Submicron Fraction Research Articles

Characterization of the South Atlantic marine boundary layer aerosol using an aerodyne aerosol mass spectrometer

Abstract. Measurements of the submicron fraction of the atmospheric aerosol in the marine boundary layer were performed from January to March 2007 (Southern Hemisphere summer) onboard the French research vessel Marion Dufresne in the Southern Atlantic and Indian Ocean (20° S–60° S, 70° W–60° E). We used an Aerodyne High-Resolution-Time-of-Flight AMS to characterize the chemical composition and to measure species-resolved size distributions of non-refractory aerosol components in the submicron range. Within the "standard" AMS compounds (ammonium, chloride, nitrate, sulfate, organics) "sulfate" is the dominant species in the marine boundary layer with concentrations ranging between 50 ng m−3 and 3 μg m−3. Furthermore, what is seen as "sulfate" by the AMS is likely comprised mostly of sulfuric acid. Another sulfur containing species that is produced in marine environments is methanesulfonic acid (MSA). There have been previously measurements of MSA using an Aerodyne AMS. However, due to the use of an instrument equipped with a quadrupole detector with unit mass resolution it was not possible to physically separate MSA from other contributions to the same m/z. In order to identify MSA within the HR-ToF-AMS raw data and to extract mass concentrations for MSA from the field measurements the standard high-resolution MSA fragmentation patterns for the measurement conditions during the ship campaign (e.g. vaporizer temperature) needed to be determined. To identify characteristic air masses and their source regions backwards trajectories were used and averaged concentrations for AMS standard compounds were calculated for each air mass type. Sulfate mass size distributions were measured for these periods showing a distinct difference between oceanic air masses and those from African outflow. While the peak in the mass distribution was roughly at 250 nm (vacuum aerodynamic diameter) in marine air masses, it was shifted to 470 nm in African outflow air. Correlations between the mass concentrations of sulfate, organics and MSA show a narrow correlation for MSA with sulfate/sulfuric acid coming from the ocean, but not with continental sulfate.

Clouds and aerosols in Puerto Rico – a new evaluation

Abstract. The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements took place in December 2004 in Puerto Rico, using some of the latest developments in online instrumentation such as aerosol mass spectrometers, cloud condensation nuclei counters and a hygroscopicity tandem differential mobility analyser. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040 m a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submicron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm−3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 g m−3 when the winds shifted from the ENE to ESE. Larger numbers of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions. Previous studies in Puerto Rico had reported the presence of a significant non-anthropogenic organic fraction in the aerosols measured and concluded that this was a factor controlling the in situ cloud properties. However, this was not observed in our case. In contrast to the 1.00±0.14 μg m−3 of organic carbon measured in 1992 and 1995, the organic matter measured in the current study of 0.17±0.35 μg m−3 is many times lower, most of which can be attributed to anthropogenic sources. During clean conditions, the submicron aerosol was observed to be almost entirely inorganic, an observation supported by the hygroscopicity measurements. This suggests that organic aerosols from marine sources may not be completely ubiquitous (either spatially or temporally) in this environment and requires further investigation to quantify their true extent and implications, with more extensive, longer-term sampling in conjunction with wind field analyses.

Agglomeration of diesel particles by an electrostatic agglomerator under positive DC voltage: Experimental study

We propose characterizing a new geometry of electrostatic agglomerator using particles produced by a diesel engine. The geometry consists of a positive DC voltage wire to cylinder electrostatic precipitator with a porous cathode. The end of the device is closed, which enables all the treated gas to pass through the filtering cathode. Owing to its very small storage surface, the cathode acts like a simple agglomerator. We demonstrate that this agglomerator is sufficiently effective for the re-entrained particles not to be measurable with an electrical low pressure impactor (ELPI), which means that they are both very few in number and largely micronic. The system can function with very short residence times, comparable with the charging times of the treated particles. Energy densities of about 1 J/l are used to achieve a number reduction exceeding 90% on the submicron fraction of particles. It seems that the nature of the cathode has very little influence on particle number decrease. Owing to its compactness, this process displays good potential for the treatment of diesel particles.

