Nanoparticle emissions on Minnesota highways

The objective of this project was to characterize on-road aerosol on highways surrounding the Minneapolis area. Data were collected under varying on-road traffic conditions and in residential areas to determine the impact of highway traffic on air quality. The study was focused on determining on-road nanoparticle concentrations, and estimating fuel-specific and particle emissions km⁻¹.On-road aerosol number concentrations ranged from 10⁴ to 10⁶ particles cm⁻³. The highest nanoparticle concentrations were associated with high-speed traffic. At high vehicular speeds engine load, exhaust temperature, and exhaust flow all increase resulting in higher emissions. Less variation was observed in particle volume, a surrogate measure of particle mass. Most of the particles added by the on-road fleet were below 50 nm in diameter. Particles in this size range may dominate particle number, but contribute little to particle volume or mass. Furthermore, particle number is strongly influenced by nucleation and coagulation, which have little or no effect on particle volume. Measurements made in heavy traffic, speeds<32 km h⁻¹, produced lower number concentrations and larger particles.Number concentrations measured in residential areas, 10–20 m from the highway, were considerably lower than on-road concentrations, but the size distributions were similar to on-road aerosol with high concentrations of very small (<20 nm) particles. Much lower number concentrations and larger particles were observed in residential areas located 500–700 m from the highway.Estimated emissions of total particle number larger than 3 nm ranged from 1.9 to 9.9×10¹⁴ particles km⁻¹ and 2.2–11×10¹⁵ particles (kg fuel)⁻¹ for a gasoline-dominated vehicle fleet.     

Deposition rates on smooth surfaces and coagulation of aerosol particles inside a test chamber

Because aerosol particle deposition is an important factor in indoor air quality, many empirical and theoretical studies have attempted to understand the process. In this study, we estimated the deposition rate of aerosol particles on smooth aluminum surfaces inside a test chamber. We investigated the influence of turbulent intensity due to ventilation and fan operation. We also investigated two important processes in particle deposition: turbophoresis, which is significant for micron particles, and coagulation, which is relevant to ultrafine particles (UFP diameter <0.1 μm) at high particle concentrations. Our analysis included semi-empirical estimates of the deposition rates that were compared to available deposition models and verified with simulations of an aerosol dynamics model. In agreement with previous studies, this study found that induced turbulent intensity greatly enhanced deposition rates of fine particles (FP diameter <1 μm). The deposition rate of FP was proportional to the ventilation rate, and it increased monotonically with fan speed. With our setup, turbophoresis was very important for coarse particles larger than 5 μm. The coagulation of aerosol particles was insignificant when the particle concentration was less than 10⁴ cm^?3 during fan operation. The model simulation results verified that the aerosol dynamics module incorporated in our Multi-Compartment and Size-Resolved Indoor Aerosol Model (MC-SIAM) was valid. The behavior of aerosol particles inside our chamber was similar to that found in real-life conditions with the same ventilation rates (0.018–0.39 h^?1) and similar air mixing modes. Therefore, our findings provide insight into indoor particle behavior.     

A mobile pollutant measurement laboratory—measuring gas phase and aerosol ambient concentrations with high spatial and temporal resolution

A mobile pollutant measurement laboratory was designed and built at the Paul Scherrer Institute (Switzerland) for the measurement of on-road ambient concentrations of a large set of trace gases and aerosol parameters with high time resolution (<15 s for most instruments), along with geographical and meteorological information. This approach allowed for pollutant level measurements both near traffic (e.g. in urban areas or on freeways/main roads) and at rural locations far away from traffic, within short periods of time and at different times of day and year. Such measurements were performed on a regular base during the project year of gas phase and aerosol measurements (YOGAM). This paper presents data measured in the Zürich (Switzerland) area on a late autumn day (6 November) in 2001. The local urban particle background easily reached 50 000 cm⁻³, with additional peak particle number concentrations of up to 400 000 cm⁻³. The regional background of the total particle number concentration was not found to significantly correlate with the distance to traffic and anthropogenic emissions of carbon monoxide and nitrogen oxides. On the other hand, this correlation was significant for the number concentration of particles in the size range 50–150 nm, indicating that the particle number concentration in this size range is a better traffic indicator than the total number concentration. Particle number size distribution measurements showed that daytime urban ambient air is dominated by high number concentrations of ultrafine particles (nanoparticles) with diameters <50 nm, which are immediately formed by traffic exhaust and thus belong to the primary emissions. However, significant variation of the nanoparticle mode was also observed in number size distributions measured in rural areas both at daytime and nighttime, suggesting that nanoparticles are not exclusively formed by primary traffic emissions. While urban daytime total number concentrations were increased by a factor of 10 compared to the nighttime background, corresponding factors for total surface area and total volume concentrations were 2 and 1.5, respectively.     

