Characterization of PM2.5 aerosols dominated by local pollution and Asian dust observed at an urban site in Korea during aerosol characterization experiments (ACE)--Asia Project

Daily fine particulate matter (PM2.5) samples were collected at Gwangju, Korea, during the Aerosol Characterization Experiments (ACE)-Asia Project to determine the chemical properties of PM2.5 originating from local pollution and Asian dust (AD) storms. During the study period, two significant events occurred on April 10-13 and 24-25, 2001, and a minor event occurred on April 19, 2001. Based on air mass transport pathways identified by back-trajectory calculation, the PM2.5 dataset was classified into three types of aerosol populations: local pollution and two AD aerosol types. The two AD types were transported along different pathways. One originated from Gobi desert area in Mongolia, passing through Hunshandake desert in Northern Inner Mongolia, urban and polluted regions of China (AD1), and the other originated in sandy deserts located in the Northeast Inner Mongolia Plateau and then flowed southward through the Korean peninsula (AD2). During the AD2 event, a smoke plume that originated in North Korea was transported to our study site. Mass balance closures show that crustal materials were the most significant species during both AD events, contributing -48% to the PM2.5 mass; sulfate aerosols (19.1%) and organic matter (OM; 24.6%) were the second greatest contributors during the AD1 and AD2 periods, respectively, indicating that aerosol properties were dependent on the transport pathway. The sulfate concentration constituted only 6.4% (4.5 microg/m3) of the AD2 PM2.5 mass. OM was the major chemical species in the local pollution-dominated PM2.5 aerosols, accounting for 28.7% of the measured PM2.5 mass, followed by sulfate (21.4%), nitrate (15%), ammonium (12.8%), elemental carbon (8.9%), and crustal material (6.5%). Together with substantial enhancement of the crustal elements (Mg, Al, K, Ca, Sc, Ti, Mn, Fe, Sr, Zr, Ba, and Ce), higher concentrations of pollution elements (S, V, Ni, Zn, As, Cd, and Pb) were observed during AD1 and AD2 than during the local pollution period, indicating that, in addition to crustal material, the AD dust storms also had a significant influence on anthropogenic elements.     

The evolution of chemical components of aerosols at five monitoring sites of China during dust storms

Daily PM_2.5 and TSP and their chemical composition with two dust events (DS1: 9–10 March and DS2: 27–30 March) were simultaneously observed for the period of 9 March–23 April 2004 from a monitoring network over China. Five monitoring sites were performed along the transport pathway of Asian dust storm, located in Northwest, North, East, and Southeast regions of China. The dust and non-dust days exhibited different characteristics with respect to the composition and the meteorological conditions. In non-dust days, particulate pollution was found to be associated with the city economy, and it primarily consisted of the crustal, the secondary, and the carbonaceous material. In the dust episodes, significant increase in the particle concentration with a large part of the secondary components diluted by the crustal components was observed at all the sites. Particles were getting more and more acidic as the episodic dust progressed eastward. Dust particles were suggested to react with SO₂/NO_X/sulfate/nitrate based on the variations of SO₄²⁻/Ca²⁺ and NO₃⁻/Ca²⁺ along the transport pathway, and the formation mechanism of sulfate and nitrate was proved to be different. Positive matrix factorization analysis showed that the sources from the upstream and the transport pathways could account for 49%, 82%, and 28% of PM mass, crust, and secondary aerosol, respectively, and the contribution decreased, as the dust made its way from source area to the coastal regions. Enrichment factors of the species presented significant correlations among different sites in the dust episodes, suggesting the significant impact of those dust emissions on the local environment.     

Chemical compositions and radiative properties of dust and anthropogenic air masses study in Taipei Basin, Taiwan, during spring of 2004

Asia is one of the major sources of not only mineral dust but also anthropogenic aerosols. Continental air masses associated with the East Asian winter monsoon always contain high contents of mineral dust and anthropogenic species and transported southeastward to Taiwan, which have significant influences on global atmospheric radiation transfer directly by scattering and absorbing solar radiation in each spring. However, few measurements for the long-range transported aerosol and its optical properties were announced in this area, between the Western Pacific and the southeastern coast of Mainland China. The overall objective of this work is to quantify the optical characteristics of different aerosol types in the Eastern Asian. In order to achieve this objective, meteorological parameters, concentrations of PM₁₀ and its soluble species, and optical property of atmospheric scattering coefficients were measured continuously with 1 h time-resolved from 11 February to 7 April 2004 in Taipei Basin (25°00′N, 121°32′E). In this work, the dramatic changes of meteorological parameters such as temperature and winds were used to determine the influenced period of each air mass. Continental, strong continental, marine, and stagnant air masses defined by the back-trajectory analysis and local meteorology were further characterized as long-range transport pollution, dust, clean marine, and local pollution aerosols, respectively, according to the diagnostic ratios. The aerosol mass scattering efficiency of continental pollution, dust, clean marine, and local pollution aerosols were ranged from 1.3 to 1.6, 0.7 to 1.0, 1.4 and 1.4 to 2.3 m² g⁻¹, respectively. Overall, there are two distinct populations of aerosol mass scattering efficiencies, one for an aerosol chemical composition dominated by dust (<1.0 m² g⁻¹) and the other for an aerosol chemical composition dominated by anthropogenic pollutants (1.3–2.3 m² g⁻¹), which were similar to the previous measurements with high degree of temporal resolution.     