Mechanochemical synthesis of solid solutions based on ZrO2 and their electrical conductivity

Zirconia-and scandia-based complex solid solutions predominantly with a monoclinic structure are prepared by mechanochemical synthesis. The dense ceramic materials, which, for the most part, have a cubic structure with grain sizes of 250–400 nm and possess good mechanical properties, are produced by sintering submicron fractions of the powders under relatively mild conditions at temperatures of 1633–1653 K. It is revealed that the powders are characterized by nanostructuring due to the complex composition and the chemical inhomogeneity. This nanostructuring is partially retained upon rapid sintering of the ceramic powders. The nanostructured ceramic materials possess a high low-temperature conductivity, which decreases after annealing. Unlike conventional ceramic materials, the nanostructured ceramic materials have identical activation energies for bulk and grain-boundary electrical conduction. The high-temperature electrical conductivity of the nanostructured ceramic materials is rather low because of the small grain sizes and impurities of the monoclinic phase.

Coupling parameter for low-temperature plasma with condensed phase

The detection of plasma crystals in the dusty plasma [1,2], and the ordered structures of the condensed grains in the plasma of combustion products (smoky plasma) [3,4] stimulated the research of mechanisms of the charged grains interaction in the low-temperature plasma and definition of the criteria parameters of phase transition. Thus it has been found out that the formation of the ordered structures of dust grains occurs in strongly coupled (nonideal) plasma. It has been suggested to use a Coulomb coupling parameter Γ, defined as the ratio of the potential energy of Coulomb interaction between neighboring particles and their kinetic temperature, in order to distinguish the weakly coupled plasma and the strongly coupled plasma [5–11]. The application of such a form of coupling parameter for the description of the condensed grains interactions in the smoky plasma is not always comprehensible, which is caused by a number of its specific properties. The principal distinction of the smoky plasma from discharge dusty plasma is its thermal collision nature. The displacement of ionization equilibrium in the plasma gas phase, caused by the presence of a noncompensate volume charge, is formed in plasma due to the interphase interaction [12]. The condensed grains are formed by homogeneous and heterogeneous condensation in the smoky plasma at burning. Therefore, the condensed phase contains a multimode distribution function for sizes of grains of submicron fraction. This enables us to consider the dusty and smoky plasma as two different kinds of plasma with a condensed disperse phase. Thus, multimode distribution functions for the mentioned grain sizes and the displacement of ionization equilibrium do not make it possible to use the coupling parameter, obtained both for the dusty and smoky plasmas. The present paper is devoted to the development of a coupling parameter applicable to the description of polydisperse systems such as the smoky plasma.

Application of synchrotron radiation for measurement of iron red-ox speciation in atmospherically processed aerosols

Abstract. In this study, ambient atmospheric particulate matter samples were collected using a size-resolved impactor sampler from three urban sites. The purpose of this study is to gain a better understanding of transformations of aerosol-bound iron as it is processed in the atmosphere. Thus, the aerosol samples were artificially aged to represent long-term transport (10 to 40 days) or short-term transport (1 to 10 days) and were measured for iron at several time points. At each time point, iron was measured in each size fraction using three different techniques; 1) inductively coupled plasma-mass spectrometry (ICPMS) for total iron, 2) x-ray absorbance near edge structure (XANES) spectroscopy for the measurement of total Fe(II) and Fe(III), and 3) a wet-chemical method to measure soluble Fe(II) and Fe(III). Prior to aging, the XANES spectroscopy results show that a majority (>60% for each size fraction) of the total iron in the PM is in the form of Fe(III). Fe(III) was shown to be a significant fraction of the soluble iron (sometimes >50%), but the relative significance of Fe(III) was found to vary depending on the site. Overall, the total soluble iron depended on the sampling site, but values ranged from less than 1% up to about 20% of the total iron. Over the course of the 40 day aging period, we found moderate changes in the relative Fe(II)/Fe(III) content. A slight increase was noted in the coarse (>2.5 µm) fraction and a slight decrease in the 0.25 to 0.5 µm fraction. The soluble fraction generally showed (excepting one day) a decrease of soluble Fe(II) prior to 10 days of aging, followed by a relatively constant concentration. In the short-term transport condition, we found that the sub-micron fraction of soluble Fe(II) spikes at 1 to 3 days of aging, then decreases to near the initial value at around 6 to 10 days. Very little change in soluble Fe(II) was observed in the super-micron fraction.

