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The concentrations and behavior of nano particles (10–1000 nm) in Delhi, a densely populated megacity, in different seasons (winter, spring, summer, monsoon, and autumn) are examined, for the first time. The concentration of particles is classified into four different sizes as N nuc (10–30 nm, nucleation), N satk (30–50 nm, small Aitken), N latk (50–100 nm, large Aitken), and N acc (100–1000 nm, accumulation mode), and the total (10–1000 nm) particle number concentration (PNC) as N total. PNC ranges between 104 cm−3 and 106 cm−3 over Delhi during the year, and the highest concentration occurs in winter. Winter concentration is 2, 1.6 and 1.3 times higher than monsoon, summer, autumn and spring concentrations, respectively. N nuc , N satk , N latk and N acc and their respective contributions to total PNC exhibit significant seasonal variations. During winter N latk and N acc contribute more to total due to coagulation, with N acc alone contributing >40% to total PNC. N nuc , N satk, and N latk are higher in spring and summer during mid-day due to nucleation and/or ultrafine particle burst events. The direct primary emissions from engine exhaust produce a prominent double hump structure during morning and evening peak hours in winter and autumn. PNC and their contributions exhibit day-night variations as they are influenced by variations in emission sources and meteorological parameters (wind speed, relative humidity, temperature, solar radiation and boundary layer height) between day and night. Carbon monoxide correlates positively with N acc in all seasons (R2 ≥ 0.5) as fossil fuel emission is a predominant source for gases and particles in the study environment. These quantitative results on seasonal variations of nano particles and air pollutants together with the knowledge on seasonal variations in meteorological parameters and atmospheric dynamics provide a foundation which can positively contribute better to the urban planning and devising mitigation measures aimed at improving air quality and public health. • Seasonal nanoparticle number concentration (PNC) in Delhi varies from 104 to 106 cm−3. • Particles in nucleation mode contribute >30% to PNC in summer, spring and monsoon. • Accumulation mode particles contribute >35% to PNC in winter and autumn. • Higher relative humidity favors coagulation resulting in higher concentration of N acc. • Correlation between N acc and Carbon Monoxide is higher due to transport emissions. [ABSTRACT FROM AUTHOR]

The adverse health effects of inhaled particulate matter (PM) are global concern. Yet, in general, estimating the exposure to PM is challenging due to the sparsity of standard air quality monitoring stations and the low accuracy of dispersion models when high spatial resolution is required. The city of Elad, Israel, is situated less than 1 km from the Migdal Tzedek stone quarry, and public concerns were raised regarding the impact of the quarry's PM emissions on the city air quality. This work describes a year-long campaign of continuous measurements of particle number concentration (PNC) in few locations in the city and its vicinity, using a network of low cost optical particle counters (OPCs). To assess the possible impact of the quarry on the city we examined the OPCs' accuracy, coherency, and their capability to detect the quarry's impact on the PNC levels in the city. Using PNC time series in two size channels from a network of five nodes, PM10 and PM2.5 records from a nearby reference air quality monitoring station, and meteorological data, we could conclude that the quarry's impact on the city was small relative to the background PNC levels. Yet, more importantly, this work demonstrates the use of a network of low cost OPCs for responding to an environmental query for which the sparse standard air quality monitoring observations were not sufficient. The trade-offs between deployment of a network of cheap low-quality instruments and the use of a single high-end device are discussed. Image 1 • A year-long PNC measurements were collected using a cheap OPC network. • The possible impact of a quarry on the air quality of a nearby city was examined. • The OPCs' were shown to capture spatial variability of airborne dust. • No impact of the quarry on the city was found. • Trade-offs between using low-cost sensor networks and reference AQM are presented. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) sources differ in urban environments and may show spatiotemporal distinct patterns for varying particle aerodynamic diameters (D P). We here assess such patterns using high-resolution PM ≤10 μm data recorded with a cargo bike along a 14 km route through urban, suburban, and rural areas in Mainz (Germany). The measurements conducted twice a day between May and August 2021 reveal decreasing particle number concentration (PNC) with increasing D P including ∼6000 times higher particle numbers at D P 0.22–0.25 μm compared to D P 4–5 μm. Total mass concentration is bi-modally distributed and dominated by particles <0.3 μm and from 3 to 5 μm representing 36 and 22% of the entire air load, respectively. PM concentrations in Mainz are significantly higher in the morning than in the afternoon, and PM 1 and PM 10 are 13 and 31% higher in urban compared to surrounding suburban and rural areas. The high-resolution measurements also revealed 30% higher PM concentrations at D P 3–5 μm in the urban compared to the rural sectors, which is indicative for road dust, brake and tyre abrasion as the main source. D P distribution in rural hotspots is generally shifted toward larger particles >3 μm, most likely related to natural dust from agricultural fields. These findings show that high-resolution PM profiles can skillfully be recorded using bikes as mobile platform to identify spatial pollution patterns and attribute D P spectra to particular emission sources. • PM 1 and PM 10 are significantly higher in the morning than in the afternoon. • PM 1 and PM 10 are 13 and 31% higher in urban compared to surrounding rural areas. • Particle numbers decrease significantly with increasing diameter along the track. • Total mass is bi-modally distributed and dominated by particles <0.3 μm and 3–5 μm. • Mass diameter distributions indicate traffic as main emission at urban hotspots. [ABSTRACT FROM AUTHOR]

Simultaneous particle number size distribution measurements were performed in the urban environment of Budapest, Vienna, and Prague, three Central European cities located within 450 km of each other. The measurement days from the continuous, 2-year long campaign were classified for new particle formation (NPF) events using an adapted classification scheme for urban sites. The total numbers of NPF event days were 152 for Budapest, 69 for Vienna, and 143 for Prague. There were 12 days when new particle formation took place at all three sites; 11 out of these 12 days were in spring and in summer. There were only 2 (Budapest-Vienna), 19 (Budapest-Prague), and 19 (Vienna-Prague) nucleation days, when NPF did not occur on the third site. The main difference was related to source and sink terms of gas-phase sulphuric acid. Air mass origin and back-trajectories did not show any substantial influence on the atmospheric nucleation phenomena. The relative contribution of particles from NPF with respect to regional aerosol to the particles originating from all sources was expressed as nucleation strength factor. The overall mean nucleation strength factors were 1.58, 1.54, and 2.01 for Budapest, Vienna, and Prague, respectively, and showed diurnal and seasonal variations. The monthly mean NSF varied from 1.2 to 3.2 in Budapest, from 0.7 to 1.9 in Vienna, and from 1.0 to 2.3 in Prague. This implies that the new particle formation in cities is a significant source of ultrafine (UF) particles, and the amount of them is comparable to the directly emitted UF particles. [ABSTRACT FROM AUTHOR]

In recent years it has been shown that aircraft emissions are a dominant source of ultrafine particles in the surroundings of airports. However, health effects of long-term (monthly to yearly) exposure to these particles are unknown. As part of an integrated research program into the health risks of ultrafine particles around Schiphol Airport, the applicability of the dispersion model STACKS+ to assess long-term exposure to ultrafine particles from aviation was assessed. A detailed comparison between modelled and measured particle number concentrations (PNC) due to aircraft emissions was carried out at ten locations in the surroundings of Schiphol Airport during two six-month periods in 2017 and 2018. In order to deduce the contribution of aviation to measured PNC, we applied a fitting method of the sum of the modelled contributions from aviation, the modelled contributions from traffic on main roads and the contributions from outside the study area estimated from the measurements, to the measured total PNC. The analysis yielded scaling factors and uncertainty estimates for each of the main contributions. We then subtracted the estimated background and modelled contributions of road traffic from the total measured PNC and took the remainder as an approximation of the measured contribution from aviation to PNC. We compared it to the modelled contribution from aviation, based on the averaged values for the six-month periods. Both six-month averaged modelled and measured PNC due to aircraft emissions (i.e., adjusted for background) showed a large range at the monitoring locations representative for population exposure (from close to zero to 10 000 particles/cm3). Spearman and Pearson correlation coefficients between model and measurement results were high (>0.83). The applied approach enabled us to obtain a robust estimate of the contribution of aviation to the measured PNC. The dispersion model is able to determine the spatially varying average concentrations due to aircraft emissions in residential areas over periods of 6 months, allowing for application in epidemiological studies into long-term exposure. • High ultrafine particle number concentrations (PNC) are found near Schiphol Airport. • A dispersion model for aircraft emissions is evaluated using measurements of PNC. • The analysis includes road traffic and background contribution to PNC. • The model is suited to study effects of long-term exposure to UFP from aviation. [ABSTRACT FROM AUTHOR]

