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Atmospheric Environment (v.42, #17)
On street observations of particulate matter movement and dispersion due to traffic on an urban road by Aditya Patra; Roy Colvile; Samantha Arnold; Emma Bowen; Dudley Shallcross; Damien Martin; Catheryn Price; James Tate; Helen ApSimon; Alan Robins (pp. 3911-3926).
Empirical models for particulate matter emissions from paved road surfaces have been criticised for their lack of realism and accuracy. To support the development of a less empirical model, a study was conducted in a busy street at the DAPPLE site in Central London to understand the processes and to identify important parameters that influence emission from paved roads. Ordinary road gritting salt was applied to the road and the particulate matter entering the air at near-road surface level was monitored using optical particle counters. The grit acted as a tracer. The grit moved rapidly along the road in the direction of traffic flow. Build-up of material at the kerb indicated material being thrown across the road by the traffic. Coarser particles were resuspended faster than the finer ones. A clear decay profile was seen in the case of particles larger than2μm; particles smaller than2μm did not show any decay pattern during the experiment duration. Grinding of material appears to control the reservoir of fine particles on the road surface. The amount of material resuspended by traffic is about 30% less than those removed along the road and a factor of 6 higher than the amount removed across the road. Resuspension accounts for 40% of the total material removed from a road segment and 70% of the material removed together along and across the road. On average a single vehicle pass removes 0.08% of material present on a road segment at that instant. The calculation scheme is obtained from a short-duration study and therefore further studies of long duration involving varying road geometry and different traffic and meteorological condition need to be carried out before applying parameter estimates presented in this paper.
Keywords: Particles; Particulate matter fluxes; Dispersion; Resuspension; Traffic-induced surface emission
SLP-2D: A new Lagrangian particle model to simulate pollutant dispersion in street canyons by J.L. Santiago; Martin F. Martín (pp. 3927-3936).
In this paper, pollutant dispersion inside a street canyon is simulated using SLP-2D (street Lagrangian particles). SLP-2D is a Lagrangian particle model developed by Research Center for Energy, Environment and Technology (CIEMAT), and it uses wind flow data provided by FLUENT CFD simulations to compute particle trajectories. The simulations presented are divided into two parts. In the first part Meroney, et al. [1996. Study of line source characteristics for 2-D physical modeling of pollutant dispersion in street canopies. Journal of Wind Engineering and Industrial Aerodynamics 62, 37–56] wind tunnel experiment is analyzed and we find good agreement between computed and experimental results. In the second part, dispersion inside real street canyons from Stockholm (Hornsgatan Street) and Berlin (Frankfurter Alee) is studied. Field data have been provided by street emission ceilings (SEC) team for use in SEC intercomparison model exercise.
Keywords: Street canyon; Lagrangian particle model; CFD; RANS simulations
A probabilistic source attribution model for nanoparticles in air suspension applied on the main roads of Madrid and Mexico City by P. Siegmann; F.J. Acevedo; K. Siegmann; Maldonado-Bascon S. Maldonado-Bascón (pp. 3937-3948).
In the first part, we present a simple Probabilistic Source Attribution (PSA) procedure, which allows an estimate of the percentage of the contribution of previously defined sources to the total particulate air pollution determined by a simple field measurement. Four kinds of air pollution sources of small particles (size in the nanometre range, certainly less than 1μm) can be distinguished on the main roads. The distinction is based on different physical and chemical surface properties of the particles observable via the ratio of the signals provided by two portable sensors with different operating principles (photoelectric charging (PC) and diffusion charging). In the second part, we apply PSA to on-road measurements in Mexico City and Madrid in the years 1999–2001, and in Madrid again in the year 2006. The results show a change in the main source of nanometric particles in Madrid from the period 1999–2001 to 2006 associated with a reduction in the nanoparticulate air pollution by a factor of 3. From the measurement performed in Mexico City, we were able to deduce that a small percentage of one source type (called superpolluters) contributes strongly to the total measured air pollution.
Keywords: Photoelectric aerosol sensor; Diffusion-charging monitor; Particle-bound polycyclic aromatic hydrocarbons; Nanoparticles; Source apportionment; Motor vehicles
Sources and factors affecting PM10 levels in two European cities: Implications for local air quality management by Sotiris Vardoulakis; Pavlos Kassomenos (pp. 3949-3963).
