Dynamic of submicrometer particles in urban environment

Many studies show that particle toxicity increases with decreasing their size, emphasizing the role of submicrometric particles, in particular of ultrafine particles (<100 nm). In fact, particles greater than 2.5 μm are quickly removed through dry and wet deposition on the timescale of hours whereas submicrometer particles may reside in atmosphere for weeks, penetrate in indoor environment, and be long-range transported. High aerosol size resolution measurements are important for a correct assessment of the deposition efficiency in the human respiratory system, and time resolution is another important requisite. Starting from such considerations, time-resolved aerosol particle number size distributions have been measured in downtown Rome. Fast Mobility Particle Sizer (FMPS) and Scanning Mobility Particle Sizer (SMPS) measurements have been carried out at the INAIL’s Pilot Station, located in downtown Rome, in an area characterized by high density of autovehicular traffic. The two instruments have allowed to investigate deeply the urban aerosol in the range of 5.6–560 and 3.5–117 nm, respectively. In particular, the FMPS measurements have confirmed the interpretation about the transition phenomena in the time interval of few seconds, timescale typically associated with the emission of gasoline and diesel engines. In downtown Rome, the hourly average size distribution is bimodal or trimodal with maxima at about 5–15, 20–30, and 70–100 nm. Particle formation in the nucleation mode was associated to freshly emitted autovehicular exhaust.     

The relationship between indoor and outdoor airborne particles in the residential environment

The relationship between indoor and outdoor airborne particles was investigated for 16 residential houses located in a suburban area of Brisbane, Australia. The submicrometer particle numbers were measured using the Scanning Mobility Particle Sizer, the larger particle numbers using the Aerodynamic Particle Sizer and an approximation of PM_2.5 was also measured using a DustTrak. The measurements were conducted for normal and minimum ventilation conditions using simultaneous and non-simultaneous measurement methods designed for the purpose of the study. Comparison of the ratios of indoor to outdoor particle concentrations revealed that while temporary values of the ratio vary in a broad range from 0.2 to 2.5 for both lower and higher ventilation conditions, average values of the ratios were very close to one regardless of ventilation conditions and of particle size range. The ratios were in the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM_2.5 fraction. Comparison of the time series of indoor to outdoor particle concentrations shows a clear positive relationship existing for many houses under normal ventilation conditions (estimated to be about and above 2 h⁻¹), but not under minimum ventilation conditions (estimated to be about and below 1 h⁻¹). These results suggest that for normal ventilation conditions, outdoor particle concentrations could be used to predict instantaneous indoor particle concentrations but not for minimum ventilation, unless air exchange rate is known, thus allowing for estimation of the “delay constant”.     

Size distribution of polycyclic aromatic hydrocarbons in a roadway tunnel in Lisbon, Portugal

Atmospheric aerosols of four aerodynamic size ranges were collected using high volume cascade impactors in an extremely busy roadway tunnel in Lisbon (Portugal). Dust deposited on the tunnel walls and guardrails was also collected. Average particle mass concentrations in the tunnel atmosphere were more than 30 times higher than in the outside urban background air, revealing its origins almost exclusively from fresh vehicle emissions. Most of the aerosol mass was concentrated in submicrometer fractions (65%), and polycyclic aromatic hydrocarbons (PAH) were even more concentrated in the finer particles with an average of 84% of total PAH present in sizes smaller than 0.49 μm. The most abundant PAH were methylated phenanthrenes, fluoranthene and pyrene. About 46% of the total PAH mass was attributed to lower molecular weight compounds (two and three rings), suggesting a strong influence of diesel vehicle emissions on the production of local particulate PAH. The application of diagnostic ratios confirmed the relevance of this source of PAH in the tunnel ambient air. Deposited dust presented PAH profiles similar to the coarser aerosol size range, in agreement with the predominant origin of coarser aerosol particles from soil dust resuspension and vehicle wear products.     