Fine and Coarse Particulate Matter Chemical Characterization in a Heavily Industrialized City in Central Mexico during Winter 2003

This paper presents the results of the first reported study on fine particulate matter (PM) chemical composition at Salamanca, a highly industrialized urban area of Central Mexico. Samples were collected at six sites within the urban area during February and March 2003. Several trace elements, organic carbon (OC), elemental carbon (EC), and six ions were analyzed to characterize aerosols. Average concentrations of PM with aerodynamic diameter of less than 10 μm (PM10) and fine PM with aerodynamic diameter of less than 2.5 μm (PM2.5) ranged from 32.2 to 76.6 μg m-3 and 11.1 to 23.7 μg m-3, respectively. OC (34%), SO4 = (25.1%), EC (12.9%), and geological material (12.5%) were the major components of PM2.5. For PM10, geological material (57.9%), OC (17.3%), and SO4 = (9.7%) were the major components. Coarse fraction (PM10 –PM2.5), geological material (81.7%), and OC (8.6%) were the dominant species, which amounted to 90.4%. Correlation analysis showed that sulfate in PM2.5 was present as ammonium sulfate. Sulfate showed a significant spatial variation with higher concentrations to the north resulting from predominantly southwesterly winds above the surface layer and by major SO2 sources that include a power plant and refinery. At the urban site of Cruz Roja it was observed that PM2.5 mass concentrations were similar to the submicron fraction concentrations. Furthermore, the correlation between EC in PM2.5 and EC measured from an aethalometer was r2 = 0.710. Temporal variations of SO2 and nitrogen oxide were observed during a day when the maximum concentration of PM2.5 was measured, which was associated with emissions from the nearby refinery and power plant. From cascade impactor measurements, the three measured modes of airborne particles corresponded with diameters of 0.32, 1.8, and 5.6 μm.

An Andean ice-core record of a Middle Holocene mega-drought in North Africa and Asia

AbstractAn ice core from the Nevado Huascaran col in the Cordillera Blanca of northern Peru contains high-resolution time series of dust concentrations and size distributions since the end of the last glacial stage. A large dust peak, dated ∼4500 years ago, is contemporaneous with a widespread and prolonged drought that apparently extended from North Africa to eastern China, evidence of which occurs in historical, archeological and paleoclimatic records. This event may have been associated with several centuries of weak Asian/Indian/African monsoons, possibly linked with a protracted cooling in the North Atlantic. During the second half of the 20th century, high austral-summer dust concentrations in the Huascaran record are significantly correlated with atmospheric conditions, such as sea-level pressure and zonal wind velocities that are consistent with El Nino-Southern Oscillation (ENSO) and positive North Atlantic Oscillation (NAO) indices, and with aridity in North Africa, southwest Asia and the Middle East. Therefore, the dominant submicron fraction of the dust may have been transported by more intense northeasterly trade winds from the African dry regions across the tropical Atlantic during a period of frequent and/or intense ENSO activity. The proposed ENSO conditions that may have been linked with drought in the monsoon region may also have contributed to aridity in tropical South America, including the Cordillera Blanca.

