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Atmospheric Environment (v.40, #18)
Collection characteristics of low-pressure impactors with various impaction substrate materials by Yuji Fujitani; Shuichi Hasegawa; Akihiro Fushimi; Yoshinori Kondo; Kiyoshi Tanabe; Shinji Kobayashi; Takahiro Kobayashi (pp. 3221-3229).
The effects of types of low-pressure impactors (DLPI; Dekati; referred to hereinafter as “LPI�; and NanoMOUDI-II; MSP) and impaction substrate materials (aluminum foils, quartz fiber filters, and polycarbonate filters) on mass size distribution were studied for diesel exhaust particles from dynamometer test (DEP) and roadside atmospheric particles for a better understanding in terms of chemical analysis of impactor sample. Particle mass size distribution measured with LPI using aluminum foils and polycarbonate filters was distorted toward smaller mode diameters than those measured with NanoMOUDI using aluminum foils in sampling DEP and roadside atmospheric particles. This difference is explained by the occurrence of particle blow off in LPI. Heavy loading due to high concentrations in a specific size range results in greater particle loading height, from which particles are easily blown off by high jet velocities. Mass size distribution of DEP measured with LPI using a quartz fiber filter was modified to larger mode diameter than that measured with NanoMOUDI using aluminum foils. Higher particle collection efficiency than the ideal condition and smaller particles than the calibrated size, collected on upper stages, resulted in larger mode diameter, owing to the occurrence of filtration as well as impaction, and a shorter jet-to-plate distance, owing to the thickness of the filter. On the other hand, mass size distribution of roadside atmospheric particles measured with LPI using quartz fiber filters was similar to that measured with NanoMOUDI using aluminum foils. It is possible that the artifact of filtration is not important because of lower particle concentrations in the roadside atmosphere than in DEP. This experimental study of mass size distributions with various impactor types and substrate materials will enhance our understanding of the size distribution of chemical components, because impaction substrate material is restricted from methods of chemical analysis even though each substrate material has different collection characteristics.
Keywords: Diesel exhaust particles; Nanoparticles; Chemical components; Particle blow off; Size distribution
Examination on photostationary state of NO x in the urban atmosphere in Japan by Jun Matsumoto; Naohiro Kosugi; Ayaka Nishiyama; Ryoko Isozaki; Yasuhiro Sadanaga; Shungo Kato; Hiroshi Bandow; Yoshizumi Kajii (pp. 3230-3239).
To investigate the photostationary state (PSS) of nitrogen oxides (NO x), fast and precise measurements of related compounds were simultaneously carried out in the urban atmosphere. A PSS parameter φ including the observed peroxy radical (RO x) was examined. Consequently, φ was not significantly different from unity in many cases. Observed NO x, O3,JNO2 and RO x could reasonably elucidate the PSS of NO x. Meanwhile, in some cases with large RO x/O3, φ was significantly less than unity. It was suggested that the reaction rate coefficients of RO x with NO could be critical for the PSS in the urban atmosphere. It was confirmed that the LIF instrument is promising to observationally approach the PSS of NO x.
Keywords: Nitrogen oxides; Photostationary state (PSS); Peroxy radicals; Laser-induced fluorescence (LIF); Reaction rate coefficients
Application of dynamic linear regression to improve the skill of ensemble-based deterministic ozone forecasts by M. Pagowski; G.A. Grell; D. Devenyi; S.E. Peckham; S.A. McKeen; W. Gong; L. Delle Monache; J.N. McHenry; J. McQueen; P. Lee (pp. 3240-3250).
Forecasts from seven air quality models and surface ozone data collected over the eastern USA and southern Canada during July and August 2004 provide a unique opportunity to assess benefits of ensemble-based ozone forecasting and devise methods to improve ozone forecasts. In this investigation, past forecasts from the ensemble of models and hourly surface ozone measurements at over 350 sites are used to issue deterministic 24-h forecasts using a method based on dynamic linear regression. Forecasts of hourly ozone concentrations as well as maximum daily 8-h and 1-h averaged concentrations are considered. It is shown that the forecasts issued with the application of this method have reduced bias and root mean square error and better overall performance scores than any of the ensemble members and the ensemble average. Performance of the method is similar to another method based on linear regression described previously by Pagowski et al., but unlike the latter, the current method does not require measurements from multiple monitors since it operates on individual time series. Improvement in the forecasts can be easily implemented and requires minimal computational cost.