Dilution and aerosol dynamics within a diesel car exhaust plume—CFD simulations of on-road measurement conditions

Vehicle particle emissions are studied extensively because of their health effects, contribution to ambient PM levels and possible impact on climate. The aim of this work was to obtain a better understanding of secondary particle formation and growth in a diluting vehicle exhaust plume using 3-d information of simulations together with measurements. Detailed coupled computational fluid dynamics (CFD) and aerosol dynamics simulations have been conducted for H₂SO₄–H₂O and soot particles based on measurements within a vehicle exhaust plume under real conditions on public roads.Turbulent diffusion of soot and nucleation particles is responsible for the measured decrease of number concentrations within the diesel car exhaust plume and decreases coagulation rates. Particle size distribution measurements at 0.45 and 0.9 m distance to the tailpipe indicate a consistent soot mode (particle diameter D_p∼50 nm) at variable operating conditions. Soot mode number concentrations reached up to 10¹³ m⁻³ depending on operating conditions and mixing.For nucleation particles the simulations showed a strong sensitivity to the spatial dilution pattern, related cooling and exhaust H₂SO_4(g). The highest simulated nucleation rates were about 0.05–0.1 m from the axis of the plume. The simulated particle number concentration pattern is in approximate accordance with measured concentrations, along the jet centreline and 0.45 and 0.9 m from the tailpipe. Although the test car was run with ultralow sulphur fuel, high nucleation particle (D_p⩽15 nm) concentrations (>10¹³ m⁻³) were measured under driving conditions of strong acceleration or the combination of high vehicle speed (>140 km h⁻¹) and high engine rotational speed (>3800 revolutions per minute (rpm)).Strong mixing and cooling caused rapid nucleation immediately behind the tailpipe, so that the highest particle number concentrations were recorded at a distance, x=0.45 m behind the tailpipe. The simulated growth of H₂SO₄–H₂O nucleation particles was unrealistically low compared with measurements. The possible role of low and semi-volatile organic components on the growth processes is discussed. Simulations for simplified H₂SO₄–H₂O–octane–gasoil aerosol resulted in sufficient growth of nucleation particles.     

Development of particle number size distribution near a major road in Helsinki during an episodic inversion situation

The influence of traffic on urban air quality is highest at low wind speeds and the presence of a temperature inversion. By relying on detailed aerosol measurements conducted simultaneously at two distances close to a major road, we studied one such episode encountered in Helsinki, Finland, during the wintertime. The observed episode was characterized by exceptionally weak dilution of traffic emissions, with particle number concentration decreasing by no more than 10–30% between 9 and 65 m distances from the road. During the nighttime with relatively minor traffic flow, dilution and particle growth by vapor condensation were found to be the dominant processes in this road-to-ambient evolution stage. The latter process shifted a significant fraction of nucleation mode particles to sizes >30 nm diameter, modifying thereby the shape of the particle number size distribution. During the rush hours in the morning, particle number concentrations were elevated by approximately an order of magnitude compared with nighttime, such that also the self-coagulation of nucleation mode particles became important. Our study demonstrates that under suitable meteorological conditions (low wind speeds coupled with temperature inversions), traffic emissions are able to affect submicron particle number concentrations over large areas around major roads and may be a dominant source of ultrafine particles in the urban atmosphere. Under conditions characterized by exceptionally slow mixing, simultaneous processing of ultrafine (nucleation and Aitken mode) particles by dilution, self- and inter-modal coagulation, as well as by condensation and evaporation seriously questions the applicability of particle number emission factors, derived from the measurements at few tens of meters from the roadside.     

