Roadside Particles Research Articles

3D Imaging of Roadside and Underground Railway Particulate Matter Structures

Air pollution in cities is associated with adverse health conditions; however, the underlying reasons are poorly understood. Previous particulate matter (PM) imaging studies have mostly used 2D microscopic techniques. In this study, the 3D appearances of roadside and underground railway station airborne PMs and the elemental characteristics of underground station PM were examined. Roadside and underground station PMs were collected using a cyclone particulate matter collection system. The 3D structures of the PMs were examined using an Olympus LEXT OLS4100 confocal microscope. Elemental characteristics of underground railway station PM were evaluated with a Zeiss EVO 50 scanning electron microscope (SEM) in backscattered electron (BSE) mode. Confocal microscopy of both PM sources indicated some particles can have sharp appearing edges. The longest axis length of roadside particles had a median (range) of 4.0 (1.3 to 6.6) μm and height of 1.4 (0.3 to 2.1) μm. SEM imaging of underground railway station PM was consistent in appearance and size with confocal imaging; BSE mode indicated compositions primarily of iron, calcium, and silicon. In conclusion, we observed that some roadside and underground railway station PMs can have sharp appearing surfaces from 3D confocal microscopy. SEM imaging of underground railway station PM was consistent with confocal microscopy and enabled elemental analysis.

Size Distribution and Source Appointment of Road Particles During Winter in Tianjin

The significant role of traffic emissions mixed from various sources in urban air pollution has been widely recognized. However, the corresponding contributions to the roadside particle distribution are poorly understood due to the mixed impacts of various sources. Particle number concentrations of different sizes at the roadside in Nankai District of Tianjin were continuously monitored using a portable aerosol particle spectrometer during the morning rush hour (07:30-09:20) from Nov. 9, 2018 to Jan. 6, 2019. Characteristic and influencing factors of particle size distributions were discussed combined with temperature and relative humidity data, while potential sources of particles at the roadside were identified based on size distribution analysis. The results showed that the average total particle number concentrations were 502 cm-3, and the concentrations of the accumulation mode and coarse mode were 500 cm-3 and 2 cm-3, respectively. The distribution of number concentrations at the roadside was unimodal and primarily concentrated at 0.25-0.50 μm, with peak sizes at 0.28-0.30 μm. The same distribution trend of particle number concentration and difference in the concentration in the same segment size were observed at different periods. Vehicle activity level was the main influencing factor of road particulate matter concentration on different weekdays; the probability of the high value of road particulate matter concentration was reduced by a reasonable combination of the vehicle tail numbers. Temperature and relative humidity were both found to be positively correlated with the number concentration of particles. With the increase in temperature and relative humidity, the total and peak particle number concentration showed an overall upward trend. In addition, the peak particle size increased from 0.28-0.30 μm to 0.35-0.40 μm when relative humidity was higher than 80%. Three sources, including road dust, brake and tire wear, and the aging particles from vehicle exhaust, were identified using positive matrix factorization in this study. Road dust contributed 8.6% of the total number concentration, which mainly consisted of particles with sizes above 5.00 μm. Brake and tire wear contributed 2.8% of the total number concentration of particles with a size range of 0.80-4.00 μm. The aging particles from vehicle exhaust contributed the most (88.5%), with a peak at 0.25-0.65 μm. The sources of roadside particles were mainly related to vehicle activity, whereas temperature and relative humidity also affected the particle number size distribution.

Impacts of traffic on roadside particle variations in varied temporal scales

Traffic is a significant pollution source in cities and has caused various health and environmental concerns worldwide. Therefore, the improved understanding of traffic impacts on particle concentrations could help mitigate air pollution. In this study, field measurements were conducted beside an arterial road in Shanghai, China, to obtain the fine-scale temporal variations in traffic volumes, meteorological parameters, and size-resolved particle concentrations. The generalized additive model was developed to reveal their associations under different analysis intervals (time scales). Results indicate that on-road traffic greatly increased the concentration and variability of roadside particles. Variations of roadside fine particles (<1 μm, having high homogeneity) closely followed those at the background point, but background variations of coarse particles (having high heterogeneity) were negligible compared with the roadside point. Roadside particles showed high variability on the 10-s scale and presented frequent stochastic spikes above the background level. The particle variability was greatly reduced on the 60-min scale, exhibiting stable variations. The association between traffic and roadside particle variations was weak on a fine temporal scale (5-min scale). However, the association showed a pronounced increase when the analysis interval was increased (60-min scale). This is because extending the analysis interval could reduce the influence of random factors (sample randomness) and emission lagging effects on the results. Moreover, with the increase of the analysis interval, the improvement of associations between variables can be well characterized by exponential curves, which could help determine the optimal analysis interval. Additionally, heavy-duty vehicles showed a lot more significant influence on particle variations compared with that of light-duty vehicles, and should be regarded as the key governance target for on-road pollution control. These findings broaden the knowledge of traffic impacts on particle concentrations, which could provide implications in air pollution abatement.

Morphological and elemental characterization of leaf-deposited particulate matter from different source types: a microscopic investigation.

