Chemical characteristics of free tropospheric aerosols over the Japan Sea coast: aircraft-borne measurements

Atmospheric aerosol particulate matter was directly collected in the free troposphere over the Japan Sea coast between 1992 and 1994 using an aircraft-borne nine-stage cascade impactor (particle size range: 0.1–8 μm). The water-soluble components in the aerosol particulate matter were analyzed by ion chromatography. Particulate sulfate and ammonium were detected in most of the samples and their size distributions showed noticeable peaks below the 1 μm particle size range. Water-soluble calcium (Ca²⁺) was detected in half of the samples; the size distribution showed that the maximum particle size was larger than 1 μm. Highly concentrated Ca²⁺ in larger particles was possibly due to transport of Kosa aerosols from the Asian continent in the free troposphere. The concentration of fine particulate sulfate and ammonium tended to increase whenever Ca²⁺ was detected, which suggests possible mixing of Kosa aerosols and non-Kosa aerosols during long-range transport of air masses containing Kosa particles.     

Sources and concentrations of gaseous and particulate reduced nitrogen in the city of Münster (Germany)

Atmospheric ammonia mixing ratios and the main inorganic ions NH₄⁺, NO₃⁻ and SO₄²⁻ of size-resolved particles in the range from 0.05 to 10 μm were measured at an urban site in Münster, Germany. High mixing ratios of ammonia with a median of 5.2 ppb and a maximum of 50 ppb were detected. The mass fraction of submicron particles was much higher during the day than at night. At night, a greater particle mass and an increased presence of particulate nitrate was measured. Recurring patterns of particle distribution were distinguished and their characteristics analysed. In half of the measurements, the accumulation mode was clearly dominating, which is an indication of aged aerosol. In some measurements, higher concentrations of fine particles were found indicating particle formation. In these cases, a smaller particle mass and about four times greater ratios of ammonia versus ammonium concentrations were observed. These data show that ammonia contributes considerably to the formation of secondary particulate material.     

Mixing properties of individual submicrometer aerosol particles in Vienna

Individual aerosol particles were collected on 5 days with different meteorological conditions in March, April and June 1991 in the urban atmosphere of Vienna in Austria. The samples collected with an impactor were examined by electron microscopy. The mixing properties of submicrometer aerosol particles with radii between 0.1 and 1 μm were studied by using the dialysis (extraction) of water-soluble material. The averaged results showed that more than 85% of particles with radii between 0.1 and 0.7 μm were hygroscopic. However, more than 50% of particles with radii larger than 0.2 μm were mixed particles (hygroscopic particles with water-insoluble inclusions), and they were dominant (80%) in the size range 0.5–0.7 μm radius. The results also showed that the number proportion of mixed particles increased with increasing radius and the abundance increased with increasing particle loading in the atmosphere. The volume fraction of water-soluble material (ε) in mixed particles tended to decrease with increasing radius, implying the formation of mixed particles by heterogeneous processes such as condensation and/or surface reaction. Some results of elemental composition in individual particles analyzed with an energy-dispersive X-ray (EDX) analyzer equipped with an electron microscope are also presented in this paper.     

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.     

On the relation between the size and chemical composition of aerosol particles and their optical properties

The light scattering and absorption coefficients of fine atmospheric aerosol particles were recorded in Hungary under rural conditions in 1998–1999 by an integrating nephelometer and particle soot absorption photometer, respectively. In some cases optical properties in the fine size range were compared to those in the coarse particles. Results obtained indicate, as expected, that fine particles control the scattering and absorption caused by the aerosol. In 1999 the size distribution of aerosol particles was also monitored by means of an electric low pressure impactor (ELPI). This makes it possible the study of the relationship between the number, surface and mass concentration in the size range of 0.1–1.0 μm and the optical characteristics by also considering the chemical composition of the particles.     

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.     

