Road Dust Resuspension Research Articles

The impact of stay-home policies during Coronavirus-19 pandemic on the chemical and toxicological characteristics of ambient PM2.5 in the metropolitan area of Milan, Italy

The goal of this study was to characterize changes in components and toxicological properties of PM2.5 during the nationwide 2019-Coronavirus (COVID-19) lockdown restrictions in Milan, Italy. Time-integrated PM2.5 filters were collected at a residential site in Milan metropolitan area from April 11th to June 3rd at 2020, encompassing full-lockdown (FL), the followed partial-lockdown (PL2), and full-relaxation (FR) periods of COVID-19 restrictions. The collected filters were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), individual organic species (e.g., polycyclic aromatic hydrocarbons (PAHs), and levoglucosan), and metals. According to online data, nitrogen dioxide (NO2) and benzene (C6H6) levels significantly decreased during the entire COVID-19 period compared to the same time span in 2019, mainly due to the government-backed shutdowns and curtailed road traffic. Similarly, with a few exceptions, surrogates of tailpipe emissions (e.g., traffic-associated PAHs) as well as re-suspended road dust (e.g., Fe, Mn, Cu, Cr, and Ti) were relatively lower during FL and PL2 periods in comparison with year 2019, whereas an increasing trend in mass concentration of mentioned species was observed from FL to PL2 and FR phases due to the gradual lifting of lockdown restrictions. In contrast, comparable concentrations of ambient PM2.5 and black carbon (BC) between lockdown period and the same time span in 2019 were attributed to the interplay between decreased road traffic and elevated domestic biomass burning as a result of adopted stay-home strategies. Finally, the curtailed road traffic during FL and PL2 periods led to ~25% drop in the PM2.5 oxidative potential (measured via 2′,7′-dichlorodihydrofluorescein (DCFH) and dithiothreitol (DTT) assays) with respect to the FR period as well as the same time span in 2019. The results of this study provide insights into the changes in components and oxidative potential of PM2.5 in the absence of road traffic during COVID-19 restrictions.

Quantifying metal emissions from vehicular traffic using real world emission factors.

Road traffic emissions are an increasingly important source of particulate matter in urban and non-road environments, where non-tailpipe emissions can contribute substantially to elevated levels of metals associated with adverse health effects. Thus, better characterization and quantification of traffic-emitted metals is warranted. In this study, real-world emission factors for fine particulate metals were determined from hourly x-ray fluorescence measurements over a three-year period (2015-2018) at an urban roadway and busy highway. Inter-site differences and temporal trends in real-world emission factors for metals were explored. The emission factors at both sites were within the range of past studies, and it was found that Ti, Fe, Cu, and Ba emissions were 2.2-3.0 times higher at the highway site, consistent with the higher proportion of heavy-duty vehicles. Weekday emission factors for some metals were also higher by 2.0-3.5 times relative to Sundays for Mn, Zn, Ca, and Fe, illustrating a dependence on fleet composition and roadway activity. Metal emission factors were also inversely related to relative humidity and precipitation, due to reduced road dust resuspension under wetter conditions. Correlation analysis revealed groups of metals that were co-emitted by different traffic activities and sources. Determining emission factors enabled the isolation of traffic-related metal emissions and also revealed that human exposure to metals in ambient air can vary substantially both temporally and spatially depending on fleet composition and traffic volume.

Chemical characteristics, oxidative potential, and sources of PM2.5 in wintertime in Lahore and Peshawar, Pakistan

