Heavy metals exposure of children from stairway and sidewalk dust in the smelting district,northeast of China

The aim of this work was to study metals accumulation in stairway (inside the residential building) and sidewalk (outside the residential building) dust, and health risk of children due to dust exposure. The investigation included the: (a) spatial distributions of Hg, Pb, Cd, Zn and Cu in stairway and sidewalk dust, (b) source analysis of metals in stairway and sidewalk dust, and (c) assessment of the children health risks due to metals exposure from stairway and sidewalk dust. In the smelting district of Huludao, the maximum Hg, Pb, Cd, Zn and Cu contents in stairway dust were 5.324, 4594, 936.8, 48 253, 1377 mg kg^?1, respectively, and were 144, 213, 8674, 760 and 69.5 times as high, respectively, as the background values in soil. A strong positive relationship was shown between the stairway and sidewalk dust for each metal (p < 0.01). The trends for Hg, Pb, Cd, Zn and Cu in the stairway and sidewalk dust were similar and with higher concentrations trending Huludao Zinc Plant (HZP). Atmospheric deposition due to metal smelting from HZP was the common source of heavy metals in the sidewalk and stairway dust. Vehicular traffic affected the metal accumulation in dust, but their contribution was slight comparing with atmospheric emission from HZP. Almost all hazard indexes (HIs) for metals due to stairway dust exposure in this study were lower than 1. The health risk for children was low if they would not play in the stairway. However, children were also experiencing the potential health risk from Cd and Pb exposure from sidewalk dust outside residential building, especially near HZP.     

The impacts of different kinds of dust events on PM10 pollution in northern China

In this study the frequencies of PM₁₀ (as key urban pollutant) in 14 key environmental protection cities in northern China were analyzed. It follows that the PM₁₀ concentration in the high-frequency period is higher with an extent 0.009–0.066 mg m⁻³ than in the low-frequency period of 2001–2002. Further the impacts of three kinds of dust events on the PM₁₀ concentration in four cities (Beijing, Hohhot, Xi’an and Lanzhou) were explored. The results showed that different kinds of dust events have different influences on variation of PM₁₀ concentration in these four cities. In Lanzhou and Hohhot, which are near the source areas of dust events, the contribution degree of these three dust events to the PM₁₀ is: floating dust>dust storm>blowing dust. Whereas, in Beijing and Xi’an situated in dust event passing areas, the mean value of PM₁₀ concentration is higher in blowing dust than in floating dust (no dust storm). In addition, the influences of dust events on PM₁₀ concentration are different in the cities on different dust event paths. In Beijing and Hohhot (on the northern path), the high PM₁₀ concentration is usually caused by blowing dust. But in both Lanzhou and Xi’an (on the western/northwestern path) the high PM₁₀ pollution concentration is usually caused by floating dust.     

Comparison of the physical and chemical characteristics of fine road dust at different urban sites

The size distribution and chemical components of a fine fraction (<2.5 μm) of road dust collected at urban sites in Korea (Gwangju) and Mongolia (Ulaanbaatar) where distinct urban characteristics exist were measured. A clear bimodal size distribution was observed for the resuspended fine road dust at the urban sites in Korea. The first mode peaked at 100–110 nm, and the second peak was observed at 435–570 nm. Ultrafine mode (~30 nm) was found for the fine road dust at the Mongolia site, which was significantly affected by residential coal/biomass burning. The contribution of the water-soluble ions to the fine road dust was higher at the sites in Mongolia (15.8–16.8%) than at those in Korea (1.2–4.8%). Sulfate and chloride were the most dominant ionic species for the fine road dust in Mongolia. As (arsenic) was also much higher for the Mongolian road dust than the others. The sulfate, chloride, and As mainly come from coal burning activity, suggesting that coal and biomass combustion in Mongolia during the heating season should affect the size and chemical components of the fine road dust. Cu (copper) and Zn (zinc), carbonaceous particles (organic carbon [OC] and elemental carbon [EC]) increased at sites in Korea, suggesting that the fine road dust at these sites was significantly affected by the high volume of traffic (engine emission and brake/tire wear). Our results suggest that chemical profiles for road dust specific to certain sites should be applied to more accurately apportion road dust source contributing to the ambient particulate matter.

Implications: Size and chemical characteristics of fine road dust at sites having distinct urban characteristics were examined. Residential coal and biomass burning and traffic affected physiochemical properties of the fine road dust. Different road dust profiles at different sites should be needed to determine the ambient PM2.5 sources more accurately.     

