local industries, vehicular emissions and natural inputs.The sampling was performed using a high volume pump. The TSP levels were determined by gravimetry and the metals by inductively coupled plasma optical emission spectroscopy (ICP-OES). Geometrical means between 55.4±15.9 and 241.5±40.0 μg m−3 were determined for TSP, which are higher than both the Brazilian primary and secondary standards of air quality. Enrichment factors show that Zn, Cu, Cd and Pb are due to anthropic emissions. Zn, Cu and Cd levels are high in comparison with other urban and industrial areas. Mean concentrations are 1.1–88 times, 2.9–60.9 times and 3.0–130.0 times higher than reported values for other industrial areas, for Zn, Cu and Cd, respectively.It was not possible to identify a geometrical or seasonal distribution within the Baixada Fluminense area performing cluster and principal component analyses.
Keywords: Airborne particulate matter; Trace metals; Industrial sources; Vehicular emissions; Principal component analysis;
Possible effect of boreal wildfire soot on Arctic sea ice and Alaska glaciers by Yongwon Kim; Hiroaki Hatsushika; Reginald R. Muskett; Koji Yamazaki (3513-3520).
The role of black carbon (BC) soot in the Arctic as an agent of climate warming through forcing/feedback of sea ice/glacier albedo is an uncertainty in need of addressing. In-situ measurements of BC-aerosols and gas byproducts from the FROSTFIRE experiment burn, 8–11 July 1999, are used with a coupled high-resolution wind field/empirical fall-out model to assess transport/dispersion and estimate deposition. Results suggest that BC-aerosols (soot) are quickly transported from central Alaska to the Arctic Ocean region of multi-year sea ice and to southern Alaska glaciers, where up to 20% can be deposited. The estimate of BC soot concentration from Alaska boreal wildfires favorably compares to in-situ sea ice observations made in 1998 and snow albedo observation on Gulkana Glacier in 2001. We hypothesize that northern boreal wildfires are a possible contributor in the reduction of first/multi-year sea ice/glacier extent by enhancing summer melting from albedo reduction. Should the occurrence and severity of northern boreal wildfires continue as in summer 2004, during which more than 670 km2 burned and was the worst wildfire year on record, there will be implications for Northern hemisphere climate warming.
Keywords: Black carbon-aerosols; Climate warming; FROSTFIRE burning experiment; Trajectory model; Transport/deposition;
Design and performance of a single-pass bubbling bioaerosol generator by Gediminas Mainelis; David Berry; Hey Reoun An; Maosheng Yao; Kevin DeVoe; Donna E. Fennell; Rudolph Jaeger (3521-3533).
We describe and analyze a new particle generator that utilizes a bursting bubble principle and eliminates carrier fluid reuse. In this Liquid Sparging Aerosolizer (LSA), a suspension of particles or microorganisms is pumped at a flow rate of 0.2–2 mL min−1 to the top surface of a porous stainless-steel disk where it forms a thin suspension film. Filtered air is then sparged through the disk into the film causing it to break into bubbles that subsequently burst, releasing particles into the air. The released particles are then captured by the sparging air stream and are carried away. Particles that impinge the glass vessel and liquid droplets not captured by the air stream drain to the bottom of the vessel and play no further role in the aerosolization process. We tested the LSA with disks of different pore sizes (0.2, 0.5, 2.0 and 10.0 μm) and different air flows (2–30 L min−1) through the porous disks while generating polydisperse and monodisperse particles. Our tests showed that the use of 0.5 and 2.0 μm porosity disks resulted in the highest output of PSL particles in the desired size range, i.e., comparable to bacterial size. Each pore size seemed to have an optimal air flow rate; the produced aerosol concentration increased with increasing suspension delivery rate. The LSA also demonstrated stability of output concentration when aerosolizing particles over extended periods of time. In addition, the size distribution of injury-sensitive Pseudomonas fluorescens bacteria virtually did not change during 90 min of continuous aerosolization by the LSA. In fact, there was no (0%) viability loss, whereas the bacterial spectrum produced by a Collison nebulizer changed significantly over 90 min and there was a 50% loss in viability. The results indicate that the new instrument could be used to generate particles for the evaluation of pathogen collection methods, inhalation and other studies where extended delivery of stable and undamaged biological aerosols is required.
Keywords: Microorganism aerosolization; Microorganism viability; Bursting bubble;
Monoterpene emissions from Beech (Fagus sylvatica) in a French forest and impact on secondary pollutants formation at regional scale by S. Moukhtar; B. Bessagnet; L. Rouil; V. Simon (3535-3547).
