Primary particle formation from vehicle emissions during exhaust dilution in the roadside atmosphere (original) (raw)
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Atmospheric particle number concentration and size distribution in a traffic–impacted area
Atmospheric Pollution Research, 2015
This study measured ambient particle number concentrations (PNC) and the particle number distributions (PND) in the urban area of Porto Alegre, Rio Grande do Sul, Brazil. The samples were analyzed using a NanoScan model 3910 from TSI (diameters between 10 and 420 nm) and were taken from sites with high density of vehicular traffic, including two roadsides, two traffic intersections, one street canyon and one urban background. Association of meteorological variables (temperature, relative humidity, solar radiation, wind direction, and wind speed) on nanoparticle concentrations was examined. The results indicated PNC averages between 4.85×10 4 cm–3 and 1.80×10 5 cm–3 for locations affected by vehicular traffic, where in highest concentrations were observed at sites corresponding to traffic intersections. In addition, all sites studied showed a trimodal average PND, with the modes centered at 14 nm, 30 nm, and 105 nm. PND was dominated by nucleation (44.9%) and Aitken (42.0%) modes being representative at the studied sites of the pollution originating from urban traffic, except at the urban background. Meteorological parameters and synoptic meteorological conditions contributed to the variation in the results between the sampled days in the same location.
Variability of non-volatile fractions of atmospheric aerosol particles with traffic influence
Atmospheric Environment, 2004
Emissions from vehicular traffic are considered to be a major source of anthropogenic submicrometer particles in the urban environment. In this study, volatile and non-volatile number and volume fractions were distinguished in particles sampled for three consecutive days (Friday, Saturday, and Sunday) close to a highway (HW) (A4) in Germany and for one day in the urban area of Aachen, Germany. A volatility tandem differential mobility analyzer (VTDMA) and a thermodenuder (TD) combined with two scanning mobility particle sizers (SMPS) were used to get insight into a sizeresolved mixing state of volatile and non-volatile particle fractions. Operating the VTDMA at 280 1C, the number size distribution of non-volatile particle cores was determined for initial particle sizes of 30, 50, 80, and 150 nm. The number size distributions from 10 to 400 nm of ambient and non-volatile aerosol particles were measured by using parallel a SMPS and TD/SMPS combination, respectively. Number size distributions measured near the HW showed a bimodal size distribution with a maximum number concentration at particle sizes between 10 and 20 nm. The TD/SMPS results for the HW site revealed that the nucleation mode disappeared after heating (completely volatile) and in total 10-20% by number of traffic-related particles were non-volatile. The VTDMA results revealed that only 22% of the 30 nm particles had a non-volatile core above the instrument detection limit of 10 nm. With increasing particle diameter, this non-volatile number fraction increased to ca. 60% for 50 nm particles and to approximately 100% for 80 and 150 nm particles. These findings mean that each particle in the upper Aitken and lower accumulation mode range contains a non-volatile core. With increasing traffic influence the number fraction of less-volatile particles representing mainly primary soot emissions increases to 62% for 50 nm particles and 71% for 80 nm particles.
Rapid physical and chemical transformation of traffic–related atmospheric particles near a highway
The health of a substantial portion of urban populations is potentially being impacted by exposure to traffic-related atmospheric pollutants. To better understand the rapid physical and chemical transformation of these pollutants, the number size distributions of non-volatile traffic-related particles were investigated at different distances from a major highway. Particle volatility measurements were performed upwind and downwind of the highway using a fast mobility particle sizing spectrometer with a thermodenuder on a mobile laboratory. The number concentration of non-denuded ultrafine particles decreased exponentially with distance from the highway, whereas a more gradual gradient was observed for non-volatile particles. The non-volatile number concentration at 27 m was higher than that at 280 m by a factor of approximately 3, and the concentration at 280 m was still higher than that upwind of the highway. The proportion of non-volatile particles increased away from the highway, representing 36% of the total particle number at 27 m, 62% at 280 m, and 81% at the upwind site. A slight decrease in the geometric mean diameter of the non-volatile particle size distributions from approximately 35 nm to 30 nm was found between 27 m and 280 m, in contrast to the growth of non-denuded particles with increasing distance from the highway. Single particle analysis results show that the contribution of elemental carbon (EC)-rich particle types at 27 m was higher than the contribution at 280 m by a factor of approximately 2. The findings suggest that people living or spending time near major roadways could be exposed to elevated number concentrations of nucleation-mode volatile particles (<30 nm), Aitken-mode non-volatile particles (30-100 nm), and EC-rich fine-mode particles (>100 nm). The impact of the highway emissions on air quality was observable up to 300 m.