Effects of airborne saline particles on vegetation in relation to variables of exposure and other factors

Saline particles are a heterogeneous group of chloride(Cl)-containing airborne materials of natural as well as anthropogenic origins. They are usually a local problem of air pollution in terms of source and dispersion, but within these areas their effects on agricultural, ornamental or natural species of plants can be of substantial practical concern. These effects include the accumulation of Cl, the production of foliar lesions, and changes in the plant's levels of mineral nutrients and metabolites, physiological processes, and growth and reproduction. Some quantitative exposure-effect relationships have been formulated for foliar Cl, foliar lesions, and changes in growth and yield. These relationships are sensitive to various factors, such as flux, duration and frequency of exposure, species and stage of development of the plant, size and chemical composition of the particle, and light, temperature, relative humidity and precipitation during or after exposure. The interactions of these factors affect the response of the plant to saline particles by determining three major sets of processes: collection and retention of particles by the foliage; penetration of material from superficial deposits into the foliar tissue; translocation of absorbed Cl (or other ionic components) and susceptibility of tissue to it within the leaf.     

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。     

Volatile organic compounds in an urban airborne environment adjacent to a municipal incinerator,waste collection centre and sewage treatment plant

The occurrence and temporal distribution of airborne volatile organic compounds (VOC) at nine closely grouped locations in a suburban environment on the edge of the coastline of the Southampton Water estuary, located on the coastline of central southern England, was studied over six monthly periods spanning 1996–1997. The sampling sites circumscribed a juxtaposed municipal incinerator, waste collection and processing centre and sewage treatment plant. Three sets of airborne samples being taken before and after the closure of the municipal incinerator. VOC with volatilities of low to medium polarity ranging broadly from those of n-butane to n-octadecane were the major focus of interest. Over 100 individual compounds were routinely found in localised samples taken during the period of study. The types and concentrations of VOC identified partly reflect the imprint of the various waste processing operations on atmospheric VOC within the local environment. The most abundant VOC classes consisted of aromatic, chlorinated and organosulphide compounds, with smaller proportions of alkanes, alkenes and cycloalkane compounds. Compounds produced by sewage-processing and waste management operations, including volatile organosulphides and various oxygenated compounds, may occasionally exceed olfactory detection thresholds and represent a source of potential odour complaints in the local urban environment.     

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.     

Assessment of personal integrated exposure to fine particulate matter of urban residents in Hong Kong

Metropolitan residents are concerned about their exposure to airborne pollutants. But establishing these exposures is challenging. A compact personal exposure kit (PEK) was developed to evaluate personal integrated exposure (PIE) from time-resolved data to particulate matter with aerodynamic diameter less than 2.5 μm (PM_2.5) in five microenvironments, including office, home, commuting, other indoor activities (other than home and office), and outdoor activities experienced both on weekdays and weekends. The study was conducted in Hong Kong. The PEK measured PM_2.5, reported location and several other factors, stored collected data, as well as reported the data back to the investigators using global system for mobile communication (GSM) telemetry. Generally, PM_2.5 concentrations in office microenvironment were found to be the smallest (13.0 μg/m³), whereas the largest PM_2.5 concentration microenvironments were experienced during outdoor activities (54.4 μg/m³). Participants spent more than 85% of their time indoors, including in offices, homes, and other public indoor venues. On average, 42% and 81% of the time were spent in homes, which contributed 52% and 79% of PIE (during weekdays and weekends, respectively), suggesting that improvement of air quality in homes may reduce overall exposures and indicating the need for actions to mitigate possible public health burdens in Hong Kong. This study also found that various indoor/outdoor microenvironments experienced by urban office workers cannot be accurately represented by general urban air quality data reported from the regulatory monitoring. Such personalized air quality information, especially while in transit or in offices and homes, may provide improved information on population exposures to air pollution.

Implications: A newly developed personal exposure kit (PEK) was used to monitor PM_2.5 exposure of metropolitan citizens in their daily life. Different microenvironments and time durations caused various personal integrated exposure (PIE). The stationary monitoring method for PIE was also compared and evaluated with PEK. Positive protection actions can be taken after understanding the major contribution to PM_2.5 exposure.     