Characteristics of re-suspended road dust and its impact on the atmospheric environment in Beijing

A sampling campaign of re-suspended road dust samples from 53 sites that could cover basically the entire Beijing, soil samples from the source regions of dust storm in August 2003, and aerosol samples from three representative sites in Beijing from December 2001 to September 2003, was carried out to investigate the characteristics of re-suspended road dust and its impact on the atmospheric environment. Ca, S, Cu, Zn, Ni, Pb, and Cd were far higher than its crustal abundances and Ca²⁺, SO₄²⁻, Cl⁻, K⁺, Na⁺, NO₃⁻ were major ions in re-suspended road dust. Al, Ti, Sc, Co, and Mg in re-suspended road dust were mainly originated from crustal source, while Cu, Zn, Ni, and Pb were mainly derived from traffic emissions and coal burning, and Fe, Mn, and Cd were mainly from industrial emissions, coal combustion and oil burning. Ca²⁺ and SO₄²⁻ mainly came from construction activities, construction materials and secondary gas-particle conversions, Cl⁻ and Na⁺ were derived from industrial wastewater disposal and chemical industrial emissions, and NO₃⁻ and K⁺ were from vehicle emissions, photochemical reactions of NO_X, biomass and vegetable burning. The contribution of mineral aerosol from inside Beijing to the total mineral aerosols was ∼30% in spring of 2002, ∼70% in summer of 2002, ∼80% in autumn of 2003, ∼20% in PM₁₀ and ∼50% in PM_2.5, in winter of 2002. The pollution levels of the major pollution species, Ca, S, Cu, Zn, Ni, Pb, Fe, Mn, and Cd in re-suspended road dust reached ∼76%, ∼87%, ∼75%, ∼80%, ∼82%, ∼90%, ∼45%, ∼51%, and ∼94%, respectively. Re-suspended road dust from the traffic and construction activities was one of the major sources of pollution aerosols in Beijing.     

Dry and wet deposition of water-insoluble dust and water-soluble chemical species during spring 2007 in Tsukuba,Japan

Dry and wet depositions were sampled daily in Tsukuba, Japan, in spring 2007. Temporal variations in the dry and wet deposition fluxes of dust and water-soluble chemical species were controlled largely by air mass origin, the water vapor mixing ratio, and Asian dust events. The contribution of local sources to dry deposition of dust was large when the wind speed was high. Dry deposition fluxes of water-soluble chemical species were larger in humid air masses than in dry air masses. Wet deposition fluxes of dust and water-soluble chemical species indicated that air masses that passed over dust source regions and industrial regions became mixed with the maritime air masses over the coastal site of the Asian continent and western part of the Japanese islands. The total deposition of dust was 4220 mg m^?2 month^?1, and that of water-soluble chemical species ranged from 10 to 636 mg m^?2 month^?1. Wet deposition fluxes of the total deposition flux of dust accounted for 72% and those of water-soluble chemical species was for 72–96%. In particular, the largest wet deposition occurred during a single Asian dust event on 3 April. This event accounted for 23% (950 mg m^?2 month^?1) of the monthly dust deposition flux and for 2–28% (0.43–51 mg m^?2 month^?1) of the monthly deposition flux of water-soluble chemical species. This result implies that the wet deposition flux associated with even one sporadic Asian dust event can have extensive impacts on both terrestrial and oceanic ecosystems in East Asia.     