Biogenic emissions from forest, crops, and grasslands are now considered major compounds in photochemical processes. Air quality analyses require more and more accurate input data, particularly emissions. Unfortunately, depending on the type of vegetation, these emissions are not always reliably defined. For example, Fagus sylvatica, which is a very abundant deciduous tree in France and in Europe, is a weak monoterpene emitter in the European inventory developed by Simpson et al. [1999. Journal of Geophysical Research 104, 8113–8152], but is a strong monoterpene emitter in Luchetta [1999. Caractérisation et quantification dans la basse atmosphère de composés organiques volatils biogéniques et anthropiques contribuant à la pollution de l’air. Ph.D. thesis, INPT Toulouse]. Beech (F. sylvatica) emission potential has never been measured in France.This study investigates the isoprene and monoterpenes emission measurements from F. sylvatica in France during a research program INTERREG III in Fossé Rhénan, during May and June 2003. A dynamic cuvette method was used. Sabinene is the main monoterpene emitted, composing more than 90% of biogenic emissions. The remaining is composed of α -pinene, β -pinene and limonene. No isoprene emissions were detected. The monoterpene emissions from F. sylvatica are affected by temperature and photosynthetic active radiation (PAR). In order to describe monoterpene emissions, the “isoprene algorithm” developed by Guenther et al. [1991. Journal of Geophysical Research 26A, 10799–10808; 1993. Journal of Geophysical Research 98D, 12609–12617] has been used. With this algorithm, simulation results and observations agree fairly well.The standard emission rate ( T = 303 K and PAR=1000 μmol m−2 s−1) for total monoterpenes is 43.5 μg gdw −1 h−1. This classifies F. sylvatica as a strong monoterpene emitter.The European inventory [Simpson, et al., 1999. Journal of Geophysical Research 104, 8113–8152], which is the standard inventory of the model CHIMERE, is adjusted using this value. This induces an annual increase of 30% in simulated monoterpene emissions in France.These two inventories are used to simulate a regional pollution event during spring 2003. No significant differences are observed for ozone concentrations. Peroxy Acyl Nitrate (PANs) and formaldehyde concentrations increase by up to 10% in the adjusted inventory.
Keywords: Fagus sylvatica; Emission rates; French ecosystem; Ozone;
Numerical simulation of the urban boundary layer over the complex terrain of Hong Kong by Hua Tong; Andrew Walton; Jianguo Sang; Johnny C.L. Chan (3549-3563).
Due to the complexity of the underlying surface, urban boundary layers may exhibit very different wind-temperature field structures compared with rural areas. In this study, an urban boundary layer model with a resolution of 500 m is applied to Hong Kong, a place characterized by complex topography with high mountains and dense urban developments. Five surface land use types are considered; grass and shrub land, trees, water, old urban areas and new town developments. The urban boundary layer model is embedded into the National Center for Atmospheric Research (NCAR) Mesoscale Model, version 5 (MM5). The initial and boundary conditions are obtained from the National Centers for Environmental Prediction (NCEP)/NCAR reanalysis dataset. The modeling approach therefore takes into account both the mesoscale background field and the urban underlying surface. The model is applied to the simulation of a pollution episode in Hong Kong. Results show good agreement with meteorological data for the surface winds and temperature. The model successfully simulates the urban heat island and the occurrence of a sea–land breeze circulation, and their impact on air pollutant transport and dispersion.
Keywords: Urban boundary layer; Energy balance model; Sea–land breeze; Complex topography;
Measuring the fractal dimension of diesel soot agglomerates by fractional Brownian motion processor by Chin-Hsiang Luo; Whei-May Grace Lee; Yan-Chiou Lai; Che-Yen Wen; Jiun-Jian Liaw (3565-3572).
This work explores the application of fractional Brownian motion (FBM) analysis to SEM micrographs of soot aggregates exhausted by a model dynamometer. By directly quantifying the surface texture of fractal-like aggregates to extract their Hurst coefficients (H), the FBM analysis was successful in parameterizing fractal dimension (D f) values, from which the relative aggregate structure variables could easily be determined. For two microscopic magnification scales (×50,000 and ×105), the soot aggregate D f fell in the range of 1.6–1.7. The experimental results closely agreed with the main conclusions derived from previous studies. An alternative approach is to clarify the impact of image properties on D f measurements due to digital image processing and data recording. A twofold change in SEM magnification size gave rise to a 7% deviation, and scaling up from the original image increased the discrepancy compared to miniaturization. In conclusion, texture characterization is useful for estimating the fractal properties of most chain-like or cluster soot aggregates.
Keywords: Soot agglomerate; Texture; Scanning electron microscopy; Fractional Brownian motion;