The spatial and temporal characteristics of TOMS AI over the Tarim Basin,China

This paper has a dual focus. One is to study the spatial characteristics of dust activities over the Tarim Basin by locating dust active hot spots. The other is to study the temporal characteristics of dust activities over the Tarim Basin by applying the Extreme Value Analysis (EVA).Hot spots (in terms of dust loading) refer to relatively small (compared to the size of the whole source area), consistently active, dust producing areas. In this paper, Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) is used to identify hot spots in the Tarim Basin. This hot spot study suggests that dust emissions are inhomogeneous in the Tarim Basin area and the formation of the two hot spots is linked to both (1) a large amount of fine sandy sediments accumulated at the hot spot areas and (2) the basin's internal dust transport pathways which are controlled by the extreme bounding topography of the basin.Extreme Value Analysis (EVA) has been widely used in a variety of areas, but has not yet been applied in dust storm research. In this paper, 13 years Tarim Basin regional daily maximum TOMS AI data time series are constructed. By examining the statistics of the time series, a new method (outlier method) is developed to identify extreme values. EVA is applied and 100-year-return values are suggested. The interpretation of the 100-year-return values is discussed by referring to historical meteorological records and also climate change projections.     

Variability of dust iron solubility in atmospheric waters: Investigation of the role of oxalate organic complexation

Atmospheric dust deposition is a major external iron source for remote surface ocean waters. Organic complexation is known to play a role in the dissolution of iron-containing minerals. In this paper, we present our study on the effect of oxalate on dust iron solubility in simulated rainwater. Our results reveal that the solubility of iron carried by analogs of different African dusts varies with the dust source. Our experiments indicate a positive linear correlation between iron solubility and oxalate concentration. Soluble iron (SFe) increases from 0.0025(±0.0005)% to 0.26(±0.01)% of total iron, considering all dust sources and with oxalate concentrations ranging from 0 to 8 μM. These results show that the observed variability of iron solubility in aerosols collected over the Atlantic Ocean is, at least partly, due to an increase in dust iron solubility, with the presence of oxalate complexation, rather than to the presence of more soluble anthropogenic iron. Considering the mineralogical composition of those particles, experiments with pure minerals (hematite, goethite and illite) were performed to study the dissolution process. We found that oxalate promotes the solubility of iron contained in clay and hence confirmed that more than 95% of SFe from soil dust is provided by clay (illite). This experimental work enables us to establish a parameterization of iron solubility in dust as a function of oxalate concentration and based on the individual iron solubility of pure iron-bearing minerals usually present in dust particles. Finally, our results emphasize that oxalate contributes to iron solubility on the same order of magnitude as the acid processes. Organic complexation appears to be a process that increases iron solubility and likely enhances the bioavailability of iron from dust.     

The impact of transpacific transport of mineral dust in the United States

We use a global chemical transport model (GEOS-Chem) to estimate the impact of transpacific transport of mineral dust on aerosol concentrations in North America during 2001. We have implemented two dust mobilization schemes in the model (GOCART and DEAD) and find that the best simulation of North American surface observations with GEOS-Chem is achieved by combining the topographic source used in GOCART with the entrainment scheme used in DEAD. This combination restricts dust emissions to year-round arid areas but includes a significant wind threshold for dust mobilization. The model captures the magnitude and seasonal cycle of observed surface dust concentrations over the northern Pacific. It simulates the free tropospheric outflow of dust from Asia observed in the TRACE-P and ACE-Asia aircraft campaigns of spring 2001. It reproduces the timing and distribution of Asian dust outbreaks in North America during April–May. Beyond these outbreaks we find persistent Asian fine dust (averaging 1.2 μg m⁻³) in surface air over the western United States in spring, with much weaker influence (0.25 μg m⁻³) in summer and fall. Asian influence over the eastern United States is 30–50% lower. We find that transpacific sources accounted for 41% of the worst dust days in the western United States in 2001.     