Dust characteristics over the North Pacific observed through shipboard measurements during the ACE-Asia experiment

To examine the diversity of chemical and physical properties of aerosol particles, in particular dust, over the North Pacific, aerosols were collected along ∼32°N latitude between 140°E and 170°W longitude aboard the NOAA R/V Ronald H. Brown during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in the spring 2001. A total of 11,482 aerosol particles were examined through individual-particle analysis. Results indicate that dust particles over this region were dominated primarily by Si-rich particles, including aluminosilicates that contain Fe. Fe is also present as separate Fe-rich particles. Additional common particle types include Ca- and S-rich particles; many of the later appear to represent soil-derived calcium carbonate and its reaction products whereas the former are predominantly reaction products of sea salt and sulfate. Particles are often aggregates of different types including pollution-derived substances and highly heterogeneous, both internally and externally. Dust particles are non-spherical, having circularities from 1.0 up to 4.5, suggesting the high degree of complexity of particle shape. The majority of dust particles were dominated by particles with median diameters from 0.67 to 1.26 μm. However, dust particles with diameters of 5 μm or even larger do exist associated with those events of dust originated from Asian desert areas. The existence of soot and Fe-rich particles over this region indicates the influence of fossil fuel sources in Asia. Aerosol Fe from both Asian desert and fossil fuel combustion may contribute to the nutrient Fe in the surface waters of the North Pacific basin. Therefore, the transport of Asian dust associated with species of fossil fuel burning in the spring may play an important role in altering the natural composition of aerosols over the North Pacific.     

Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol

A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas–aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon–nitrogen oxide (HC/NO_x) mixtures irradiated in the presence of fine (<2.5 μm) particulate matter. The goal was to determine to what extent photochemical oxidation products of aromatic hydrocarbons contribute to secondary organic aerosol formation through uptake on pre-existing inorganic aerosols in the absence of liquid water films. Irradiations were conducted with toluene, p-xylene, and 1,3,5-trimethylbenzene in the presence of NO_x and ammonium sulfate aerosol, with propylene added to enhance the production of radicals in the system. The secondary organic aerosol yields were determined by dividing the mass concentration of organic fraction of the aerosol collected on quartz filters by the mass concentration of the aromatic hydrocarbon removed by reaction. The mass concentration of the organic fraction was obtained by multiplying the measured organic carbon concentration by 2.0, a correction factor that takes into account the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. The mass concentrations of ammonium, nitrate, and sulfate concentrations as well as the total mass of the aerosols were measured. A reasonable mass balance was found for each of the aerosols. The largest secondary organic aerosol yield of 1.59±0.40% was found for toluene at an organic aerosol concentration of 8.2 μm⁻³, followed by 1.09±0.27% for p-xylene at 6.4 μg m⁻³, and 0.41±0.10% for 1,3,5-trimethylbenzene at 2.0 μg m⁻³. In general, these results agree with those reported by Odum et al. and appear to be consistent with the gas–aerosol partitioning theory developed by Pankow. The presence of organic in the aerosol did not affect significantly the hygroscopic properties of the aerosol.     

Mixing properties of submicrometer aerosol particles in the urban atmosphere—with regard to soot particles

Individual aerosol particles were collected on three days with different meteorological conditions in June 2000 in the urban atmosphere of Tsukuba, Japan. The samples collected with an electrostatic aerosol sampler (EAS) were examined by electron microscopy. The mixing properties of submicrometer aerosol particles of 0.02–0.2 μm radius were studied using the dialysis (extraction) of water-soluble material. Atmospheric aerosol particles were classified into four types with respect to the mixtures of water-soluble and water-insoluble material. The proportions of particles with water-soluble material (hygroscopic particles) ranged from 20% to 80% in the whole radius range and tended to increase with increasing radius. Moreover, by the morphological appearance, soot-containing particles were classified into two types, i.e., externally mixed soot-particles and internally mixed soot-particles. The number fractions of internally mixed soot-particles increased with increasing radius. It is found that the volume fraction of water-soluble material (ε) for the internally mixed soot-particles increased with increasing radius. In a “polluted” case, the sample showed a dominant number fraction (75%) of internally mixed soot-particles in the larger radius range of 0.1–0.2 μm.     