The chemical characteristics, oxidative potential, and sources of PM2.5 were analyzed at the urban sites of Lahore and Peshawar, Pakistan in February 2019. Carbonaceous species, water soluble ions, and metal elements were measured to investigate the chemical composition and sources of PM2.5. The dithiothreitol (DTT) consumption rate was measured to evaluate the oxidative potential of PM2.5. Both cities showed a high exposure risk of PM2.5 regarding its oxidative potential (DTTv). Carbonaceous and some of the elemental species of PM2.5 correlated well with DTTv in both Lahore and Peshawar. Besides, the DTTv of PM2.5 in Lahore showed significant positive correlation with most of the measured water soluble ions, however, ions were DTT-inactive in Peshawar. Due to the higher proportions of carbonaceous species and metal elements, Peshawar showed higher mass-normalized DTT activity of PM2.5 compared to Lahore although the average PM2.5 concentration in Peshawar was lower. The high concentrations of toxic metals also posed serious non-carcinogenic and carcinogenic risks to the residents of both cities. Principle component analysis coupled with multiple linear regression was applied to investigate different source contributions to PM2.5 and its oxidative potential. Mixed sources of traffic and road dust resuspension and coal combustion, direct vehicle emission, and biomass burning and formation of secondary aerosol were identified as the major sources of PM2.5 in both cities. The findings of this study provide important data for evaluation of the potential health risks of PM2.5 and for formulation of efficient control strategies in major cities of Pakistan.

Assessment of the ability of roadside vegetation to remove particulate matter from the urban air.

The development of urbanised areas together with the growing transport infrastructure and traffic volume are the main cause of air quality deterioration due to the increasing concentrations of particulate matter. Dust pollution is a threat to human health. It can cause the development of lung, larynx or circulatory system cancer. Due to the ability to accumulate dust particles on the leaf surface, the contribution of trees in the process of phytoremediation of air pollution has started to be appreciated. An analysis of the elemental composition of particulate matter (PM) stored on the leaves surface was also carried out, which showed high average concentration of: C > O > Si > Fe (above 8wt.%). It was also observed single particles with a high concentration of heavy metals: Ti, Mn, Ba, Zn, Cr, Pb, Sn, Ni and REE (rare earth elements). The major origin of PM are vehicular emissions, soil and re-suspended road dust. This paper presents also a comparison of selected tree, shrub and vine species differing in their ability to accumulate particulate matter. It was experimentally determined the average leaf surface of individual plant species and established the amount of particulate matter with aerodynamic diameter between 10 and 100μm, 2.5 and 10μm, and 0.2 and 2.5μm deposited on the leaf surface and in waxes. Some species of vines (Parthenocissus quinquefolia), shrubs (Forsythia x intermediata) and coniferous trees, such as Betula pendula 'Youngii', Quercus rubra, Cratageus monogyna, Acer pseduoplatanus, Tilia cordata Mill. or Platanus orientalis turned out to be the most efficient in the process of phylloremediation.

PM10 and PM2.5 emission factors for non-exhaust particles from road vehicles: Dependence upon vehicle mass and implications for battery electric vehicles

Governments around the world are legislating to end the sale of conventionally fuelled (gasoline and diesel) internal combustion engine vehicles (ICEV) and it is assumed that battery-electric vehicles (BEV) will take their place. It has been suggested that due to their increased weight, non-exhaust emissions of particles from BEV may exceed all particle emissions, including exhaust, from an ICEV. This paper examines the vehicle weight-dependence of PM10 and PM2.5 emissions from abrasion (brake, tyre and road surface wear) and road dust resuspension and generates a comparison of the two vehicle types. The outcome is critically dependent upon the extent of regenerative braking relative to use of friction brakes on the BEV, but overall there will be only modest changes to the total local emissions of particles from a passenger car built to current emissions standards.

Modeled and measured near-road PM2.5 concentrations: Indianapolis and Providence cases