Direct measurements and parameterisation of aerosol flux,concentration and emission velocity above a city

Articles have recently been published on aerosol size distributions and number concentrations in cities, however there have been no studies on transport of these particles. Eddy covariance measurements of vertical transport of aerosol in the size range 11 nm<D_p<3 μm are presented here. The analysis shows that typical average aerosol number fluxes in this size range vary between 9000 and 90,000 cm⁻² s⁻¹. With concentrations between 3000 and 20,000 cm⁻³ this leads to estimates of particle emission velocity between 20 and 75 mm s⁻¹. The relationships between number flux and traffic activity, along with emission velocity and boundary layer stability are demonstrated and parameterised. These are used to derive an empirical parameterisation for aerosol concentration in terms of traffic activity and stability. The main processes determining urban aerosol fluxes and concentrations are discussed and quantified where possible. The difficulties in parameterising urban activity are discussed.     

Street level versus rooftop concentrations of submicron aerosol particles and gaseous pollutants in an urban street canyon

Gaseous air pollutants and aerosol particle concentrations were monitored in an urban street canyon for two weeks. The measurements were performed simultaneously at two different heights: at street level (gases 3 m, aerosol particles 1.5 m) and at a rooftop 25 m above the ground. The main objective of the study was to investigate the vertical changes in concentrations of pollutants and the factors leading to the formation of the differences. The physical parameters controlling the concentration gradients (e.g. the flow and micrometeorology) were not directly measured and the conclusions of the study rely mostly on the high time resolution concentration measurements. It was concluded that dilution and dispersion decreases the concentrations of pollutants emitted at street level by a factor of roughly 5 between the two sampling heights. However, for some compounds the chemical reactions were seen to be of more importance when the vertical gradient is formed. In order to determine the processes leading to gradients in aerosol particle concentrations the photochemical formation of submicrometer aerosol particles was investigated using a theoretical expression based on the measured data. It was clearly seen that most of the particles originate from traffic in the vicinity of the measurement site. Also a few events were detected which might have been due to local gas-to-particle conversion.     

Using NOx and CO monitoring data to indicate fine aerosol number concentrations and emission factors in three UK conurbations

It is increasingly accepted that although exposure to elevated concentrations of PM₁₀ is associated with an increased risk of mortality and morbidity, the relationship may not be causal. Rather, there is evidence that number concentrations may be a more appropriate metric than mass concentrations in evaluating health risk. Number concentrations are not routinely monitored and spatial and temporal patterns are poorly quantified. CO and NO_x are co-pollutants with their major urban source in common with fine particles, i.e. road vehicle emissions; are routinely monitored in many cities and are also related to ill health. Datasets of particle number concentration measurements from approximately month-long field campaigns in Manchester, Edinburgh and Birmingham (UK) are compared with simultaneous concentrations of CO and NO_x from nearby fixed monitors. It was found that it might be possible to reliably predict particle number concentrations (diameters>100 nm) on an hourly basis in Manchester city centre from knowledge of NO_x or CO concentrations alone. The influences of meteorology, spatial variability in emissions and lack of co-location upon the correlations are investigated using cluster analysis. The cluster analysis revealed that these relationships may vary between cities and are dependent upon monitor location but in ways that can be ascribed. For two out of three sites there existed a linear relationship between average cluster aerosol and gas concentrations. This indicates that although airmass aging disrupts the short-term linear relationship, the relationship in the average survives. An emission ratio of particles (approx. 100–500 nm diameter) to NO_x of approximately 50 cm⁻³ ppb⁻¹ was estimated in Manchester and Birmingham. Particle mass spectrometry measurements indicated that organic compounds dominated these particles and an emission rate of 0.58 ton km⁻² a⁻¹ of organic particulate matter from road transport has been estimated for the Greater Manchester conurbation.     