Assessment of the aerosol water content in urban atmospheric particles by the hygroscopic growth measurements in Sapporo,Japan

Aerosol water content (AWC) of urban atmospheric particles was investigated based on the hygroscopic growth measurements for 100 and 200 nm particles using a hygroscopicity tandem differential mobility analyzer in Sapporo, Japan in July 2006. In most of the humidogram measurements, presence of less and more hygroscopic mode was evident from the different dependence on relative humidity (RH). The volume of liquid water normalized by that of dry particle (V_w(RH)/V_dry) was estimated from the HTDMA data for 100 and 200 nm particles. The RH dependence of V_w(RH)/V_dry was well represented by a fitted curve with a hygroscopicity parameter κ_eff. The κ_eff values for 200 nm particles were in general higher than those for 100 nm particles, indicating a higher hygroscopicity of 200 nm particles. Based on the κ_eff values, the volume mixing ratios of water-soluble inorganic compounds (ammonium sulfate equivalent) were estimated to be on average 31% and 45% for 100 and 200 nm particles, respectively. The diurnal variation of κ_eff, with relatively higher values in the noontime and nighttime and lower values in the morning and evening hours, was observed for both particle sizes. The V_w(RH)/V_dry values under ambient RH conditions were estimated from κ_eff to range from 0.05 to 2.32 and 0.06 to 2.43 for 100 nm and 200 nm particles, respectively. The degree of correlation between κ_eff and V_w(RH)/V_dry at ambient RH suggests a significant contribution of the variation of κ_eff to atmospheric AWC in Sapporo.     

Effects of a constructional intervention on airborne and deposited particulate matter in the Portuguese National Tile Museum, Lisbon

In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes on both ground and first floor. Although this design was meant to protect the museum collection from ambient air pollutants, small openings between the glass panes remain, creating a semi-enclosed corridor. The effects of the glass panes on the indoor air quality were evaluated in a comparative study by monitoring the airborne particle concentration and the extent of particle deposition at the enclosed corridor as well as inside the museum building. Comparison of the indoor/outdoor ratio of airborne particle concentration demonstrated a high natural ventilation rate in the enclosed corridor as well as inside the museum building. PM₁₀ deposition velocities on vertical surfaces were estimated in the order of 3?×?10^?4 m s^?1 for both indoor locations. Also, the deposition rates of dark-coloured and black particles in specific were very similar at both indoor locations, causing visual degradation. The effectiveness of the glass panes in protecting the museum collection is discussed.     

Pedestrian exposure to size-resolved particles in Milan

Measurement campaigns for airborne particles along a pedestrian route in the city center of Milan were performed by means of a portable instrument consisting of an optical particle counter and a global positioning system (GPS) signal receiver. Based on the size-resolved particle number concentration data and on proper density factors experimentally determined for Milan urban area, the mass concentrations were calculated in terms of particulate matter with aerodynamic diameters < or =10 microm (PM10), < or =2.5 pm (PM2.5), and < or =1 microm (PM1). Besides directly measuring the personal exposure to PM throughout the route, the measurement campaigns pointed out small spatial and temporal variations of the concentration ranges in the different urban microenvironments visited along the route as well as very peculiar features of the particles levels in the underground subway. These findings suggested that the personal exposure of pedestrians in the city center could be estimated by simply taking into account the exposure at the open air and in the subway. The comparison between measured and calculated exposures according to the microenvironment-based estimation results in reasonable accordance, even though the estimations tend to slightly underestimate (12%) the actual measured exposure.     

Sources of personal exposure to fine particles in Toronto, Ontario, Canada

Individuals are exposed to particulate matter from both indoor and outdoor sources. The aim of this study was to compare the relative contributions of three sources of personal exposure to fine particles (PM2.5) by using chemical tracers. The study design incorporated repeated 24-hr personal exposure measurements of air pollution from 28 cardiac-compromised residents of Toronto, Ontario, Canada. Each study participant wore the Rupprecht & Patashnick ChemPass Personal Sampling System 1 day a week for a maximum of 10 weeks. During their individual exposure measurement days the subjects reported to have spent an average of 89% of their time indoors. Particle phase elemental carbon, sulfate, and calcium personal exposure data were used in a mixed-effects model as tracers for outdoor PM2.5 from traffic-related combustion, regional, and local crustal materials, respectively. These three sources were found to contribute 13% +/- 10%, 17% +/- 16%, and 7% +/- 6% of PM2.5 exposures. The remaining fraction of the personal PM2.5 is hypothesized to be predominantly related to indoor sources. For comparison, central site outdoor PM2.5 measurements for the same dates as personal measurements were used to construct a receptor model using the same three tracers. In this case, traffic-related combustion, regional, and local crustal materials were found to contribute 19% +/- 17%, 52% +/- 22%, and 10% +/- 7%, respectively. Our results indicate that the three outdoor PM2.5 sources considered are statistically significant contributors to personal exposure to PM2.5. Our results also suggest that among the Toronto subjects, who spent a considerable amount of time indoors, exposure to outdoor PM2.5 includes a greater relative contribution from combustion sources compared with outdoor PM2.5 measurements where regional sources are the dominant contributor.     