Keywords: Photochemical air quality; Modeling; Ozone; Ensemble forecast
Characteristics and sources of polycyclic aromatic hydrocarbons and fatty acids in PM2.5 aerosols in dust season in China by Ximei Hou; Guoshun Zhuang; Yele Sun; Zhisheng An (pp. 3251-3262).
The concentrations and distributions of 10 polycyclic aromatic hydrocarbons (PAHs) and seven fatty acids (FAs) in PM2.5 collected in dust season in six sites located in the source regions and on the pathway of the two dust storm episodes over China in 2004 were observed. The average concentrations of the total PAHs in Beijing were ∼10 times higher than those measured in 1980s, indicating that the PAH pollution has been much aggravated due to the rapid development and the motorization in the past 20 years. In non-dust storm days, the highest PAH was found at Yulin (YL) in the dust source region, as there are three large coal mines located around YL. The characteristic ratios of the individual PAH at the six sites indicated that coal combustion and traffic emission were the major contributors to PAHs in urban areas. The high abundances of oleic acid and linoleic acid in the aerosols suggested that cooking emission was the main source of FAs in urban areas. In dust storm episodes, the total concentrations of PAHs and FAs decreased sharply after the dust storm, while the ratios of PAH/PM2.5 and FAs/PM2.5 increased, demonstrating that the organic pollutants were cleared out through deposition or transport of the dust particles after dust episodes passed. The ratio of PAH(4)/PAH(5,6) was developed to be a tracer to deduce the sources of PAHs in the aerosols based on the different environmental behavior of PAH(4) and PAH(5,6) during the long-range transport. The higher ratios of PAH(4)/PAH(5,6) in BNU-DE2 suggested that the PAHs in the dust aerosols in the urban area in the dust storm episode were from the long-range transport, whereas the lower ratios in YL-DE2 and DL-DE2, which were similar to the ratios in non-dust days, implied that the local emission contributed greatly to the organic pollutants in the aerosols in the dust source regions. The ratio of FAs, C18:1/C18:0, could also be used to trace the sources of the organic pollutants in the dust storm episode.
Keywords: Aerosol; PM; 2.5; PAH; Fatty acids; Dust storm
Variation of selected air quality indicators over the city of Beirut, Lebanon: Assessment of emission sources by N.A. Saliba; S. Moussa; H. Salame; M. El-Fadel (pp. 3263-3268).
It is well established that the Mediterranean region experiences high pollution episodes as a result of its closed location and hot-humid long summers. However, few long-term field measurements have been conducted along the Eastern Mediterranean coast in general and in Arab countries, in particular. Hence, a six-month field study of major indicators like CO, SO2, PM10 and O3 were conducted in Beirut, Lebanon. Measurements on an upwind site showed that the monthly average concentrations of CO, SO2 and O3 were lower than the USEPA air quality standards while the monthly average concentrations of PM10 were higher. Diurnal variations showed that vehicle-induced emissions contribute significantly to CO levels while winter heaters constitute the major source of SO2. High diurnal and nocturnal levels of PM10 and O3 are the results of several local and long-range transport phenomena.
Keywords: CO; SO; 2; PM; 10; O; 3; Diurnal and seasonal variations; Eastern mediterranean
Influence of tobacco smoke on indoor PM10 particulate matter characteristics by L. Paoletti; B. De Berardis; L. Arrizza; V. Granato (pp. 3269-3280).
