成都市道路细颗粒物污染特征

2013年9月20—28日,通过采集成都市城区道路大气环境中的PM2.5样品,分析测定了其中可溶性无机离子、碳组分和金属元素含量。结果表明,PM2.5中Fe、Mn、Ti、Si、Al等主要来源于机动车行驶产生的道路扬尘,Pb、Cu、Ni和Zn等主要来源于机动车尾气及零部件磨损;PM2.5中水溶性无机离子占道路大气环境细颗粒物的33.7%,A/C比值为0.95,表明细颗粒物偏弱碱性;机动车尾气排放的OC1、OC2、OC4和EC1等4种碳组分占道路大气环境细颗粒物碳组分的65.8%,且OC/EC比值为2.9,有二次有机碳(SOC)产生。     

Mixing properties of individual submicrometer aerosol particles in Vienna

Individual aerosol particles were collected on 5 days with different meteorological conditions in March, April and June 1991 in the urban atmosphere of Vienna in Austria. The samples collected with an impactor were examined by electron microscopy. The mixing properties of submicrometer aerosol particles with radii between 0.1 and 1 μm were studied by using the dialysis (extraction) of water-soluble material. The averaged results showed that more than 85% of particles with radii between 0.1 and 0.7 μm were hygroscopic. However, more than 50% of particles with radii larger than 0.2 μm were mixed particles (hygroscopic particles with water-insoluble inclusions), and they were dominant (80%) in the size range 0.5–0.7 μm radius. The results also showed that the number proportion of mixed particles increased with increasing radius and the abundance increased with increasing particle loading in the atmosphere. The volume fraction of water-soluble material (ε) in mixed particles tended to decrease with increasing radius, implying the formation of mixed particles by heterogeneous processes such as condensation and/or surface reaction. Some results of elemental composition in individual particles analyzed with an energy-dispersive X-ray (EDX) analyzer equipped with an electron microscope are also presented in this paper.     

Spatial distribution of submicrometre particles and CO in an urban microscale environment

Traffic is the major source of submicrometre particles in an urban environment but the spatial distribution of particles around an urban site has not been measured. The aim of this paper was to investigate the relationship of CO and particles at a busy central urban location surrounded by buildings. This study measured the concentration and size distribution of submicrometre particles at a fixed location and concentrations of submicrometre particles and CO at 10 locations around a square site in the Brisbane Central Business District (CBD). Changes in concentration were assessed as a function of traffic volume and wind direction and speed.Fixed site measurements of submicrometre particle number concentration varied between 7.9×10² (±40) and 2.6×10⁵ (±1.3×10⁴) cm⁻³ and showed a strong positive correlation with traffic flow rate, confirming that vehicles were the major source of urban submicrometre particles. The particle concentration decreased exponentially with increasing wind speed.Average particle concentrations around the site ranged between 19.7×10³ (±8.2×10³) and 32.5×10³ (±16.6×10³) cm⁻³. Analysis of the particle measurements around the site showed that time and location both had a statistically significant effect on mean particle concentration around the square over the period of the study.Around the site, CO concentration was relatively constant (within instrument error), ranging between 2.2 (±1.9) and 4.5 (±3.0) ppm. Again both time and location had a statistically significant effect on CO concentration during the measurement period. However, CO concentration was not significantly correlated to particle number concentration around the site and examination of between-site comparisons with the two pollutants showing different spatial and temporal trends.The significant difference in the concentration trends between the locations around the square indicates that there is considerable inhomogeneity in the particle concentration around the site. One implication of this is that careful thought must be given to locations of air intakes of air-conditioning systems in urban environments.     