Long-range transport of polycyclic aromatic hydrocarbons (PAHs) from the eastern Asian continent to Kanazawa,Japan with Asian dust

Aerosol particles were collected for 1 year, starting in April 2003, in rural areas of Kanazawa, Ishikawa, Japan to understand the role of Asian dust as a long-range transporter of polycyclic aromatic hydrocarbons (PAHs). Three sampling intervals were designated in this study, namely: (1) Dust period 1 (March 11–19, 2003); (2) Dust period 2 (March 28, 2003–April 9, 2003); and (3) Dust period 3 (April 9, 2004–April 25, 2004). The Asian dust particles are predominantly in the coarse particle size range (2.1–11 μm). PAH analyses were performed separately on both the coarse and fine (<1.1 μm) particle ranges. Seasonal trends in PAH concentrations for coarse and fine particles showed that the Asian dust particles in Dust period 3 contained significant amounts of less-volatile PAHs such as benzo[a]pyrene (BaP) and benzo[g,h,i]perylene (BghiP). A kinetic model developed in this study shows that almost none of these PAHs would be accumulated on Asian dust particles in the atmosphere, due to their extremely slow adsorption rates. These PAHs would have to originate from PAH-polluted soil particles around industrialized areas. Back trajectory analyses suggest that the Asian dust in Dust period 3 came from loess regions around industrialized areas. This indicates that geologic materials play a significant role in the atmospheric circulation of PAHs.     

Polycyclic aromatic hydrocarbons (PAHs) in the aerosol in Beijing, China, measured by aminopropylsilane chemically-bonded stationary-phase column chromatography and HPLC/fluorescence detection

We developed a useful analytical method for the determination of polycyclic aromatic hydrocarbons (PAH) concentrations in the aerosol of China. We used an accelerated solvent extraction (ASE) method for the extraction of PAHs from the aerosol samples, in order to reduce the extraction time and the solvent volume used. The optimum purification method was developed, with aminopropylsilane chemically-bonded stationary-phase column chromatography, in order to remove many co-extractives which cannot be removed by conventional purification methods using silica-gel column chromatography. HPLC/fluorescence detection (FLD) was adopted as the analytical method, because it has very high sensitivity to PAH and it is easy to install, operate, and maintain as compared with GC/MS. With the analytical method developed in this study, the recovery and precision (RSD) for most of the PAHs ranged from 75% to 129% and from 2.8% to 22.7%, respectively. The concentrations of PAHs in the aerosol samples collected from October 2003 to April 2005 in Beijing, China were determined using the newly developed method. SigmaPAHs, which is the sum of the concentrations of all detected PAHs, was 177.8 +/- 239.9 ng m(-3) (n = 64). The SigmaPAHs concentration in the heating season (305.1 +/- 279.0 ng m(-3), n = 33) was 7.2 times higher than that in the non-heating season (42.3 +/- 32.0 ng m(-3), n = 31). These strong seasonal variations in atmospheric PAH concentration are possibly due to coal combustion for residential heating in winter.     

Characteristics and provenance of dustfall during an unusual floating dust event

This study aims to investigate the characteristics, provenance, and particle-related pollution of an intense dustfall event that occurred in Beijing on 16–17 April 2006. Satellite images reveal that the aeolian dust originated in northeastern Alxa League of Inner Mongolia and passed southeastward across northern Ningxia, middle Inner Mongolia, northern Shaanxi, Shanxi, and Hebei provinces. The dust then moved out of continental China in the vicinity of Beijing and Tianjin. The floating dust led to severe air pollution in Huhhot, Datong, and Beijing. We measured dustfall by collecting dust samples, investigated particle morphology, and calculated the mass medium diameter (MMD) of the dustfall using a scanning electron microscope (SEM). Major elements and mineral content of the dust particles were determined by electron probe and powder X-ray diffractometer, respectively. The relative abundance of dustfall during this event was 12.5–15.0 g m^?2, making up about 10% of the total annual dustfall in Beijing. Dustfall amounted to 205 thousand tons in Beijing, the largest amount observed in recent years. The dust particles were mostly angular, subangular and subrounded in morphology, and the MMD was nearly 12 μm. Particles <10 μm accounted for 54.7% by number, but fine sand particles (larger than 50 μm) made up 53.7% by volume. Particles with diameters larger than 20 μm made up of the predominant volume of the samples (90.35%). Hence, this dustfall event was characterized by a high content of fine sand and coarse silt particles. The principal elements in the dust particles were C, O, Si, Al, Fe, and Ca, whereas the major minerals were quartz, Na-feldspar, calcite, and clay minerals.     

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.     

Source diagnostics of polycyclic aromatic hydrocarbons in urban road runoff, dust, rain and canopy throughfall

Diagnostic ratios and multivariate analysis were utilized to apportion polycyclic aromatic hydrocarbon (PAH) sources for road runoff, road dust, rain and canopy throughfall based on samples collected in an urban area of Beijing, China. Three sampling sites representing vehicle lane, bicycle lane and branch road were selected. For road runoff and road dust, vehicular emission and coal combustion were identified as major sources, and the source contributions varied among the sampling sites. For rain, three principal components were apportioned representing coal/oil combustion (54%), vehicular emission (34%) and coking (12%). For canopy throughfall, vehicular emission (56%), coal combustion (30%) and oil combustion (14%) were identified as major sources. Overall, the PAH's source for road runoff mainly reflected that for road dust. Despite site-specific sources, the findings at the study area provided a general picture of PAHs sources for the road runoff system in urban area of Beijing.     