Traffic-related ultrafine particles (UFP; <100 nm diameter) are ubiquitous in urban air. While studies have shown that UFP are toxic, epidemiological evidence of health effects, which is needed to inform risk assessment at the population scale, is limited due to challenges of accurately estimating UFP exposures. Epidemiologic studies often use empirical models to estimate UFP exposures; however, the monitoring strategies upon which the models are based have varied between studies. Our study compares particle number concentrations (PNC; a proxy for UFP) measured by three different monitoring approaches (central-site, short-term residential-site, and mobile on-road monitoring) in two study areas in metropolitan Boston (MA, USA). Our objectives were to quantify ambient PNC differences between the three monitoring platforms, compare the temporal patterns and the spatial heterogeneity of PNC between the monitoring platforms, and identify factors that affect correlations across the platforms. We collected >12,000 h of measurements at the central sites, 1000 h of measurements at each of 20 residential sites in the two study areas, and >120 h of mobile measurements over the course of ∼1 year in each study area. Our results show differences between the monitoring strategies: mean 1 min PNC on-roads were higher (64,000 and 32,000 particles/cm 3 in Boston and Chelsea, respectively) compared to central-site measurements (23,000 and 19,000 particles/cm 3 ) and both were higher than at residences (14,000 and 15,000 particles/cm 3 ). Temporal correlations and spatial heterogeneity also differed between the platforms. Temporal correlations were generally highest between central and residential sites, and lowest between central-site and on-road measurements. We observed the greatest spatial heterogeneity across monitoring platforms during the morning rush hours (06:00-09:00) and the lowest during the overnight hours (18:00-06:00). Longer averaging times (days and hours vs. minutes) increased temporal correlations (Pearson correlations were 0.69 and 0.60 vs. 0.39 in Boston; 0.71 and 0.61 vs. 0.45 in Chelsea) and reduced spatial heterogeneity (coefficients of divergence were 0.24 and 0.29 vs. 0.33 in Boston; 0.20 and 0.27 vs. 0.31 in Chelsea). Our results suggest that combining stationary and mobile monitoring may lead to improved characterization of UFP in urban areas. [ABSTRACT FROM AUTHOR]

The health effects of long-term exposure to ultrafine particles (UFPs) are poorly understood. Data on spatial contrasts in ambient ultrafine particles (UFPs) concentrations are needed with fine resolution. This study aimed to assess the spatial variability of total particle number concentrations (PNC, a proxy for UFPs) in the city of Rome, Italy, using land use regression (LUR) models, and the correspondent exposure of population here living. PNC were measured using condensation particle counters at the building facade of 28 homes throughout the city. Three 7-day monitoring periods were carried out during cold, warm and intermediate seasons. Geographic Information System predictor variables, with buffers of varying size, were evaluated to model spatial variations of PNC. A stepwise forward selection procedure was used to develop a “base” linear regression model according to the European Study of Cohorts for Air Pollution Effects project methodology. Other variables were then included in more enhanced models and their capability of improving model performance was evaluated. Four LUR models were developed. Local variation in UFPs in the study area can be largely explained by the ratio of traffic intensity and distance to the nearest major road. The best model (adjusted R 2 = 0.71; root mean square error = ±1,572 particles/cm³, leave one out cross validated R 2 = 0.68) was achieved by regressing building and street configuration variables against residual from the “base” model, which added 3% more to the total variance explained. Urban green and population density in a 5,000 m buffer around each home were also relevant predictors. The spatial contrast in ambient PNC across the large conurbation of Rome, was successfully assessed. The average exposure of subjects living in the study area was 16,006 particles/cm³ (SD 2165 particles/cm³, range: 11,075–28,632 particles/cm³). A total of 203,886 subjects (16%) lives in Rome within 50 m from a high traffic road and they experience the highest exposure levels (18,229 particles/cm³). The results will be used to estimate the long-term health effects of ultrafine particle exposure of participants in Rome. [ABSTRACT FROM AUTHOR]

The major sources of fine particulate matter (PM 2.5 ) in New York City (NYC) were apportioned by applying positive matrix factorization (PMF) to two different sets of particle characteristics: mass concentrations using chemical speciation data and particle number concentrations (PNC) using number size distribution, continuously monitored gases, and PM 2.5 data. Post-processing was applied to the PMF results to: (i) match with meteorological data, (ii) use wind data to detect the likely locations of the local sources, and (iii) use concentration weighted trajectory models to assess the strength of potential regional/transboundary sources. Nine sources of PM 2.5 mass were apportioned and identified as: secondary ammonium sulfate, secondary ammonium nitrate, road traffic exhaust, crustal dust, fresh sea-salt, aged sea-salt, biomass burning, residual oil/domestic heating and zinc. The sources of PNC were investigated using hourly average number concentrations in six size bins, gaseous air pollutants, mass concentrations of PM 2.5 , particulate sulfate, OC, and EC. These data were divided into 3 periods indicative of different seasonal conditions. Five sources were resolved for each period: secondary particles, road traffic, NYC background pollution (traffic and oil heating largely in Manhattan), nucleation and O 3 -rich aerosol. Although traffic does not account for large amounts of PM 2.5 mass, it was the main source of particles advected from heavily trafficked zones. The use of residual oil had limited impacts on PM 2.5 mass but dominates PNC in cold periods. [ABSTRACT FROM AUTHOR]

Ship emissions are a growing concern, especially in coastal areas, for potential impacts on human health and climate. International mitigation strategies to curb these emission, based on low-sulphur content fuels, have proven useful to improve local air quality. However, the effect on climate forcing is less obvious. Detailed information on the influence of shipping to particles of different sizes is needed to investigate air quality and climate interaction. In this work, the contributions of maritime emissions to atmospheric concentrations of gaseous pollutants (NO, NO 2 , SO 2 , and O 3 ) and of particles (sizes from 0.009 μm to 30 μm) were investigated considering manoeuvring (arrival and departure of ships) and hotelling phases (including loading/unloading activities). Results showed that the size distributions of shipping contributions were different for the two phases and could be efficiently described, using measured data, considering four size-ranges. The largest contribution to particles concentration was observed for D p < 0.25 μm, however, a secondary maximum was observed at D p = 0.35 μm. The minimum contribution was observed at D p around 0.8–0.9 μm with a negligible contribution from hotelling for size range 0.4–1 μm. The comparison of 2012 and 2014 datasets showed no significant changes of gaseous and particulate pollutant emissions and of the contribution to particle mass concentration. However, an increase of the contribution to particle number concentration (PNC) was observed. Results suggested that harbour logistic has a relevant role in determining the total impact of shipping on air quality of the nearby coastal areas. Additionally, future policies should focus on PNC that represents an important fraction of emissions also for low-sulphur fuels. DOAS remote sensing proved a useful tool to directly measure NO 2 and SO 2 ship emissions giving estimates comparable with those of emission inventory approach. [ABSTRACT FROM AUTHOR]

In this paper, we studied concentrations of cloud condensation nuclei (CCN) and CCN activity measured at a suburb site of Qingdao in the North China during a non-heating period from 19 May to 3 June 2013 and a heating period from 6 November to 6 December 2013. Concentrations of CCN during the non-heating period were 3.1 ± 1.9 (mean ± standard deviation), 4.9 ± 3.4, 5.6 ± 3.9, 6.1 ± 4.3 and 6.5 ± 4.6 in unit of ×10 3 cm −3 at supersaturation (SS) of 0.2%, 0.4%, 0.6%, 0.8% and 1.0%, respectively. The corresponding CCN activities of atmospheric particles were 0.28 ± 0.17, 0.43 ± 0.24, 0.48 ± 0.26, 0.52 ± 0.27 and 0.54 ± 0.28, respectively. Concentrations of CCN during the heating period were 3.1 ± 1.3, 6.4 ± 2.3, 8.5 ± 2.9, 9.6 ± 3.5 and 10 ± 3.9 in unit of ×10 3 cm −3 at SS of 0.2%, 0.4%, 0.6%, 0.8% and 1.0%, respectively. The corresponding CCN activities were 0.11 ± 0.06, 0.24 ± 0.11, 0.31 ± 0.14, 0.35 ± 0.15 and 0.37 ± 0.15, respectively. At SS ≥ 0.4%, concentrations of CCN were significantly larger during the heating period than during the non-heating period with 95% confidence because of larger particle number concentrations associated. However, CCN activities were significantly lower during the heating period than during the non-heating period at each SS. The lower CCN activities during the heating period were analyzed in terms of origins, median mobility diameter and possible chemical composition of atmospheric particles. However, when new particle formation events during the heating and the non-heating periods were considered alone, CCN activities of grown new particles at the same size range sometimes appeared to be constant regardless of the heating or non-heating periods. [ABSTRACT FROM AUTHOR]

Quantification of disproportionate contribution made by signalised traffic intersections (TIs) to overall daily commuting exposure is important but barely known. We carried out mobile measurements in a car for size–resolved particle number concentrations (PNCs) in the 5–560 nm range under five different ventilation settings on a 6 km long busy round route with 10 TIs. These ventilation settings were windows fully open and both outdoor air intake from fan and heating off (Set 1 ), windows closed, fan 25% on and heating 50% on (Set 2 ), windows closed, fan 100% on and heating off (Set 3 ), windows closed, fan off and heating 100% on (Set 4 ), and windows closed, fan and heating off (Set 5 ). Measurements were taken sequentially inside and outside the car cabin at 10 Hz sampling rate using a solenoid switching system in conjunction with a fast response differential mobility spectrometer (DMS50). The objectives were to: (i) identify traffic conditions under which TIs becomes hot–spots of PNCs, (ii) assess the effect of ventilation settings in free–flow and delay conditions (waiting time at a TI when traffic signal is red) on in–cabin PNCs with respect to on–road PNCs at TIs, (iii) deriving the relationship between the PNCs and change in driving speed during delay time at the TIs, and (iv) quantify the contribution of exposure at TIs with respect to overall commuting exposure. Congested TIs were found to become hot–spots when vehicle accelerate from idling conditions. In–cabin peak PNCs followed similar temporal trend as for on–road peak PNCs. Reduction in in–cabin PNC with respect to outside PNC was highest (70%) during free–flow traffic conditions when both fan drawing outdoor air into the cabin and heating was switched off. Such a reduction in in–cabin PNCs at TIs was highest (88%) with respect to outside PNC during delay conditions when fan was drawing outside air at 25% on and heating was 50% on settings. PNCs and change in driving speed showed an exponential–fit relationship during the delay events at TIs. Short–term exposure for ∼2% of total commuting time in car corresponded to ∼25% of total respiratory doses. This study highlights a need for more studies covering diverse traffic and geographical conditions in urban environments so that the disparate contribution of exposure at TIs can be quantified. [ABSTRACT FROM AUTHOR]