In this study we evaluate the influence of tobacco smoke on the physico-chemical characteristics of PM10 in different environments: outdoors, a smoking room, the same room after a 7-day absence of smokers and in a smoke-free office. The latter office was close to the smoking room, separated by a corridor. The coarse (PM10−2.1) and fine (PM2.1) fractions of PM10 collected in the monitored areas were analysed by scanning electron microscopy, equipped with a thin-window system for X-ray microanalysis (SEM/EDX). Photo-electron spectroscopy (XPS) was used to study the elemental composition of the particulate and to identify the chemical state of atomic species detected. Four clusters of particles for both “fine� and “coarse� fractions were identified: carbonaceous particles, soil erosion particles, Ca-sulphates and metal compound particles. EDX spectra showed that a percentage of carbonaceous particles carried S, Si and metal traces. High-resolution XPS spectra of the C1s region showed a significant greater occurrence of the C–O/C–N functional group in the particulate fine fraction collected in the smoking room compared to that collected outdoors. The carbonaceous component of coarse fraction collected in the smoking room appeared dissimilar from the same component detected in the other areas. After the 7-day absence of smokers this component of the PM10−2.1 fraction was similar to the corresponding coarse fraction collected at the outdoor location. The carbonaceous component of fine fraction collected in the smoking room, containing tobacco smoke products, such as organic carbon and nicotine, was traceable in the neighbouring areas, even several days after suspension of smoking activity.
Keywords: Tobacco smoke; Indoor; Outdoor; Particulate; Physico-chemical characterization
The rapid and continuous monitoring of gaseous elemental mercury (GEM) behavior in ambient air by K.-H. Ki-Hyun Kim; Vinit K. Mishra; Sungmin Hong (pp. 3281-3293).
In order to examine the environmental behavior of elemental mercury (GEM or Hg°) at varying time scales, Hg concentration data were obtained at 1-s intervals using a rapid Hg monitoring system (Lumex Hg analyzer). The Hg data sets obtained from a total of 24 experiments were analyzed in two different manners—either as raw data (collected at 1-s intervals) or after modification into two arbitrarily extended intervals (i.e., 10s and 1min). To meaningfully interpret those rapidly monitored Hg data, we evaluated both the raw and modified data sets in varying respects. The environmental behavior of Hg, while exhibiting clear distinctions over diurnal and/or seasonal scales, was found to experience sharp changes for a very short time period, usually less than a few tens of seconds to a minute. During such a short duration, a five- to ten-fold increase in Hg concentration was commonly found. As a means to evaluate the temporal factors associated with Hg behavior, the correlation analysis was made using both the original and modified data sets between the various statistical parameters (mean, median, min, and max). The overall results of this study confirm that the temporal variability of Hg, while maintaining highly stable and systematic patterns (e.g., over diurnal or seasonal scale), can be dramatically dynamic over very short time intervals such as a few tens of seconds or minutes.
Keywords: Atmospheric mercury; GEM; Fast sensor; Short-term measurements
Diel pattern of soil respiration in N-amended soil under maize cultivation by Weixin Ding; Yan Cai; Zucong Cai; Xunhua Zheng (pp. 3294-3305).
To understand maize- and N-induced diel variations in CO2 emission, we examined hourly CO2 emissions during the three typical growth stages of maize in sandy loam soil. There was a distinct diel pattern in soil CO2 emissions, with the peak occurring between 14:00 and 18:00 and the trough occurring between 0:00 and 4:00. Maize presence delayed the time of the peak. The absolute amount and diel fluctuation of CO2 emissions tended to diminish with time in the bare soil fertilized with 150kgNha−1 (BS). In contrast, N-fertilized maize (N150) significantly enhanced the total amount of CO2 emissions and the peak-trough differences in CO2 emissions, which reached a maximum at the pollination stage and then decreased. Control soil (CK) containing maize but no N fertilizer had highest overall CO2 emissions but reduced diel fluctuation because rhizosphere respiration was elevated in the nighttime. Soil temperature accounted for 61–71% of diel variation in the BS treatment but for only 44–59% and 38–58% in the N150 and CK treatments, respectively. Photosynthesis rates affected diel variation at the seedling and pollination stages. Both temperature and photosynthesis rates together explained up to 67–84% of diel variation at the seedling and pollination stages in the N150 treatment, but only 61% at the seedling stage in the CK treatment due to more CO2 released in the nighttime. The increased nighttime CO2 release, in turn, decreased the effect of temperature and even reduced the influence of photosynthesis rate on diel variations in CO2 release. Based on the present results, the best time for obtaining a representative daily CO2 measurement was found to be approximately 8:00 at the seedling stage and 9:00–11:00 at the other growth stages. The current findings indicate that N addition reduces soil CO2 emissions and its diel fluctuation.
