scholarly journals Quantification of an atmospheric nucleation and growth process as a single source of aerosol particles in a city

2017 ◽  
Vol 17 (24) ◽  
pp. 15007-15017 ◽  
Author(s):  
Imre Salma ◽  
Veronika Varga ◽  
Zoltán Németh
Keyword(s):  
Growth Process ◽  
Particle Number ◽  
Urban Climate ◽  
Particle Diameter ◽  
City Centre ◽  
Time Interval ◽  
Single Source ◽  
Mean Values ◽  
Early Afternoon ◽  
The City

Abstract. 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 (NSFNUC) and for a general day (NSFGEN) 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 accumulation-mode (regional background) concentrations (particles with equivalent diameters of 100–1000 nm; N100−1000) 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 N100−1000 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 nucleation-mode 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.

scholarly journals Quantification of atmospheric nucleation and growth process as a single source of aerosol particles in a city

2017 ◽  
Author(s):  
Imre Salma ◽  
Veronika Varga ◽  
Zoltán Németh
Keyword(s):  
Growth Process ◽  
Particle Number ◽  
Particle Diameter ◽  
City Centre ◽  
Background Concentration ◽  
Time Interval ◽  
Single Source ◽  
Mean Values ◽  
Early Afternoon ◽  
The City

Abstract. Effects of new aerosol particle formation (NPF) and particle diameter growth process as a single source on 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 separately for nucleation days (NSFnucl days) and for all days (NSFall days) were derived for seasons and full years. The former characteristics represents the concentration increment of ultrafine (UF) particle numbers with respect to background concentration due solely to nucleation specifically on nucleation days. The latter factor expresses the contribution of nucleation process to the background particle number concentrations in general, thus on a longer time interval such as season or year. The nucleation source had the largest effect on particle 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 particle number 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 the largest in winter, which was explained with the substantially lower background concentration levels on nucleation days than that on non-nucleation days. On an annual time scale, 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 lower limits of 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 nucleation-mode particles was assessed by decay curve analysis of N6–25 concentrations in time, and a mean of 2:30 was obtained. The present study suggests that the health-related consequences of atmospheric NPF and growth process in cities should also be considered in addition to its urban climate implications.

scholarly journals On the spatial distribution and evolution of ultrafine aerosols in urban air

2012 ◽  
Vol 12 (7) ◽  
pp. 16603-16646 ◽  
Author(s):  
M. Dall'Osto ◽  
X. Querol ◽  
A. Alastuey ◽  
C. O'Dowd ◽  
R. M. Harrison ◽  
...  
Keyword(s):  
Ultrafine Particles ◽  
Particle Number ◽  
Ground Level ◽  
City Centre ◽  
Atmospheric Conditions ◽  
Urban Background ◽  
Study Region ◽  
Urban City ◽  
Regional Background ◽  
The City

Abstract. Sources and evolution of ultrafine particles (<0.1 μ m diameter) were investigated both horizontally and vertically in the large urban agglomerate of Barcelona, Spain. Within the SAPUSS project (Solving Aerosol Problems by Using Synergistic Strategies), a large number of instruments was deployed simultaneously at different monitoring sites (road, two urban background, regional background, urban tower 150 μa.s.l., urban background tower site 80 m a.s.l.) during a 4 week period in September-October 2010. Particle number concentrations (N>5nm) are highly correlated with black carbon (BC) at all sites only under strong vehicular traffic influences. By contrast, under clean atmospheric conditions (low condensation sinks, CS) such correlation diverges towards much higher N/BC ratios at all sites, indicating additional sources of particles including secondary production of freshly nucleated particles. This is also evident in the urban background annual mean diurnal trend of N/BC, showing a midday peak in all seasons. Size-resolved aerosol distributions (N10-500) as well as particle number concentrations (N>5nm) allow us to identify two types of nucleation and growth events: a regional type event originating in the whole study region and impacting almost simultaneously the urban city of Barcelona and the surrounding background area; and an urban type which originates only within the city centre but whose growth continues while transported away from the city to the regional background. Furthermore, during these clean air days, higher N are found at tower level than at ground level only in the city centre whereas such a difference is not so pronounced at the remote urban background tower. In other words, this study suggests that the column of air above the city ground level possesses the best compromise between low CS and high vapour source, hence enhancing the concentrations of freshly nucleated particles. By contrast, within stagnant polluted atmospheric conditions, higher N and BC concentrations are always measured at ground level relative to tower level at all sites. Our study suggests that the city centre is a source of both non-volatile traffic primary (29–39%) and secondary freshly nucleated particles (up to 61–71%) at all sites. We suggest that organic compounds evaporating from freshly emitted traffic particles are a possible candidate for new particle formation within the city and urban plume.