Modeling analyses were developed to evaluate near-road PM2.5 concentrations predicted by the AERMOD dispersion modeling chain under real-world conditions, and to assess the sensitivity of modeled near-road concentrations to the choice of dispersion model (AERMOD or CAL3QHCR), meteorological data, and travel data processing approach. We evaluate PM2.5 monitoring sites near major freeways in Indianapolis, Indiana (for 2016) and Providence, Rhode Island (for 2015–2016). The modeling analyses are built upon bottom-up estimates of temporally and spatially resolved roadway PM2.5 emissions based on traffic monitoring data and local vehicle fleet emission factors. The dispersion model simulations use local meteorological data collected at or close to the near-road monitoring sites. Predictions involved a modeling chain that included travel activity data processing, emissions modeling (MOVES and AP-42), and air quality dispersion modeling. We estimated the difference between PM2.5 concentrations at the near-road monitor and at nearby urban air quality monitoring sites (the measured near-road “increment”), and compared modeled results to the measured increments. Based on monitoring data, estimates of multi-day-averaged near-road PM2.5 increments were 0.9 ± 0.6 μg/m3 at Indianapolis and 1.4 ± 0.2 μg/m3 at Providence (where the uncertainty represents the 95% confidence interval on the mean value), and were comparable to measured PM2.5 increments at these sites in the near-road literature. Modeled roadway contributions to multi-day-averaged near-road concentrations substantially exceeded measured values based on the near-road monitoring data. The average near-road PM2.5 increment modeled with AERMOD was more than 300% (factor of four) larger than the measured increment at Indianapolis, and more than 500% (factor of six) larger than the measured increment at Providence. These biases reflect cumulative uncertainty throughout the near-road PM2.5 modeling chain. The emissions modeling component may have contributed to the modeling chain biases in two ways. First, the relative contribution of modeled non-exhaust emissions (PM2.5 brake wear, tire wear, and re-suspended road dust) compared to tailpipe exhaust emissions was higher than what has been documented in several published studies. Second, other research findings indicate that the U.S. EPA MOVES2014 model may over-predict tailpipe PM2.5 exhaust. The dispersion modeling component may have also contributed to the modeling chain biases. For example, when local meteorological data were used, AERMOD results were relatively insensitive to wind direction on a daily averaged basis; as a result, modeled concentrations exceeded measured values regardless of whether the near-road monitor was upwind or downwind of the roadway. In summary, this work provides a unique evaluation of PM2.5 concentrations predicted by the near-road modeling chain, and provides valuable information to understand potential sources of uncertainty in the near-road modeling process.

Correction and source apportionment of vehicle emission factors obtained from Bolu Mountain Highway Tunnel, Turkey

Total suspended particulate (TSP) samples were collected in the atmosphere of Bolu Mountain Highway Tunnel located on the axis of Edirne-Istanbul-Ankara on the main artery of Turkey, by using PUF samplers between 24 and June 29, 2018. Thirty-five major and trace metals, 11 water-soluble anions and cations, and OC and EC concentrations were determined at the entrance and the exit of the tunnel. Emission factor calculations were carried out with and without correction of the data set against crustal contributions. The non-crustal net concentration data set was used as an input for the factor analysis and factor analysis-multiple linear regression. Factor analysis identified five sources, namely, (1) road dust re-suspension, (2) road cover material and tyre wear abrasion, (3) brake pad solid lubricants, (4) diesel combustion emission, and (5) gasoline- LPG combustion emission. Contributions of identified sources on the TSP concentrations and emission factors were quantified by using the FA-MR technique and the results were discussed. Tin and Sb were identified and reported as the best marker for the brake-related non-exhaust emissions in the road tunnel. FA-MR results showed that 46, 60, 49, and 37% of Ba, Cu, Fe, and Mn, respectively were contributed by dust re-suspension. The main sources of EC (39%) and OC (49%) were observed to be gasoline-LPG emissions and 69% of sulfate and 62% of Pb in TSP fraction was contributed by diesel emission. Tin and Sb were mainly affected by the brake pad solid lubricant factor and 64% of Sn and 53% of Sb were contributed by this factor.

Loadings, chemical patterns and risks of inhalable road dust particles in an Atlantic city in the north of Portugal