Wind modeling of Chihuahuan Desert dust outbreaks

The Chihuahuan Desert region of North America is a significant source of mineral aerosols in the Western Hemisphere, and Chihuahuan Desert dust storms frequently impact the Paso del Norte (El Paso, USA/Ciudad Juarez, Mexico) metropolitan area. A statistical analysis of HYSPLIT back trajectory residence times evaluated airflow into El Paso on all days and on days with synoptic (non-convective) dust events in 2001–2005. The incremental probability—a measure of the areas most likely to have been traversed by air masses arriving at El Paso during dusty days—was only strongly positively associated with the region west–southwest of the city, a zone of known dust source areas. Focused case studies were made of major dust events on 15 April and 15 December 2003. Trajectories approached the surface and MM5 (NCAR/Penn State Mesoscale Model) wind speeds increased at locations consistent with dust sources observed in satellite imagery on those dates. Back trajectory and model analyses suggested that surface cyclones adjacent to the Chihuahuan Desert were associated with the extreme dust events, consistent with previous studies of dust storms in the Southern High Plains to the northeast. The recognition of these meteorological patterns serves as a forecast aid for prediction of dust events likely to impact the Paso del Norte.     

Detection of Asian dust (Hwangsa) over the Yellow Sea by decomposition of unpolarized infrared reflectivity

The periodical occurrence of Asian dust (Hwangsa) in East Asia during every spring and winter is of great consequence to regional human health and visibility. One weakness of the previous methods based on the brightness temperature (BT) differences or optical depths is that they can not accurately detect the dust events over the Yellow Sea. This study proposes a unique technique of decomposing unpolarized reflectivities to distinguish between dust and clouds over the sea surface. Many current infrared (IR) satellite instruments such as MTSAT-1R measure the unpolarized radiance. In this process, an approximate relationship between vertically and horizontally polarized reflectivities is validated for the IR wavelengths of 3–12 μm. The radiances observed from an IR geostationary satellite and the simulated sea surface temperature (SST) are used for a case study of Asian dust events. The results show qualitatively the reasonable spatial agreements with MODIS true color images for these Asian dust events. The proposed method in this study can be utilized for the operational purpose to detect the signal of Asian dust over sea surface.     

Dynamic responses of photosystem II in the Namib Desert shrub, Zygophyllum prismatocarpum, during and after foliar deposition of limestone dust

The effects of limestone dust deposition on vegetation in desert ecosystems have not yet been reported. We investigated these effects in a succulent shrub from the Namib Desert at a limestone quarry near Skorpion Zinc mine (Namibia). Effects of limestone dust were determined in Zygophyllum prismatocarpum (dollar bush) plants with heavy, moderate and no visible foliar dust cover by means of chlorophyll a fluorescence measurements. Limestone dust deposition decreased overall plant performance through loss of chlorophyll content, inhibition of CO(2) assimilation, uncoupling of the oxygen-evolving complex and decreased electron transport. Importantly, dynamic recovery occurred after termination of limestone extraction at the quarry. Recovery was accelerated by rainfall, mainly because of dust removal from leaves and stimulation of new growth. These results indicate that limestone dust has severe effects on photosynthesis in desert shrubs, but that recovery is possible and that, in arid environments, this process is modulated by rainfall.     

Variability of atmospheric dust loading over the central Tibetan Plateau based on ice core glaciochemistry

A Mt. Geladaindong (GL) ice core was recovered from the central Tibetan Plateau (TP) spanning the period 1940–2005 AD. High-resolution major ion (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, SO₄^2?, NO₃^?) time-series are used to investigate variations in atmospheric dust loading through time. The crustal source ions vary seasonally with peaks in dust concentrations occurring during the winter and spring which are consistent with atmospheric dust observations at local meteorological stations. However, both similarities and dissimilarities are displayed between the decadal variation of atmospheric dust in the GL core and dust observation records from meteorological stations, which can be attributed to local environmental effects at the stations. This paper compares the 1980s and 1970s as case periods for low and high atmospheric dust loading, respectively, two periods reflecting shifts in spring atmospheric circulation (a weakening of zonal and meridional winds) from the 1970s (a period of enhanced dust aerosol transportation to central TP) to the 1980s (a period of diminished dust aerosol transportation to central TP), especially a significant decrease of meridional wind speeds in the 1980s. GL ice core dust proxies (Ca²⁺ and K⁺) are correlated with Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data in spring over the TP and in the northwestern China (especially for K⁺). Thus variability of crustal ions in central TP ice core provides a proxy for reconstructing a history of atmospheric dust loading not only on the TP, but also in northwestern China.     