Size segregated water uptake of the urban submicrometer aerosol in Beijing

Physical and chemical properties of submicrometer aerosol particles were measured in summer 2004 (June/July) and winter 2005 (January/February) in Beijing, Peoples Republic of China, using a Twin-Differential Mobility Particle Sizer (T-DMPS), a Hygroscopicity-Tandem Differential Mobility Analyzer (H-TDMA), and a Micro Orifice Uniform Deposit Impactor (MOUDI). Particle number–size distributions were measured in the diameter range Dp = 3–800 nm and hygroscopic properties were determined at initial dry particle diameters of Dp_j (j = 30, 50, 80, 150, 250, and 350 nm) at a relative humidity (RH) of 90%. Hygroscopic properties were compared with chemical analyses of aerosol samples taken with the MOUDI. Based on the hygroscopicity data, the total hygroscopic particle volume was modeled, including dependence on dry particle size, season and level of pollution using a simple approach.Overall, the chemical analysis showed ammonium sulfate to be the major inorganic component of the urban submicrometer aerosol in Beijing along with relatively high fractions of elemental carbon (10–25%) and organic matter (15–60%) depending on particle size and season.The hygroscopic growth distributions (H-TDMA) subdivided the aerosol population into three different groups of particles with varying growth factors depending on dry particle size, namely nearly hydrophobic (growth factor = 0.96–1.07), less hygroscopic (1.06–1.29) and more hygroscopic (1.26–1.62).Hydrophobic particle fractions indicating freshly emitted soot/carbonaceous particles varied between 10 and 32% depending on dry particle size and season. During heavily polluted times, a decreasing number of hydrophobic particle fractions indicated that the urban submicrometer aerosol in Beijing was highly influenced by more aged aerosol transported from the industrial regions around Beijing containing sulfate as a major component.Based on model calculations, the urban submicrometer aerosol in Beijing showed strong compositional variations. The calculated total hygroscopic volume fractions varied between 16 and 65% depending on size, level of pollution and season.     

Relation between particle mass and number for submicrometer airborne particles

The relationship between particle mass and the number of ambient air particles for the submicrometer size range was examined using a tapered element oscillating microbalance (TEOM) to determine the mass concentration, and a scan-ning mobility particle sizer (SMPS) to determine the volume concentration and total number of particles. The techniques were validated through their application to the estimation of submicrometer particle density for two laboratory generated aerosols of known bulk density (sodium chloride and di-2-ethylhexyl-sebacate). Further evaluation was done with the submicrometer fraction of laboratory generated environmental tobacco smoke (ETS), for which the estimated density of 1.18±0.06 g/cm³ was very close to the previously reported literature value of 1.12 g cm³. Finally, ambient air particles were examined and an estimate of the average submicrometer particle densities for these aerosols was found to vary from 1.2 to 1.8 g cm^-3 depending on the time of day. This high variation in the density of the ambient air submicrometer particles, makes it hard to estimate the mass concentration from the SMPS number concentration with better than 60% uncertainty, based on an assumed density value.     

Assessment of exposure to airborne ultrafine particles in the urban environment of Lisbon, Portugal

The aim of this study was the assessment of exposure to ultrafine in the urban environment ofLisbon, Portugal, due to automobile traffic, and consisted of the determination of deposited alveolar surface area in an avenue leading to the town center during late spring. This study revealed differentiated patterns for weekdays and weekends, which could be related with the fluxes of automobile traffic. During a typical week, ultrafine particles alveolar deposited surface area varied between 35.0 and 89.2 microm2/cm3, which is comparable with levels reported for other towns such in Germany and the United States. These measurements were also complemented by measuring the electrical mobility diameter (varying from 18.3 to 128.3 nm) and number of particles that showed higher values than those previously reported for Madrid and Brisbane. Also, electron microscopy showed that the collected particles were composed of carbonaceous agglomerates, typical of particles emitted by the exhaustion of diesel vehicles.     