Road dust resuspension has a significant contribution to the atmospheric particulate matter levels in urban areas, but loadings, emission factors, and chemical source profiles vary geographically, hampering the accuracy of emission inventories and source contribution estimates. Given the dearth of studies on the variability of road dust, in the present study, an in-situ resuspension chamber was used to collect PM10 samples from seven representative streets in Viana do Castelo, the northernmost coastal city in Portugal. PM10 samples were analysed for organic and elemental carbon by a thermo-optical technique, elemental composition by ICP-MS and ICP-AES, and organic constituents by GC–MS. Emission factors were estimated to be, on average, 340 and 41.2 mg veh−1 km−1 for cobbled and asphalt pavements, respectively. Organic carbon accounted for 5.56 ± 1.24% of the PM10 mass. Very low concentrations of PAHs and their alkylated congeners were detected, denoting a slight predominance of petrogenic compounds. Si, Al, Fe, Ca and K were the most abundant elements. The calculation of various geochemical indices (enrichment factor, geoaccumulation index, pollution index and potential ecological risk) showed that road dust was extremely enriched and contaminated by elements from tyre and brake wear (e.g. Sb, Sn, Cu, Bi and Zn), while lithophile elements showed no enrichment. For As, the geochemical and pollution indices reached their maximum in the street most influenced by agricultural activities. Sb, Cd, Cu and As can pose a very high ecological risk. Sb can be regarded as the pollutant of highest concern, since it represented 57% of the total ecological risk. Hazard indices higher than 1 for some anthropogenic elements indicate that non-carcinogenic effects may occur. Except for a street with more severe braking, the total carcinogenic risks can be considered insignificant.

Black carbon and size-segregated elemental carbon, organic carbon compositions in a megacity: a case study for Istanbul

In this study, black carbon (BC), particulate matter (PM), nitrogen oxides (NOx), and sulphur dioxide (SO2) were monitored between May 2019 and February 2020. During this sampling period, size-segregated particle samples were collected by a high-volume cascade impactor, once a week. Elemental carbon (EC) and organic carbon (OC) were investigated on the size-segregated particles. The study was carried out at Esenler district of Istanbul. Main sources in the vicinity of the sampling area are Central Coach Station of Istanbul, residential buildings, small-scale industrial facilities, and O-1 and O-2 highway connection. The average BC concentration was 2763 ± 1974 ng/m3. PM10 and PM2.5 concentrations were 38.2 ± 17.4 and 21.5 ± 12.4 μg/m3, respectively. BC comprised 12.8% and 7.2% of PM2.5 and PM10, respectively. Diurnal variation of BC had a similar trend with NO2 concentrations, which showed peak concentrations during rush hours. BC had high Pearson correlation coefficients with NO, NO2, and PM2.5. The geographical position of possible emission sources was estimated through conditional probability function. The Central Coach Station of Istanbul had the highest geographical possibility for BC sources. EC and OC exhibited bimodal size distribution. The coarse mode peak was at 0.95–1.5-μm size bin for OC, whilst it was at 1.5–3-μm size bin for EC. Since EC and BC exhibit the same origin with different measurement principles, we concluded that resuspension of road dust also contributed ambient BC concentrations.

Fundamental study on the estimation of resuspended road dust in urban areas

Fundamental study on the estimation of resuspended road dust in urban areas

Geochemical, Mineralogical and Morphological Characterisation of Road Dust and Associated Health Risks

Road dust resuspension, especially the particulate matter fraction below 10 µm (PM10), is one of the main air quality management challenges in Europe. Road dust samples were collected from representative streets (suburban and urban) of the city of Viana do Castelo, Portugal. PM10 emission factors (mg veh−1 km−1) ranging from 49 (asphalt) to 330 (cobble stone) were estimated by means of the United Stated Environmental Protection Agency method. Two road dust fractions (<0.074 mm and from 0.0074 to 1 mm) were characterised for their geochemical, mineralogical and morphological properties. In urban streets, road dusts reveal the contribution from traffic emissions, with higher concentrations of, for example, Cu, Zn and Pb. In the suburban area, agriculture practices likely contributed to As concentrations of 180 mg kg−1 in the finest road dust fraction. Samples are primarily composed of quartz, but also of muscovite, albite, kaolinite, microcline, Fe-enstatite, graphite and amorphous content. Particle morphology clearly shows the link with natural and traffic related materials, with well-formed minerals and irregular aggregates. The hazard quotient suggests a probability to induce non-carcinogenic adverse health effects in children by ingestion of Zr. Arsenic in the suburban street represents a human health risk of 1.58 × 10−4.