Size distribution of polycyclic aromatic hydrocarbons in urban and suburban sites of Beijing, China

PAHs in five-stage size segregated aerosol particles were investigated in 2003 at urban and suburban sites of Beijing. The total concentration of 17 PAHs ranged between 0.84 and 152 ng m(-3), with an average of 116 ng m(-3), in urban area were 1.1-6.6 times higher than those measured in suburban area. It suggested a serious pollution level of PAHs in Beijing. PAHs concentrations increased with decreasing the ambient temperature. Approximately 68.4-84.7% of PAHs were adsorbed on particles having aerodynamic diameter 2.0 microm. Nearly bimodal distribution was found for PAHs with two and three rings, more than four rings PAHs, however, followed unimodal distribution. The overall mass median diameter (MMD) for PAHs decreased with increasing molecular weight. Diagnostic ratios and normalized distribution of PAHs indicated that the PAHs in aerosol particles were mainly derived from fossil fuel combustion. Coal combustion for domestic heating was probably major contributor to the higher PAHs loading in winter, whereas PAHs in other seasons displayed characteristic of mixed source of gasoline and diesel vehicle exhaust. Biomass burning and road dust are minor contributors to the PAHs composition of these aerosol particles. Except for source emission, other factors, such as meteorological condition, photochemical decay, and transportation from source to the receptor site, should to be involved in the generation of the observed patterns.     

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.     

Processes driving the short-term variability of polycyclic aromatic hydrocarbons in the Baltimore and northern Chesapeake Bay atmosphere,USA

Polycyclic aromatic hydrocarbons (PAHs) were measured in the Baltimore and adjacent Chesapeake Bay in July 1997. Time series of 4- and 12-h samples were taken at two sites 15 km apart in order to evaluate the influence of a number of processes on the short-term variability of PAH in the Baltimore and northern Chesapeake Bay atmospheres. PAH concentrations were 2–3-fold higher in the Baltimore atmosphere than in the adjacent Chesapeake Bay atmosphere. For example, gas-phase phenanthrene and pyrene concentrations were 12.5 and 2.14 ng m⁻³ in the Baltimore site and 5.57 and 0.548 ng m⁻³ in the Chesapeake Bay, respectively. The influence of wind direction, wind speed and temperature was evaluated by multiple linear regressions which indicated that atmospheric gas-phase PAH concentrations over the Chesapeake Bay were significantly higher when the air mass was from the urban/industrial Baltimore area. Furthermore, the increase of gas-phase low-MW PAH concentrations with temperature and wind speed suggests that volatilization from the bay is an important source of pollutants to the atmosphere, at least when air masses are not influenced by the Baltimore urban and industrial area. Indeed, while on the long-term, the Chesapeake Bay is a receptor of atmospherically deposited PAHs, on the short-term and during appropriate meteorological conditions, the bay acts as a source of pollutants to the atmosphere. Aerosol-phase PAH concentrations and temporal trends showed a strong dependence on aerosol soot content due to the high affinity of PAHs to the graphitic structure of soot. These results confirm the important influence of urban areas as a source of pollution to adjacent aquatic environments and as a driving factor of the short-term variability, either directly by transport of urban-generated pollutants or by volatilization of previously deposited pollutants. Conversely, the complex diurnal trends of gas-phase PAHs at the Baltimore site suggests that degradation processes dominate the diurnal trends of PAHs in urban atmospheres. This conclusion is supported by estimated rate constants for PAH reaction with OH radicals which show good agreement with reported values within a factor of two.     

Aerosol optical,chemical and physical properties at Gosan,Korea during Asian dust and pollution episodes in 2001

In order to understand the influence of dust and anthropogenic pollution aerosols on regional climate in East Asia, we analyzed the aerosol optical, chemical and physical properties for two cases with high aerosol loading and assessed the radiative forcing of these cases. The 1st case study is a heavy dust episode (DE) in April (during ACE-Asia) 2001 and the 2nd case is a regional-scale pollution event in November 2001. The Ångström exponent (Å) for DE was 0.38 from sunphotometer measurements. The mean single scattering albedo (550 nm) at the surface reported during the pollution episode (PE, 0.88) was lower than that of DE (0.91). The concentrations of organic (OC) and elemental carbon (EC) measured during the PE were about 90% and 30% higher than DE. The aerosol mass scattering efficiency (α_s) of PE is a factor of about 2 higher than that of the DE. The difference in the mass absorption efficiency (α_a) of EC during DE and PE is small and within the measurement uncertainty. The diurnally averaged aerosol radiative forcing efficiency (ΔDFE, W m⁻² τ⁻¹) during DE is similar to results of other studies at Gosan.     