scholarly journals Mobile measurements of ship emissions in two harbour areas in Finland

2014 ◽  
Vol 7 (1) ◽  
pp. 149-161 ◽  
Author(s):  
L. Pirjola ◽  
A. Pajunoja ◽  
J. Walden ◽  
J.-P. Jalkanen ◽  
T. Rönkkö ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Particle Number ◽  
City Centre ◽  
Particulate Emissions ◽  
Size Distributions ◽  
So2 Emissions ◽  
The Baltic Sea ◽  
Eu Directive ◽  
The Baltic ◽  
The City

Abstract. Four measurement campaigns were performed in two different environments – inside the harbour areas in the city centre of Helsinki, and along the narrow shipping channel near the city of Turku, Finland – using a mobile laboratory van during winter and summer conditions in 2010–2011. The characteristics of gaseous (CO, CO2, SO2, NO, NO2, NOx) and particulate (number and volume size distributions as well as PM2.5) emissions for 11 ships regularly operating on the Baltic Sea were studied to determine the emission parameters. The highest particle concentrations were 1.5 × 106 and 1.6 × 105 cm−3 in Helsinki and Turku, respectively, and the particle number size distributions had two modes. The dominating mode peaked at 20–30 nm, and the accumulation mode at 80–100 nm. The majority of the particle mass was volatile, since after heating the sample to 265 °C, the particle volume of the studied ship decreased by around 70%. The emission factors for NOx varied in the range of 25–100 g (kg fuel)−1, for SO2 in the range of 2.5–17.0 g (kg fuel)−1, for particle number in the range of (0.32–2.26) × 1016 # (kg fuel)−1, and for PM2.5 between 1.0–4.9 g (kg fuel)−1. The ships equipped with SCR (selective catalytic reduction) had the lowest NOx emissions, whereas the ships with DWI (direct water injection) and HAMs (humid air motors) had the lowest SO2 emissions but the highest particulate emissions. For all ships, the averaged fuel sulphur contents (FSCs) were less than 1% (by mass) but none of them was below 0.1% which will be the new EU directive starting 1 January 2015 in the SOx emission control areas; this indicates that ships operating on the Baltic Sea will face large challenges.

scholarly journals Lisbon Urban Heat Island Updated: New Highlights about the Relationships between Thermal Patterns and Wind Regimes

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
António Lopes ◽  
Elis Alves ◽  
Maria João Alcoforado ◽  
Raquel Machete
Keyword(s):  
Urban Heat Island ◽  
Urban Climate ◽  
City Centre ◽  
Heat Island ◽  
Local Wind ◽  
Urban Heat ◽  
Thermal Patterns ◽  
Wind Regimes ◽  
The Relationship ◽  
The City