A study of the horizontal and vertical profile of submicrometer particles in relation to a busy road

Epidemiological studies are consistently reporting an association between fine particulate pollution and ill-health. Motor vehicle emissions are considered to be the main source of fine particles in ambient urban air of cities which are not directly influenced by industrial emissions. The aim of this work was to assess the influence of a major arterial road on concentration levels of airborne fine particles in its vicinity. Measurements of over 500 particle size distributions in the particle size range 16–626 nm, were made using two scanning mobility particle sizers (SMPS). A subsequent comparison of the recorded values from differing locations is discussed, with reference made to topographic and climatic influences. Both horizontal and vertical profile measurements of fine particle number size distributions are described; the combination of the two yielding information as to the relative exposures of occupants of buildings in the vicinity of a major arterial route. With the exception of measurements in close proximity to the freeway (about 15 m), the horizontal profile measurements did not provide any evidence of a statistically significant difference in fine particle number concentration with respect to distance at ground level up to a distance of 200 m within the study area. The vertical profile measurements also revealed no significant correlation between particle concentration and height. However, for buildings in the immediate proximity to the arterial road (about 15 m) concentrations around the building envelope are very high, comparable to those in the immediate vicinity of the road, indicating undiluted concentrations drawn directly from the freeway. This finding has a significant implication for management of indoor air quality in the buildings located in the immediate vicinity of major roads.     

State of mixture of atmospheric submicrometer black carbon particles and its effect on particulate light absorption

The state of mixture of light-absorbing carbonaceous particles was investigated in relation to light absorption properties using electron microscopic examinations, black carbon (BC) analyses of quartz filter by thermal/optical reflectance (TOR) method, measurements with two continuous light-absorbing photometers at a suburban site of Tsukuba, about 60 km northeast of Tokyo. The volume fraction of water-soluble material (?) in individual particles is important for assessing particulate light-absorbing and/or scattering of atmospheric aerosols. The values of ? in BC particles were evaluated by electron micrographs before and after dialysis (extraction) of water-soluble material. The mass absorption coefficient (MAC in units of m² g^?1) tended to increase with increasing the average ? in BC particles with the radius range of 0.05–0.5 μm. Thus, our results indicate that coatings of water-soluble material around BC particles can enhance the absorption of solar radiation. Moreover, the single scattering albedo (SSA) will increase because a large amount of coating material will scatter more light.     

Characteristics of puff dispersion in an urban environment

Instantaneous releases of sulfur hexafluoride tracer were carried out as part of the Joint Urban 2003 field campaign in Oklahoma City. Data from 10 fast-response tracer samplers were used to examine the crosswind and along-wind spread of the tracer, the decay of tracer concentrations, and the retention of tracer within approximately 1 km of the release locations. The time variation of the median values of the tracer concentrations, normalized by the peak value observed at a given sampler, could be approximately described by an exponential decay with characteristic decay times on the order of 1–2 min. The longer times were found for early morning releases and the shorter times were associated with later morning or afternoon releases, suggesting that atmospheric stability or the depth of the mixed layer may affect puff dispersion even in urban environments. The median retention times required for 99% of the exposure to be realized at a given location were found to be correlated reasonably well with the median decay times. These characteristic time scales should be regarded as lower limits for concentration decay because the analysis excluded a number of anomalous cases in which the decaying concentrations exhibited an extended tail that indicated a very slow ventilation rate. The median values of the along-wind dispersion parameter σ_x grouped into downwind distance ranges can be described by a linear variation with distance with an initial “hold up” contribution due to building effects of about 30–45 m, but there are considerable variations about this relationship. Downwind 0.5–1 km from the release point the lateral puff dispersion (σ_y) was roughly 70% of the along-wind dispersion.     

urban ecolocsy and the air environment

A feature of the 62nd annual meeting of the Air Pollution Control Association, held June 22-26, 1969 in New York City, was a plenary session on Urban Ecology and the Air Environment. Moderated by Norman Cousins, editor of The Saturday Review of Literature, the session developed the theme through the outspoken and personal viewpoints of four distinguished panelists: Austin N. Heller, Aaron J. Teller, Barry Commoner, and Stewart L. Udall. The essence of their remarks appears on the following pages.     