Particulate matter (PM) deposition on urban green enables the collection of particulate pollution from a diversity of contexts, and insight into the physico-chemical profiles of PM is key for identifying main polluting sources. This study reports on the morphological and elemental characterization of PM2-10 deposited on ivy leaves from five different environments (forest, rural, roadside, train, industry) in the region of Antwerp, Belgium. Ca. 40,000 leaf-deposited particles were thoroughly investigated by particle-based analysis using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) and their physico-chemical characteristics were explored for PM source apportionment purposes. The size distribution of all deposited particles was biased towards small-sized PM, with 32% of the particles smaller than 2.5μm (PM2.5) and median diameters of 2.80-3.09μm. The source type influenced both the particles' size and morphology (aspect ratio and shape), with roadside particles being overall the smallest in size and the most spherical. While forest and rural elemental profiles were associated with natural PM, the industry particles revealed the highest anthropogenic metal input. PM2-10 profiles for roadside and train sites were rather comparable and only distinguishable when evaluating the fine (2-2.5μm) and coarse (2.5-10μm) PM fractions separately, which enabled the identification of a larger contribution of combustion-derived particles (small, circular, Fe-enriched) at the roadside compared to the train. Random forest prediction model classified the source type correctly for 61-85% of the leaf-deposited PM. The still modest classification accuracy denotes the influence of regional background PM and demands for additional fingerprinting techniques to facilitate source apportionment. Nonetheless, the obtained results demonstrate the utility of leaf particle-based analysis to fingerprint and pinpoint source-specific PM, particularly when considering both the composition and size of leaf-deposited particles.

Chemical composition of atmospheric aerosols in the general environment and around a trunk road in the Tokyo metropolitan area

To evaluate the influence of vehicle exhaust particles on the urban atmosphere, atmospheric aerosols collected in the general environment and at a trunk road sampling site in the Tokyo metropolitan area were analyzed for carbonaceous and ionic components. Samples were collected as fine (<2.1 μm) and coarse particle (2.1–7.0 μm) from April 2003 to March 2004 using low-volume Andersen sampler. The carbonaceous components were analyzed by a thermal method and a thermal/optical method. Elemental carbon (EC) determined by thermal method was higher than those by thermal/optical method, and slope of linear regression of the thermal method versus the thermal/optical method differed at both sampling points. These results suggested possible analytical artifacts, a difference in the composition of the carbonaceous components of the aerosols, or both. The EC concentrations in fine particles in the roadside were higher than in the general environment by 5 μg m −3, and it was accounted for 68% of the difference of the mass concentration. The mass concentration reconstructed by the mass closure model using element analysis results corresponded more closely to the observed mass concentration in the general environment samples than in the roadside samples. It is suggested that the contribution of the organic compounds in the roadside particles was underestimated. Diesel vehicle emission control regulations implemented in October 2003 seem to have had an effect because there was a significant difference in the average concentration of suspended particulate matter and NO x before and after implementation of the regulations. Moreover, the EC/TC ratio has been decreasing over time.

Possible Routes for Lead Accumulation in Feral Pigeons (Columba Livia)

This study examined possible routes for lead (Pb) accumulation in resident pigeons collected from rural, urban, and four industrial sites in Korea. The accumulation pattern of Pb was comparable to the study sites. The highest Pb concentration was found in the bone, followed by kidney, liver, and lung of pigeons. Highest Pb residues in bones were found in urban (Seoul), and two industrial complex areas (Busan and Ulsan), which were about 15 times higher than rural area (Duckjuk island), and followed by Ansan and Yochon industrial areas. Regional Pb variations in liver, kidney, and lung tissues were also similar pattern with the bone Pb difference. These findings indicate that Pb accumulation in tissues of pigeons may be affected by the Pb exposure in their respective habitats. Crop contents and gizzard materials were investigated as representing the ingested items. No difference of Pb concentration was observed in major foods (maize and/or wheat) of crop contents in the study sites except Busan, whereas variations of Pb levels in gizzard materials were indicative of a similar pattern with tissue Pb differences. The Pb concentration in tissues of pigeons did not correspond well to the atmospheric Pb levels. With regard to possible Pb sources, ingested items especially materials present in the gizzard are important sources for Pb contamination to pigeons because Pb-containing sources may be expected to present in roadside particles, dusts, paint chips and building flakes. However, air Pb value being low may not affect significant as the regional variations in tissues of pigeons.

The physical nature of airborne particulate matter (PM&lt;SUB align=right&gt;10) in Plymouth, UK

Plymouth aerosol has been directly collected on to transmission electron microscopy grids at both roadside and background sites at the University of Plymouth. Photographs of 50 randomly selected particles were taken. The particle images were collected and measured using a Quantimet 570 image analyser. Two box-counting procedures approximating to fractal dimensions were applied to the collected particle images. Comparison of the fractal dimensions of roadside and background particles shows there is a structural change in particles from road to background in the 220-320 nm size range. Within this range, roadside particles are both more dense and have a more convoluted surface than the same size aerosol in the background. It is reasonable to assume that roadside particles will therefore have a deeper lung penetration and greater surface loading of material than their counterparts in the background aerosol.

CHARACTERIZATION OF ROAD-SIDE AEROSOLS BY PIXE AND SEM-EDX ANALYSIS

The characteristics of the road-side particles were examined. The elemental concentrations of aerosol particle collected on the road-side were measured both by PIXE analysis as a bulk sample and SEM-EDX analysis as individual particle sample. For the data set of SEM-EDX, cluster analysis was applied. On an average, more than 80% of the aerosol particles are consisted of lighter elements such as C, O, N and H. Main metal components contained in the roadside particles were Si, Ca, Fe and Al that were mainly originated in soil.