Effect of co-firing on the properties of submicron aerosols from biomass combustion

As part of a more general study on particle formation process (and, specifically, the submicron fraction of the particle size distribution) in biomass combustion, the effect of combining biomass with other sulfur-enriched fuels (such as coal and coke) on particulate emissions has been investigated. Pulverized orujillo (an olive oil production process residue) combustion, alone, resulted in an important submicron particle mode composed of, essentially, potassium chloride (KCl) and potassium sulfate (K 2SO 4) in almost the same mass proportion. Differently, experiments in which pure gases (sulfur dioxide, SO 2) and other sulfur-containing fuels (coal and coke) were added to the orujillo combustion lead to a total disappearance of chlorine in those particles. Orujillo was responsible for the key element (i.e., potassium) in the fine particles emitted in co-combustion of the fuel blends; coal and coke served only as “sulfur sources” in this process. These results are interpreted in the framework of the fine particle formation model in biomass combustion, and give a basic support to previous field and laboratory measurements on deposit formation and corrosion in biofired boilers. Chlorides being associated to boiler corrosion and molten deposit formation at relatively low wall temperatures, the present results show that cofiring of biomass with other traditional fuels (even in small amounts) can be a feasible way to appreciably attenuate such adverse effects in industrial boilers.

Advances in characterization of size‐resolved organic matter in marine aerosol over the North Atlantic

Size‐segregated marine aerosols were collected at Mace Head Atmospheric Research Station (Ireland) during spring and autumn 2002 corresponding with the phytoplankton bloom periods in the North Atlantic. Strict control of the sampling, air mass back trajectory analysis, and analysis of pollutant tracers allowed the selection of a set of samples representative of clean marine conditions. A comprehensive chemical characterization of both (1) water‐soluble and water‐insoluble organic fraction and (2) water‐soluble inorganic ions was performed. The selected samples illustrated a consistent picture in terms of chemical composition. The supermicron mode predominantly comprises sea‐salt aerosol with a mass concentration of 10.16 ± 0.80 μg m−3, the remainder being non‐sea‐salt (nss) sulphate, 0.03 ± 0.01 μg m−3, and nitrate, 0.13 ± 0.04 μg m−3. By comparison, the mass of sea salt, nss sulphate, and nitrate in the submicron mode is found to be 0.39 ± 0.08 μg m−3, 0.26 ± 0.04 μg m−3, and 0.02 ± 0.01 μg m−3, respectively. Water‐soluble organic carbon (WSOC) is observed in the submicron mode with a mass concentration of 0.25 ± 0.04 μg m−3, comparable to that of nss sulphate, and in the supermicron mode with a mass concentration of 0.17 ± 0.04 μg m−3. The WSOC to total carbon (TC) ratio is found to be 0.20 ± 0.12 for the submicron fraction and 0.29 ± 0.08 for the supermicron fraction, while the black carbon (BC) to TC ratio is, on average, 0.032 ± 0.001 for both aerosol modes. The remaining carbon, water‐insoluble organic carbon, contributes 0.66 ± 0.11 μg m−3 and 0.26 ± 0.06 μg m−3 to the submicron and supermicron modes, respectively and, thus, represents the dominant submicron aerosol species. Furthermore, the WSOC chemical composition comprises mainly aliphatic and only partially oxidized species and humic‐like substances, resulting in appreciable surface‐active properties. The observed organic matter chemical features (size‐dependent concentration, hydrophobic nature of a substantial fraction of the organic matter, and low oxidized and surface‐active WSOC species) are consistent with the hypothesis of a primary marine source; bubble‐bursting processes, occurring at the surface of the North Atlantic Ocean during phytoplankton blooms, effectively transfer organic matter into marine aerosol particles, particularly enriching the fine‐aerosol fraction.