Exposure to ultrafine particles and PM2.5 in four Sydney transport modes

Concentrations of ultrafine (<0.1 μm) particles (UFPs) and PM_2.5 (<2.5 μm) were measured whilst commuting along a similar route by train, bus, ferry and automobile in Sydney, Australia. One trip on each transport mode was undertaken during both morning and evening peak hours throughout a working week, for a total of 40 trips. Analyses comprised one-way ANOVA to compare overall (i.e. all trips combined) geometric mean concentrations of both particle fractions measured across transport modes, and assessment of both the correlation between wind speed and individual trip means of UFPs and PM_2.5, and the correlation between the two particle fractions. Overall geometric mean concentrations of UFPs and PM_2.5 ranged from 2.8 (train) to 8.4 (bus) × 10⁴ particles cm^?3 and 22.6 (automobile) to 29.6 (bus) μg m^?3, respectively, and a statistically significant difference (p < 0.001) between modes was found for both particle fractions. Individual trip geometric mean concentrations were between 9.7 × 10³ (train) and 2.2 × 10⁵ (bus) particles cm^?3 and 9.5 (train) to 78.7 (train) μg m^?3. Estimated commuter exposures were variable, and the highest return trip mean PM_2.5 exposure occurred in the ferry mode, whilst the highest UFP exposure occurred during bus trips. The correlation between fractions was generally poor, and in keeping with the duality of particle mass and number emissions in vehicle-dominated urban areas. Wind speed was negatively correlated with, and a generally poor determinant of, UFP and PM_2.5 concentrations, suggesting a more significant role for other factors in determining commuter exposure.     

Application of cluster analysis to identify sources of airborne particles

A sampling programme for determining the concentrations in particulate matter of SO₄²⁻, Fe, Pb, Zn, K, Ca, Mg, Cd, Cr and Ni was established in the city of Valladolid for 13 months. Seasonal variations and enrichment factors were determined, then source apportionment techniques were applied. A multivariate clustering Q-technique has been used to identify specific sources. Each one of the six retained clusters has been interpreted by analyzing the composition of their centroids and the common attributes of the samples belonging to each one of them. To simplify the interpretation, some external auxiliary variables were chosen: percentage of the samples corresponding to the heating season period, minimum temperature, weekends, precipitation, daily average wind speed, etc. The reliability and practical significance of the results were studied after comparing the results obtained by two different initial partitions P1 and P2.This algorithm identified a crustal source (Fe, K, Ca and Mg), residual fuel burning (SO₄²⁻, Zn, Cd and Ni) and indirect vehicle exhaust (Pb). In addition, a double source for Cr (soil and coal ashes), a pollution ‘episode’ cluster, a low pollution cluster and an average pollution cluster have been identified.     

Measurements of ultrafine particles and other vehicular pollutants inside a mobile exposure system on Los Angeles freeways

A mobile exposure and air pollution measurement system was developed and used for on-freeway ultrafine particle health effects studies. A nine-passenger van was modified with a high-efficiency particulate air (HEPA) filtration system that can deliver filtered or unfiltered air to an exposure chamber inside the van. State-of-the-art instruments were used to measure concentration and size distribution of fine and ultrafine particles and the concentration of carbon monoxide (CO), black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (PAHs), fine particulate matter (PM2.5) mass, and oxides of nitrogen (NOx) inside the exposure chamber. This paper presents the construction and technical details of the van and air pollutant concentrations collected in 32 2-hr runs on two major Los Angeles freeways, Interstate 405 (1-405; mostly gasoline traffic) and Interstate 710 (1-710; large proportion of heavy-duty diesel traffic). More than 97% of particles were removed when the flow through the filter box was switched from bypass mode to filter mode while the vehicle was driving on both freeways. The filtration system thus provides a great particulate matter exposure contrast while keeping gas-phase pollutant concentrations the same. Under bypass mode, average total particle number concentration observed inside the exposure chamber was around 8.4 x 10(4) and 1.3 x 10(5) particles cm(-3) on the I-405 and the I-710 freeways, respectively. Bimodal size distributions were consistent and similar for both freeways with the first mode around 16-20 nm and the second mode around 50-55 nm. BC and particle-bound PAH concentrations were more than two times greater on the I-710 than on the I-405 freeway. Very weak correlations were observed between total particle number concentrations and other vehicular pollutants on the freeways.     