Distribution of polybrominated diphenyl ethers and dust particle size fractions adherent to skin in indoor dust,Pretoria, South Africa

In order to determine human exposure to the indoor toxicant, selection of dust fraction and understanding dust particle size distribution in settled indoor dust are very important. This study examined the influence of dust particle size on the concentration of polybrominated diphenyl ethers (PBDEs) congeners, assessed the distribution of dust particle size and characterized the main indoor emission sources of PBDEs. Accordingly, the concentrations of PBDE congeners determined in different indoor dust fractions were found to be relatively higher in the order of dust particle size: 45–106 μm?>?(<45 μm)?>?106–150 μm. The finding shows arbitrary selection of dust fractions for exposure determination may result in wrong conclusions. Statistically significant moderate correlation between the concentration of Σ₉PBDEs and organic matter content calculated with respect to the total dust mass was also observed (r?=?0.55, p?=?0.001). On average, of total dust particle size <250 μm, 93.4 % (m/m%) of dust fractions was associated with less than 150 μm. Furthermore, of skin adherent dust fractions considered (<150 μm), 86 % (v/v%) is in the range of particle size 9.25–104.7 μm. Electronic materials treated with PBDEs were found the main emission sources of PBDE congeners in indoor environment. Based on concentrations of PBDEs determined and mass of indoor dust observed, 150 μm metallic sieve is adequate for human exposure risk assessment. However, research in this area is very limited and more research is required to generalize the fact.     

Application of neutral electrolyzed water spray for reducing dust levels in a layer breeding house

Reducing airborne dust is an essential process for improving hen housing environment. Dust reduction effects of neutral electrolyzed water (pH 8.2) spray were investigated in a commercial tunnel-ventilated layer breeding house during production in northern China. A multipoint sampler was used to measure airborne dust concentration to study the dust reduction effects and distribution in the house. Compared with the control treatment (without spray), airborne dust level was reduced 34% in the 3 hr after spraying 216 mL m^?2 neutral electrolyzed water in the breeding house. The dust concentration was significantly higher during the periods of feed distribution (1.13 ± 0.13 mg m^?3) and artificial insemination (0.72 ± 0.13 mg m^?3) compared with after spray (0.47 ± 0.09 mg m^?3) and during lights-off period (0.29 ± 0.08 mg m^?3) in the three consecutive testing days (P < 0.05). The experimental cage area was divided into four zones along the length of the house, with zone 1 nearest to the evaporative cooling pad and zone 4 nearest to the fans. The air temperature, relative humidity, airflow rate, and dust concentration were measured at the sampling points of the four zones in 3 consecutive days and mortality of the birds for the duration of a month were investigated. The results showed that the air temperature, airflow rate, dust concentration, and number of dead birds increase from zone 1 to zone 4 in the tunnel-ventilated layer breeding house.

Implications: It is difficult to effectively reduce hen house airborne dust levels and limited information is available on airborne dust distribution in tunnel-ventilated hen houses. This work investigates (i) the application of neutral electrolyzed water spray for reducing dust in a layer breeding houses; (ii) dust concentration variations in 24-hr house operation; as well as (iii) the effects of location on dust concentrations. It was demonstrated that neutral electrolyzed water spray can be efficiently used for dust reduction in poultry houses. Further, a better understanding of the dust concentration variations in 24-hr house operation and in different spatial zones can contribute to bird housing environment management and poultry house design so as to improve bird health.     

Factors influencing on the bioaccessibility of polybrominated diphenyl ethers in size-specific dust from air conditioner filters

Size-specific concentrations and bioaccessibility of polybrominated diphenyl ethers (PBDEs) in dust from air conditioner filters were measured, and the factors influencing the PBDE bioaccessibility were determined. Generally, the PBDE concentrations increased with decreasing dust particle size, and BDE209 (deca-BDE) was generally the predominant congener. The bioaccessibility ranged from 20.3% to 50.8% for tri- to hepta-BDEs, and from 5.1% to 13.9% for BDE209 in dust fractions of varied particle size. The bioaccessibility of most PBDE congeners decreased with increasing dust particle size. The way of being of PBDE (adsorbed to dust surface or incorporated into polymers) in dust significantly influenced the bioaccessibility. There was a significant negative correlation between the tri- to hepta-BDE bioaccessibility and organic matter (OM) contents in dust. Furthermore, tri- to hepta-BDE bioaccessibility increased with increasing polarity of OMs, while with decreasing aromaticity of OMs. The tri- to hepta-BDE bioaccessibility significantly positively correlated with the surface areas and pore volumes of dust. Using multiple linear regression analysis, it was found that the OM contents and pore volumes of dust were the most important factors to influence the tri- to hepta-BDE bioaccessibility and they could be used to estimate the bioaccessibility of tri- to hepta-BDEs according to the following equation: bioaccessibility (%) = 45.05 − 0.49 × OM% + 1.79 × pore volume. However, BDE209 bioaccessibility did not correlate to any of these factors.     