The impact of biomass burning on the oxidative potential of PM2.5 in the metropolitan area of Milan

In this study, we investigated the impact of biomass burning on the oxidative potential of PM2.5 in the metropolitan area of Milan, Italy. PM2.5 samples were collected on quartz filters during cold (December 2018–February 2019) and warm (May 2019–July 2019) seasons at the Municipality of Bareggio, a small town located approximately 14 km northwest of the Milan city center. The PM2.5 constituents were chemically analyzed, and its corresponding oxidative potential was measured by means of the dithiothreitol (DTT) assay. Total PM2.5 mass concentration was significantly higher in winter (71.82 ± 4.17 μg/m3) compared to summer (16.67 ± 0.27 μg/m3), mainly a result of enhanced biomass burning emissions combined with higher atmospheric stability and lower mixing during the cold season. The enhanced biomass burning activities during the winter period also resulted in very high polycyclic aromatic hydrocarbons (PAHs) concentrations (72.81 ± 16.59 ng/m3) which were more than 150-fold higher than the warm period values (0.40 ± 0.07 ng/m3). PAH concentrations were highly correlated with chemical markers of biomass burning (i.e., levoglucosan (R2 = 0.79), and K+/K (R2 = 0.87)) in the winter period. Spearman correlation analysis between DTT and PM2.5 chemical species showed a dominant role of secondary organic aerosols (SOA) and vehicular emissions in summer-time PM2.5 oxidative potential (i.e., the capacity of PM2.5 species to oxidize target molecules), while in the wintertime, the DTT values were highly correlated with chemical markers of biomass burning, vehicular activities, and re-suspended road dust. Multiple linear regression (MLR) analysis identified biomass burning (41%) as the dominant contributor to DTT, followed by SOA (20%), re-suspended road dust (18%), and vehicular emissions (16%). Our results underscore the importance of biomass burning to the overall oxidative potential of PM2.5 in the metropolitan area of Milan, urging the need to promulgate effective mitigation policies targeting these emissions.

Evaluation of particulate matter emissions from non-passenger diesel vehicles in Qatar

ABSTRACT Road traffic is one of the main sources of particulate matter (PM) in the atmosphere. Despite its importance, there are significant challenges in the quantitative evaluation of its contribution to airborne concentrations. In order to propose effective mitigation scenarios, the proportions of PM traffic emissions, whether they are exhaust or non-exhaust emissions, should be evaluated for any given geographical location. In this work, we report on the first study to evaluate particulate matter emissions from all registered heavy duty diesel vehicles in Qatar. The study was applied to an active traffic zone in urban Doha. Dust samples were collected and characterized for their shape and size distribution. It was found that the particle size ranged from few to 600 μm with the dominance of small size fraction (less than 100 μm). In-situ elemental composition analysis was conducted for side and main roads traffic dust, and compared with non-traffic PM. The results were used for the evaluation of the enrichment factor and preliminary source apportionment. The enrichment factor of anthropogenic elements amounted to 350. The traffic source based on sulfur elemental fingerprint was almost 5 times higher in main roads compared with the samples from non-traffic locations. Moreover, PM exhaust and non-exhaust emissions (tyre wear, brake wear and road dust resuspension) were evaluated. It was found that the majority of the dust was generated from tyre wear with 33% followed by road dust resuspension (31%), brake wear (19%) and then exhaust emissions with 17%. The low contribution of exhaust PM10 emissions was due to the fact that the majority of the registered vehicle models were recently made and equipped with efficient exhaust PM reduction technologies. Implication: This study reports on the first results related to the evaluation of PM emission from all registered diesel heavy duty vehicles in Qatar. In-situ XRF elemental analysis from main, side roads as well as non-traffic dust samples was conducted. Several characterization techniques were implemented and the results show that the majority of the dust was generated from tyre wear, followed by road dust resuspension and then brake wear; whereas exhaust emissions were tremendously reduced since the majority of the registered vehicle models were recently made and equipped with efficient exhaust PM reduction technologies. This implies that policy makers should place stringent measures on old vehicle license renewals and encourage the use of metro and public transportation.