Atmospheric Environment, 2005
On-road size-resolved particulate emission factors were computed using concurrently measured carbon monoxide (CO) as a freeway dilution indicator and correlating roadside particle measurements to CO measurements. The emission factors derived for the total particle number agree well with previous on-road investigations. However, this study extends this analysis to produce unique receptor-dependent, size-resolved, road and grid-level emission factor distributions. Both mileage-and fuel-based particle number and mass emission factors at road and grid levels, along with CO emission factors, are presented and the results from freeways with distinctly different percentages of heavyduty diesel truck traffic are compared. The effects of plume processing on particle number near roadways are shown to be much more profound than on particle mass, further indicting that the adverse health effects observed near roadways are at least partially related to particle numbers. r
Atmospheric Environment, 2004
The spatial variability of aerosol number and mass along roads was determined in different regions (urban, rural and coastal-marine) of the Netherlands. A condensation particle counter (CPC) and an optical aerosol spectrometer (LAS-X) were installed in a van along with a global positioning system (GPS). Concentrations were measured with high-time resolutions while driving allowing investigations not possible with stationary equipment. In particular, this approach proves to be useful to identify those locations where numbers and mass attain high levels ('hot spots'). In general, concentrations of number and mass of particulate matter increase along with the degree of urbanisation, with number concentration being the more sensitive indicator. The lowest particle numbers and PM 1 -concentrations are encountered in a coastal and rural area: o5000 cm À3 and 6 mg m À3 , respectively. The presence of sea-salt material along the North-Sea coast enhances PM >1 -concentrations compared to inland levels. High-particle numbers are encountered on motorways correlating with traffic intensity; the largest average number concentration is measured on the ring motorway around Amsterdam: about 160 000 cm À3 (traffic intensity 100 000 veh day À1 ). Peak values occur in tunnels where numbers exceed 10 6 cm À3 . Enhanced PM 1 levels (i.e. larger than 9 mg m À3 ) exist on motorways, major traffic roads and in tunnels. The concentrations of PM >1 appear rather uniformly distributed (below 6 mg m À3 for most observations). On the urban scale, (large) spatial variations in concentration can be explained by varying intensities of traffic and driving patterns. The highest particle numbers are measured while being in traffic congestions or when behind a heavy diesel-driven vehicle (up to 600 Â 10 3 cm À3 ). Relatively high numbers are observed during the passages of crossings and, at a decreasing rate, on main roads with much traffic, quiet streets and residential areas with limited traffic. The number concentration exhibits a larger variability than mass: the mass concentration on city roads with much traffic is 12% higher than in a residential area at the edge of the same city while the number of particles changes by a factor of two (due to the presence of the ultrafine particles (aerodynamic diameter o100 nm). It is further indicated that people residing at some 100 m downwind a major traffic source are exposed to (still) 40% more particles than those living in the urban background areas. r
In an urban site affected by fresh vehicle exhaust emissions, the ambient air number concentrations of particles coarser than 3 nm (N) was split into two components, N = N1 + N2. This was done using a method based on the high correlation between black-carbon (BC) and number (N) concentrations which is typically observed in ambient air and is the result of vehicle exhaust emissions. The component N1 accounts for "those aerosol components directly emitted in the particle phase" and "those components nucleating immediately after emission". The component N2 accounts for the new particle formation enhancements during the "dilution and cooling of the vehicle exhaust" and is also influenced by "in situ new particle formation in ambient air". The contribution of N1 to N exhibits a maximum of 55% during the morning rush hours (07:00-08:00). The contribution of N2 to N exhibits a daily evolution with a broad maximum during daylight (as solar radiation intensity), while for about 7 h (11:00-17:00) the N2 contribution to N is about 70%. During some "afternoon N2 events", N2 contributions exceeded 90%. Enhancements in the new particle formation processes may increase the N/BC concentrations ratio in one order of magnitude, from 4.82 × 10 6 particles/ng BC to 47 × 10 6 particles/ng BC and during some events up to 97 × 10 6 particles/ng BC. The results show evidence of the high potential of the vehicle exhausts and of the urban atmosphere to trigger new particle formation if the ambient air conditions are favourable. The method used in this study is useful in assessing future changes in the number to BC relationship due to forthcoming regulations in the vehicle exhaust emissions. ᭧