The effects of aging processes on critical supersaturation ratios of ultrafine carbon aerosols

The condensation properties of polydisperse aged ultrafine carbon aerosols (particle diameter<1 μm) have been investigated by means of a variable supersaturation condensation nucleus counter. The critical supersaturation (S_c), as the point, where 50% of all particles have been activated and grew to droplets was compared to the median dry particle diameter for pure carbon aerosols, benzo[a]pyrene-tagged carbon aerosols and external mixtures of the carbon particles with sodium chloride and sulphuric acid aerosols. Additionally, ozone as oxidising gaseous compound was added in some of the experiments. Simple coagulation of pure and benzo[a]pyrene-tagged carbon particles resulted in only slightly lower values for S_c due to the increased median particle diameter. The formation of soluble functionalities on the particle surface, i.e. the coagulation with the soluble sodium chloride and sulphuric acid aerosols or the chemical decomposition of benzo[a]pyrene into polar, hydrophilic products due to the reaction with ozone resulted in significant lower values for S_c for the modified carbon aerosol. The necessary supersaturations for the increased hydrophilic particles dropped to atmospherically relevant values of 3% after 5 h reaction time (benzo[a]pyrene decomposition) and 15 h (coagulation with soluble particles), respectively.     

Change of the ambient particle size distribution in East Germany between 1993 and 1999

Size distribution of particle number concentrations in the geometric equivalent diameter range 0.01–2.5 μm were determined in three communities, Zerbst, Bitterfeld and Hettstedt of the state of Sachsen-Anhalt in Eastern Germany, in the first half of 1993 and 1999. A Mobile Aerosol Spectrometer (MAS) consisting of a differential mobility particle spectrometer (DMPS) and a laser aerosol spectrometer (LAS-X) were used for size-selective particle number concentration measurements from which mass concentrations were derived based on an apparent mean density of the ambient aerosol of the closely situated city of Erfurt.The total number concentration was governed by ultra-fine particles (<0.1 μm) (81% in 1993 and 90% in 1999) and 0.1–0.5 μm size fraction dominates total mass concentration (approximately 80%). While the mass concentration of fine particles (PM2.5) decreased from 39 to 19 μg m⁻³, the geometric means of total number concentration showed constant concentration (13.3×10³ cm⁻³ in 1993 and 13.3×10³ cm⁻³ in 1999, p=0.975) and the geometric means of number concentration of ultra-fine particles (UP) between 10 and 30 nm increased from 5.9×10³ to 8.2×10³ cm⁻³ from 1993 to 1999 (p=0.016). The temporal changes of number and mass concentrations in the three communities are similar. The clear shift to smaller particle sizes within this six years period was caused by changes of the most prominent sources, traffic and domestic heating, since formerly dominating industries in Bitterfeld and Hettstedt had vanished grossly.     

Size segregated water uptake of the urban submicrometer aerosol in Beijing

Physical and chemical properties of submicrometer aerosol particles were measured in summer 2004 (June/July) and winter 2005 (January/February) in Beijing, Peoples Republic of China, using a Twin-Differential Mobility Particle Sizer (T-DMPS), a Hygroscopicity-Tandem Differential Mobility Analyzer (H-TDMA), and a Micro Orifice Uniform Deposit Impactor (MOUDI). Particle number–size distributions were measured in the diameter range Dp = 3–800 nm and hygroscopic properties were determined at initial dry particle diameters of Dp_j (j = 30, 50, 80, 150, 250, and 350 nm) at a relative humidity (RH) of 90%. Hygroscopic properties were compared with chemical analyses of aerosol samples taken with the MOUDI. Based on the hygroscopicity data, the total hygroscopic particle volume was modeled, including dependence on dry particle size, season and level of pollution using a simple approach.Overall, the chemical analysis showed ammonium sulfate to be the major inorganic component of the urban submicrometer aerosol in Beijing along with relatively high fractions of elemental carbon (10–25%) and organic matter (15–60%) depending on particle size and season.The hygroscopic growth distributions (H-TDMA) subdivided the aerosol population into three different groups of particles with varying growth factors depending on dry particle size, namely nearly hydrophobic (growth factor = 0.96–1.07), less hygroscopic (1.06–1.29) and more hygroscopic (1.26–1.62).Hydrophobic particle fractions indicating freshly emitted soot/carbonaceous particles varied between 10 and 32% depending on dry particle size and season. During heavily polluted times, a decreasing number of hydrophobic particle fractions indicated that the urban submicrometer aerosol in Beijing was highly influenced by more aged aerosol transported from the industrial regions around Beijing containing sulfate as a major component.Based on model calculations, the urban submicrometer aerosol in Beijing showed strong compositional variations. The calculated total hygroscopic volume fractions varied between 16 and 65% depending on size, level of pollution and season.     