Seasonal characteristics of water-soluble organic carbon in atmospheric particles in the inland Kanto plain,Japan

An investigation of water-soluble organic carbon (WSOC) in atmospheric particles was conducted as an index of the formation of secondary organic aerosol (SOA) from April 2005 to March 2006 at Maebashi and Akagi located in the inland Kanto plain in Japan. Fine (<2.1 μm) and coarse (2.1–11 μm) particles were collected by using an Andersen low-volume air sampler, and WSOC, organic carbon (OC), elemental carbon (EC), and ionic components were measured. The mean mass concentrations of the fine particles were 22.2 and 10.5 μg m^?3 at Maebashi and Akagi, respectively. The WSOC in fine particles accounted for a large proportion (83%) of total WSOC. The concentration of fine WSOC ranged from 1.2 to 3.5 μg-C m^?3 at Maebashi, rising from summer to fall. At Akagi, it rose from spring to summer, associated with the southerly wind from urban areas. The WSOC/OC ratio increased in summer at both sites, but the ratio at Akagi was higher, which we attributed to differences in primary emissions and secondary formation between the sites. The fine WSOC concentration was significantly positively correlated with concentrations of SO₄^2?, EC, and K⁺, and we inferred that WSOC was produced by photochemical reaction and caused by the combustion of both fuel and biomass. We estimated that SOA accounted for 11–30% of the fine particle mass concentration in this study, suggesting that SOA is a significant year-round component in fine particles.     

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.     

Internally mixed sea salt, soot, and sulfates at Macao, a coastal city in South China

Direct observation of the mixing state of aerosol particles in a coastal urban city is critical to understand atmospheric processing and hygroscopic growth in humid air. Morphology, composition, and mixing state of individual aerosol particles from Macao, located south of the Pearl River Delta (PRD) and 100 km west of Hong Kong, were investigated using scanning electron microscopy (SEM) and transmission electron microscopy coupled with energy-dispersive X-ray spectrometry (TEM/EDX). SEM images show that soot and roughly spherical particles are prevalent in the samples. Based on the compositions of individual aerosol particles, aerosol particles with roughly spherical shape are classified into coarse Na-rich and fine S-rich particles. TEM/EDX indicates that each Na-rich particle consists of a Na-S core and NaNO3 shell. Even in the absence of heavy pollution, the marine sea salt particles were completely depleted in chloride, and Na-related sulfates and nitrates were enriched in Macao air. The reason could be that SO2 from the polluted PRD and ships in the South China Sea and NO2 from vehicles in the city sped up the chlorine depletion in sea salt through heterogeneous reactions. Fresh soot particles from vehicular emissions mainly occur near curbside. However, there are many aged soot particles in the sampling site surrounded by main roads 200 to 400 m away, suggesting that the fresh soot likely underwent a quick aging. Overall, secondary nitrates and sulfates internally mixed with soot and sea salt particles can totally change their surface hygroscopicity in coastal cities.     

Physicochemical characterisation of diesel exhaust particles: Factors for assessing biological activity

A range of microscopy and analytical techniques have been used to investigate the physicochemical properties of diluted DEP that may be important in determining its biological activity. Transmission electron microscopy demonstrated four basic categories of particle morphology: (1) “spherulites” [individual particles]; (2) “chains” or “clusters” of spherulites; (3) “spherules”, [large bodies of spherulites]; (4) “flake-like bodies”. Image analysis of TEM photomicrographs determined empirical morphological parameters (30 nm mean spherulite diameter, aspect ratio 1.5, mean particle area 0.078 μm, equivalent spherical diameter 0.23 μm, roundness 2.76) and derived parameters (0.313 μm² surface area, 3.7 μm² pg surface area per mass and 0.042 μm³ volume) of DEP. Distributions of the particle sizes by number showed 10.1% were ultrafine (<0.1 μm), 89.5% fine (0.1–2.0 μm), 0.4% coarse (>2.5 μm), but distributions based on a mass value were different (0.01% ultrafine; 52.6% fine, 47.4% coarse). In contrast, impacted DEP contained 60.87% ultrafine, 39.13% fine and 0% coarse particles by number. Field emission scanning electron microscopy of spherulites revealed smooth surfaces and flocculated spherules with large surface areas. Electron probe X-ray micro-analysis demonstrated the presence of C, O, Na, Mg, K, Al, Si, P, S, Cl, Ca along with a range of metals (Ti, Mn, Fe, Zn, Cr), that were heterogeneous in distribution. Inductively coupled plasma mass and atomic emission spectrometry identified Mg, P, Ca, Cr, Mn, Zn, Sr, Mo, Ba, Na, Fe, S, and Si as the mobile sorbed metals readily removed during sonication in water from DEP suspensions. X-ray Diffraction confirmed previous observations of the presence of nanometer sized crystallites of disordered graphite. Comparison of microscopy and analytical results between sonicated and impacted DEP revealed a physicochemical difference that must be taken into account in any toxicological investigations.     