Size Distributions of Organic Functional Groups in Ambient Aerosol Collected in Houston, Texas Special Issue ofAerosol Science and Technologyon Findings from the Fine Particulate Matter Supersites Program

The size distributions of aliphatic carbon, carbonyl, and organonitrate functional groups in ambient aerosol were determined at three sites during an air quality field study conducted during August and September 2000, in Houston, Texas. Samples were collected using a Hering low-pressure impactor and were analyzed, in transmission mode, using Fourier transform infrared spectroscopy. The submicron fractions of the samples exhibited patterns seen in other urban areas. Carbonyl and organonitrate group absorbances showed maxima in the 0.05–0.26 μm and the 0.5–1.0 μm size fractions, and based on these absorbances appear to be primarily due to secondary organic aerosol. Aliphatic carbon absorbances in the submicron aerosol showed maxima in the 0.076–0.12 μm size fraction and the 0.5–1.0 μm size fraction. Weak correlation between ozone concentrations and aliphatic carbon absorbances suggest that some of these aliphatic functional groups are due to primary emissions. For the supermicron aerosol, all three functional groups exhibit maxima in the 2–4 μm size fraction. These coarse size fractions observed in Houston were not observed in similar samples collected in Los Angeles. In addition, some of the aerosol samples collected in Houston display organic functional group concentrations, especially for organonitrates, that are significantly higher than the median concentrations. Samples with very high organic functional group concentrations had molar ratios of carbonyl and organonitrate functional groups that are suggestive of either primary emissions or secondary organic aerosol formation processes that are not commonly observed in other urban areas.

Environmental snapshots from ACE‐Asia

On five occasions spanning the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) field campaign in spring 2001, the Multiangle Imaging Spectroradiometer spaceborne instrument took data coincident with high‐quality observations by instruments on two or more surface and airborne platforms. The cases capture a range of clean, polluted, and dusty aerosol conditions. With a three‐stage optical modeling process, we synthesize the data from over 40 field instruments into layer‐by‐layer environmental snapshots that summarize what we know about the atmospheric and surface states at key locations during each event. We compare related measurements and discuss the implications of apparent discrepancies, at a level of detail appropriate for satellite retrieval algorithm and aerosol transport model validation. Aerosols within a few kilometers of the surface were composed primarily of pollution and Asian dust mixtures, as expected. Medium‐ and coarse‐mode particle size distributions varied little among the events studied; however, column aerosol optical depth changed by more than a factor of 4, and the near‐surface proportion of dust ranged between 25% and 50%. The amount of absorbing material in the submicron fraction was highest when near‐surface winds crossed Beijing and the Korean Peninsula and was considerably lower for all other cases. Having simultaneous single‐scattering albedo measurements at more than one wavelength would significantly reduce the remaining optical model uncertainties. The consistency of component particle microphysical properties among the five events, even in this relatively complex aerosol environment, suggests that global, satellite‐derived maps of aerosol optical depth and aerosol mixture (air‐mass‐type) extent, combined with targeted in situ component microphysical property measurements, can provide a detailed global picture of aerosol behavior.

Temperature, classification and dewatering in 10 mm hydrocyclones

Small diameter hydrocyclones have had an increasing use in performing difficult phase separations in many industries. Further, these 10 mm diameter hydrocyclones also have the potential to be applied to fine particle classification, in particular to collect the sub-micron fraction. The key operating parameters that affect the dewatering and classification performance of 10 mm hydrocyclones are the operating pressure and feed solids concentration, both of which have previously been studied in detail. Previous studies on larger cyclones have modified the viscosity by temperature, solids concentration and sucrose addition. In industrial operations, the role of temperature may be significant, either due to climatic variations, or by active manipulation. In particular, the effect of temperature on the relationship between the water recovery and the bypass fraction has not been described. This is of importance, as fine classification requires both a small bypass and cutsize, while dewatering would benefit from a large bypass, small cutsize and, if possible, a low water recovery. In the present study, the effect of temperature between 10 and 60 °C was studied on low concentration suspensions of silica flour in water using a 10 mm diameter hydrocyclone. It was observed that the phase separation improves for increasing temperatures. The cutsize was decreased from 5.3 to 2.8 μm, while the water recovery decreased simultaneously. The bypass fraction, however, also increased significantly (from 0.36 to 0.48) with temperature, increasing the solids recovery and, importantly, did not follow the same trend as the water recovery. This has not been reported previously. The corrected cutsize changes were successfully predicted using the equilibrium orbit theory, while the solids recovery was interpreted using residence time relationships. These described satisfactorily the relationship with liquid viscosity changes due to temperature.