Contribution of particle counting in assessment of exposure to airborne microorganisms

The aim of the study was to determine the relationship between airborne bacterial concentrations and particle counts measured simultaneously at different sites. Andersen single stage viable particle samplers were used for microbial measurements while a Laser particle counter gave the cumulated counts of particles larger than 0.5 μm diameter. The first phase of the study was performed in two experimental rooms where the basic level of microbial contamination was low. Peaks of concentrations were generated by human activity and both bacterial and particle counts were monitored over 1 h. In the second phase, measurements were run for several days in three different buildings normally occupied. Natural variations of bacterial and particle counts were monitored: microbial measurements were performed each hour while particle counts were started with a 10 min frequency. Statistics revealed strong positive correlations between bacterial and particle counts in four sites out of five. Analyses of covariance used to compare the regression lines obtained in each area showed that except for two natural sites, the regression lines were significantly different, indicating that no absolute relationship can be established between the two parameters. Therefore, particle counting should, of course, not take the place of microorganism measurements, but combining particle counting with bioaerosols measurements may allow detection of rapid variations instantaneously and indicate further microbial measurements. This strategy should improve the assessment of people“s real exposure to airborne microorganisms.     

Concentrations of ultrafine,fine and PM2.5 particles in three European cities

Total number concentrations, number concentrations of ultrafine (0.01–0.1 μm) and accumulation (0.1–0.5 μm) particles, as well as mass concentration of PM_2.5 particles and blackness of PM_2.5 filters, which is related to Black Smoke were simultaneously monitored in three European cities during the winter period for three and a half months. The purpose of the study was to describe the differences in concentration levels and daily and diurnal variations in particle number and mass concentrations between European cities. The results show statistically significant differences in the concentrations of PM_2.5 and the blackness of the PM_2.5 filters between the cities, but not in the concentrations of ultrafine particles. Daily PM_2.5 levels were found to be poorly correlated with the daily total and ultrafine number concentrations but better correlated with the number concentration of accumulation particles. According to the principal component analysis airborne particulate pollutants seem to be divided into two major source categories, one identified with particle number concentrations and the other related to mass-based information. The present results underline the importance of using both particle number and mass concentrations to evaluate urban air quality.     

Isomer distribution of nitrotriphenylenes in airborne particles, diesel exhaust particles, and the products of gas-phase radical-initiated nitration of triphenylene

The formation of mutagenic nitro-polycyclic aromatic hydrocarbons (NPAHs) 1- and 2-nitrotriphenylene (1- and 2-NTP) via gas-phase OH or NO₃ radical-initiated reactions of triphenylene was demonstrated for the first time using a flow reaction system. In contrast with the results of conventional electrophilic nitration, 2-NTP was formed in larger yield than 1-NTP, but this is consistent with the mechanism proposed for gas-phase radical-initiated nitration of PAH. In diesel exhaust particle (DEP) samples, both 1- and 2-NTP were identified and their concentrations determined, as well as 1-nitropyrene (1-NP), which is a representative combustion-derived NPAH: the mean concentrations of 1-NTP, 2-NTP, and 1-NP were 4.7, 1.9, and 32 pmol mg_DEP^–1, respectively. The mean 2-NTP/1-NTP, 1-NTP/1-NP, and 2-NTP/1-NP ratios in samples of airborne particles collected in a residential area in Osaka, Japan, were>1.55,<0.25, and 0.37, respectively; these values are much higher than those of the DEP samples. This finding indicates that there is another source for airborne NTPs, especially 2-NTP, apart from diesel exhaust. These results strongly suggest that airborne NTPs originate from atmospheric processes such as radical-initiated reactions of triphenylene, and this has a significant influence on the atmospheric occurrence of NTPs.