Despite improvements in vehicle and fuel technology that have led to reductions in primary particle emissions, high PM10 levels have been observed in recent years in several European cities, including Athens (Greece) and Birmingham (UK). In certain cases, high PM10 concentrations have persisted over periods of several hours, resulting in exceedences of EU target values. In order to design effective PM10 control strategies, it is essential to develop an understanding of local and remote sources of particulate matter, as well as of the factors influencing its temporal and spatial variability in urban areas. In this study, PM10 data from Athens and Birmingham were analysed for relationships to other pollutants (NO x, CO, O3 and SO2) and meteorological parameters (wind velocity, temperature, relative humidity, precipitation, solar radiation and atmospheric pressure) during a 3-year period (2001–2003). Significant positive correlations between PM10 and NO x, CO, and solar radiation were observed at the selected monitoring sites during cold seasons. On the other hand, negative correlations between PM10 and O3, wind speed and precipitation were observed during the same seasons. However, these correlations became weaker during warm seasons, probably due to secondary aerosol formation and enhanced soil dust re-suspension. Furthermore, principal component and regression analyses were used to quantify the contribution of non-combustion sources to the observed PM10 background levels. This contribution ranged between 45% and 70% in Birmingham and 41–74% in Athens. Finally, several winter and summer PM10 episodes from each city were analysed using a back trajectory model, in order to identify the origin of the polluted air masses. It was found that long-range transport of particles from continental Europe had a marked effect on PM10 background levels in Birmingham, while the local weather had a stronger influence on PM10 levels in Athens.
Keywords: Particulate matter; PM; 10; Urban background; Seasonal variability; Non-combustion sources
Spatial and temporal variations in airborne particulate matter (PM10 and PM2.5) across Spain 1999–2005 by X. Querol; A. Alastuey; T. Moreno; M.M. Viana; S. Castillo; J. Pey; Rodriguez S. Rodríguez; Artinano B. Artiñano; P. Salvador; Sanchez M. Sánchez; S. Garcia Dos Santos; M.D. Herce Garraleta; R. Fernandez-Patier; S. Moreno-Grau; L. Negral; Minguillon M.C. Minguillón; E. Monfort; M.J. Sanz; Palomo-Marin R. Palomo-Marín; E. Pinilla-Gil; E. Cuevas; J. de la Rosa; Sanchez A. Sánchez de la Campa (pp. 3964-3979).
Average ranges of particulate matter (PM10 and PM2.5) concentrations and chemical composition in Spain show significant variations across the country, with current PM10 levels at several industrial and traffic hotspots exceeding recommended pollution limits. Such variations and exceedances are linked to patterns of anthropogenic and natural PM emissions, climate, and reactivity/stability of particulate species. PM10 and PM2.5 concentrations reach 14–22μgPM10m−3 and 8–12μgPM2.5m−3 at most rural/regional background sites, 25–30μgPM10m−3 and 15–20μgPM2.5m−3 at suburban sites, 30–46μgPM10m−3 and 20–30μgPM2.5m−3 at urban background and industrial sites, and 46–50μgPM10m−3 and 30–35μgPM2.5m−3 at heavy traffic hotpots. Spatial distributions show sulphate and carbon particle levels reach maxima in industrialised areas and large cities (where traffic emissions are higher), and nitrate levels increase from the Atlantic to the Mediterranean (independent of the regional NO x emissions). African dust outbreaks have an influence on the number of exceedances of the daily limit value, but its additional load on the mean annual PM10 levels is only highly significant in Southern Iberia and Canary and Balearic islands. The marine aerosol contribution is near one order of magnitude higher in the Canaries compared to the other regions. Important temporal influences include PM intrusion events from Africa (more abundant in February–March and spring–summer), regional-scale pollution episodes, and weekday versus weekend activity. Higher summer insolation enhances (NH4)2SO4 but depletes particulate NO3− (as a consequence of the thermal instability of ammonium nitrate in summer) and Cl− (due to HCl volatilisation resulting from the interaction of gaseous HNO3 with the marine NaCl), as well as generally increasing dry dust resuspension under a semi-arid climate. Average trace metal concentrations rise with the highest levels at industrial and traffic hotspots sites, in some cases (Ti, Cr, Mn, Cu, Zn, As, Sn, W, and Pb) exceeding rural background levels by over an order of magnitude.
Keywords: PM; 10; PM; 2.5; Spain; Geochemistry; Metals
Evaluation and application of a statistical model for assessment of long-range transported proportion of PM2.5 in the United Kingdom and in Finland by Jaakko Kukkonen; Ranjeet Sokhi; Lakhu Luhana; Härkönen Jari Härkönen; Timo Salmi; Mikhail Sofiev; Ari Karppinen (pp. 3980-3991).
