Spatio-temporal variability and principal components of the particle number size distribution in an urban atmosphere (original) (raw)
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Meteorological dependence of size-fractionated number concentrations of urban aerosol particles
Atmospheric Environment, 2006
We utilized a long-term data set of aerosol particle number size distributions (8-400 nm) in the urban background air of Helsinki during 1998-2000. We analyzed the number concentrations of both ultra-fine particles (UFP diameter o100 nm) and the fraction of fine particles (FP, diameter o2.5 mm) larger than 100 nm (accumulation mode), and we also investigated their dependencies on the relevant meteorological parameters. The meteorological parameters were obtained by a meteorological pre-processing model. Among the meteorological parameters considered in this study (wind speed and direction, temperature, atmospheric pressure, relative humidity, Monin-Obukhov length and mixing height), the ambient temperature and local wind conditions were found to be the most important factors that control the number concentrations of FP. We described the dependencies of FP number concentrations on meteorological variables by using an empirically based mathematical function that contains the ambient temperature, local wind speed and direction as independent variables. According to statistical analyses, the predicted number concentrations of accumulation mode particles follow this relationship more closely than those of UFP's. This is mainly due to the origin and type of aerosol particles in the accumulation mode size range, being mainly regional and long-range transported. The main limitations of the mathematical function presented in this study are during new particle formation events, precipitation and long-range pollution episodes of aerosol particles. This study provides an attempt to predict the particle number concentrations of FP by utilizing a simple model that connects the relationship between the aerosol particle number concentrations and the relevant meteorological parameters. r
A detailed investigation of ambient aerosol composition and size distribution in an urban atmosphere
Environmental Science and Pollution Research, 2013
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Atmospheric Environment, 2004
Mass size distributions of atmospheric aerosols have been sampled in the region of Vienna, a typical city in central Europe, at an urban and a rural site. The aerosol was collected simultaneously by cascade impactors. Two experiments which had a duration of 4 weeks each, were performed in An evaluation of the mass size distributions is represented in this paper. Emphasis is on the relationships of different aerosol components in a local and a regional context. The main results are as follows. The main components of the atmospheric aerosol are a fine aerosol, the accumulation aerosol, and a coarse aerosol. Specific coarse modes with modal diameters of 4.7 mm average and geometric standard deviations of about 3 occur at the urban and at the rural site, some times surprisingly strong. The fine and the coarse modes are very likely related to motor-car traffic. Usually the PM 2.5 and PM 10 aerosols are regionally strongly correlated. Occasionally, this correlation is effectively disturbed by local and/or regional emissions. Time series of correlation coefficients reveal an episodic character of the atmospheric aerosol. Periods of strong inter-site correlations of PM 2.5 and PM 10 indicate the dominance and the co-variation of the accumulation aerosols or the dominance and the co-variation of the coarse modes. r
Modal structure and spatial–temporal variations of urban and suburban aerosols in Helsinki—Finland
Atmospheric Environment, 2005
Particle number size distributions were measured in the urban and suburban atmosphere of Helsinki. In the absence of a direct traffic emission influence, the temporal variation of the aerosol particle number concentrations and their particle size distribution characteristics can be generalized within the Helsinki metropolitan region. In general, the particle number size distributions are characterized by three modes: nucleation (o25 nm), Aitken (25-90 nm), and accumulation (490 nm). Under certain conditions such as overlapping between the nucleation and Aitken modes, it is possible to characterize the particle number size distributions by two modes: ultrafine mode (o100 nm) and accumulation mode (4100 nm). Traffic combustions are considered as one of the major sources of ultrafine particles (UFP, D p o100 nm) in the urban atmosphere. The total particle number concentration is highest in the urban centers (as high as 140 000 cm À3 , more than 90% is UFP), In general, 70-80% of the submicrometer particle number concentration is UFP in the suburban atmosphere. Close to major highways, the geometric mean diameters of the submicrometer modes are smaller and the total number concentrations can exceed 60 000 cm À3 (more than 60% is nucleation mode particles). According to the wind speed and temperature analysis, the submicrometer aerosol particles in the urban and suburban atmosphere consist of two components: UFP that is diluted with wind speeds and inversely proportional to the ambient temperature, and particles larger than 100 nm in diameter that is re-suspended with wind and proportional to the ambient temperature. The correlation analysis showed that UFP number concentrations are best correlated within the urban areas. Particles larger than 100 nm showed good correlation factors (about 0.80) within the Helsinki metropolitan area, which is an indication of similar kinds of aerosols such as regional transported particles. r
2007
A physicochemical characterization, including aerosol number size distribution, chemical composition and mass concentrations, of the urban fine aerosol captured in MILAN, BARCELONA and LONDON is presented in this article. The objective is to obtain a comprehensive picture of the microphysical processes involved in aerosol dynamics during the: 1) regular evolution of the urban aerosol (daily, weekly and seasonal basis) and in the day-to-day variations (from clean-air to pollution-events), and 2) the link between "aerosol chemistry and mass concentrations" with the "number size distribution".