Characterization,identification of road dust PAHs in central Shanghai areas,China

Road dust samples were collected from central Shanghai in winter (January) and summer (August), respectively. Sixteen polycyclic aromatic hydrocarbons (PAHs) in the United States Environmental Protection Agency (USEPA) priority-controlled list were determined by GC/MS. Total PAH (t-PAH) concentrations in winter samples ranged from 9176 to 32,573 ng g⁻¹ with a mean value of 20,648 ng g⁻¹, while they varied from 6875 to 27,766 ng g⁻¹ in summer with an average of 14,098 ng g⁻¹. Spatial variation showed that city park (CP) samples had the lowest t-PAH concentration, while industrial area (ID) and traffic area (TR) and commercial area (CO) were the most polluted, in both seasons. PAH homologues concentrations were getting higher with the more rings and higher molecular weight (HMW) in all areas. The study of effective factors showed that grain size was only a minor factor influencing the accumulation of PAHs, whereas total organic carbon (TOC) was found to be closely correlated with t-PAH concentration. Prevailing winds could directly affect on the spatial distribution of PAHs. Chemical source apportionment studies took the form of principal component analysis (PCA), followed by compositional analysis. It was demonstrated that road dust PAHs in central Shanghai mainly came from the mixing of traffic and coal combustion. The contribution percentages of pyrogenic and petrogenic sources were respectively 71.0% and 11.4% in winter, while they were, 64.9% and 14.1% in summer, respectively. Road dust PAHs in Shanghai city mostly came from local sources.     

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.     

Role of Chinese wind-blown dust in enhancing environmental pollution in Metropolitan Seoul

A suite of rock magnetic experiments and intensive microscopic observations were carried out on Asian dust deposits in Seoul, Korea, collected on 19 and 23 March 2002, 9 April 2002 and 12 April 2003. Desert-sand and loess from the dust source regions in China were also analyzed as a comparison. Asian dust showed a higher magnetic concentration than the source region samples, indicating a significant influx of magnetic particles into Asian dust had occurred during its transportation. Electron microscopy identified carbon-bearing iron-oxides as the added material. These iron-oxides were likely to have been produced by anthropogenic pollution (fossil fuel combustion) while the wind-blown dusts passing across the industrial areas of eastern China and western Korea. Such wind-paths were confirmed by a simulation of the air-mass trajectories. The magnetic technique appears to be useful for determining the anthropogenic pollution of Asian dust.     

Determination of polycyclic aromatic hydrocarbons in urban street dust: implications for human health

The determination of sixteen polycyclic aromatic hydrocarbons in urban street dust has been done. Samples were collected from 12 sampling locations in a city centre location (Newcastle upon Tyne, north east England) and extracted using in situ pressurised fluid extraction followed by gas chromatography mass spectrometry. From the results it was possible to identify three groups, with respect to PAH concentration, with PAH contents ranging between 0.6-2.3 mg kg⁻¹, 15.6-22.5 mg kg⁻¹ and 36.1-46.0 mg kg⁻¹. The total PAH content of samples from these sampling sites has been compared to 22 urban locations around the world; comparable levels were found in these samples compared to the other cities around the world.The potential source of PAHs has been investigated by investigating the proportion of pyrogenic and petrogenic material in urban street dust using specific individual PAH ratios. The results indicate that the PAH content of urban street dust from the chosen sites are more likely to be due to pyrogenic sources i.e. vehicle exhaust emissions. The particle size fractions (<63 μm; 63-125 μm; 125-250 μm; 250-500 μm; 500-1000 μm; and 1000-2000 μm) of individual PAHs in three selected sampling sites was investigated. In two of the selected sites the PAH content was independent of particle size whereas in sampling site 10 elevated PAH levels are noted in the <63 μm size fraction. Sampling site 10 is located at the junction of three road tributaries which are used as major access points to the east of the city centre. Finally, the potential health risk for unintentional consumption of PAHs was assessed in terms of a mean daily intake (based on an ingestion rate of 100 mg d⁻¹). It was found that all 4-6 membered ring PAHs had concentrations in excess of the mean daily intake thereby reflecting a potential health risk, particularly in the smallest size particle fractions.     

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.     

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.