Dust events as a risk factor for daily hospitalization for respiratory and cardiovascular diseases in Minqin,China

Dust events are common air pollution events in parts of the world with arid, semi-arid, or desert areas. There is little research on the association between respiratory and cardiovascular health and dust events in places which are close to the deserts. The aim of this study is to evaluate the health effects of dust events in a location where traffic and industry are underdeveloped and dust events are most frequent in China. The setting allows the opportunity to reduce confounding by anthropogenically derived particulate matter and to confirm the health effects of dust events. The present study was done using daily counts of hospitalizations in Minqin (1994–2003) for respiratory and cardiovascular diseases (International Classification of Diseases, Tenth revision) for males and females. Using a semi-parametric generalized additive model and controlling for long-term temporal trends, day of the week, meteorological factors, and seasonal influence, counts of hospitalization were analyzed for dust events in a Poisson regression.Relative risks (RRs) were used to estimate the risk of dust events for respiratory and cardiovascular hospitalizations. In the year-round model, dust events with a lag of 3 days were significantly associated with total respiratory hospitalization for males and females, with RRs of 1.14 (95% confidence interval (CI) 1.01–1.29) and 1.18 (95% CI 1.00–1.41); dust events with a lag of 4 days were significantly associated with upper respiratory tract infection (URTI) in males (RR 1.28, 95% CI 1.04–1.59), and dust events with a lag of 6 days were significantly associated with pneumonia in males, with an RR of 1.17 (95% CI 1.00–1.38). A significant association between dust events with a lag of 3 days and hypertension in males was also found (RR 1.30, 95% CI 1.03,1.64). In the seasonal analysis model, the associations between the dust events and respiratory and cardiovascular hospitalizations were stronger in spring and in winter, respectively.The results show the health effects of dust events on respiratory and cardiovascular hospitalizations, and the characteristic seasonal distribution of the health effects. In addition, the health effects of dust events are consistent with recent animal and human data showing the respiratory and cardiovascular effects of particulate matter.     

Organophosphorus flame retardants in house dust from the Philippines: occurrence and assessment of human exposure

The use of organophosphorus flame retardants (PFRs) as flame retardants and plasticizers has increased due to the ban on common polybrominated diphenyl ether mixtures. However, only limited information on PFR contamination is available so far from Southeast Asia. In the present study, residual levels of PFRs in house dust and exposure through dust ingestion were investigated in the Philippines. House dust samples (n?=?37) were collected from Malate (residential area) and Payatas (municipal dumping area) in the Philippines and analyzed using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry. Among the targeted seven PFRs, triphenyl phosphate (TPP) was the predominant compound. Median levels of ΣPFRs in Malate (530 ng/g) were two times higher (p?<?0.05) than in Payatas (240 ng/g). The estimated daily intake of PFRs in the Philippines (of areas studied) via house dust ingestion was below the guideline values. House dust may be an important contributor in the overall exposure of humans to TPP even when considering dietary sources. To our knowledge, this is a first report on PFR contamination in house dust from developing country. PFRs were ubiquitously detected in the home environments in the Philippines. Although estimated exposure levels through dust ingestion were below the guideline, it was suggested that toddlers are at higher risk. Therefore, further investigations to understand the behavior of PFRs in house and other microenvironments and overall exposure pathways for the country’s populace to PFRs are necessary.     

Suppression of precipitation by dust particles originated in the Tibetan Plateau

Dust aerosols play an important role in modulating the hydrologic cycle. The Tibetan Plateau (TP) is little polluted by human activities as an ideal site to study the effect of dust aerosol on precipitation. In this study, observational data of dust storms and precipitation in the TP and its vicinities as well as CALIPSO satellite data were used to analyze the distributions and vertical structure of dust storms on the plateau. The results showed that dust storms occur with high frequency and raise dust particles into the troposphere from ground level to a height of 5–9 km to modulate the hydrologic cycle in the TP. There are significant negative correlations between dust aerosol and precipitation in the dust source regions during the period of both 40 and 200 years. It is found that the role of precipitation in suppressing dust storms could be unimportant, while dust aerosol may play an important role in suppressing precipitation in the hinterland of the TP. Our study provides a potential approach to better understand the climate changes in the TP.     

