| 1. |
- Ketzel, M., et al.
(författare)
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Estimation and validation of PM2.5/PM10 exhaust and non-exhaust emission factors for practical street pollution modelling
- 2007
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Ingår i: Atmos. Environ.. - : Elsevier BV. ; 41, s. 9370-9385
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Tidskriftsartikel (refereegranskat)abstract
- In order to carry out efficient traffic and air quality management, validated models and PM emission estimates are needed. This paper compares current available emission factor estimates for PM10 and PM2.5 from emission databases and different emission models, and validates these against eight high quality street pollution measurements in Denmark, Sweden, Germany, Finland and Austria.The data sets show large variation of the PM concentration and emission factors with season and with location. Consistently at all roads the PM10 and PM2.5 emission factors are lower in the summer month than the rest of the year. For example, PM10 emission factors are in average 5–45% lower during the month 6–10 compared to the annual average.The range of observed total emission factors (including non-exhaust emissions) for the different sites during summer conditions are 80–130 mg km−1 for PM10, 30–60 mg km−1 for PM2.5 and 20–50 mg km−1 for the exhaust emissions.We present two different strategies regarding modelling of PM emissions: (1) For Nordic conditions with strong seasonal variations due to studded tyres and the use of sand/salt as anti-skid treatment a time varying emission model is needed. An empirical model accounting for these Nordic conditions was previously developed in Sweden. (2) For other roads with a less pronounced seasonal variation (e.g. in Denmark, Germany, Austria) methods using a constant emission factor maybe appropriate. Two models are presented here.Further, we apply the different emission models to data sets outside the original countries. For example, we apply the “Swedish” model for two streets without studded tyre usage and the “German” model for Nordic data sets. The “Swedish” empirical model performs best for streets with studded tyre use, but was not able to improve the correlation versus measurements in comparison to using constant emission factors for the Danish side. The “German” method performed well for the streets without clear seasonal variation and reproduces the summer conditions for streets with pronounced seasonal variation. However, the seasonal variation of PM emission factors can be important even for countries not using studded tyres, e.g. in areas with cold weather and snow events using sand and de-icing materials. Here a constant emission factor probably will under-estimate the 90-percentiles and therefore a time varying emission model need to be used or developed for such areas.All emission factor models consistently indicate that a large part (about 50–85% depending on the location) of the total PM10 emissions originates from non-exhaust emissions. This implies that reduction measures for the exhaust part of the vehicle emissions will only have a limited effect on ambient PM10 levels.
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| 2. |
- Ketzel, M, et al.
(författare)
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Modelling the fate of ultrafine particles from exhaust pipe to rural background: an analysis of time scales for dilution, coagulation and deposition
- 2004
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 38:17, s. 2639-2652
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the time scales of various dynamic processes during the evolution of the particle size distribution from its emission from a vehicle exhaust pipe through its dilution at kerbside and urban level. In addition, the situation in a road tunnel or near a highway is discussed. The derived formula framework allows the estimation of approximated time scales based on a given particle size distribution for the processes dilution with background air, coagulation, deposition and condensation. The variation of the time scales for these processes with "lifetime" of the exhaust particles and the dependence of the time scales on the particle size is shown. We identify the spatial or temporal scales under which the discussed processes are important and have to be included in operational particle pollution models. (C) 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Ketzel, Matthias, et al.
(författare)
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Multi-plume aerosol dynamics and transport model for urban scale particle pollution
- 2005
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 39:19, s. 3407-3420
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Tidskriftsartikel (refereegranskat)abstract
- The Multi-plume Aerosol dynamics and Transport (MAT) model has been developed to study the dynamics of the particle size distribution in urban environments. The MAT model uses a novel multi-plume scheme for vertical dispersion and routines of the aerodynamics models AERO3. It treats the processes: emission from a near ground source, dilution with background air, deposition, coagulation and condensation. The employed plume approach is computationally efficient compared to grid models and is therefore suitable for calculating longer time series. The treatment of the different processes in the model was validated against analytical solutions and literature data and later the full model was applied to a field data set from the Copenhagen area. The range of changes in particle concentration including all processes compared to an inert treatment of particles lies between 13% and 23% of loss in total number concentration and 2% loss and 8% gain for the total volume concentration. This agrees well with measurements in Copenhagen that indicated total number concentration (ToN) losses in the range of 15-30% between kerbside and urban rooftop level. The model also reproduces the shift of the maximum in the size distribution to slightly larger diameters between street and urban rooftop level. Because of the uncertainties in the parameters describing the different processes and their similar influence on the particle size distribution, it is possible to obtain similar results with different parameter combinations. More research and model validation is needed to narrow the range of possible input parameters and model assumptions for this type of modelling.