Chemistry and sources of PM2.5 and volatile organic compounds breathed inside urban commuting and tourist buses

Inhalable particulate matter (size <2.5 μm: PM2.5) inside commuting and tourist buses moving through the city of Barcelona, Spain, was chemically analysed. The analyses show PM dominated by organic carbon (mostly 10–20 μg/m3) and elemental carbon (mostly 3–6 μg/m3; OC/EC = 3.4), followed by SO42, Fe, Ca, K, Al2O3, Mg, and Na, with calculated mineral content being around one third that of total carbon. Elemental carbon levels are higher inside diesel buses than those powered by natural gas or electricity, and higher in the upper floor of open-top double decker tourist buses than in the lower floor. Overall, major element concentrations inside the buses are typically 2–8 times higher than 24 h-averaged urban background levels, although some metallic trace elements, notably Cu and Sb, are exceptionally enriched due to the presence of brake particles, especially on routes involving higher gradients and therefore more brake use. In contrast, Cu and Sb concentrations in electric buses are unexceptional, presumably because these buses rely more on regenerative braking and are hermetically sealed when moving. Seasonal differences reveal PM to be more mineral in winter (Al2O3 1.3 μg/m3 vs. summer average of 0.3 μg/m3), with summer enrichment in Na, Mg, P, V, Ni and SO42− being attributed to marine aerosols contaminated by port emissions. Source apportionment calculations identify 6 main factors: road dust resuspension, metalliferous (brake wear and metallurgy), local urban dust, secondary sulphate and shipping (6%), vehicle exhaust (19%), and an indoor source (46%) interpreted as likely related to the textile fibres and skin flakes of bus occupants. Volatile Organic Compounds measured inside all buses except one were dominated by 2-Methylpentane (14–36 μg/m3), Toluene (10–30 μg/m3), Xylene isomers (10–28 μg/m3, with m- » o- > p-Xylene) and n-Pentane (5–15 μg/m3). ƩBTEX concentrations were <70 μg/m3, with Toluene being commonest, followed by m-Xylene, with p-Xylene, o-Xylene and Ethylbenzene each below 7 μg/m3 and Benzene concentrations always less than the EU limit value of 5 μg/m3. The VOCs mixture is similar to that recently reported from inside Barcelona taxis (although inside the larger volume bus VOC concentrations are lower than in the taxis) and is interpreted as providing a chemical fingerprint characterising traffic-contaminated ambient air in the city road environment. The notable exception to the VOC content was a brand new hybrid diesel bus still offgassing volatiles to such an extent that Ʃ(alkane + alkene + aromatic) indoor concentrations exceeded 800 μg/m3, with ƩBTEX ten times higher than normal.

Elemental composition of PM0.25 collected in an urban site of Argentina: A first case study

A total of 175 aerosol samples were collected during the winter-spring months of 2014–2015 in Córdoba, Argentina. The samples were collected in five size fractions that ranged from <0.25 to 10 μm using a SIOUTAS impactor in a 6-h period and analyzed by synchrotron radiation X-ray fluorescence to obtain elemental aerosol mass concentrations for As, Ca, Co, Cr, Cu, Fe, K, Mn, Ni, Pb, Si, S, Ti, V, and Zn. An analysis of the distribution of the elements in the different collected fractions was performed to infer the most likely sources of particulate matter. From the analysis, it was found that the particulate matter fraction smaller than 0.25 μm was mostly affected by emissions from traffic and combustion, while the particulate matter fraction ranging from 2.5 to 10 μm was mostly influenced by re-suspension of road dust. In addition, the results indicated the presence of Si, typically found in coarse particulate matter and in large amounts in particles smaller than 0.25 μm. To infer the sources of aerosols causing the deterioration of air quality, principal component analysis was performed. The smallest particles, due to their toxicity, are likely to produce more adverse health effects than larger size fractions. These results show the need to monitor their atmospheric emissions in order to preserve air quality. Synchrotron radiation X-ray fluorescence analysis of the elemental composition of particles smaller than 0.25 μm in Córdoba city constitutes the first contribution to the knowledge base of the concentrations of toxic metals in this size fraction. These results are relevant because there is a lack of data in South American cities.