Size-selected particles in an urban atmosphere of Brisbane,Australia

Interpretations of source contributions and the behaviour of particles in the urban atmosphere of Brisbane were made by comparing the results of elemental analyses with the measured meteorological conditions, PM₁₀, light scattering, gaseous pollutant concentrations and particle size distributions.Carbon was determined to be the most abundant element in the fine particles (FP). Although many of the other elements in the greater relative abundances are usually associated with natural origins, the major influence resulting in changes to FP mass was concluded to be by elements from anthropogenic sources. This conclusion was based on the significant positive relationships between the anthropogenic elements (e.g., Pb, Br, C, Ti, V, Mn, etc.) with the FP mass. The major influence on the PM₁₀ mass concentrations was determined to be the elements usually associated with natural origins such as Na and Cl. In addition, the positive relationship of submicrometre particle number concentrations with FP carbon and with vehicular-emitted gaseous species including NO_x and CO implied a significant contribution of vehicle exhausts to aerosols in this size range.     

Measurements of the physical properties of particles in the urban atmosphere

Measurements of the physical properties of particles in the atmosphere of a UK urban area have been made, including particle number count by condensation nucleus counters with different lower particle size cut-offs; particle size distributions using a Scanning Mobility Particle Sizer; total particle Fuchs surface area using an epiphaniometer and particle mass using Tapered Element Oscillating Micro-balance (TEOM) instruments with size selective (PM₁₀ and PM_2.5) inlets. Mean particle number counts at three sites range from 2.86×10⁴ to 9.60×10⁴ cm^-3. A traffic-influenced location showed a substantially higher ratio of particle number to PM₁₀ mass than a nearby background location despite being some 70 m from the roadway. Operating two condensation nucleus counters in tandem to determine particles in the 3–7 nm size range by difference showed signficant numbers of particles in this range, apparently related to homogeneous nucleation processes. Measurements with the Scanning Mobility Particle Sizer showed a clear difference between roadside size distributions and those at a nearby background location with an additional mode in the roadside samples below 10 nm diameter. Particle number counts were found to show a significant linear correlation with PM₁₀ mass (r²=0.44; n=44 for 24 h data at an urban background location), although during one period of high pollution a curvilinear relationship was found. Measurements of the diurnal variation in PM₁₀ mass, particle number count and Fuchs surface area show the same general pattern of behaviour of the three variables, explicable in terms of vehicle emission source strength and atmospheric dispersion, although the surface area growth was out of phase with the particle number and mass. It appears that particle number gives the clearest indication of recent road traffic emissions.     

Air pollution records on selenite in the urban environment

Black crusts (BC) on selenite, i.e. gypsum stone used in buildings and monuments in the city of Bologna (northern Italy) have been studied.The crusts have been compared with genetically identical ones encountered on gypsum outcrops in the area surrounding the same city, in a relatively clean rural environment.Because of gypsum's high solubility, also in the past, BC began to form and embed particles of atmospheric aerosol as soon as the stone was used in construction, even though the SO₂ levels in the air were probably much lower than today. Unlike other types of stone (sandstone, limestone, marbles), selenite is currently undergoing a deceleration of dissolution processes, following the acidification of the environment caused by industrialisation. For this reason the BC on selenite are older (up to 580±45 yr), thicker (up to 4 cm) and far more stable than those encountered on other types of building stones used in the same area.The BC are stratified: at the base, in contact with the stone, the crust contains numerous prismatic black particles originating from wood combustion; immediately above the base layer these particles progressively increase; finally, in the outer part of the crust one encounters the characteristic black, spongy spherical fly-ash originating from the combustion of mineral oils.From the chemical point of view, a comparison between urban and rural crusts shows that elements such as C, Si, K, Fe, V, Cr, Ni, Zn, Ga, As and Pb are due to present-day and/or past pollutant sources within the city itself.Moreover, the chemical data from the stratigraphy of the BC show that, while C and K were more abundant in the past than now, elements such as Fe, V, Cr, (Mn, Ni), Cu, (Zn), (Ga), As, Pb characterise recent and current urban atmospheres.     

On the nature of nitrate particles in a coastal urban area

Application of micro spot and electron microscopy techniques to individual particles in a coastal urban site revealed the following:

• 1.(a) sulfate particles, some of them mixed, dominated the sub-μm (0.3–0.8 μm) size range;
• 2.(b) nitrates were found mostly in the μm size range, in the form of NaNO₃.