Keywords: CO; 2; emission; Diel variation; Maize; N fertilization; Rhizosphere respiration; Temperature
Gas phase reaction of selected isothiocyanates with OH radicals using a smog chamber-mass analyzer system by Ronald Sommerlade; Perihan Ekici; Harun Parlar (pp. 3306-3315).
Relative rate constants for the gas phase reaction of methyl isothiocyanate (1), ethyl isothiocyanate (2), allyl isothiocyanate (3), phenyl isothiocyanate (4), 2-methylphenyl isothiocyanate (5), benzoyl isothiocyanate (6), and 4-methoxyphenyl isothiocyanate (7) with OH radicals have been determined at 297±2K and 9.21×10−2Atm in a 20L smog chamber-coupled online with a quadrupole mass analyzer, in which the concentration of the reaction partners could be determined online every minute. Some of the photoproducts could be detected and identified by HRGC-MS and HRGC-FTIR spectroscopy. The rate constants of the isothiocyanates obtained for the OH radical reactions ranged between 12.8 and 99.5×10−12cm3molecule−1s−1. The indicated errors were of 2-least-squares standard deviations. The lifetimes of the investigated compounds in the troposphere due to reactions with the OH-radicals were calculated and ranged from 3.5 to 18.8h by using the tropospheric concentration of OH radicals of 8.0×105moleculescm−3 over a period of 24h.
Keywords: Isothiocyanates; Gas phase reaction; Troposphere; OH radicals; Atmospheric lifetime
A model of annual orographic precipitation and acid deposition and its application to Snowdonia by A.J. Dore; M. Mousavi-Baygi; R.I. Smith; J. Hall; D. Fowler; T.W. Choularton (pp. 3316-3326).
A model of orographic rainfall has been used to estimate annual precipitation and acid wet deposition at a 1km resolution for the Snowdonia mountains in North Wales. Comparison with measurements and existing rainfall maps of the UK showed that this approach was successful in reproducing the high annual precipitation peaks of up to 4000mm annually that occur in this area. At 13 out of the 17 measurement sites, the modelled annual precipitation differed from long-term annual average measurements by no more than 25%. The process model was compared with a procedure used to map wet deposition of pollutants across the United Kingdom at a 5km resolution. Significant differences between the two deposition data sets were apparent. With the mapping procedure, maximum wet deposition was correlated to areas of high precipitation in the northeast of the domain. With the process model, however, maximum deposition was observed over the smaller hills in the southwest of the domain, the first orographic barrier reached by the air mass in south-westerly flow. High exceedances of critical loads for acidic deposition to soils were calculated using the mapping procedure and found to be due to the high annual precipitation in Snowdonia. The seeder–feeder model represents a useful tool, which could be used for estimating annual wet deposition of pollutants and exceedance of critical loads in hill areas at a much finer resolution than the national transport models and deposition mapping routines that are commonly employed in the United Kingdom.
Keywords: Acid rain; Critical loads; Nitrate; Orographic precipitation; Seeder–feeder effect; Snowdonia; Sulphate
Urban smoke concentrations at Kew, London, 1898–2004 by R.G. Harrison (pp. 3327-3332).
Historical smoke concentrations at monthly resolution for the early twentieth century are found for Kew Observatory, London, using the atmospheric electricity proxy technique. Smoke particles modify the electrical properties of urban air: an increase in smoke concentration reduces air's electrical conductivity and increases the Potential Gradient (PG). Calibrated PG data are available from Kew since 1898, and air conductivity was measured routinely between 1909 and 1979 using the technique developed by C.T.R. Wilson. Automated smoke observations at the same site overlap with the atmospheric electrical measurements from 1921, providing an absolute calibration to smoke concentration. This shows that the late nineteenth century winter smoke concentrations at Kew were approximately 100 times greater than contemporary winter smoke concentrations. Following smoke emission regulations reducing the smoke concentration, the electrical parameters of the urban air did not change dramatically. This is suggested to be due to a composition change, with an increase in the abundance of small aerosol compensating for the decrease in smoke.