Carbon content of atmospheric aerosols in a residential area during the wood combustion season in Sweden

Carbonaceous aerosol particles were observed in a residential area with wood combustion during wintertime in Northern Sweden. Filter samples were analyzed for elemental carbon (EC) and organic carbon (OC) content by using a thermo-optical transmittance method. The light-absorbing carbon (LAC) content was determined by employing a commercial Aethalometer and a custom-built particle soot absorption photometer. Filter samples were used to convert the optical signals to LAC mass concentrations. Additional total PM₁₀ mass concentrations and meteorological parameters were measured. The mean and standard deviation mass concentrations were 4.4±3.6 μg m⁻³ for OC, and 1.4±1.2 μg m⁻³ for EC. On average, EC accounted for 10.7% of the total PM₁₀ and the contribution of OC to the total PM₁₀ was 35.4%. Aethalometer and custom-built PSAP measurements were highly correlated (R²=0.92). The hourly mean value of LAC mass concentration was 1.76 μg m⁻³ (median 0.88 μg m⁻³) for the winter 2005–2006. This study shows that the custom-built PSAP is a reliable alternative for the commercial Aethalometer with the advantage of being a low-cost instrument.     

Particle volatility in the vicinity of a freeway with heavy-duty diesel traffic

During February–March 2006, a major field sampling campaign was conducted adjacent to the Interstate 710 (I-710) freeway in Los Angeles, CA. I-710 has high traffic volumes (ca. 11,000 vehicles h⁻¹) and a high percentage (17–18%) of heavy-duty diesel vehicle (HDDV) traffic. The volatility of ambient particles of 20, 40, 80 and 120 nm in diameter was investigated using a Tandem Differential Mobility Analyzer (TDMA) at two locations—close to the freeway (10 m) and approximately 150 m downwind. The smallest particles (20 nm) are largely volatile at both locations. Larger particles, e.g., ⩾40 nm) showed evidence of external mixing, with the non-volatile fraction increasing with particle size. Particle volatility increased with decreasing ambient temperature. The HDDVs contribute to relatively larger non-volatile particle number and volume fractions and greater external mixing than earlier observations at a pure light-duty gasoline vehicle freeway [Kuhn et al., 2005c. Atmospheric Environment 39, 7154–7166]. Finally, the fraction of externally mixed soot particles decreased as the downwind distance increased from the I-710, due to atmospheric processes such as vapor adsorption and condensation as well as particle coagulation.     

Carbonaceous aerosol in jet engine exhaust: emission characteristics and implications for heterogeneous chemical reactions

Characteristic parameters of black carbon aerosol (BC) emitted from jet engine were measured during ground tests and in-flight behind the same aircraft. Size distribution features were a primary BC mode at a modal diameter D≈0.045 μm, and a BC agglomeration mode at D<0.2 μm. The total BC number concentration at the engine exit was 2.9×10⁷ cm^-3 with good agreement between model results and in-flight measured number concentrations of non-volatile particles with D⩾0.014 μm. A comparison between total number concentration of BC particles and the non-volatile fraction of the total aerosol at the exit plane suggests that the non-volatile fraction of jet engine exhaust aerosol consists almost completely of BC. In-flight BC mass emission indices ranged from 0.11 to 0.15 g BC (kg fuel)^-1. The measured in-flight particle emission value was 1.75±0.15×10¹⁵ kg^-1 with corresponding ground test values of 1.0–8.7×10¹⁴ kg^-1. Both size distribution properties and mass emission indices can be scaled from ground test to in-flight conditions. Implications for atmospheric BC loading, BC and cirrus interaction and the potential of BC for perturbation of atmospheric chemistry are briefly outlined.     