The latter was verified by X-ray analysis of individual nitrates. Apparently the NaNO₃ particles were formed through heterogeneous reaction of gaseous HNO₃ with sea salt particles.     

Carbonyl compounds in the urban environment of Athens,Greece

The concentration levels of 15 selected carbonyl compounds in 62 samples were determined at two sites in Athens basin from June to December 2000. Formaldehyde was the most abundant species (0.05-39 microg m(-3)), which comprised from 22% to 37% of the total measured compounds, followed by acetaldehyde (4.32-49 microg m(-3)), acetone/acrolein (0.64-198 microg m(-3)) and butanal (0.79-140 microg m(-3)). The mean formaldehyde/acetaldehyde and acetaldehyde/propanal molar ratios were calculated. No significant seasonal differences were observed for all the carbonyls. Photochemical production was found to weigh upon atmospheric levels for 83-93% in summer days, dropping below 33% in the winter. The importance of formaldehyde and acetaldehyde as a source of hydroxyl radicals in Athens was also assessed.     

Lead and cadmium in indoor air and the urban environment

The present study was conducted to find potential terrestrial biomonitors for heavy metals in indoor air in an urban environment. TSP, PM(10), and PM(2.5) were collected in three retirement facilities in the urban area of Vienna. In addition, particulate matter and soil, vegetation, and isopods (Porcellio scaber L.) were collected in the adjacent garden areas. Aerosols were sampled with a low-volume air sampler. The sampled materials were wet ashed and total lead and cadmium contents were determined. Water-soluble heavy metal concentrations were measured in aqueous extracts from air exposed filters, soil, and vegetation. Lead and cadmium were analyzed by graphite furnace AAS. Lead contents in the vegetation were inferred from water-soluble lead in soils. Lead in isopods generally reflected the contents in vegetation. Cadmium in plants probably derived from soil solutions as well as from atmospheric input. Isopods reflected the total cadmium contents in soils. Particulate matter was dominated by PM(2.5), both with respect to mass concentrations and to heavy metal contents. The indoor aerosol was found to be influenced by human activity, indoor sources, and outdoor particles. Relationships between indoor airborne heavy metals and the contents in vegetation (lead and cadmium: positive) and isopods (lead: negative) were identified to have the potential for biomonitoring indoor air quality.     

Trends of ambient carbonyl compounds in the urban environment of Hong Kong

The concentrations of C₁–C₈ carbonyl compounds were measured at two urban sites in Hong Kong from October 1997 to September 2000. The daily total carbonyl concentrations were found to range from 2.4 to 37 μg m⁻³. Formaldehyde was the most abundant species, which comprised from 36 to 43% of the total detected carbonyls, followed by acetaldehyde (18–21%) and acetone (8–20%). The highest 24-hour average concentrations measured were 10 and 7.7 μg m⁻³ for formaldehyde and acetaldehyde, respectively. Seasonal and temporal variations in the concentrations of formaldehyde and acetaldehyde were not obvious, but lowest concentrations often occurred from June to August. The mean formaldehyde/acetaldehyde molar ratios at the two sites in summer (2.8±1.1 and 2.5±1.2) were significantly higher (p⩽0.01) than those in winter periods (1.9±0.6 and 2.0±0.6). The phenomena were explained by influences of both photochemical reactions and local meteorological conditions. Better correlations between formaldehyde and acetaldehyde, and between NO_x and each of the two major carbonyls were obtained in winter periods indicating direct vehicular emissions were the principal sources. The ambient formaldehyde and acetaldehyde concentrations in the urban atmosphere of Hong Kong were within the normal ranges reported in the literature for other urban sites world-wide.     

Source apportionment of settleable particles in an impacted urban and industrialized region in Brazil

Environmental Science and Pollution Research - Settleable particulate matter (SPM), especially coarser particles with diameters greater than 10 μm, has been found culprit of high...