Keywords: Atmospheric electricity; Air pollution; Black carbon; Air conductivity
Exposure assessment of particulate matter air pollution before, during, and after the 2003 Southern California wildfires by Jun Wu; Arthur M Winer; Ralph J Delfino (pp. 3333-3348).
Exposure to biomass smoke has been associated with increased respiratory illness and symptoms. The goal of this study was to estimate daily particulate matter (PM; PM10 and PM2.5) concentrations at a zip-code level for southern California before, during and after the 2003 southern California wildfires. On average, heavy smoke from the fires increased PM10 and PM2.5 concentration by 160 and 100μgm−3, respectively. Missing PM concentrations from the every 3rd or 6th day routine measurements or due to the incapacitation of monitors and/or stations by the fires were estimated based on (1) temporal profiles of continuous TEOM or BAM data at co-located or closely located sites; and (2) light extinction, meteorological conditions, and smoke information extracted from MODIS satellite images at a 250m resolution. Light extinction coefficient, smoke, and relative humidity were the most important factors strongly associated with PM concentrations, especially PM2.5. Spatial interpolations of PM concentrations were performed using inverse distance weighting (IDW), kriging or cokriging methods for the non-fire periods. Kriging was not superior to IDW in many cases due to the small number of monitoring stations. Since the fire and smoke created highly heterogeneous pollution surfaces, typical IDW and kriging could not work during the fires. Polygons were created based on satellite images to represent each smoke-covered area under different smoke densities. Concentrations were assigned to each polygon using measured or valid estimated concentrations at the corresponding monitoring stations, or at other stations under similar smoke conditions. In summary, population-weighted PM10 and PM2.5 concentrations were 190 and 90μgm−3, and 125 and 75μgm−3 under heavy and light smoke conditions, respectively, in contrast to concentrations of 40 and 20μgm−3 for PM10 and PM2.5, respectively, during the non-fire periods. The methodology we developed in this study is also applicable to other regions to a greater or lesser extent based on the availability of satellite, visibility and air quality data.
Keywords: Particulate matter; Satellite image; Visibility; Smoke; Spatial interpolation
Gas cooking and reduced lung function in school children by Hanns Moshammer; H.-P. Hans-Peter Hutter; Manfred Neuberger (pp. 3349-3354).
Outdoor nitrogen dioxide (NO2) is associated with reduced respiratory health. This could be due to a unique biological effect of this gaseous pollutant or because it serves as a surrogate of fine particles from incineration sources. Cooking with gas in small kitchens produces high concentrations of gaseous irritants (mainly nitrogen dioxide), but not fine particles.To study the relative impact of cooking with gas on lung function parameters in a cross sectional study of school children.Nearly all elementary school children (2898 children aged 6–10 years) living in the city of Linz (capital of Upper Austria) underwent lung function testing. In a questionnaire administered simultaneously to their parents, information on household conditions including cooking and tobacco smoke exposure was collected. Impact of cooking with gas on lung function controlling for various confounders was analyzed using loglinear multiple regression.Gas cooking reduced lung function parameters ranging from 1.1% (not significant) for MEF25 up to 3.4% (p=0.01) for peak expiratory flow (PEF).Gas stoves can have an adverse impact on children's respiratory health. Parents and caretakers should be advised to insure good ventilation while and after cooking, especially in small and poorly ventilated rooms. This study adds to the growing evidence that gaseous pollutants from incineration sources affect respiratory health directly.
Keywords: Nitrogen dioxide; Spirometry; Indoor pollutants; Respiratory health
Population exposure to benzene: One day cross-sections in six European cities by P.P. Pascual Pérez Ballesta; Robert A. Field; Richard Connolly; Natale Cao; Antonia Baeza Caracena; Emile De Saeger (pp. 3355-3366).