Temperature, classification and dewatering in 10 mm hydrocyclones

Small diameter hydrocyclones have had an increasing use in performing difficult phase separations in many industries. Further, these 10 mm diameter hydrocyclones also have the potential to be applied to fine particle classification, in particular to collect the sub-micron fraction. The key operating parameters that affect the dewatering and classification performance of 10 mm hydrocyclones are the operating pressure and feed solids concentration, both of which have previously been studied in detail. Previous studies on larger cyclones have modified the viscosity by temperature, solids concentration and sucrose addition. In industrial operations, the role of temperature may be significant, either due to climatic variations, or by active manipulation. In particular, the effect of temperature on the relationship between the water recovery and the bypass fraction has not been described. This is of importance, as fine classification requires both a small bypass and cutsize, while dewatering would benefit from a large bypass, small cutsize and, if possible, a low water recovery. In the present study, the effect of temperature between 10 and 60 °C was studied on low concentration suspensions of silica flour in water using a 10 mm diameter hydrocyclone. It was observed that the phase separation improves for increasing temperatures. The cutsize was decreased from 5.3 to 2.8 μm, while the water recovery decreased simultaneously. The bypass fraction, however, also increased significantly (from 0.36 to 0.48) with temperature, increasing the solids recovery and, importantly, did not follow the same trend as the water recovery. This has not been reported previously. The corrected cutsize changes were successfully predicted using the equilibrium orbit theory, while the solids recovery was interpreted using residence time relationships. These described satisfactorily the relationship with liquid viscosity changes due to temperature.

Size resolved mass concentration and elemental composition of atmospheric aerosols over the Eastern Mediterranean area

Abstract. A Berner low pressure impactor was used to collect size-segregated aerosol samples at Finokalia, located on the north-eastern coast of Crete, Greece during July 2000 and January 2001. Several samples were also collected during the summer campaign aboard the research vessel "AEGAIEO" in the Aegean Sea. Gravimetric analysis and inversion techniques yielded daily PM1 and PM10 mass concentrations. The samples were also analysed by PIXE giving the elemental size distributions of Al, Si, K, Ca, Ti, Mn, Fe, Sr, S, Cl, Ni, V, Cu, Cr, Zn, and Pb. The crustal elements and sea-salt had a unimodal supermicron size distribution. Sulphur was found predominantly in submicron fractions. K, V, and Ni exhibited a bimodal distribution with a submicron mode produced by forest fires and oil combustion. The anthropogenic elements had broad and not well-defined distributions. The time series for PM1 and PM10 mass and elemental concentrations showed both daily and seasonal variation. Higher mass concentrations were observed during two incursions of Saharan dust, whilst higher concentrations of S, Cu, Zn, and Pb were encountered in samples collected in air masses arriving from northern Greece or the western coast of Turkey. Elevated concentrations of chlorine were found in samples with air masses either originating above the Atlantic Ocean and arriving at Finokalia via western Europe or recirculating over the western coast of the Black Sea.