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| 4. |
- Ketzel, M, et al.
(författare)
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Particle and trace gas emission factors under urban driving conditions in Copenhagen based on street and roof-level observations
- 2003
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Ingår i: Atmospheric Environment. - 1352-2310. ; 37:20, s. 2735-2749
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous measurements of particle size distribution (size/range 10-700 nm) inside an urban street canyon and a nearby urban background location in Copenhagen in May-November 2001 were used to separate the traffic source contribution in the street canyon from the background levels. The background concentrations are highly variable due to changing contributions from long-range transport and local sources showing a diurnal pattern with a shift to smaller particle sizes during midday hours. The average ratio background/street concentration is 0.26 for NOx and 0.35, 0.42, 0.60, 0.64, respectively, for CO, total particle number (ToN), surface and volume. The particle size distribution of the traffic source shows during daytime and evening hours (6-24) a maximum at particle sizes of 20-30 nm independent of the changing heavy-duty vehicle share during the same time interval. The particle number concentration highly correlated (R > 0.83) with NOx through a wide range of particle sizes. The method of inverse modelling was applied to estimate average fleet emission factors typical of urban conditions in Denmark. Emission factors per average vehicle were estimated as (2.8 +/- 0.5) x 10(14) particles/km, (1.3 +/- 0.2) g NOx/(veh km) and (11 +/- 2) g CO/(veh km). We observe two types of 'nanoparticle events' (a) in background, probably due to photochemistry and (b) in the night hours when traffic is dominated by diesel taxis. During night hours (0-5), the maximum in the emitted particle size distribution, is shifted to smaller sizes of about 15-18 nm. This shift to smaller particle sizes is related to an increase in the average NOx and ToN emission per vehicle by a factor of 2-3 and a reduced CO emission also by a factor of 2-3. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Ketzel, M, et al.
(författare)
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Particle size distribution and particle mass measurements at urban, near-city and rural level in the Copenhagen area and Southern Sweden
- 2004
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7324. ; 4, s. 281-292
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Tidskriftsartikel (refereegranskat)abstract
- Particle size distribution (size-range 3-900 nm) and PM10 was measured simultaneously at an urban background station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus regional sources of particle number and mass concentration. The total particle number (ToN) and NOx are well correlated at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500# cm(-3), 4500# cm(-3) and 7700# cm(-3) at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. Measures to reduce the local urban emissions of NOx and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions. The traffic source contributes strongest in the 10-200 nm particle size range. The maximum of the size distribution shifts from about 20-30 nm at kerbside to 50-60 nm at rural level. Particle formation events were observed in the 3-20 nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of preexisting aerosol particles. The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28 nm in the urban location compared to 22 nm at kerbside. Assuming NOx as an inert tracer on urban scale allows to estimate that ToN at urban level is reduced by 15-30% compared to kerbside. Particle removal processes, e. g. deposition and coagulation, which are most efficient for smallest particle sizes (<20 nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.
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| 6. |
- Ottosen, T. -B., et al.
(författare)
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Analysis of the impact of inhomogeneous emissions in the Operational Street Pollution Model (OSPM)
- 2015
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 8:10, s. 3231-3245
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Tidskriftsartikel (refereegranskat)abstract
- Semi-parameterized street canyon models, as e.g. the Operational Street Pollution Model (OSPM (R)), have been frequently applied for the last two decades to analyse levels and consequences of air pollution in streets. These models are popular due to their speed and low input requirements. One often-used simplification is the assumption that emissions are homogeneously distributed in the entire length and width of the street canyon. It is thus the aim of the present study to analyse the impact of this assumption by implementing an inhomogeneous emission geometry scheme in OSPM. The homogeneous and the inhomogeneous emission geometry schemes are validated against two real-world cases: Hornsgatan, Stockholm, a sloping street canyon; and Jagtvej, Copenhagen; where the morning rush hour has more traffic on one lane compared to the other. The two cases are supplemented with a theoretical calculation of the impact of street aspect (height / width) ratio and emission inhomogeneity on the concentrations resulting from inhomogeneous emissions. The results show an improved performance for the inhomogeneous emission geometry over the homogeneous emission geometry. Moreover, it is shown that the impact of inhomogeneous emissions is largest for near-parallel wind directions and for high aspect ratio canyons. The results from the real-world cases are however confounded by challenges estimating the emissions accurately.
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