Ships and harbour emissions are currently increasing, due to the increase of tourism and trade, with potential impact on global air pollution and climate. At local scale, in-port ship emissions influence air quality in coastal areas impacting on health of coastal communities. International legislations to reduce ship emissions, both at Worldwide and European levels, are mainly based on the use of low-sulphur content fuel. In this work an analysis of the inter-annual trends of primary contribution, ε , of tourist shipping to the atmospheric PM 2.5 concentrations in the urban area of Venice has been performed. Measurements have been taken in the summer periods of 2007, 2009 and 2012. Results show a decrease of ε from 7% (±1%) in 2007 to 5% (±1%) in 2009 and to 3.5% (±1%) in 2012. The meteorological and micrometeorological conditions of the campaigns were similar. Tourist ship traffic during measurement campaigns increased, in terms of gross tonnage, of about 25.4% from 2007 to 2009 and of 17.6% from 2009 to 2012. The decrease of ε was associated to the effect of a voluntary agreement (Venice Blue Flag) for the use of low-sulphur content fuel enforced in the area between 2007 and 2009 and to the implementation of the 2005/33/CE Directive in 2010. Results show that the use of low-sulphur fuel could effectively reduce the impact of shipping to atmospheric primary particles at local scale. Further, voluntary agreement could also be effective in reducing the impact of shipping on local air quality in coastal areas. [ABSTRACT FROM AUTHOR]

Aerosols in the lower troposphere over Japan are considered being influenced by those transported from Asian continent by westerly winds. In this study, we investigated the seasonal variation of aerosol number concentrations measured by means of optical particle counters at Mt. Kiso-Komagatake (2610 m altitude) in central Japan during the period from January 2010 to May 2013. We also collected aerosol samples in different seasons during part of the observation period and investigated their elemental compositions using transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX). The seasonal variation of the number concentrations suggested that accumulation-mode particles (particle diameter > 0.3 μm) increased during late spring perhaps owing to gas-to-particle conversion by means of photochemical reactions. The number concentrations of supermicron particles (>1 μm) were highest in spring, during which Asian dust events were frequent. Short-duration spikes in aerosol number concentrations, which were attributed to long-range transport from the Asian continent, were frequently observed in all seasons except summer. TEM analysis indicated that sulfate was the predominant component of accumulation-mode particles throughout the year. The number fraction of carbonaceous particles was also considerable, especially in samples in fall. The predominant components of supermicron particles collected during winter, spring and fall, and summer were sulfate, minerals, and sea salt, respectively. Our results suggest that the lower tropospheric air over central Japan is strongly influenced by long-range transport of aerosols in all seasons except summer. [ABSTRACT FROM AUTHOR]

Aerosol chemical and physical properties were measured in 2010 at Neumayer research station, Antarctica. Samples for chemical analysis (ion chromatography) were collected using a Teflon/Nylon filter combination (TNy) sampler, and with a multi stage low pressure impactor (SDI). Particle number concentration was measured continuously with a Grimm OPC optical particle counter. Total particle number concentration varied largely throughout the year, and the highest number concentrations for particles larger than 0.3 μm were observed simultaneously with the highest sea salt concentrations. About 50% of the sea salt aerosol mass was found in the submicron size range. Below 0.2 μm of particle aerodynamic diameter the contribution of sea salt aerosols was negligible. Further analysis showed that sea salt aerosols had undergone physico-chemical processes, either during the transportation, or during their formation. High degree of chloride depletion was observed during austral summer, when the presence of acidic gases exhibit their characteristic seasonal maximum. Apart from chloride depletion, excess chloride relating to sodium was also detected in one SDI sample, indicating actually a sodium depletion by mirabilite formation on freshly formed sea ice areas. Analysis of selected episodes showed that the concentration of sea salt particles, their modal structure, and their chemical composition is connected with their source areas, their formation mechanisms, and local transport history. [ABSTRACT FROM AUTHOR]

For the first time in Germany, we obtained high-resolution spatial distributions of particle numbers and nitrogen oxides in an urban agglomeration using a tram system. In comparison to particle numbers the NOx concentration decreased much faster with a significantly steeper gradient when going from the inner city to the surrounding area. In case of NOx the decrease was 70% while for particle number concentration it was only 50%. We found an area in the rural surrounding with a second increase of particle numbers without simultaneous enhanced NOx levels. The source of the high particle numbers could be ascribed to industry emissions about 5-10 km away. The mean spatial distribution of particle number concentration depended on wind direction, wind velocity and boundary layer stability. The dependency was particularly strong in the rural area affected by industrial emissions, where individual wind directions led to concentration differences of up to 25%. The particulate concentration was 40% higher during low wind velocities (1-5 m s-1) than during high wind velocities (>5 m s-1). We observed similar findings for the impact of boundary layer stability on particle numbers concentration. Particle pollution was 40% higher for stable stratification compared to neutral or unstable cases. [ABSTRACT FROM AUTHOR]

Particle number size distributions in a mobility diameter range of 6–1000 nm and size-resolved number concentrations were determined with a time resolution of 10 min for a near-city background, city centre, street canyon and road tunnel environments in Budapest. Median N 6–100 concentrations for the sites listed were 3.1 × 103, 9.3 × 103, 19.4 × 103 and 123 × 103 cm−3, respectively. Contributions of the ultrafine (UF) particles (<100 nm) to the total particle number for all locations were rather large (up to 86%), and do not seem to vary substantially in time. Diurnal variations of the mean N 6–100 concentrations had different patterns for both the various urban sites, and for workdays and weekends. Nucleation strength factor (NSF) was introduced for the first time to quantify the relative importance of new particle formation with respect to all sources of UF particles. During the daytime in summer, nucleation in the near-city background was a major production process of UF particles with a daily mean relative contribution of 42%. In the city centre and street canyon, the daily mean relative contributions of nucleation to the UF particles were 30% and 23%, respectively. Median particle diameters for the background, city centre, street canyon and road tunnel environments were 61, 42, 35 and 42 nm, respectively, so they were jointly influenced with the anthropogenic impact and aerosol ageing. Monthly mean frequency of new particle formation and growth events in the background seems somewhat larger, while it appears smaller for the street canyon in comparison to the city centre. [ABSTRACT FROM AUTHOR]

Roadside vegetation barriers are used in many urban areas to restrict air and noise pollution from reaching roadside pedestrians, but their effectiveness in limiting the movement of nanoparticles is not yet known. This study investigates the influence of a roadside vegetation barrier on particle number distribution (PND) and concentration (PNC) and associated exposure under different wind directions. Size-resolved particles in the 5–560 nm size range were measured along a busy roadside in Guildford (Surrey, UK) using a fast response differential mobility spectrometer (DMS50). A custom-built solenoid switching system, together with the DMS50, was used to make sequential measurements at the front (L 2), middle (L 3) and back (L 4) of the vegetation barrier; L 1 was in parallel to L 2 at a vegetation-free location. Measured data were divided into the three predominant wind directions: cross-road (NW–SW), cross-footpath (NE–SE) and along-road (NW–NE). The consistency in the shape of PNDs and the corresponding geometric mean diameters at the three sites (L 2, L 3, L 4) indicate an identical removal effect of vegetation barrier for all sizes of particles. Comparison of the PNCs at two parallel locations (with and without the vegetation barrier) showed ∼11% higher PNCs (1.99 ± 1.77 × 105 cm−3) at L 2 than those at L 1 during cross-road winds, showing the impeding effect of the vegetation barrier. Such differences were insignificant during the remaining wind directions. Cross-road winds indicate the effect of vegetation barrier; the PNCs were decreased by 14 and 37% at L 3 and L 4, respectively, compared with L 2. During cross-footpath winds, particles were carried away by the wind from the sampling location. Significant decrease in PNCs were consequently seen at L 3 (1.80 ± 1.01 × 104 cm−3) and L 4 (1.49 ± 0.91 × 104 cm−3) compared with L 2 (6.26 ± 3.31 × 104 cm−3). The PNCs at these locations showed modest differences during the cross-footpath and along-road winds. Respiratory deposited doses (RDD) at L 4 were found to be the lowest during all wind directions compared with the L 1–L 3. The vegetation barrier efficiently reduced the RDD by ∼36% during cross-road winds. Our results show the mitigation potential of vegetation barriers in limiting near-road nanoparticles exposure and the measured data can facilitate performance evaluation of theoretical models. [ABSTRACT FROM AUTHOR]