We have developed a simple statistical model for the estimation of the long-range transport (LRT) contribution to PM2.5 concentrations. The modelling is based on linear regressions of the ‘Co-operative programme for monitoring and evaluating the long-range transmission of air pollutants in Europe’ (EMEP) background ionic components (SO42−, NO3−, NH4+) with the monitored PM2.5 concentrations. We present an evaluation and application of the model against data measured in the United Kingdom (UK) and in Finland. We have studied the correlation of ion sum values with the PM2.5 data measured at two EMEP stations in Finland (i.e., a comparison of ionic sum and PM2.5 at one station). The statistical correlations of the PM2.5 concentrations with the ion sum values were very high ( R2 varied from 0.77 to 0.83) at both of the stations considered; this provides confidence that the ion sum is a good proxy variable for the LRT PM2.5. The comparison of different modelling options using the data measured in the UK showed that the regression model gave systematically substantially better results than the model using merely sulphate concentrations. Similarly, using the distance weighted ion sum based on data from two EMEP stations gave better correlation, compared with the option of using only one EMEP station. The evaluated average LRT contribution accounted for 35–37% of the regional air PM2.5 concentrations in UK from 1998 to 2000. The corresponding contributions at two urban stations in London were 24–31%. We conclude that the model is a useful and simple tool for the assessment of LRT PM2.5 that is applicable within a fairly good accuracy.
Keywords: Long-range transport; PM; 2.5; Model; EMEP; Ionic component
Analysis and evaluation of selected PM10 pollution episodes in the Helsinki Metropolitan Area in 2002 by P. Päivi Aarnio; Jyrki Martikainen; Tareq Hussein; Ilkka Valkama; Vehkamaki Hanna Vehkamäki; Larisa Sogacheva; Harkonen Jari Härkönen; Ari Karppinen; Tarja Koskentalo; Jaakko Kukkonen; Markku Kulmala (pp. 3992-4005).
In this study, we developed two methods to distinguish the long-range transport (LRT) episodes from local pollution (LP) episodes. The first method is based on particle number concentrations ratio between accumulation mode (diameter >90nm) and Aitken mode (diameter 25–90nm). The second method is based on a proxy variable (interpolated ion sum) for long-range transported PM2.5. The ion-sum is available from the measurements of sulphate, nitrate and ammonium at the nearest EMEP stations. We also utilised synoptic meteorological weather charts, locally measured meteorological data, and air mass back-trajectories to support the evaluation of these methods. We selected nine time periods (i.e. episodes) with daily average PM10>50μgm−3 in the Helsinki Metropolitan Area during year 2002. We characterized the episodes in terms of PM10 and PM2.5 concentrations and the fraction of fine particles in PM10 at an urban traffic and regional background air quality monitoring sites. Three of these episodes were clearly of local origin. They were characterized by a low average fraction of PM2.5 (<0.2) in PM10 at the urban traffic monitoring site, low ratio between PM10 concentrations at the regional background site and at the urban traffic site (<0.2), low average ion sums (1.5–2.5μgm−3) and low accumulation to Aitken mode ratios (0.13–0.26). Four of the episodes had distinct LRT characteristics: a high fraction of fine particles in PM10 (0.5–0.6) at the urban traffic site, a high ratio between PM10 concentrations at the regional background site and at the urban traffic site (0.7–0.8), high interpolated values for the ion sum (6.6–11.9μgm−3), and high accumulation to Aitken mode ratios (0.75–0.85). During the remaining two episodes there was significant contribution from both local sources and LRT. A detailed analysis of meteorological variables and air mass back-trajectories gave support to these findings. These characteristics can be utilised in a simple procedure to distinguish between LRT and LP episodes. Further quantitative investigations to these characteristics provide an indication to the episode strength. The quantitative results presented in the current study are applicable to the Helsinki Metropolitan Area and similar cities. Nevertheless, developing these methods for other cities require analyses of the meteorological conditions, behavior of the PM concentrations, and air-mass back trajectories for that specific city.
Keywords: Particulate matter; Long-range transport; Local characterization; Ion sum; Number concentration
An online coupled meteorological and air quality modeling study of the effect of complex terrain on the regional transport and transformation of air pollutants over the Western United States by Dongchul Kim; William R. Stockwell (pp. 4006-4021).
One of the most prominent of characteristics of the western United States that affects its meteorology is the complexity of its mountainous terrain. The meteorological Mesoscale Model, version 5 with Chemistry (MM5-Chem), an online-coupled atmospheric chemistry model, was used to investigate the effect of this terrain on a high air pollution event in the free troposphere. The simulations were evaluated by comparisons with data from the North American Regional Reanalysis (NARR). Complex terrain was shown to have an important influence on the vertical transport of air pollutants on the regional scale; emissions from ground level were vertically mixed as high as 5km above sea surface level for the wintertime conditions simulated. The simulations showed that the vertical transport of emissions from the Earth's surface could have a more significant effect on mid and upper level chemical concentrations than chemical production. The vertical transport was caused predominately by terrain forced flow over the mountains’ ridge-line and the terrain forced flow was affected by the mountain peak height and the complexity of the terrain downwind.
Keywords: Meteorology; Air pollution; Vertical transport; Regional transport; Complex terrain; Online coupled models