Particulate size distributions and mass measured at a motorway during the BAB II campaign

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 particles cm⁻³ for particles with diameters close to 20 nm and 5000 particles cm⁻³ for particles with diameters close to 70 nm. 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 0.6–1.3 μg m⁻³ for the chosen measurement sites approximately 60 m from the road at a height of 6 m. 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 80 nm, 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 20 nm particles.     

Experimental study of the air pollution transport by synchronised monitoring of atmospheric aerosols

Particulate pollution transport is estimated by means of cross-correlation and regression analyses. The aerosol particle size number spectrum in the form of 12 fraction concentrations is measured in units cm⁻³ (particles per cm³) every 10 minutes during three approximately 20-day measurement campaigns simultaneously in two measurement points in Estonia. The distance between these points is approximately 100 km for two campaigns, and 7 km for the third campaign. Two electrical aerosol spectrometers designed at Tartu University, having a wide particle diameter range (10 nm–10 μm), are used. The spectrometer's record is the mean particle spectrum for the 10 min measurement time. The air pollution transport is investigated during the time intervals when the air mass moves from one measurement point towards the other. The time series of aerosol size fraction concentrations for both locations are prewhitened to eliminate auto-correlation and to achieve stationary series of the ARIMA residuals. Then the cross-correlation function of these two series of residuals is calculated. The time lag corresponding to the mode of this function is treated as the mean time of pollution transport from the windward measurement point to the leeward one. For the submicron aerosol fraction (d=60 nm–1 μm) 3–5 h time lags are found. Mostly these time lags coincide with the mean wind velocities on some of the pressure levels (ground, 850 and 700 hPa) available in the study. In cross-wind cases the fraction concentrations measured in two points separated by 100 km were uncorrelated, but for the two points separated by 7 km there was quite a high correlation with zero time lag. The part of local and distant sources in the formation of the particle concentration in the leeward location is estimated by regression analysis.     

Roadside measurements of fine and ultrafine particles at a major road north of Gothenburg

Particle measurements were conducted at a road site 15 km north of the city of Gothenburg for 3 weeks in June 2000. The size distribution between 10 and 368 nm was measured continuously by using a differential mobility particle sizer (DMPS) system. PM_2.5 was sampled on a daily basis with subsequent elemental analysis using EDXRF-spectroscopy. The road is a straight four-lane road with a speed limit of 90 kph. The road passing the site is flat with no elevations where the vehicles run on a steady workload and with constant speed. The traffic intensity is about 20,000 cars per workday and 13,000 vehicles per day during weekends. The diesel fuel used in Sweden is low in sulphur content (<10 ppm) and therefore the diesel vehicles passing the site contribute less to particle emissions in comparison with other studies. A correlation between PM_2.5 and accumulation mode particles (100–368 nm) was observed. However, no significant correlation was found between number concentrations of ultrafine particles (10–100 nm) and PM_2.5 or the accumulation mode number concentration. The particle distribution between 10 and 368 nm showed great dependency on wind speed and wind direction, where the wind speed was the dominant factor for ultrafine (10–100 nm) particle concentrations. The difference in traffic intensity between workday and weekend together with wind data made it possible to single out the traffic contribution to particle emissions and measure the size distribution. The results presented in combination with previous studies show that both PM_2.5 and the mass of accumulation mode particles are bad estimates for ultrafine particles.     