Submicron aerosol mass balance at urban and semirural sites in the Milan area (Italy)

During the Pianura Padana Produzione di Ozono (PIPAPO) field campaign (May–June 1998), aerosol measurements were performed at an urban site and a semirural site to determine the particulate matter chemical composition in the Milan area. Aerosol samples were collected on filters for subsequent chemical analysis using virtual impactors. Possible sampling artifacts for semivolatile particulate species were addressed. Our NH4NO3 measurements were successfully compared with artifact free wet denuder‐wet aerosol collector sampler data. Positive sampling artifacts for organic species were corrected using the back‐to‐back filter technique, allowing us to assess the lower limit for particulate organic carbon (POC) concentrations. Aerosol size distributions were measured on‐line with differential mobility analyzers (DMA). The variations in the submicron aerosol mass concentration estimated from chemical analyses compared well with the variations in the submicron particle volume calculated from number size distributions. At both sites, 70% of the PM10 mass was found in the submicron fraction. The mean submicron aerosol mass concentrations were 28 μg m−3 and 20 μg m−3 at the urban site and the semirural site, respectively. The correlations between NH4+ and NO3− + 2SO4= indicate that strong acids were fully neutralized at both sites. At the urban site the submicron concentrations of NH4NO3, (NH4)2SO4, and POC were 8.1 μg m−3, 6.3 μg m−3, and 6.4 μgC m−3, respectively. At the semi‐rural site, these concentrations were 4.9 μg m−3, 4.0 μg m−3, and 5.6 μgC m−3, respectively. These results show that sulfate and nitrate contribute about the same amount to submicron aerosol mass concentration, and that particulate organic matter (POM) could be the major component of the aerosol submicron mass in the Milan region, especially in semirural areas. The correlation between normalized concentrations of POM and O3 observed at the semirural site suggests that POM results at least partly from photochemical oxidation of volatile organic compounds (VOC). It is likely that reducing anthropogenic VOC emissions would lead to lower POC and total submicron aerosol concentrations in semirural areas around Milan.

Propagation of atmospheric aerosol and the area of representativeness of its measurements in the Baltic Sea region

Area of representativeness (AR) of atmospheric aerosol measurements and horizontal dimensions of a cloud of particles are estimated by time series of aerosol particle size number spectrum measured simultaneously at two locations. The distances between sampling points are varied, 7, 30, 50, 100 or 375 km. The spectrum in form of 12 fraction concentrations is measured every 10 or 15 min during five 2–4 week measurement campaigns in Estonia. During one measurement campaign one measurement point was in Estonia (Tahkuse) and the other in Finland (Hyytiälä). Two electrical aerosol spectrometers (EAS) designed at University of Tartu, having diameter range 10 nm–10 μm, were used. At Hyytiälä, the particle size spectrum ( d=3–500 nm ) was measured by two Hauke type differential mobility analysers (DMA). The transport of the submicron fraction ( d=60 nm –1 μm ) of atmospheric aerosol is investigated during the time intervals when an air mass moves from the one measurement point towards the other or crosswise to this direction. Sample cross-correlation functions (SCCF) are calculated between prewhitened time series. The time lag corresponding to the mode of these functions are found to be 3–5 h for upwind–downwind case and zero for crosswind case. This time lag should indicate the mean time of pollution transport for upwind–downwind case. A certain minimal distance between sampling points should exist, when statistically significant correlation between the time series cannot be found. Considering this circumstance, the half-width of the AR is estimated. It is found to be more than 100 km but less than 375 km when the sampling points are located on the same line with the wind direction; and more than 50 km but less than 100 km when the sampling points are located on a straight line crosswise to the wind direction. The pollutant concentrations in the limits of AR are estimated by regression analysis. To support these results, the dispersion calculations by HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectories) model are used.

Analysis of aerosol distribution inside the object "shelter" at the Chernobyl nuclear reactor site.

Results of the aerosol sampling inside the Object Shelter at the Chornobyl nuclear reactor site are considered in the work. The results show a consistent and significant contribution of submicron fraction to the total aerosol activity. Different methods of interpretation of impactor data series are compared in order to indicate and detect in the most effective way the submicron fraction as a separate component of the distribution. The methods used are as follows-method of probabilistic-logarithmic scale, method of likelihood function, non-linear approximation by sum of several log-normal distributions, and restoration of the initial distribution using passage functions of impactor cascades. Practically all the collected data on aerosol distribution inside the Shelter show a distinct submicron component. The contribution of the submicron component into the total aerosol activity is about 35%. Influence of the actual aerosol distribution on the dose coefficients is analyzed.