Abstract: Aerosols in the lower troposphere over Japan are considered being influenced by those transported from Asian continent by westerly winds. In this study, we investigated the seasonal variation of aerosol number concentrations measured by means of optical particle counters at Mt. Kiso-Komagatake (2610 m altitude) in central Japan during the period from January 2010 to May 2013. We also collected aerosol samples in different seasons during part of the observation period and investigated their elemental compositions using transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX). The seasonal variation of the number concentrations suggested that accumulation-mode particles (particle diameter > 0.3 μm) increased during late spring perhaps owing to gas-to-particle conversion by means of photochemical reactions. The number concentrations of supermicron particles (>1 μm) were highest in spring, during which Asian dust events were frequent. Short-duration spikes in aerosol number concentrations, which were attributed to long-range transport from the Asian continent, were frequently observed in all seasons except summer. TEM analysis indicated that sulfate was the predominant component of accumulation-mode particles throughout the year. The number fraction of carbonaceous particles was also considerable, especially in samples in fall. The predominant components of supermicron particles collected during winter, spring and fall, and summer were sulfate, minerals, and sea salt, respectively. Our results suggest that the lower tropospheric air over central Japan is strongly influenced by long-range transport of aerosols in all seasons except summer. [Copyright &y& Elsevier]

Abstract: Particle number concentration was measured between June 2009 and June 2010 at Akrotiri research station in a rural/suburban region of western Crete (Greece). Overall, the available data covered 157 days during the aforementioned period of measurements. The objectives were to study the number size distribution characteristics of ambient aerosols and furthermore to identify new particle formation events and to evaluate particle formation rates and growth rates of the newborn particles. Aerosol particles with mobility diameters between 10 and 1100 nm were measured using a Scanning Mobility Particle Sizer (SMPS) system. Measurements were performed at ambient relative humidities. The median total particle number concentration was 525 #/cm3 whereas the number concentration ranged between 130 #/cm3 and 9597 #/cm3. The average percentage of particles with diameters between 10 nm and 100 nm (N10–100) to total particles was 53% during summer and spring, but reached 80% during winter. Maximum average contribution of nano-particles (10 nm < D p < 50 nm) to total particles was recorded also in winter and was attributed partly to the effect of local heating. Furthermore, back trajectories (HYSPLIT model) showed that different air mass origins are linked to different levels of particle number concentrations, with higher values associated with air masses passing from polluted areas before reaching the Akrotiri station. Modal analysis of the measured size distribution data revealed a strong nucleation mode during winter (15–25 nm), which can be correlated with emissions from local sources (domestic heating). The nucleation mode was observed also during the spring campaigns and was partly linked to new particle formation events. On the contrary, an accumulation mode (80–120 nm) prevailed in the measurements during summer campaigns, when the station area was influenced by polluted air masses arriving mainly from Eastern Europe. In total, 13 new particle formation events were recorded during the 157 days of measurements. Nucleation events were associated with low values of N100 particle number concentration and reduced coagulation sinks. Mean growth and formation rates were calculated and showed values equal to 6 nm hr−1 and 13 cm−3 s−1, respectively. [Copyright &y& Elsevier]

Particle number size distributions were simultaneously measured at the Guangzhou (GZ) urban site (23.13°N, 113.26°E) and the Back-garden (BG) rural site (23.5°N, 113.03°E) in the Pearl River Delta (PRD) region in July, 2006. It provided new findings into the evolution of particle number size distribution and new particle formation (NPF) in two different environments. Number concentration of particles (20 nm–10 μm diameter) at GZ was about 70% higher than at BG and significantly affected by traffic emission. However, number concentrations of the regional aerosols (100–660 nm) were (6 ± 3) × 103 cm−3 at both sites. At BG, the diurnal variation of particle number size distributions showed an obvious particle growth process beginning at about 9:00 (LT), probably caused by NPF. In contrast, particle number concentrations in the size rages of 20–45 nm, 45–100 nm, and 100–660 nm showed similar trends with two main peaks at about 12:00 (LT) and 19:00 (LT) at GZ. NPF events were observed at both sites, but the occurrence frequency at GZ was about 50% lower than at BG. Regional NPF events at both sites probably in the same air mass were simultaneously observed with similar growth rates, concentrations and production rates of the condensable vapors, and condensational sinks on July 6. On the whole, deceasing traffic emission will improve air quality efficiently in the aspect of particle number concentration and fine particulate pollution in the summer of PRD should be controlled in a regional scale, especially with stagnant air mass from South China Sea. [ABSTRACT FROM AUTHOR]

A method for investigating ship emissions, known as the plume capture and analysis system (PCAS) is described. The PCAS is applied to the task of measuring airborne pollutant emission factors (EFs) and particle size distributions aboard two dredgers, although the technique is also suitable for remote measurements. EFs were measured relative to the fuel consumption using the fuel combustion derived plume CO2. Each measurement typically took 6 min to complete and during one day, 40–50 measurements were possible. EFs for particle number (PN), NO x , SO2, and PM2.5 were independent within a targeted dilution factor range of 50–1000 suitable for onboard and remote sampling. For the Amity, the EF ranges were PN: 2.2–9.6 × 1015 (kg-fuel)−1; NO x : 35–72 g (NO2) (kg-fuel)−1, SO2 0.6–1.1 g (SO2) (kg-fuel)−1and PM2.5: 0.7–6.1 g (PM2.5) (kg-fuel)−1. For the Brisbane they were PN: 1.0–1.5 × 1016 (kg-fuel)−1, NO x : 3.4–8.0 g (NO2) (kg-fuel)−1, SO2: 1.3–1.7 g (SO2) (kg-fuel)−1 and PM2.5: 1.2–5.6 g (PM2.5) (kg-fuel)−1. Particle number emission factors as a function of size as well as the count median diameter (CMD), and geometric standard deviation of the size distributions are provided. This size distributions were consistently uni-modal in the range below 500 nm for both vessels, and this CMD always lay within the accumulation mode range. [ABSTRACT FROM AUTHOR]

Abstract: Potential adverse effects on children health may result from school exposure to airborne particles. To address this issue, measurements in terms of particle number concentration, particle size distribution and black carbon (BC) concentrations were performed in three school buildings in Cassino (Italy) and its suburbs, outside and inside of the classrooms during normal occupancy and use. Additional time resolved information was gathered on ventilation condition, classroom activity, and traffic count data around the schools were obtained using a video camera. Across the three investigated school buildings, the outdoor and indoor particle number concentration monitored down to 4 nm and up to 3 μm ranged from 2.8 × 104 part cm−3 to 4.7 × 104 part cm−3 and from 2.0 × 104 part cm−3 to 3.5 × 104 part cm−3, respectively. The total particle concentrations were usually higher outdoors than indoors, because no indoor sources were detected. I/O measured was less than 1 (varying in a relatively narrow range from 0.63 to 0.74), however one school exhibited indoor concentrations higher than outdoor during the morning rush hours. Particle size distribution at the outdoor site showed high particle concentrations in different size ranges, varying during the day; in relation to the starting and finishing of school time two modes were found. BC concentrations were 5 times higher at the urban school compared with the suburban and suburban-to-urban differences were larger than the relative differences of ultrafine particle concentrations. [Copyright &y& Elsevier]

Abstract: Background: The toxic effects of ultrafine particles (UFP) are a public health concern. However, epidemiological studies on the long term effects of UFP are limited due to lacking exposure models. Given the high spatial variation of UFP, the assignment of exposure levels in epidemiological studies requires a fine spatial scale. The aim of this study was to assess the performance of a short-term measurement protocol used at a large number of locations to derive a land use regression (LUR) model of the spatial variation of UFP in Girona, Spain. Methods: We measured UFP for 15min on the sidewalk of 644 participants’ homes in 12 towns of Girona province (Spain). The measurements were done during non-rush traffic hours 9:15–12:45 and 15:15–16:45 during 32 days between June 15 and July 31, 2009. In parallel, we counted the number of vehicles driving in both directions. Measurements were repeated on a different day for a subset of 25 sites in Girona city. Potential predictor variables such as building density, distance to bus lines and land cover were derived using geographic information systems. We adjusted for temporal variation using daily mean NOx concentrations at a central monitor. Land use regression models for the entire area (Core model) and for individual towns were derived using a supervised forward selection algorithm. Results: The best predictors of UFP were traffic intensity, distance to nearest major crossroad, area of high density residential land and household density. The LUR Core model explained 36% of UFP total variation. Adding sampling date and hour of the day to the Core model increased the R 2 to 51% without changing the regression slopes. Local models included predictor variables similar to those in the Core model, but performed better with an R 2 of 50% in Girona city. Independent LUR models for the first and second measurements at the subset of sites with repetitions had R 2’s of about 47%. When the mean of the two measurements was used R 2 improved to 72%. Conclusions: LUR models for UFP were developed, based on a highly cost-effective short-term monitoring campaign at a large number of sites, with fair performance. Complementing the approach with further strategies to address sources of temporal variation of UFP is likely to result in improved models as indicated by the good performance of the model based on the subset of sites with one repeated measurement. Our approach is promising for UFP and possibly for other PM components requiring active sampling. [Copyright &y& Elsevier]