Urban growth implies significant modifications in the urban climate. To understand the influence of the city of Lisbon on the urban boundary layer, a mesoscale meteorological network was installed in 2004. The main goals of the present study are to update the results of the research published in 2007 and to bring more precise information about the relationship between the Urban Heat Island (UHI) and the regional and local wind systems. The highest frequencies of the UHI were found in the city centre (Restauradores). In the green park of Monsanto, the highest frequency occurred between −2 and 0°C. During the summer, the effect of the breezes was observed in Belém, lowering the temperature. The “strong” UHI (intensity >4°C) occurred more often during the summer, with median values of 2°C by night and 1.8°C by day. The highest frequencies of UHI occurred for winds between 2 and 6 m/s and were not associated with atmospheric calm, as pointed out in the literature. Winds above 8 m/s inhibit the occurrence of strong UHI in Lisbon. Summer nighttime strong UHI should be further investigated, due to the heat stress consequences on the population and probable increase of energy consumption.

scholarly journals Multi-Temporal Change Detection Analysis of Vertical Sprawl over Limassol City Centre and Amathus Archaeological Site in Cyprus during 2015–2020 Using the Sentinel-1 Sensor and the Google Earth Engine Platform

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1884
Author(s):  
Athos Agapiou
Keyword(s):  
Change Detection ◽  
Satellite Images ◽  
Archaeological Site ◽  
Google Earth ◽  
City Centre ◽  
Time Interval ◽  
High Resolution Satellite Images ◽  
Multi Temporal ◽  
Google Earth Engine ◽  
The City

Urban sprawl can negatively impact the archaeological record of an area. In order to study the urbanisation process and its patterns, satellite images were used in the past to identify land-use changes and detect individual buildings and constructions. However, this approach involves the acquisition of high-resolution satellite images, the cost of which is increases according to the size of the area under study, as well as the time interval of the analysis. In this paper, we implemented a quick, automatic and low-cost exploration of large areas, for addressing this purpose, aiming to provide at a medium resolution of an overview of the landscape changes. This study focuses on using radar Sentinel-1 images to monitor and detect multi-temporal changes during the period 2015–2020 in Limassol, Cyprus. In addition, the big data cloud platform, Google Earth Engine, was used to process the data. Three different change detection methods were implemented in this platform as follow: (a) vertical transmit, vertical receive (VV) and vertical transmit, horizontal receive (VH) polarisations pseudo-colour composites; (b) the Rapid and Easy Change Detection in Radar Time-Series by Variation Coefficient (REACTIV) Google Earth Engine algorithm; and (c) a multi-temporal Wishart-based change detection algorithm. The overall findings are presented for the wider area of the Limassol city, with special focus on the archaeological site of “Amathus” and the city centre of Limassol. For validation purposes, satellite images from the multi-temporal archive from the Google Earth platform were used. The methods mentioned above were able to capture the urbanization process of the city that has been initiated during this period due to recent large construction projects.

scholarly journals Análise de Microclimas na Cidade de Viçosa do Ceará: Abordagem na Perspectiva do Conforto Térmico (Analysis of the Microclimate in Viçosa Ceará: Approach in View of Thermal Comfort)

2012 ◽  
Vol 5 (1) ◽  
pp. 47 ◽  
Author(s):  
Filipe Da Silva Peixoto ◽  
Marta Celina Linhares Sales
Keyword(s):  
Thermal Comfort ◽  
Effective Temperature ◽  
Urban Climate ◽  
City Centre ◽  
Heat Island ◽  
Humid Climate ◽  
Heat Islands ◽  
Environmental Features ◽  
Different Types ◽  
The City