This paper describes the experimental methodology and basic results of the PEOPLE project (Population Exposure to Air Pollutants in Europe). Simultaneous diffusive measurements of outdoor, indoor and human exposure benzene concentrations were made during one day campaigns. Six cities were assessed, namely: Brussels and Lisbon (22 October 2002), Bucharest and Ljubljana (27 May 2003), Madrid (3 December 2003) and Dublin (28 April 2004). In general, human exposure to benzene was higher than concentrations reported at urban background monitoring sites. Traffic was the dominant source of benzene in all the six cities that were studied. The highest exposure levels from the commuting groups were car users. The control group, with no influence from commuting or smoking, reported concentrations closer to the background level of the city. The smoking group had the highest level of exposure. The level of exposure of school children was similar to that of the commuting groups. Indoor locations that were influenced by smoking sources, or with free access to busy streets, reported relatively high concentrations. The highest indoor concentrations were measured in bars and inside motor vehicles. When considering the six cities together, a linear relationship was evident between ambient levels and human exposure. Daily median values of human exposure for non-smoking commuters were 1.5 times the level of urban background and 0.6 times the maximum outdoor value (hotspot).
Keywords: Population exposure; Benzene; Personal monitoring; Air quality directives; Traffic emission
Particulate air pollution in six Asian cities: Spatial and temporal distributions, and associated sources by N.T. Kim Oanh; N. Upadhyay; Y.-H. Zhuang; Z.-P. Hao; D.V.S. Murthy; P. Lestari; J.T. Villarin; K. Chengchua; H.X. Co; N.T. Dung; E.S. Lindgren (pp. 3367-3380).
A monitoring program for particulate matter pollution was designed and implemented in six Asian cities/metropolitan regions including Bandung, Bangkok, Beijing, Chennai, Manila, and Hanoi, within the framework of the Asian regional air pollution research network (AIRPET), coordinated by the Asian Institute of Technology. As uniform the methodologies as possible were intended with an established QA/QC procedure in order to produce reliable and comparable data by the network. The monsoon effects and seasonal changes in the sources/activities require long-term monitoring to understand the nature of air pollution in the cities. During phase 1 (2001–2004) of the AIRPET around 3000 fine and coarse particulate matter samples were collected from characteristic urban sites, which provide insight into temporal and spatial variations of PM in the cities. In all six cities, the levels of PM10 and PM2.5 were found high, especially during the dry season, which frequently exceeded the corresponding 24h US EPA standards at a number of sites. The average concentrations of PM2.5 and PM10 in the cities ranged, respectively, 44–168 and 54–262μgm−3 in the dry season, and 18–104 and 33–180μgm−3 in the wet season. Spatial and temporal distribution of PM in each city, the ratios of PM2.5 to PM10, and the reconstructed mass were presented which provide useful information on possible PM sources in the cities. The findings help to understand the nature of particulate matter air pollution problems in the selected cities/metropolitan regions.
Keywords: Monitoring; Particulate matter; Contributing sources; Asian cities; AIRPET
δ13C of volatile organic compounds (VOCS) in airborne samples by thermal desorption-gas chromatography-isotope ratio-mass spectrometry (TD-GC-IR-MS) by Nicole Turner; Mark Jones; Kliti Grice; Daniel Dawson; Marisa Ioppolo-Armanios; Steven J. Fisher (pp. 3381-3388).
This paper is a preliminary investigation into the use of a thermal desorption-gas chromatography-isotope ratio mass spectrometry (TD-GC-IR-MS) method to determine stable carbon isotopic compositions ( δ13C) of low molecular-weight volatile organic compounds (VOCs) in airborne samples (e.g. industrial and car exhaust emissions) as a means of differentiating their sources in the environment. A TD-GC-IR-MS method for obtaining δ13C of VOCs (benzene, toluene, chlorobenzene, ethylbenzene, m-xylene and propylbenzene) in air samples has been optimised, and is proven to be both reproducible and linear. The δ13C of the VOC standards was found to be comparable (within analytical error) to that obtained from direct GC-IR-MS analysis. This novel method of VOC analysis is valuable in environmental and forensic investigations.