Abstract: Particle number concentration (PNC) and transition metal content are implicated in the health effects of airborne particulate matter (PM) but they are difficult to measure so consequently their temporal and spatial variations are not well characterized. Daily concentrations of PNC and particle-bound water-soluble metals (V, Cr, Mn, Fe, Ni, Cu, As, Cd and Pb) were measured at background and kerbside sites in Glasgow and London to examine if other metrics of air pollution such as optical darkness (absorbance) of collected filter samples of PM, gravimetric PM, and NO, NO2 and CO gas concentrations, can be used as surrogates for the temporal and spatial variations of the former. NO2 and NOx exhibited a high degree of within-site correlation and with PNC and water-soluble metals (Fe, Cu, As, Cd, Pb) at background sites in both cities. There is therefore potential to use NO2 and NOx as surrogates for PNC and water-soluble metal at background sites. However, correlation was weaker in complex street canyon environments where pollutant concentrations are strongly affected by local sources and the small-scale variations in pollutant dispersion induced by the wind regimes within street canyons. The corollary of the high correlation between NO2 and PNC and water-soluble metals at the background sites is that the latter pollutants may act as confounders for health effects attributed to NO2 from such sites. Concentrations of CO cannot be used as a surrogate for PNC. Increments in daily NOx and NO2 concentrations between trafficked and background sites were shown to be a simple and novel surrogate for daily spatial variation of PNC; for example, increments in NOx explained 78–79% of the variance in PNC at the paired sites in both Glasgow and London, but relationships were city specific. The increments in NOx also explained 70% of the spatial variation in Cu and Ni in Glasgow but not in London. Weekly NO2 measurements derived from passive diffusion tubes were also shown to correlate well with increments in PNC. A high temporal correlation between PNC and 1,3-butadiene and benzene (which can also be measured by passive sampler) implies that passive sampler measurements may be a straightforward tool for deriving long-term spatial patterns in PNC. [Copyright &y& Elsevier]

Abstract: This study reports the diurnal, seasonal and annual variation of ultrafine particles (UFP) in a large city. Particle number (PN) concentrations were measured in Toronto, Canada on a major arterial roadway between March 2006 and May 2011 using a Fast Mobility Particle Sizer. The PN in the size range of 8–300 nm decreased during the measurement period primarily due to changes in the vehicle fleet. PN50 (particles with diameters less than 50 nm) decreased by 21% between 2006 and 2010. Notably, the majority of the reduction occurred during the winter months. PN50 exhibited the strongest seasonality and diurnal trend. PN50–100 (particles between 50 and 100 nm) and PN100–300 (particles between 100 and 300 nm) decreased by 17% and 24%, respectively. Correlation analysis between gas phase criteria pollutants showed good correlation between PN50–100 and NO2, SO2, and PM2.5. In contrast, PN50 exhibited the highest correlation with temperature, NO and NO2. A multiple linear regression model was developed for each size fraction. The model adequately explained the annual, seasonal and day-to-day variability of PN50–100 (R 2 = 0.64) and PN100–300 (R 2 = 0.83). The model captured the annual and seasonal variability of PN50 but only partially explained the day-to-day variability (R 2 = 0.52). The long-term reductions in PN50 indicate that policy interventions are having some success in slowly decreasing UFP concentrations in Toronto. [Copyright &y& Elsevier]

Abstract: In this paper, we compare the Generalised Linear Model (GLM) and Generalised Additive Model (GAM) for modelling the particle number concentration (PNC) of outdoor, airborne ultrafine particles in Helsinki, Finland. We examine temporal trends in PNC and examine the relationship between PNC and rainfall, wind speed and direction, humidity, temperature and solar insolation. Model choice is via the Akaike Information Criterion (AIC). We have shown that the Generalised Additive Model provides a better fit than the equivalent Generalised Linear Model (ELM) when fitting models with the same covariates with equivalent degrees of freedom (AIC and BIC for the GAM are 10266.52 and 10793.04, AIC and BIC for the ELM are 10297.19 and 10885.97, both have an R 2 value of 0.836). We also present results that show that modelling both temporal trends and the effect of rainfall, wind speed and direction, humidity, temperature and solar insolation yields a better fitting model, according to the AIC, than either temporal trends or meteorological conditions by themselves. The model is applicable to any longitudinal monitoring-type measurement campaign where long time series are recorded. Use of this technique may be inappropriate for very short measurement campaigns. Attempting to fit a representative daily trend to one or two days’ measurements may lead to a high degree of uncertainty; inclusion of a yearly trend requires having at least a year’s worth of data with few gaps, particularly large gaps. In such a situation, the temporal trends may end up being penalised to zero and the model reverts to one largely influenced by meteorology. [Copyright &y& Elsevier]

Abstract: The Japanese Ministry of the Environment established a new PM2.5 air quality standard in September 2009, which has lead to increased public interest in air quality improvement. Concentrations of primary particles such as elemental carbon have decreased during the last decade, but secondary particles have become a major concern. When ground-based observations are carried out, the influence of neighboring emissions must be considered. At the same time, as much as possible, particles must be collected in places that will allow the average behavior of secondary particles to be understood. Making observations using aircraft in city skies is advantageous in that samples taken there are not influenced by local exhaust, such observations can cover a wide range at one time, and they are useful in understanding the spatial character of secondary particles. Using a helicopter for sampling, we measured the spatial variation of particle size distribution (0.5–10 μm) on the coastline and over inland areas in the South Kanto region, including the Tokyo metropolitan area, nine times in three days starting on July 30, 2008. The vertical profile of pollutant concentrations was approximately constant between the altitudes of 300 m and 600 m, but concentrations varied both temporally and spatially. Data gathered in level flights at an altitude of 600 m showed that the particle number concentration increased while the mean particle diameter decreased as we flew north (inland). The particle number concentration and its relationship with the mean particle diameter showed a well-organized distribution. A volumetric change of more than 3-fold was seen in the distribution of particles sampled in the inland area, whereas no clear volumetric change was seen in the distribution of particles sampled along the coast. The particle number concentration, mean particle diameter, and particle volume changed at rates of 0.74 cm−3 km−1, −0.48 nm km−1, and 0.057 μm3 cm−3 km−1, respectively, with increasing distance from the coastline. The incremental volumetric growth rates were seen to relate positively in proportion to the NO2 concentration in particular. [Copyright &y& Elsevier]

Abstract: The ambient particle number concentration and size distribution have been measured in an urban background site in Madrid, a continental Mediterranean area, over more than two years (Oct 2006–Dec 2008). The objective was to study the sources and processes affecting or contributing to fine and ultrafine particles in this area. They have been measured with a TSI–SMPS (15–600 nm) instrument and with a modified Vienna type DMA (3–80 nm) and a CPC 3025 (TSI) during 6 months. The average particle number concentration was lower than in other sites as it is an urban background site and because of its location in the Mediterranean area. The particle number concentrations have shown a clear seasonal influence: maximum values were observed every year in the period November–January, coinciding with atmospheric stagnant conditions and pollution episodes, while minimum values were measured in springtime, a period in which wind speed produced high atmospheric dilution. The Aitken and accumulation modes have shown similar seasonal behavior, with two maxima related to vehicle emissions. The nucleation mode had a third maximum observed at noon during spring and summer. The size distributions were bimodal during most of the time: the first mode was centered on 20–50 nm and was associated with fresh particles related to vehicle exhaust emission; the second mode, between 50 and 160 nm, mainly corresponded to the evolution of the first mode. The evolution of the size distributions reveals a marked annual cycle related to the season, with an increase of median diameters during summer and a decrease during winter. Different evolutions of particle size distribution corresponding to different meteorological and seasonal scenarios were identified. The influence of higher wind speeds on particle size distribution has been confirmed to cause a decrease in the particle number concentration and in the size distribution mode. Particle nucleation is not a frequent phenomenon in this measurement site, where 63 events per year have been observed. They mainly occurred during spring and summer periods, with the minimum number during winter. This suggests that insolation and temperature are important variables in nucleation. Class Ia nucleation events mainly occurred during spring and summer. High wind speeds were important during class II events, as the particles suffered low growth or lost their semivolatile compounds. [Copyright &y& Elsevier]

Abstract: Measurements of airborne particle number size distributions, particle number and PM2.5 concentrations were conducted at two bus stations of different designs: open station and canyon station, operated according to the same timetables and fleet compositions, as well as at a reference point in Brisbane, Australia. Simultaneous traffic and meteorological parameters were also monitored, aiming to quantify particle characteristics and investigate the impact of station design and meteorological conditions on particle emissions at the two bus stations. It was found that there was no significant difference in average particle number concentrations in the size range 7–3000nm (PN7–3000) between the two stations (fine days: p =0.90 and rainy days: p =0.80), and that PN50–120 contributed to the largest proportion of particle number concentrations. PN20–30 were observed to increase at the open station during all time periods, except 0:00–7:00, which is likely to be attributed to the lower average daily temperature at the open station (around 7°C lower than at the canyon station). During precipitation, it was found that particle number concentration in the size range 25–250nm decreased greatly, and the average daily reduction in PM2.5 concentration on rainy days compared to fine days was 44.2% and 22.6% at the open and canyon station, respectively. The effect of ambient wind speeds on particle number concentration was also examined, and no relationship was found between particle number concentration and wind speed for the entire measurement period. In addition, 33 pairs of average half-hourly PN7–3000 concentrations were calculated and identified at the two stations, during the same time of a day, and with the same ambient wind speeds and precipitation conditions. The results of a paired t-test showed that the average half-hourly PN7–3000 concentrations at the two stations were not significantly different at the 5% confidence level (t =0.06, p =0.96), which indicates that the different station designs were not a crucial factor for influencing PN7–3000 concentrations. This finding implies that the timescale of dispersion at the bus stations was comparatively long, and that the source contribution was more important compared to the atmospheric dispersions associated with different station designs. [Copyright &y& Elsevier]