Atmospheric environment, 1984
Aktract-Data on massconcentration levels and particle size distribution based on samples simultaneously collected at three different areas of a city in winter and in summer were aualysed and compared. In summer concentrations were consistent at all three sites, while in winter wntly higher concentrations were recorded in a densely populated city eentre with traditional spaoe heating Tfic investi@ed correlations and regression equations indicate that the city Ccntre acts as a major source of particulate pollution in the winter time and that it influences air pollution in other parts of the town, especially in the south in the direction of prevalent NE winds. All comxntration levels were within the limits established by Whitby and Liu in Ametin cities. The part& size distribution was bimodal and very consistent for the three sites but there was a sigaificant shift towards smaller particles in winter.
Temporal variations of atmospheric aerosol in four European urban areas
Environmental Science and Pollution Research, 2011
The concentrations of PM(10) mass, PM(2.5) mass and particle number were continuously measured for 18 months in urban background locations across Europe to determine the spatial and temporal variability of particulate matter. Daily PM(10) and PM(2.5) samples were continuously collected from October 2002 to April 2004 in background areas in Helsinki, Athens, Amsterdam and Birmingham. Particle mass was determined using analytical microbalances with precision of 1 μg. Pre- and post-reflectance measurements were taken using smoke-stain reflectometers. One-minute measurements of particle number were obtained using condensation particle counters. The 18-month mean PM(10) and PM(2.5) mass concentrations ranged from 15.4 μg/m(3) in Helsinki to 56.7 μg/m(3) in Athens and from 9.0 μg/m(3) in Helsinki to 25.0 μg/m(3) in Athens, respectively. Particle number concentrations ranged from 10,091 part/cm(3) in Helsinki to 24,180 part/cm(3) in Athens with highest levels being measured in winter. Fine particles accounted for more than 60% of PM(10) with the exception of Athens where PM(2.5) comprised 43% of PM(10). Higher PM mass and number concentrations were measured in winter as compared to summer in all urban areas at a significance level p < 0.05. Significant quantitative and qualitative differences for particle mass across the four urban areas in Europe were observed. These were due to strong local and regional characteristics of particulate pollution sources which contribute to the heterogeneity of health responses. In addition, these findings also bear on the ability of different countries to comply with existing directives and the effectiveness of mitigation policies.
Atmospheric Chemistry and Physics, 2017
Effects of a new aerosol particle formation (NPF) and particle diameter growth process as a single source of atmospheric particle number concentrations were evaluated and quantified on the basis of experimental data sets obtained from particle number size distribution measurements in the city centre and near-city background of Budapest for 5 years. Nucleation strength factors for a nucleation day (NSF NUC) and for a general day (NSF GEN) were derived separately for seasons and full years. The former characteristic represents the concentration increment of ultrafine (UF) particles specifically on nucleation days with respect to accumulationmode (regional background) concentrations (particles with equivalent diameters of 100-1000 nm; N 100−1000) due solely to the nucleation process. The latter factor expresses the contribution of nucleation to particle numbers on general days; thus, it represents a longer time interval such as season or year. The nucleation source had the largest effect on the concentrations around noon and early afternoon, as expected. During this time interval, it became the major source of particles in the near-city background. Nucleation increased the daily mean concentrations on nucleation days by mean factors of 2.3 and 1.58 in the near-city background and city centre, respectively. Its effect was largest in winter, which was explained by the substantially lower N 100−1000 levels on nucleation days than those on non-nucleation days. On an annual timescale, 37 % of the UF particles were generated by nucleation in the near-city background, while NPF produced 13 % of UF particles in the city centre. The differences among the annual mean values, and among the corresponding seasonal mean values, were likely caused by the variability in controlling factors from year to year. The values obtained represent the lower limits of the contributions. The shares determined imply that NPF is a non-negligible or substantial source of particles in near-city background environments and even in city centres, where the vehicular road emissions usually prevail. Atmospheric residence time of nucleationmode particles was assessed by a decay curve analysis, and a mean of 02:30 was obtained. The present study suggests that the health-related consequences of the atmospheric NPF and growth process in cities should also be considered in addition to its urban climate implications.
Atmospheric Environment, 2012
h i g h l i g h t s < Characteristic (signature) aerosol number size distributions have been extracted from a large data set. < K-means cluster analysis was applied. < The size distributions retain the main information of the large data set. < Signature size distribution offer a simple way of source apportionment. < The method can also be applied at other study sites. a b s t r a c t A cluster analysis algorithm was applied to reduce the amount and complexity of 30 min aerosol number size distributions in a three year data set (2006e2008) at a urban background station in Helsinki, Finland. Only after objective validity tests to determine the appropriate number of clusters, a k-means cluster algorithm was applied to extract seven characteristic size distributions from the data set. The average total number concentrations of the clustered size distributions range from 6067 cm À3 to 12,818 cm À3 with modal diameters between 5 and 193 nm. The clustered size distributions were analyzed in terms of their physical properties (shape, log-normal modes, mode diameter), temporal occurrence (e.g. time of day, season) and their relation to local meteorology.