Determination of buffering capacity of total suspended particle and its source apportionment using the chemical mass balance approach

The samples of total suspended particle (TSP) from sources and TSP in the ambient atmosphere were collected in 2006 at Tianjin, People's Republic of China and analyzed for 16 chemical elements, two water-soluble ions, total carbon, and organic carbon. On the basis of the chemical mass balance (CMB) model, the contributions of different TSP sources to the ambient TSP were identified. The results showed that resuspended dust has the biggest contributions to the concentration of ambient TSP. The buffering capacity of each TSP source was also determined by an analytical chemistry method, and the result showed that the constructive dust (the dust emitted from construction work) had the strongest buffering capacity among the measured sources, whereas the coal combustion dust had the weakest buffering capacity. A calculation formula of the source of buffering capacity of ambient TSP was developed based on the result of TSP source apportionment and the identification of the buffering capacity of each TSP source in this study. The results of the source apportionment of the buffering capacity of ambient TSP indicated that open sources (including soil dust, resuspended dust, and constructive dust) were the dominant sources of the buffering capacity of the ambient TSP. Acid rain pollution in cities in Northern China might become serious with a decrease of open source pollution without reducing acidic sources. More efforts must be made to evaluate this potential risk, and countermeasures should be proposed as early as possible.     

烟气和粉尘性质对除尘效率影响的仿真研究

应用欧拉-拉格朗日多相流模型对影响电除尘器内部气流分布的烟气含尘浓度、烟气湿度、粉尘粒径及真密度等因素进行了数值仿真。分析了烟气和粉尘性质对除尘效率的影响。由于在仿真过程中考虑了烟气特性和粉尘性质等因素,不仅可获得各因素对气流分布均匀性的影响,而且仿真结果更能反映电除尘器气流分布的实际情况。提出的烟气和粉尘性质仿真方法可以为电除尘器除尘效率分析提供新的途径。     

A methodology for the quantification of the net African dust load in air quality monitoring networks

This paper proposes and validates a methodology for the quantification of the daily African PM load during dust outbreaks in southern Europe. The daily net dust load in PM10 attributable to an African episode in a given region can be obtained by subtracting the daily regional background (RB) level from the PM10 concentration value at an RB station. As demonstrated in this paper, the daily RB level can be obtained by applying a monthly moving 30th percentile to the PM10 time series at an RB station after a prior extraction of the data of the days with African dust transport. The daily PM10 RB levels obtained can be subtracted from the daily PM10 levels recorded at the same RB site only on days when the occurrence of African dust outbreaks was demonstrated, the difference being the daily net African dust load. It is thus possible to quantify the African dust contribution during an African PM event in southern Europe without the need for PM speciation.The validation of this methodology was performed by comparing the estimated net dust load during African dust outbreaks at three RB stations and the crustal load determined by chemical speciation of PM10 filters. The correlation (r²>0.6) and the equivalence (correlation lines’ slopes ∼1) were significant in the three cases.     

Size- and density-distributions and sources of polycyclic aromatic hydrocarbons in urban road dust

Polycyclic aromatic hydrocarbons (PAHs) present in size- and density-fractionated road dust were measured to identify the important fractions in urban runoff and to analyse their sources. Road dust was collected from a residential area (Shakujii) and a heavy traffic area (Hongo Street). The sampling of road dust from the residential area was conducted twice in different seasons (autumn and winter). The collected road dust was separated into three or four size-fractions and further fractionated into light (<1.7 g/cm3) and heavy (>1.7 g/cm3) fractions by using cesium chloride solution. Light particles constituted only 4.0+/-1.4%, 0.69+/-0.03% and 3.4+/-1.0% of the road dust by weight for Shakujii (November), Shakujii (February) and Hongo Street, respectively but contained 28+/-10%, 33+/-3% and 44+/-8% of the total PAHs, respectively. The PAH contents in the light fractions were 1-2 orders of magnitude higher than those in the heavy fractions. In the light fractions, the 12PAH contents in February were significantly higher than the 12PAH contents in November (P<0.01), whereas in the heavy fractions, no significant difference was found (P>0.05). Cluster analysis revealed that there was a significant difference in the PAH profiles between locations rather than between size-fractions, density-fractions and sampling times. Multiple regression analysis indicated that asphalt/pavement was the major source of Shakujii road dust, and that tyre and diesel vehicle exhaust were the major sources of finer and coarser fractions collected from Hongo Street road dust, respectively.