O estudo foi realizado na cidade de Viçosa do Ceará, cujas características geoambientais proporcionam um tipo climático de enclave úmido, ou seja, resulta em uma área de maior umidade e menor temperatura média isso devido ao efeito da altitude, em meio às áreas mais rebaixadas que configuram a depressão sertaneja, portanto, são áreas de condições geoambientais mais favoráveis ao conforto térmico. Buscou-se nos pontos de análise a distinção de diferentes tipos de uso e ocupação do solo, associado às características naturais que causam diferentes microclimas intraurbanos. Esses foram analisados através do levantamento de dados de temperatura do ar, temperatura efetiva, umidade do ar, e altitude. O levantamento foi realizado entre às 08 e 17 horas no dia 29 de outubro de 2009, período de primavera no hemisfério sul, correspondente ao período quente e seco no nordeste setentrional.  Os dados foram tratados de forma a evidenciar os diferentes microclimas qualitativa e espacialmente, através de gráficos comparativos e mapa de isolinhas de temperatura efetiva. Foi observado que sob o efeito das ilhas de calor, identificadas nos pontos dois (Centro da Cidade) e três (Praça do Coreto), a atmosfera do local se comporta de maneiras distintas, e esses pontos caracterizaram-se pela conservação de temperatura efetiva de 26 ºC às 15 horas, quando em condições normais essa temperatura tenderia a um decréscimo maior, situação observada nos demais pontos ambos com 24,8 ºC às 15 horas. A atmosfera da cidade de Viçosa do Ceará sofre o fenômeno da ilha de calor, que se mostra no espaço onde o uso e ocupação do solo são mais intensificados.   Palavras- chaves: Clima urbano. Viçosa do Ceará. Espaço Urbano.   Analysis of the Microclimate in Viçosa Ceará: Approach in View of Thermal Comfort   ABSTRACTThe study was conducted in Viçosa do Ceará, whose geo-environmental features provide a kind of enclave humid climate, which in the state of Ceará is configured as an area of ​​geo-environmental conditions more favorable for thermal comfort. Sought on the points of analysis to distinguish different types of land use and land cover, associated with natural features that cause different microclimates in space city. These were analyzed using the survey data of air temperature, actual temperature, humidity, and altitude. The survey was conducted between at 08 and 17 hours on October 29, 2009, the data were treated to highlight the qualitatively different microclimates and spatially, through graphs and comparative map of isolines of effective temperature. We note that under the effect of heat islands, identified in section 2 (City Centre) and 3 (Square Bandstand), the atmosphere of the site behaves differently, and these points were characterized by the conservation of effective temperature of 26 C for 15 hours, when this temperature under normal conditions would tend to a larger decrease observed in the other two points to 24.8 º C at 15 hours. The atmosphere of the city of Viçosa do Ceará suffers the heat island phenomenon, which appears in the space where the use and occupation are more intensified. Keywords: Urban climate. Viçosa- Ce. Space Urban. 

scholarly journals Functional Dimensions at 'Kuala Lumpur Waterfront'

2016 ◽  
Vol 1 (1) ◽  
pp. 7-17
Author(s):  
Nurul Syala Abdul Latip ◽  
Shuhana Shamsudin ◽  
Mohd Shahir Liew
Keyword(s):  
Publishing House ◽  
Urban River ◽  
City Centre ◽  
Time Interval ◽  
Kuala Lumpur ◽  
Main Mode ◽  
Contextual Integration ◽  
Medium Level ◽  
Mode Of Transportation ◽  
The City

The 'Kuala Lumpur Waterfront' may be unfamiliar to many. Kuala Lumpur is a city that originates at the confluence of two rivers, the Klang and Gombak Rivers. The waterfront used to be very busy with activities when it was once a trading post for the export of tin. This was once the lifeline of the city - its main mode of transportation. The activity at the waterfront has changed over the years along with the social, economic and physical development of the city. Many waterfront cities throughout the world have gone through similar changes when the mode of transportation changed from water to the motor system. A number of cities have made efforts to integrate the cities' activities with their water body. This research attempts to investigate the functional aspects at the Kuala Lumpur waterfront within the city centre in terms of its level of contextual integration with the urban rivers in the current context. The technique adopted for this research is field observations which include building use survey and time interval observation to investigate the Junctional aspects in ten demarcated zones along the Kuala Lumpur waterfront within the city centre. The research concluded with the finding that all the zones have medium level of contextual integration between the waterfront and the urban river in terms of its building use, which depends much on the continuity of activities, their positioning location, accessibility and the provision of space and facilities. © 2016 The Authors. Published for AMER ABRA by e-International Publishing House, Ltd., UK.. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning & Surveying, UniversitiTeknologi MARA, Malaysia. DOI: http://dx.doi.org/10.21834/aje-bs.v1i1.164 Keywords: Contextual integration, waterfront, urban river, activity

scholarly journals On the spatial distribution and evolution of ultrafine particles in Barcelona