Atmospheric Environment, 2012
Particle emissions from diesel engine cars depend firstly on exhaust aftertreatment systems but the use of the vehicle becomes also crucial. In urban areas, this use depends on: transport demand, route choices, traffic density, street conditions, weather, driver behaviour and topographical characteristics of the roads. Nowadays, most diesel vehicles in urban areas across Europe are equipped with exhaust aftertreatment systems aiming to reduce the total mass of emitted particles. In comparison to earlier aftertreatment systems, the implementation of modern procedures is causing a reduction in the size of the emitted particles up to a nanometric range. The main goal of this work is the characterization of particle size and number distribution in the submicrometric range from a modern diesel vehicle emission in real traffic conditions in the city of Madrid with the purpose of assessing the actual weight of the different city parameters influencing the particle emission. In order to accomplish this objective, up to 12 on board emission measurement experiments have been performed with a Euro IV Diesel passenger car driving along a single urban circuit in Madrid City. To cover the main external factors, stretch, traffic conditions and driving directions have been considered as independent variables for this study. Assuming a proper car operating conditions, the results show that street characteristics, vehicle density and topographic features are the main factors conditioning the particle emission. Extrapolating our results, a diesel standard passenger car circulating across a city like Madrid can emit more nanoparticles per kilometre (up to 114% more in this study) at peak hour than at off peak hour. Moreover, the driving direction can also influence dramatically the emission of nanoparticles per second. This difference in the emission rate depends on the street but in our study it can be higher than 110% depending on the driving direction.
Atmospheric Chemistry and Physics, 2006
Number concentrations and size distributions of traffic related aerosol particles were measured at a roadside in Helsinki during two winter campaigns (10-26 February 2003, 28 January-12 February 2004) and two summer campaigns (12-27 August 2003, 6-20 August 2004). The measurements were performed simultaneously at distances of 9 m and 65 m from the highway. Total number concentrations were measured by a condensation particle counter (CPC) and particle size distributions by a scanning mobility particle sizer (SMPS) and an electrical low pressure impactor (ELPI). This study concentrates on data that were measured when the wind direction was from the road to the measurement site. The total concentrations in the wintertime were 2-3 times higher than in the summertime and the concentrations were dominated by nucleation mode particles. The particles smaller than 63 nm (aerodynamic diameter) constituted ∼90% of all particles in the wintertime and ∼80% of particles in the summer time. The particle total concentration increased with increasing traffic rate. The effect of traffic rate on particles smaller than 63 nm was stronger than on the larger particles. The particle distributions at the roadside consisted of two distinguishable modes. The geometric mean diameter (GMD) of nucleation mode (Mode 1) was 20.3 nm in summer and 18.9 nm in winter. The GMD of the larger mode consisting mostly of traffic related soot particles (Mode 2) was 72.0 nm in summer and 75.1 nm in winter. The GMD values of the modes did not depend on the traffic rate. The average particle density for each mode was determined by a parallel density fitting method based on the size distribution measurement made by ELPI and SMPS. The average density value for Mode 1 particles
Atmospheric Environment, 2006
Atmospheric particulate matter (PM) presence at four urban sites in the city of Milan (Italy) is characterised in terms of particle size distribution (number, surface, volume) for the cold and warm season. Simultaneous monitoring of particle number concentration (from 300 nm up to 20 mm of diameter) has been performed between August 2002 and December 2004 by means of a low-volume particle size laser analyser. The monitoring sites are characterised by a different exposure to traffic emissions, enabling for the assessment of the role of this source on both PM concentration levels and on particle size distributions. Data from an urban background site, not directly exposed to traffic emission, a site in a residential area of the city, and two kerbside sites (one at open air, one in a road tunnel) directly exposed to the traffic emissions are compared. Weekdays' and weekends' data from the urban background site are analysed for assessing the effect of the reduced traffic circulation on Sundays.