Dendrograms, heat maps and principal component analysis – the practical use of statistical methods for source apportionment of trace elements in PM10

Dendrogram (DE), heat map (HM) and principal component analysis (PCA) methods were used in order to identify possible emission sources of As, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb and Se in ambient PM10 collected in the surroundings of working power plants. Each statistical tool resulted in slightly different clusters. The best approximation of possible emission sources was received by the use of statistical analysis of trace-element concentrations combined with characterization of the sampling sites. In the study, PCA was indicated as the most useful statistical tool for source apportionment of trace elements in PM10. Major sources identified by PCA included: (1) coal combustion, (2) soil and road-dust resuspension, (3) the use of pesticides and (4) waste incineration.

Characteristics of tail pipe (Nitric oxide) and resuspended dust emissions from urban roads – A case study in Delhi city

IntroductionPersonal exposure to elevated vehicle exhaust and non-exhaust emissions at urban roadside leads to carcinogenic health effects, respiratory illness and nervous system disorders. In this paper, an attempt has been made to investigate the exhaust and non-exhaust emissions emitted from selected roads in Delhi city. MethodsBased on the vehicular density per hour and speed, three categories of roads have been considered in the present study: (a) low density road (≤1000 vehicles/hour, V ≥ 10 m/s); (b) medium density road (>1000 vehicles/hour but ≤ 2000 vehicles/hour, V ≥ 7.5 m/s < 10 m/s); and (c) high density road (>2000 vehicles/hour, V < 7.5 m/s). At the selected roads, real-world exhaust emissions were measured using AVL DiTEST 1000 analyser. The silt load measurements were also carried out as per EPA AP-42 methodology at the selected roads. ResultsResults indicated real-world NO exhaust emissions of 0.5 g/m3 (2.03 g/km) on high-density roads and 0.23 g/m3 (0.67 g/km) on low and medium density roads. These values were significantly higher than the Bharat Standard (BS) IV (0.25 g/km). The silt load on the different types of roads indicated 3, 25 and 44 g/m2 -day dust deposition on, low, medium and high-density road, respectively. PM2.5 and PM10 emission rates were measured using US-EPA AP-42 methodology and were found to be least at low-density roads with values of 0.54 and 2.22 g/VKT (VKT -Vehicle Kilometer Travelled) respectively, and highest for high density roads with values of 12.40 and 51.25 g/VKT respectively. ConclusionThe present study reveals that both tailpipe (exhaust) and resuspend able road dust (non-exhaust) emissions contributes significantly and deteriorates local air quality. Although there exists emission standards, but there are no enforced regulations for non-exhaust emissions (resuspension of road dust). Hence, there is need to regulate non-exhaust emissions on urban roads.

Characteristics and sources of PM2.5 and reactive gases near roadways in two metropolitan areas in Canada

With concern in recent years about adverse health effects for populations living or spending significant amounts of time near large roadways, an investigation of the air quality characteristics and potential sources influencing levels of PM and its chemical composition was undertaken in Toronto and Vancouver. Three near-road monitoring stations were established in the downtown area and beside a large highway in Toronto, and beside a major trucking route in Vancouver. 24-hour integrated samples were concurrently collected at these near-road and nearby urban background sites. This study has provided detailed chemical data for PM2.5 and reactive gases (NH3, HONO and HNO3) for a year in 2015–2016. Differences between pollutant concentrations at the near-road and background urban sites were identified, and compared with observations at other urban locations. The traffic contribution was quantified as the concentration increment between the near-road and background sites. The highest increments due to traffic were observed for elemental carbon, select trace metals (e.g. Fe, Ba, Cu, Sb, Zn) and reactive gases (NH3, HONO). In general, the percent contribution of local traffic-related emissions followed a descending order of Toronto highway > Vancouver truck route > downtown Toronto for most of these pollutants. It appears that the influence of traffic-related emissions on air pollution near roads depends more on the proportion of large trucks in the fleet than the total traffic volume. Application of principal component analysis (PCA) coupled with multi-linear regression (MLR) analysis to the local traffic increment pollutant data, as well as knowledge of chemical markers representative of different sources, helped to identify the possible sources of traffic-related PM2.5. These sources include non-exhaust (brake wear abrasion, resuspended road dust) and vehicular exhaust (mixed gasoline/diesel, diesel and lubricating oil combustion) emissions. The contribution of each of the sources varied between sites. In particular, the contribution of diesel exhaust emissions, presumably from highly polluting heavy-duty vehicles and trucks, was significant at the truck route (Vancouver) and the highway (Toronto) sites. Furthermore, the substantial contribution of non-exhaust emissions (brake wear and resuspension of road dust) to PM2.5, and thus metals, with differences between sites due to traffic characteristics or local meteorology was identified. Emissions related to lube oil combustion were not statistically significant. Overall, this work delivered valuable information that serves as input for further studies involving other roads and cities in order to generate reliable and representative results for air quality management and associated health outcomes.