2013 ◽  
Vol 13 (2) ◽  
pp. 741-759 ◽  
Author(s):  
M. Dall'Osto ◽  
X. Querol ◽  
A. Alastuey ◽  
C. O'Dowd ◽  
R. M. Harrison ◽  
...  
Keyword(s):  
Ultrafine Particles ◽  
Particle Number ◽  
Ground Level ◽  
City Centre ◽  
Atmospheric Conditions ◽  
Urban Background ◽  
Urban City ◽  
Regional Background ◽  
The City ◽  
Background Area

Abstract. Sources and evolution of ultrafine particles were investigated both horizontally and vertically in the large urban agglomerate of Barcelona, Spain. Within the SAPUSS project (Solving Aerosol Problems by Using Synergistic Strategies), a large number of instruments was deployed simultaneously at different monitoring sites (road, two urban background, regional background, urban tower 150 m a.s.l., urban background tower site 80 m a.s.l.) during a 4 week period in September–October 2010. Particle number concentrations (N>5 nm) are highly correlated with black carbon (BC) at all sites only under strong vehicular traffic influences. By contrast, under cleaner atmospheric conditions (low condensation sink, CS) such correlation diverges towards much higher N/BC ratios at all sites, indicating additional sources of particles including secondary production of freshly nucleated particles. Size-resolved aerosol distributions (N10–500) as well as particle number concentrations (N>5 nm) allow us to identify three types of nucleation and growth events: (1) a regional type event originating in the whole study region and impacting almost simultaneously the urban city of Barcelona and the surrounding urban background area; (2) a regional type event impacting only the regional background area but not the urban agglomerate; (3) an urban type event which originates only within the city centre but whose growth continues while transported away from the city to the regional background. Furthermore, during these clean air days, higher N are found at tower level than at ground level only in the city centre whereas such a difference is not so pronounced at the remote urban background tower. In other words, this study suggests that the column of air above the city ground level possesses the optimal combination between low CS and high vapour source, hence enhancing the concentrations of freshly nucleated particles. By contrast, within stagnant polluted atmospheric conditions, higher N and BC concentrations are always measured at ground level relative to tower level at all sites. Our study suggests that the city centre of Barcelona is a source of non-volatile traffic primary particles (29–39% of N>5 nm), but other sources, including secondary freshly nucleated particles contribute up to 61–71% of particle number (N>5 nm) at all sites. We suggest that organic compounds evaporating from freshly emitted traffic particles are a possible candidate for new particle formation within the city and urban plume.

scholarly journals O (DES)CONFORTO NO CONJUNTO HABITACIONAL DEOCLÉCIO ARTUZZI I, DOURADOS -MS, NO VERÃO DE 2018

2019 ◽  
Vol 8 (2) ◽  
pp. 133-144
Author(s):  
Steffanny Cristina Pereira Santos ◽  
Charlei Aparecido da Silva ◽  
Vladimir Aparecido  dos Santos
Keyword(s):  
High Temperatures ◽  
Low Income ◽  
Growth Process ◽  
Urban Climate ◽  
Peripheral Region ◽  
Thermal Discomfort ◽  
The City ◽  
Housing Estates ◽  
Low Income Housing