Keywords: Thermal desorption; Environmental contaminants; Volatile organic compounds; Stable carbon isotopes; Airborne samples
Temporal considerations in the measurement of indoor mass transfer coefficients by Glenn C. Morrison; Deborah J. Wiseman (pp. 3389-3395).
Indoor pollutant mass transport, characterized by the “transport-limited deposition velocity�, vt, is dynamic and measurements of this mass-transfer coefficient can be influenced by changing conditions. We find that for large, but realistic, changes in indoor transport conditions during the sampling period, time-averaged measurements of vt can be in error by 40% or more. Measurements using a highly surface reactive species, such as nitric acid, incur the greatest error. The measurement error incurred for species that are moderately surface reactive, such as ozone, varies depending on the type of surfaces available for deposition. Further, the greater the magnitude and frequency in the fluctuations, the greater the error anticipated from time-averaged measurements of vt. An analysis of continuous flux measurements from field experiments in apartments, a lab and an office suggest that time-averaged measurements of vt will typically be in error by 5–15%.
Keywords: Mass-transfer coefficient; Pollutant transport; Pollutant deposition; Indoor air; Temporal measurement
Experimental measurements and numerical simulations of particle transport and distribution in ventilated rooms by Z. Zhang; Q. Chen (pp. 3396-3408).
Prediction of particle dispersion and distribution in a room is very important for creating and maintaining a healthy indoor environment. The present study used a CFD program with a Lagrangian particle tracking method to predict particle dispersion and concentration distribution in ventilated rooms. Since the Lagrangian method could generate great uncertainty in particle concentration calculations, this study first investigated such uncertainty using a statistical approach. It was found that the stability of the concentration solution became well controlled as a sufficient number of particles were analyzed. Although the overall computational cost was considerable, the numerical results agreed well with associated experimental data. In all cases studied, particle size distribution was monodisperse, and particle diameter ranged from 0.31 to 4.5μm. Particle deposition rate was neglected, and particles were hence removed only by the ventilation system. Thus the particle removal performance of different ventilation systems can be evaluated. Three ventilation systems have been studied, including ceiling and side wall supply systems and an underfloor air distribution (UFAD) system. It was found that the UFAD system had a better particle removal performance than the ceiling and side wall supply systems in the study. However, resuspended particles at the floor level can still cause problems in an UFAD system.
Keywords: Fine particles; Indoor air; Underfloor air distribution; Ventilation systems; Lagrangian particle tracking; CFD
Aerosol characteristics from the Taiwan aerosol supersite in the Asian yellow-dust periods of 2002 by C.-T. Chung-Te Lee; M.-T. Ming-Tung Chuang; C.-C. Chang-Chuan Chan; T.-J. Tsun-Jen Cheng; S.-L. Song-Lih Huang (pp. 3409-3418).
The occurrence of Asian dust storms, and the subsequent transport of yellow dust (YD) greatly influences the air quality of lee-side countries such as Korea and Japan. The dust is also frequently transported in a southward direction by a strong cold high-pressure system that affects the air quality in Taiwan. This study reports the aerosol properties that were monitored continuously at the Taiwan aerosol supersite during YD events in 2002. Based on the observations of meteorology and aerosols, we divided the time interval of a YD event into a before period, during period, and after period. Among the seven observed YD events, the second event was marked with the maximum hourly PM10 level at 502μgm−3, and with the longest during period for a total of 147h. The averages of the hourly PM10 and PM2.5−10 were much higher in the during period as compared to those in the before period. It is interesting to note that the time lapse in the during period was well correlated with the maximum level of both PM10 and PM2.5−10. It must be noted that the PM2.5 levels were dramatically increased in the after period, which was due to the accumulation of particles influenced by the anticyclonic outflow. The aerosol size distribution in the third YD event verified that supermicron particles dominated in the during period, and that submicron particles were predominant in the before and after periods. For the chemical properties of the aerosols, time series results indicated that sulfates were mostly contributed by the dust transport, and the others were more related to vehicle exhausts. However, they all accumulated in the period of atmospheric stagnancy.
Keywords: Aerosol supersite; Atmospheric aerosols; Asian yellow dust; Aerosol characterization