Abstract: The aim of this work was to quantify exposure to particles emitted by wood-fired ovens in pizzerias. Overall, 15 microenvironments were chosen and analyzed in a 14-month experimental campaign. Particle number concentration and distribution were measured simultaneously using a Condensation Particle Counter (CPC), a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle Sizer (APS). The surface area and mass distributions and concentrations, as well as the estimation of lung deposition surface area and PM1 were evaluated using the SMPS-APS system with dosimetric models, by taking into account the presence of aggregates on the basis of the Idealized Aggregate (IA) theory. The fraction of inhaled particles deposited in the respiratory system and different fractions of particulate matter were also measured by means of a Nanoparticle Surface Area Monitor (NSAM) and a photometer (DustTrak DRX), respectively. In this way, supplementary data were obtained during the monitoring of trends inside the pizzerias. We found that surface area and PM1 particle concentrations in pizzerias can be very high, especially when compared to other critical microenvironments, such as the transport hubs. During pizza cooking under normal ventilation conditions, concentrations were found up to 74, 70 and 23 times higher than background levels for number, surface area and PM1, respectively. A key parameter is the oven shape factor, defined as the ratio between the size of the face opening in respect to the diameter of the semicircular oven door, and particular attention must also be paid to hood efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influences on the frequency of new particle formation events at this area. The factors affecting the coagulation sink are evaluated. The relatively lower ambient relative humidities may weaken the coagulation sink and facilitate the occurrence of new particle formation events during noontime, while the surmise of nucleation and growth involving organic matter may imply an actually higher coagulation sink than expected. These factors have a significant influence on the ultimate fate of the newly formed nuclei and new particle formation. A comparison of event and non-event days indicates that the coagulation sink is not the only decisive factor affecting new particle formation, other factors including the precursor vapors and photochemical activity are none the less important either. Competition of coagulation sink and high source rate leads to the occurrence of new particle formation events at Xinken. [Copyright &y& Elsevier]

This study presents a comparison between measured and modelled particle number concentrations (PNCs) in the 10–300nm size range at different heights in a canyon. The PNCs were modelled using a simple modelling approach (modified Box model, including vertical variation), an Operational Street Pollution Model (OSPM) and Computational Fluid Dynamics (CFD) code FLUENT. All models disregarded any particle dynamics. CFD simulations have been carried out in a simplified geometry of the selected street canyon. Four different sizes of emission sources have been used in the CFD simulations to assess the effect of source size on mean PNC distributions in the street canyon. The measured PNCs were between a factor of two and three of those from the three models, suggesting that if the model inputs are chosen carefully, even a simplified approach can predict the PNCs as well as more complex models. CFD simulations showed that selection of the source size was critical to determine PNC distributions. A source size scaling the vehicle dimensions was found to better represent the measured PNC profiles in the lowest part of the canyon. The OSPM and Box model produced similar shapes of PNC profile across the entire height of the canyon, showing a well-mixed region up to first ≈2m and then decreasing PNCs with increased height. The CFD profiles do correctly reproduce the increase from road level to a height of ≈2m; however, they do not predict the measured PNC decrease higher in the canyon. The PNC differences were largest between idealised (CFD and Box) and operational (OSPM) models at upper sampling heights; these were attributed to weaker exchange of air between street and roof-above in the upper part of the canyon in the CFD calculations. Possible reasons for these discrepancies are given. [Copyright &y& Elsevier]

Two-year measurements of particle number size distribution (3nm–10μm) were conducted in Beijing, China since March 2004. Their seasonal, weekly and diurnal variations and dependencies on meteorological parameters were investigated. The annual average particle number concentrations of the nucleation mode (3–20nm), Aitken mode (20–100nm), and accumulation mode (0.1–1μm) are 9000cm−3, 15,900cm−3, and 7800cm−3, respectively. Particle number concentrations in Beijing are generally higher than that in cities of developed countries, especially for the accumulation mode particles. Both the highest total particle number concentration and the lowest volume concentration occurred in spring due to the frequent nucleation events. However, the minimum particle number concentration was observed in summer, and the maximum volume concentration in fall. The diurnal variation of the nucleation mode particles was mainly influenced by nucleation events, primarily in spring and winter. The diurnal variation of number concentration of the Aitken mode particles closely correlates with the traffic densities in all the four seasons. At the same time, obvious contribution of the growth of the nucleation mode to the number concentration of the Aitken mode particle has been also found in spring, summer, and fall. Significant differences in diurnal patterns of particle number concentrations between workdays and weekends are not observed in Beijing. Local wind speed plays an important role in shaping the particle number size distributions in the urban area of Beijing. With increasing wind speed, the nucleation and coarse mode particle number concentrations increase, while the number concentrations of the Aitken mode and accumulation mode particles decrease. A “U-shape relationship” between the total particle volume concentration and wind speed is observed. Frequently low wind speed (lower than 3m s−1) in Beijing is one of key factors leading to the poor air quality and low visibility. [Copyright &y& Elsevier]

Fleet aggregate emission factors for particle number for light duty vehicles and heavy duty vehicles are available from a number of field studies by calculation from airborne concentrations. Data are also available from laboratory chassis dynamometer studies in which particle number emissions from engines of a range of capacity and technologies have been measured. In this study the data from the PARTICULATES project database of laboratory test bed measurements have been aggregated to estimate fleet average particle number emission factors for light duty and heavy duty vehicles which have then been compared with the results of field measurement studies. Measurements carried out by [Jones, A.M., Harrison, R.M., 2006. Estimation of the emission factors of particle number and mass fractions from traffic at a site where mean vehicle speeds vary over short distances. Atmospheric Environment 40, 7125–7137] at the Marylebone Road London, represented an ‘urban’ fleet and were estimated by the aggregated laboratory measured emission factors within one or two standard deviations of their values. For light and heavy duty vehicles travelling with an average speed of 39.5kmh−1 the NO x emission factors were estimated to be 0.62 and 5.88gveh−1 km−1, respectively, and the PM2.5 emission factors were estimated to be, respectively, 0.017 and 0.17gveh−1 km−1. The total particle number emission factors (including volatiles) were estimated for light and heavy duty vehicles travelling according ‘urban’ Common ARTEMIS Driving Cycle (CADC) to be 6.31×1013 and 70.6×1013 numveh−1 km−1 and these were both within one standard deviation of the values measured using the field data. Similarly, the fractionated solid particle number emission factors (excluding volatiles), measured for the aerodynamic diameter ranges, 30–50nm, 50–100nm and 100–1000nm, were estimated to within one standard deviation of the equivalent measured emission factors for the light duty vehicles and to within two standard deviations of the equivalent measured emission factors for the heavy duty vehicles. Extending this work to estimate the total number emission factors measured by other research groups, conditions representing both the ‘rural’ and ‘highway’ Common ARTEMIS Driving Cycles were considered. For the light duty vehicles, a general increase in the calculated value of the total number emission factor was observed with increased fleet speed and the observed scatter was accounted for by the split in the fleet according to the vehicle''s fuel, whether gasoline or diesel. The calculated values of the total number emission factors for the heavy duty vehicles also show an increase with speed after 60kmh−1. High values are observed at 20kmh−1 suggesting an underlying inverted binomial trend similar to that observed for gaseous emission factors and arguably supported by the field measured values. The scatter of the calculated points about this trend was accounted for by the distribution of the fleet across the vehicle weight and emission legislation categories. With the exception of three of the field research studies considered – where the measured emission factors were significantly underestimated by the aggregated laboratory emission factors – there was a general agreement in the order of magnitude between the calculated and field emission factors, but not to the high degree shown for the Marylebone Road data. Furthermore, dilution temperature, fuel sulphur content and tunnel deposition effects did not individually account for the observed discrepancies in this work and point to the need for correction factors derived from these parameters..... [Copyright &y& Elsevier]

A 2-week intensive measurement campaign of indoor and outdoor air pollution was carried out in September 2006, in a primary school to investigate indoor–outdoor correlations of particle number (PN) concentrations, and the impact of air exchange rate (ACH) on the indoor PN concentration. The ACHs in the classroom for different conditions associated with window opening and the operational status of air conditioners (A/C) and fans were tested. As expected, the lowest ACH (0.12h−1) was found when the windows were closed and A/C and fans were off. In contrast, the highest ACH (7.92h−1) was observed when the windows were opened and A/C and fans were all on. The analysis of the PN I/O ratios at different ACHs in the absence of indoor sources indicates that the mean I/O ratio was 0.621±0.007 (mean±95% confidence interval) when the windows were closed, and A/C and fans were off; 0.524±0.023 when windows were closed, fans were off and A/C was on; and 0.502±0.029 when windows were closed, A/C was off and fans were on. To further understand the relationship between indoor and outdoor PN concentrations, the impact of outdoor PN concentration on I/O ratios at different ACHs was investigated. It was found that the relationship between outdoor PN concentration and the I/O ratio at different ACHs followed a power trendline with an equation of I/O ratio=A PNout −b (A and b are coefficients, PNout is outdoor PN concentration), suggesting that the penetration efficiency decreased with increasing outdoor PN concentration. It is the first time we found that when the outdoor PN concentration increased there was an associated increase in the concentration of nano-particles, which have been demonstrated to have higher deposition rates and lower penetration efficiencies. Based on the above equation, the study also showed a significant effect of ACH on indoor PN concentrations under stable outdoor PN concentrations. In general, the higher the ACH was, the lower the indoor PN concentration was. [Copyright &y& Elsevier]