Chemical composition and complex refractive index of Saharan Mineral Dust at Izaña,Tenerife (Spain) derived by electron microscopy

Samples from two strong homogeneous dust plumes from the Saharan desert reaching Izaña (Tenerife, Spain) in July and August 2005 were taken with a miniature impactor system and filter samplers. Size, aspect ratio and chemical composition of more than 22,000 individual particles were studied by scanning electron microscopy. The mineralogical phase composition of about 200 particles was investigated by transmission electron microscopy. In addition, the aerosol size distribution was measured with an optical particle spectrometer. In all samples, the aerosol was dominated by mineral dust with an average composition (by volume) of 64% silicates, 6% quartz, 5% calcium-rich particles, 14% sulfates, 1% hematite, 1% soot and 9% other carbonaceous material. Sulfate was found predominantly as coating on other particles with an average thickness of approximately 60 nm. The aerosol calcium content is correlated with the calcite concentrations of soils in the source region, highest values were observed for northern and central Algeria and Morocco. The average aspect ratio of the particles was 1.64. The distributions of the aspect ratios are parameterized by log-normal functions for modeling purpose. Single-scattering albedo (0.95) and asymmetry factor (0.74–0.81) was measured by polar aerosol photometry on filter samples using a light source resembling the solar spectrum. The apparent soot content of the sample (1 vol%) was determined by the same technique. From the mineralogical data, an average complex refractive index of 1.59–9×10⁻³i for visible light was derived. The imaginary part of the complex refractive index decreases with increasing particle size from −2.5×10⁻²i to <−10⁻³i, reflecting the decreasing hematite and soot contents. The imaginary part derived from optical measurements was −7×10⁻³i.     

Size-resolved,real-time measurement of water-insoluble aerosols in metropolitan Atlanta during the summer of 2004

During the month of August 2004, the size-resolved number concentration of water-insoluble aerosols (WIA) from 0.25 to 2.0 μm was measured in real-time in the urban center of Atlanta, GA. Simultaneous measurements were performed for the total aerosol size distribution from 0.1 to 2.0 μm, the elemental and organic carbon mass concentration, the aerosol absorption coefficient, and the aerosol scattering coefficient at a dry (RH=30%) humidity. The mean aerosol number concentration in the size range 0.1–2.0 μm was found to be 360±175 cm⁻³, but this quantity fluctuated significantly on time scales of less than one hour and ranged from 25 to 1400 cm⁻³ during the sample period. The mean WIA concentration (0.25–2.0 μm) was 13±7 cm⁻³ and ranged from 1 to 60 cm⁻³. The average insoluble fraction in the size range 0.25–2.0 μm was found to be 4±2.5% with a range of 0.3–38%. The WIA population was found to follow a consistent diurnal pattern throughout the month with concentration maxima concurring with peaks in vehicular traffic flow. WIA concentration also responded to changes in meteorological conditions such as boundary layer depth and precipitation events. The temporal variability of the absorption coefficient followed an identical pattern to that of WIA and ranged from below the detection limit to 55 Mm⁻¹ with a mean of 8±6 Mm⁻¹. The WIA concentration was highly correlated with both the absorption coefficient and the elemental carbon mass concentration, suggesting that WIA measurements are dominated by fresh emissions of elemental carbon. For both the total aerosol and the WIA size distributions, the maximum number concentration was observed at the smallest sizes; however the WIA size distribution also exhibited a peak at 0.45 μm which was not observed in the total population. Over 60% of the particles greater than 1.0 μm were observed to be insoluble in the water sampling stream used by this instrumentation. Due to the refractive properties of black carbon, it is highly unlikely that these particles could be composed of elemental carbon, suggesting a crustal source for super-micron WIA.     

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.     

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.