PM10 levels at urban, suburban, and background locations in the eastern Mediterranean: local versus regional sources with emphasis on African dust

PM10 levels were determined at different locations in a coastal site in the eastern Mediterranean to assess the relative contribution of local versus regional sources. Two campaigns were conducted: during the first, PM10 was monitored at three urban locations (kerbside/traffic/background) at different sampling periods, whereas during the second one, PM10 was simultaneously measured at two locations (urban/suburban). Both campaigns have shown that African dust transport was a major carrier of coarse particles. Daily PM10 concentrations of 547 μg m−3 and 234 μg m−3 were measured during the first and the second campaigns, respectively, both of them associated with severe dust storms. However, some dust episodes influenced lesser PM10 levels. The contribution from dust episodes to the measured concentration was estimated at 2–527 μg m−3 during the first campaign and 4–218 μg m−3 during the second campaign. Classification into dusty and non-dusty days has shown that local anthropogenic sources also influence ambient PM10 concentrations; however, few exceedances of the daily limit of 50 μg m−3 occurred during both campaigns. Particularly, it was found that domestic heating during cold months was a major contributor to PM10 levels followed by emissions from traffic with higher contribution of the latter during summer months (high touristic season) as well as non-traffic emissions (road dust resuspension). Hourly average PM10 concentration during the second campaign has shown that traffic-related emissions and/or road dust resuspension were associated with up to 40 μg m−3 whereas during wintertime late evening hours, PM10 concentration from heating reached up to 60 μg m−3 at the central urban location.

Contribution of road dust from Low Impact Development (LID) construction sites to atmospheric pollution from heavy metals

The re-suspension of road dust due to intense Low Impact Development (LID) construction activities may be a major contributor to atmospheric metal pollution. However, the distribution characteristics, mobility potential, and pollutant load of atmospheric particles at LID construction sites are not clear. Consequently, management practices to mitigate air pollution from LID construction are lacking. We investigated the atmospheric metal pollution from road dust produced during different construction stages of rain gardens and porous pavements and estimated the ecological risks posed by the heavy metals. Although concentrations of heavy metals in road dust at LID construction sites were lower than at sites without LID construction, the ecological risks posed by the atmospheric heavy metals at LID construction sites were generally higher due to the greater mass of road dust produced during LID construction. Hence, LID management practices should focus on the removal of road dust, especially finer particles (<44 μm) produced during early construction stages. In roads, the zones influenced by LID construction is related to road types based on traffic volume; these road types in descending order of zone influenced by LID construction are: arterial road (400–600 m) > collector road (100–150 m) > access road (50–100 m) > laneway (30–50 m). Based on the study sites, we estimate LID construction in China will contribute 2.31 and 6.23 times as much as the current load of atmospheric particles by 2020 and 2030; and we project atmospheric heavy metals will be 1.45–2.18 and 2.82–4.73 times greater than the current load by 2020 and 2030 from the intense LID construction. Based on our results, several regulatory recommendations are presented to mitigate air pollution at LID construction sites.