Abstract: The number of ultrafine particles in urban air may be more health relevant than the usually measured mass of particles smaller than 2.5 or 10μm. Epidemiological studies typically assess exposure by measurements at a central site. Limited information is available about how well measurements at a central site reflect exposure to ultrafine particles. The goals of this paper are to assess the relationships between particle number (PN) and mass concentrations measured outdoors at a central site, right outside and inside the study homes. The study was conducted in four European cities: Amsterdam, Athens, Birmingham and Helsinki. Particle mass (PM10 and PM2.5), PN, soot and sulfate concentrations were measured at these sites. Measurements of indoors and outdoors near the home were made during 1 week in 152, mostly non-smoking, homes. In each city continuous measurements were also performed at a central site during the entire study period. The correlation between 24-h average central site outdoor and indoor concentrations was lower for PN (correlation among cities ranged from 0.18 to 0.45) than for PM2.5 (0.40–0.80), soot (0.64–0.92) and sulfate (0.91–0.99). In Athens, the indoor–central site correlation was similar for PN and PM2.5. Infiltration factors for PN and PM2.5 were lower than for sulfate and soot. Night-time hourly average PN concentrations showed higher correlations between indoor and central site, implying that indoor sources explained part of the low correlation found for 24-h average concentrations. Measurements at a central site may characterize indoor exposure to ambient particles less well for ultrafine particles than for fine particle mass, soot and sulfate. [Copyright &y& Elsevier]

The number of ultrafine particles may be a more health relevant characteristic of ambient particulate matter than the conventionally measured mass. Epidemiological time series studies typically use a central site to characterize human exposure to outdoor air pollution. There is currently very limited information how well measurements at a central site reflect temporal and spatial variation across an urban area for particle number concentrations (PNC). The main objective of the study was to assess the spatial variation of PNC compared to the mass concentration of particles with diameter less than 10 or 2.5μm (PM10 and PM2.5). Continuous measurements of PM10, PM2.5, PNC and soot concentrations were conducted at a central site during October 2002–March 2004 in four cities spread over Europe (Amsterdam, Athens, Birmingham and Helsinki). The same measurements were conducted directly outside 152 homes spread over the metropolitan areas. Each home was monitored during 1 week. We assessed the temporal correlation and the variability of absolute concentrations. For all particle indices, including particle number, temporal correlation of 24-h average concentrations was high. The median correlation for PNC per city ranged between 0.67 and 0.76. For PM2.5 median correlation ranged between 0.79 and 0.98. The median correlation for hourly average PNC was lower (range 0.56–0.66). Absolute concentration levels varied substantially more within cities for PNC and coarse particles than for PM2.5. Measurements at the central site reflected the temporal variation of 24-h average concentrations for all particle indices at the selected homes across the urban area. A central site could not assess absolute concentrations across the urban areas for particle number. [Copyright &y& Elsevier]

Numerous epidemiological studies have demonstrated the association between particle mass (PM) concentration in outside air and the occurrence of health related problems and/or diseases. However, much less is known about indoor PM concentrations and associated health risks. In particular, data are needed on air quality in schools, since children are assumed to be more vulnerable to health hazards and spend a large part of their time in classrooms. On this background, we evaluated indoor air quality in 64 schools in the city of Munich and a neighbouring district outside the city boundary. In winter 2004–2005 in 92 classrooms, and in summer 2005 in 75 classrooms, data on indoor air climate parameters (temperature, relative humidity), carbon dioxide (CO2) and various dust particle fractions (PM10, PM2. 5) were collected; for the latter both gravimetrical and continuous measurements by laser aerosol spectrometer (LAS) were implemented. In the summer period, the particle number concentration (PNC), was determined using a scanning mobility particle sizer (SMPS). Additionally, data on room and building characteristics were collected by use of a standardized form. Only data collected during teaching hours were considered in analysis. For continuously measured parameters the daily median was used to describe the exposure level in a classroom. The median indoor CO2 concentration in a classroom was 1603ppm in winter and 405ppm in summer. With LAS in winter, median PM concentrations of 19. 8μgm−3 (PM2. 5) and 91. 5μgm−3 (PM10) were observed, in summer PM concentrations were significantly reduced (median PM2. 5=12. 7μgm−3, median PM10=64. 9μgm−3). PM2. 5 concentrations determined by the gravimetric method were in general higher (median in winter: 36. 7μgm−3, median in summer: 20. 2μgm−3) but correlated strongly with the LAS-measured results. In explorative analysis, we identified a significant increase of LAS-measured PM2. 5 by 1. 7μgm−3 per increase in humidity by 10%, by 0. 5μgm−3 per increase in CO2 indoor concentration by 100ppm, and a decrease by 2. 8μgm−3 in 5–7th grade classes and by 7. 3μgm−3 in class 8–11 compared to 1–4th class. During the winter period, the associations were stronger regarding class level, reverse regarding humidity (a decrease by 6. 4μgm−3 per increase in 10% humidity) and absent regarding CO2 indoor concentration. The median PNC measured in 36 classrooms ranged between 2622 and 12,145particlescm−3 (median: 5660particlescm−3). The results clearly show that exposure to particulate matter in school is high. The increased PM concentrations in winter and their correlation with high CO2 concentrations indicate that inadequate ventilation plays a major role in the establishment of poor indoor air quality. Additionally, the increased PM concentration in low level classes and in rooms with high number of pupils suggest that the physical activity of pupils, which is assumed to be more pronounced in younger children, contributes to a constant process of resuspension of sedimented particles. Further investigations are necessary to increase knowledge on predictors of PM concentration, to assess the toxic potential of indoor particles and to develop and test strategies how to ensure improved indoor air quality in schools. [Copyright &y& Elsevier]

Abstract: Long-term air quality measurements from a roadside monitoring site of the Swiss national air pollution-monitoring network (NABEL) are analysed for average real-world road traffic emission factors (EFs) by evaluation of concentration differences under upwind and downwind conditions. Time series of relative EFs for NO x , NO, NO2, CO, SO2, number of fine particles, and elemental carbon (EC) are estimated for the total vehicle fleet and converted into absolute EFs by scaling them with emission factors from an emission model [HBEFA, 2004. Handbuch für Emissionsfaktoren des Strassenverkehrs (handbook of emission factors for road traffic). Umweltbundesamt Berlin, Bundesamt für Umwelt, Wald und Landschaft Bern, Infras AG, Bern (published on CD-ROM, see also www.hbefa.net] for a specific reference year. For NO x , NO, NO2, CO, and SO2 the EFs of the total vehicle fleet decreased during the time period from 1992 to 2004 by 44%, 51%, 5%, 71%, and 55%, respectively. The much smaller negative trend of NO2 compared to NO x indicates that the NO2/NO x road traffic emissions ratio increased during this period (from 14% in 1992 to 23% in 2004). It is shown that this trend is caused by increasing primary NO2 road traffic emissions rather than by increasing secondary NO2 formation via reaction of NO with O3. Data for total particle number concentrations and EC are only available since the year 2004. For 2004, the estimated average emission of total particles with diameter larger than 7nm is 7.9×1014 km−1 veh−1, for EC an average emission factor of 21mgkm−1 veh−1 is obtained. [Copyright &y& Elsevier]

Abstract: Number and mass concentrations of atmospheric particles were measured at a surface site on the southwestern Japan coast from March to May 2002. Particles were collected when Asian dust appeared at the site in this period, and later characterized with their morphology and elemental composition from electron microscopic analysis. The mass concentration of suspended particulate matters with diameter smaller than 10μm (SPM10) during dust episodes was predominated by particles larger than 1.0μm (coarse particles), which were mainly mineral dust with a small fraction of sea salt. As dust-loading low-pressure systems were approaching, SPM10 and the number concentration of coarse particles decreased gradually until the arrival of cold fronts. After that, they increased due to dust arrival except during rainfall. Time series of the number concentration of coarse particles during dust plume passages was not in parallel with that of accumulation mode particles in the range of 0.1–0.3μm and they were even inverse in some episodes, reflecting a horizontal structure with multiple intervals of dust and secondary particles. The electron microscopic analysis confirmed the frequent mixture of sea salt in dust particles and suggested that the probability for dust particles to become mixtures with sea salt was likely dependent on the vertical thermodynamic structure of the marine boundary layer, through which aloft dust particles descended to the ground. More mineral dust particles mixed with sea salt in cases with deep mixing layers than with shallow mixing layers. No correlation between the mixture degree and the transport time for dust particles to travel in the marine atmosphere from the Asian continent to southwestern Japan was found. [Copyright &y& Elsevier]