A cidade de Dourados - MS apresenta predomínio de características climáticas tropicais com temperaturas elevadas, tal condição em conjunto com seu processo de crescimento justificam estudos sobre o clima urbano da mesma. Este trabalho tem como objetivo apresentar a análises dos dados de temperatura do ar e umidade relativa a partir do Índice de Desconforto Térmico de Thom (1959) em conjuntos habitacionais para pessoas de baixa renda localizados na região periférica da cidade. Os dados coletados apontaram que a forma de estruturação deste tipo de bairro e os materiais construtivos das casas influenciam no conforto ou desconforto térmico dos moradores.  Palavras-chave: Clima Urbano; Conjuntos habitacionais; Desconforto térmico.   Abstract The city of Dourados-MS presents predominance of characteristics with the climate of high temperatures, with the condition of grouping its growth process justifying the studies on the urban climate of the same. This work aims to present the temperature databases of the Thom Thermal Incompatibility Index (1959) in low-income housing complexes in the peripheral region of the city. The data found point out that the structuring of this type of neighborhood and the constructive materials of the houses influence the non-leisure or the thermal discomfort of the residents. Keys-words: Urban Climate; Housing estates; Thermal discomfort.

scholarly journals Consequences of dynamic and timing properties of new aerosol particle formation and consecutive growth events

2018 ◽  
Author(s):  
Imre Salma ◽  
Zoltán Németh
Keyword(s):  
Dynamic Properties ◽  
Meteorological Data ◽  
Particle Diameter ◽  
Chemical Species ◽  
Particle Growth ◽  
Particle Formation ◽  
City Centre ◽  
Timing Properties ◽  
The City ◽  
Event Occurrence

Abstract. Dynamic properties, i.e. particle formation rate J6 and particle diameter growth rate GR10, and timing properties, i.e. starting time (t1) and duration time interval (Δt) of 247 quantifiable (class 1A) atmospheric new particle formation (NPF) and consecutive particle diameter growth events identified in the city centre and near-city background of Budapest over 6 full measurement years together with related gas-phase H2SO4 proxy, condensation sink (CS) of vapours, basic meteorological data and concentrations of criteria pollutant gases were derived, evaluated, discussed and interpreted. In the city centre, nucleation ordinarily starts at 09:15 UTC+1, and it is maintained for approximately 3 h. The NPF and growth events produce 4.6 aerosol particles with a diameter of 6 nm in 1 cm3 of air in 1 s, and cause the particles with a diameter of 10 nm to grow with a typical rate of 7.3 nm h−1. Nucleation starts approximately 1 h earlier in the near-city background, it shows substantially smaller J6 (with a median of 2.0 cm−3 s−1) and GR10 values (with a median of 5.0 nm h−1), while the duration of nucleation is similar to that in the centre. Monthly distributions of the dynamic properties and daily maximum H2SO4 proxy do not follow the mean monthly pattern of the event occurrence frequency. The factors that control the event occurrence and that govern the intensity of particle formation and growth are not directly linked. Condensing atmospheric chemical species and/or their processes in the city centre seem to contribute equally to new particle formation and particle growth. In the near-city background, however, chemical compounds available and their processes power particle growth more than particle formation. There is a minimum growth rate of approximately 1.8 nm h−1 that is required for nucleated particles to reach the lower end of the diameter interval measured (6 nm) under the actual/local conditions. Monthly distributions and relationships among the properties mentioned provided several indirect evidence that chemical species other than H2SO4 largely influence the particle growth and possibly atmospheric NPF process as well. The J6, GR10 and Δt can be described by log-normal distribution. Most of the extreme dynamic properties could not be explained by H2SO4 proxy, CS, meteorological data or pollutant gas concentrations. Approximately 40 % of the NPF and growth events exhibited broad beginning, which can be an urban feature. For 9 % of all cases, it was feasible to calculate 2 separate sets of dynamic properties. The later onset frequently shows more intensive particle formation and growth than the first onset by a typical factor of approximately 1.4. The first event is of regional type, while the second event, superimposed on the first, is often associated with sub-regional, thus urban NPF and growth process.

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