On radiative effects of black carbon and sulphate aerosols

Most aerosol particles, such as sulphate and sea-salt particles, mainly scatter solar radiation, whilst soot (in the form of elemental carbon or “black” carbon, BC) in addition leads to considerable absorption. This scattering and absorption by the aerosol particles constitute the so-called direct aerosol effect. In this paper, we present results from a study of possible direct effects of tropospheric BC and sulphate aerosols, with an emphasis on BC aerosols, along a line from North Africa through Europe into the Arctic. Radiative budgets in a cloud-free atmosphere are estimated. Based on model-calculated distributions of BC and sulphate (provided by Seland and Iversen, 1998) and assumed size distributions of the background aerosol, new size distributions are obtained by adding natural, biomass burning and fossil fuel contributions to the background aerosol. Added nucleation mode particles are assumed externally mixed, whereas added accumulation mode BC and sulphate is internally mixed with the background according to condensational growth and Brownian coagulation theory. Humidity effects are taken into account by use of the Köhler equation. Mie calculations provide the resulting optical parameters, and the forcing is finally estimated by use of a radiative transfer model. A reference run and a series of eleven test-runs are performed to investigate the sensitivity of various assumptions on the contribution to upward TOA irradiance from BC and non-sea-salt sulphate. The tests suggest a high sensitivity to presence of BC and to particle swelling due to humidity. The sensitivity to assumed distribution of BC on particle size is more moderate. The same is true for the vertical resolution and the number concentration of the background aerosol. The effect of mixing organic carbon (OC) internally with biomass burning BC nucleation mode particles is characterized as moderate. The role of OC is, however, still uncertain. The same holds true for the optical thickness of the background atmosphere, for which we found a high sensitivity in this study. Other assumptions that were investigated had only small effects on the forcing. For the reference run we find a minimum in the aerosol forcing of approximately −5 W m^-2 near the most polluted areas in Europe, and a maximum of approximately 2 W m^-2 over North Africa. A warming effect is also found for the Arctic region, with forcing values up to 0.4 W m^-2.     

Secondary organic aerosol importance in the future atmosphere

In order to investigate the secondary organic aerosol (SOA) response to changes in biogenic volatile organic compounds (VOC) emissions in the future atmosphere and how important will SOA be relative to the major anthropogenic aerosol component (sulfate), the global three-dimensional chemistry/transport model TM3 has been used. Emission estimates of biogenic VOC (BVOC) and anthropogenic gases and particles from the literature for the year 2100 have been adopted.According to our present-day model simulations, isoprene oxidation produces 4.6 Tg SOA yr⁻¹, that is less than half of the 12.2 Tg SOA yr⁻¹ formed by the oxidation of other BVOC. In the future, nitrate radicals and ozone become more important than nowadays, but remain minor oxidants for both isoprene and aromatics. SOA produced by isoprene is estimated to almost triple, whereas the production from other BVOC more than triples. The calculated future SOA burden change, from 0.8 Tg at present to 2.0 Tg in the future, is driven by changes in emissions, oxidant levels and pre-existing particles. The non-linearity in SOA formation and the involved chemical and physical feedbacks prohibit the quantitative attribution of the computed changes to the above-mentioned individual factors. In 2100, SOA burden is calculated to exceed that of sulfate, indicating that SOA might become more important than nowadays. These results critically depend on the biogenic emissions and thus are subject to the high uncertainty associated with these emissions estimated due to the insufficient knowledge on plant response to carbon dioxide changes. Nevertheless, they clearly indicate that the change in oxidants and primary aerosol caused by human activities can contribute as much as the change in BVOC emissions to the increase of the biogenic SOA production in the future atmosphere.     

The impact of biomass burning on the environmental aerosol concentration in Gaborone,Botswana