Abstract: From 1 May to 25 May 2001, the BAB II campaign was carried out at the motorway BAB (656) near Heidelberg. Atmospheric concentrations of particulate matter and gases were measured together with the meteorological conditions. This paper is focused on the particulate matter measured upwind and downwind from the motorway at ground level. In order to determine the source contribution from the motorway traffic, it was necessary to measure upwind and downwind simultaneously due to variations in background concentrations. The particle number contribution from the motorway was found to be 35,000 particlescm−3 for particles with diameters close to 20nm and 5000 particlescm−3 for particles with diameters close to 70nm. Bimodal size distributions were observed on the downwind side, whereas the upwind side showed unimodal size distributions. For particulate mass, it can be estimated that the contribution from the motorway to the PM1 concentrations is in a range 0.6–1.3μgm−3 for the chosen measurement sites approximately 60m from the road at a height of 6m. The soot measurements showed diurnal variation; however, the upwind downwind difference was not measured. Correlation factors showed good correlation between total particle number and number of particles with diameters below 80nm, CO and NO. There was no correlation between particle number and PM10, which is due to the observation that particle number was dominated by the 20nm particles. [Copyright &y& Elsevier]

Abstract: Fine particulate matter (PM2.5) and particle number concentrations were monitored in the Helsinki subway system during a two-weeks’ measurement campaign in March 2004. The PM2.5 samples was analysed for elemental composition and carbon fraction. The average daytime PM2.5 concentrations were 47 (±4) and 60 (±18)μgm−3 at the two underground subway stations and 19 (±6) and 21 (±4)μgm−3 at a ground level station and in subway cars, respectively. For the same measurement period, the corresponding PM2.5 concentrations at the urban background and street canyon monitoring sites were 10 (±7) and 17 (±10)μgm−3. The particle number (D&#60;500nm) concentrations and size distributions at the underground subway station were very similar to those measured at the urban background monitoring site indicating that the source of particles of this size is street traffic. The average daytime particle number concentration was 31000 (±14000)particlescm−3 compared to 27000 (±17000)particlescm−3 at an urban background monitoring site (D&#60;320nm). The average daytime black carbon concentration was 6.3 (±1.8)μgm−3, the concentration of elemental carbon 4.0 (±2.0) and organic carbon 7.4 (±1.6)μgm−3. The most enriched element in PM2.5 samples was iron, the concentration of which ranged from 0.7 (±0.3)μgm−3 at the ground level subway station to 29 (±7)μgm−3 at the underground subway station. Other enriched elements included Mn, Cr, Ni, and Cu. We calculated that 30min commuting +9min stay at the stations per day increased the exposure to PM2.5 mass by only approximately 3% compared to staying in urban traffic environment, but the exposure to iron in PM2.5 increased nearly 200%, to Mn 60%, and to Cu 40%. [Copyright &y& Elsevier]

Abstract: A mobile laboratory equipped with gas analysers, a particle number counter and a scanning mobility particle sizer was employed to measure the exhaust particle size distributions of a diesel Euro III passenger car, chasing its exhaust plume on a high-speed track at 50, 100 and 120kmh−1. Emissions from the same vehicle were also measured in the laboratory under the same driving conditions, using a partial flow sampling system with constant sampling conditions. The vehicle was equipped with an oxidation catalyst and was operated on diesel fuel with 280ppmwt. sulphur content. Similar results for the exhaust aerosol behaviour were found in both sampling environments, despite the different dilution ratio, sampling temperature and residence time of the aerosol in dilute conditions. A relatively constant soot particle mode was formed in all cases and, in addition, a nucleation mode started to form at 100kmh−1 and became more stable at 120kmh−1. No nucleation mode was observed at 50kmh−1 road load. The similar behaviour of nucleation mode particles both in the chasing and the laboratory tests indicated that such small volatile particles are a true vehicle emission component and not a dilution artefact. Additional measurements in the laboratory with varying engine load revealed that the nucleation mode formation is sensitive to exhaust gas temperature and its occurrence in increased temperature is repeatable and stable for long sampling times. The findings of this study indicate that nucleation mode particles are an actual emission component of diesel passenger cars and they need to be considered in relevant exhaust aerosol characterization studies. [Copyright &y& Elsevier]

The monitoring data for the PM mass fractions of PM1, PM2.5, PM10 and TSP as well as the particle number concentrations at four sites in Austria (3 urban and 1 rural) and over a 1 year period are presented within this paper. The mass concentrations discussed are mostly based on TEOM measurements, but beta absorption and HiVol gravimetric sampling has been used in parallel. The data are compared with other European and world wide information available so far—for PM1 the data base still is very poor. Generally the data fit into the Central European context as far as the long-term averages and the daily and seasonal pattern and the ratios between the various fractions are concerned. Annual means of mass concentrations for PM1, PM2.5 and PM10 are in the order of 16, 20 and 28 μg m−3 at the urban sites and a little bit lower at the rural site. In average PM1 counted for about 50–60% and PM2.5 for about 70% of PM10.The number concentrations at the urban sites are in the upper European level and show a distinct seasonal cycle. At the rural site no seasonal influence can be seen. [Copyright &y& Elsevier]

AUPHEP was started in 1999 as a 5 years program to investigate the situation of the atmospheric aerosol with respect to effects on human health. At four different sites in Austria (3 urban and one rural site) an extended monitoring program was conducted for PM1, PM2.5 and PM10 as well as particle number concentration for 12 months each. Beside continuous measurements using TEOM and beta attenuation high-volume sampling of PM2.5 and PM10 provided samples for chemical analyses of various ions, heavy metals and organic compounds. Furthermore, carbonaceous material (TC, EC, OC) year round and PAHs on selected days were analyzed. From collocated public monitoring stations also pollutant gases (SO2, NO, NO2, O3, CO) and meteorological components are available. In winter and summer campaigns aerosol size spectra including chemical components were measured for at least one week each. All data are collected in a project data base (CD-ROM).While extensive data analysis will be presented in following papers, some general results are presented within this paper: annual averages for PM1 are between 10 and 20 μg m−3, for PM2.5 between 15 and 26 mg m−3 and for PM10 between 20 and 38 μg m−3. Number concentrations are between 10,000 and 30,000 cm−3. Urban concentrations are usually higher in winter, rural concentrations in summer. PM2.5 is in average around 70% of PM10, for PM1 this fraction is about 57%.Several studies on health effects are included in this project: a cross-sectional study on preschool and school children regarding lung function measurements and questionnaires about respiratory impairment in the surrounding area of the monitoring sites as well as time series studies on mortality and respiratory morbidity on the general population. [Copyright &y& Elsevier]

Typical classification schemes for large data sets of single-particle mass spectra involve statistical or neural network analysis. In this work, a new approach is evaluated in which particle spectra are pre-selected on the basis of an above threshold signal intensity at a specified m/z (mass to charge ratio). This provides a simple way to identify candidate particles that may contain the specific chemical component associated with that m/z. Once selected, the candidate particle spectra are then classified by the fast adaptive resonance algorithm, ART 2-a, to confirm the presence of the targeted component in the particle and to study the intra-particle associations with other chemical components. This approach is used to characterize metals in a 75,000 particle data set obtained in Baltimore, Maryland. Particles containing a specific metal are identified and then used to determine the size distribution, number concentration, time/wind dependencies and intra-particle correlations with other metals. Four representative elements are considered in this study: vanadium, iron, arsenic and lead. Number concentrations of ambient particles containing these elements can exceed 10,000 particles cm-3 at the measurement site. Vanadium, a primary marker for fuel oil combustion, is observed from all wind directions during this time period. Iron and lead are observed from the east–northeast. Most particles from this direction that contain iron also contain lead and most particles that contain lead also contain iron, suggesting a common emission source for the two. Arsenic and lead are observed from the south–southeast. Particles from this direction contain either arsenic or lead but rarely both, suggesting different sources for each element. [Copyright &y& Elsevier]

Diurnal variation of indoor submicrometer (0.007–0.808 μm) particle number and particle mass (approximation of PM2.5) concentrations was investigated in 15 houses in a residential suburb of Brisbane during winter in 1999. Continuous monitoring for more than 48 h was conducted using a condensation particle counter (CPC) and a photometer (DustTrak) in the kitchen of each house, and the residents kept diaries of the activities conducted. In addition, data from a central monitoring station was used to investigate indoor/outdoor relationships. The results show that there were clear diurnal variations in both particle number and approximation of PM2.5 concentrations, for all the investigated houses. The pattern of diurnal variations varied from house to house, however, there was always a close relationship between the concentration and human indoor activities. The average number and mass concentrations during indoor activities were (18.2±3.9)×103 particles cm−3 and (15.5±7.9) μg m−3, respectively, and under non-activity conditions, (12.4±2.7)×103 particles cm−3 (11.1±2.6)±μg m−3, respectively. In general, there was a poor correlation between mass and number concentrations and the correlation coefficients were highly variable from day to day and from house to house. This implies that conclusions cannot be drawn about either one of the number or mass concentration characteristics of indoor particles, based on measurement of the other. The study also showed that it is unlikely that particle concentrations indoors could be represented by measurements conducted at a fixed monitoring station due to the large impact of indoor and local sources. [Copyright &y& Elsevier]