Biomass burning, in the form of savanna fires and firewood for cooking and warmth, is widespread during the dry winter months in Southern Africa. This study was carried out to investigate its impact on the environment in Gaborone, Botswana, which is a small-sized city with very little pollution from industrial sources. Measurements of aerosol size and number concentrations were carried out at the University of Botswana campus in Gaborone from September 1999 to July 2000 using two automatic laser scattering particle counters. Particles were monitored in eight size ranges from 0.1 to 5.0 μm. The mean daily particle concentrations were found to vary from about 200 cm⁻³ on clear visibility days during the summer to a high of over 9000 cm⁻³ on cold winter evenings, when there was a significant smoke haze over the city. Particle concentrations were noticeably higher during the winter than in the summer. During a typical winter day, the total particle concentration peaked between 18 and 23 h, often showing an increase of over four-fold from mid-morning minimum values. The aerosol number size distributions under various conditions were investigated and the corresponding surface area and volume distributions were derived. In general, both the surface and volume distributions were bimodal with peaks close to 0.2 μm and at 5.0 μm or greater. A hand-held counter with a minimum detectable particle size of 0.3 μm was used to monitor the size and number concentrations of aerosols across the city. The results indicate a consistent pattern of maximum concentration in the highly populated areas close to the city centre, falling significantly in the sparsely populated outlying areas by up to an order of magnitude during peak biomass burning, suggesting that much of the smoke particles in the city are removed by wind.     

Iron,manganese and copper emitted by cargo and passenger trains in Zürich (Switzerland): Size-segregated mass concentrations in ambient air

Particle emissions caused by railway traffic have hardly been investigated in the past, due to their obviously minor influence on air quality compared to automotive traffic. In this study, emissions related to particle abrasion from wheels and tracks were investigated next to a busy railway line in Zürich (Switzerland), where trains run nearly exclusively with electrical locomotives. Hourly size-segregated aerosol samples (0.1–1, 1–2.5 and 2.5–10 μm) were collected with a rotating drum impactor (RDI) and subsequently analyzed by synchrotron radiation X-ray fluorescence spectrometry (SR-XRF). In this way, hourly elemental mass concentrations were obtained for chromium, manganese, iron and copper, which are the elements most relevant for railway abrasion. Additionally, daily aerosol filters were collected at the same site as well as at a background site for subsequent analysis by gravimetry and wavelength dispersive XRF (WD-XRF). Railway related ambient air concentrations of iron and manganese were calculated for the coarse (2.5–10 μm) and fine (<2.5 μm) particle fraction by means of a Mn/Fe ratio investigation. The comparison to train type and frequency data showed that 75% and 60% of the iron and manganese mass concentrations related to cargo and passenger trains, respectively, were found in the coarse mode. The railway related iron mass concentration normalized by the train frequency ranges between 10 and 100 ng m⁻³ h iron in 10 m distance to the tracks, depending on train type. It is estimated that the personal exposure next to a busy railway line above ground is more than a magnitude lower than inside a subway station.     

Identification and assessment of ship emissions and their effects in the harbour of Göteborg,Sweden

The effect of ship emissions in the urban environment of Göteborg has been studied by multivariate analysis. The simultaneous measurements of relevant gases and sub-micron particles make identification of ship plumes possible. Increased concentrations of these species due to ship emissions are quantified for ships entering the inner part of the harbour. Annual depositions of SO₂ and NO₂ are estimated to be 220 and 115 kg km⁻² yr⁻¹, respectively. Exposure of transient particles (less than 0.1 μm in diameter) to this part of the harbour increased by a factor of 3 in number concentration when a ship plume was recorded. Ni, Pb, V and Zn are shown to have positive correlation with NO emissions from ships.     

Measurement of aerosol number size distributions in the Yangtze River delta in China: Formation and growth of particles under polluted conditions

Particle size distribution is important for understanding the sources and effects of atmospheric aerosols. In this paper we present particle number size distributions (10 nm–10 μm) measured at a suburban site in the fast developing Yangtze River Delta (YRD) region (near Shanghai) in summer 2005. The average number concentrations of ultrafine (10–100 nm) particles were 2–3 times higher than those reported in the urban areas of North America and Europe. The number fraction of the ultrafine particles to total particle count was also 20–30% higher. The sharp increases in ultrafine particle number concentrations were frequently observed in late morning, and the particle bursts on 5 of the 12 nucleation event days can be attributed to the homogeneous nucleation leading to new particle formation. The new particle formation events were characterized with a larger number of nucleation-mode particles, larger particle surface area, and larger condensational sink than usually reported in the literature. These suggest an intense production of sulfuric acid from photo-oxidation of sulfur dioxide in the YRD. Overall, the growth rate of newly formed particles was moderate (6.4 ± 1.6 nm h^?1), which was comparable to that reported in the literature.