Sub-micron particle dewatering using hydrocyclones

Hydrocyclones are used for dewatering of solid–liquid suspensions in many industries. Generally, however, large diameter cyclones are used and their application is restricted to large (>25 μm) particles. Small diameter (10 mm) hydrocyclones have the potential to be applied to fine particle (<10 μm) suspensions and, in particular, to collect the sub-micron fraction. This is due to the very small cutsizes that are achieved in these cyclones. In order to apply these small hydrocyclones industrially, knowledge of the range of their classification performance is required. It is found that these cyclones exhibit a fish-hook partition curve, and a high bypass fraction. The very small cutsize (<5 μm) and the relatively large bypass makes the effective collection of sub-micron particles possible. While in most hydrocyclone applications it is found that the bypass fraction equals the water recovery to the underflow, in 10 mm hydrocyclones the bypass fraction is considerably larger than the water recovery. This results in a high particle recovery to the underflow, as well as low water recovery, resulting in a high concentration ratio. Results will be presented to show the separation performance of different hydrocyclone outlet configurations and pressure drops. A general model will be presented that describes the fish-hook and that gives an explanation for its origin. It will be shown that 10 mm hydrocyclones yield a new operating regime for their application to sub-micron solid–liquid separation, as a result of high solids recoveries and low water recoveries.

Water‐soluble nitrogen at the New Hampshire sea coast: HNO3, aerosols, precipitation, and fog

An intensive sampling program was carried out from May 1994 through November 1997 on the shore of the Gulf of Maine in New Castle, New Hampshire. Daily (24 hour averages) samples of bulk aerosol and gas phase HNO3, precipitation, and 20 aerosol size distributions were obtained. Particulate NH4+ and gas phase HNO3 were the dominant water‐soluble nitrogen species in the atmosphere. There was a summer peak in the mixing ratios of both of these species. Daily mixing ratios of HNO3 and all aerosol species were highly variable, yet the annual averages tended to be similar from one year to the next. The concentrations of all the inorganic species we measured in precipitation were generally higher than those of two National Acid Deposition Program (NADP) coastal sites. In particular, the annual volume‐weighted means for NO3− (22–27 μmol/L) and NH4+ (11–17 μmol/L) were found to be 20%–60% and 40%–90% higher, respectively, than those reported from Cape Cod, Massachusetts. Nitrate was the dominant inorganic nitrogen ion in precipitation at New Castle. In autumn, concentrations of continentally derived species in precipitation decreased substantially while sea salts increased. There was insufficient NH3 to fully neutralize HNO3 and H2SO4 in aerosols and precipitation. The overall atmospheric chemistry in this region was heavily dominated by anthropogenic pollution products. The samples collected were used in conjunction with 1000 hPa streamlines to classify sampled air masses according to their surface level transport and chemistry. Eight characteristic groups were defined; of these the three primary groups were polluted continental, ″clean″ continental, and marine. Highly variable mixing ratios of HNO3 and aerosol species were observed within each group from day to day, yet each group had a unique average chemical signature. On average, the HNO3 and aerosol mixing ratios observed in 1995 were roughly a factor of 2 lower than seen for the groups in other years. Overall, mixed conditions occurred in 42% of the samples, continental species were dominant in 37%, and marine species were dominant in 21%. Rain occurred frequently under sea‐salt‐dominant conditions; about 47% of the days classified as such had rain events. Fog chemistry and average aerosol chemical size distributions were evaluated based on which species dominated their chemical signatures, marine, continental, or a relatively even mixture of the two. Particulate NO3− was associated with sea‐salt Na+ in the coarse aerosol fraction peaking at approximately 4 μm in diameter. There was also a distinct secondary peak in the submicron fraction observed in air dominated by continental aerosols. Particulate NH4+ was associated with non‐sea‐salt SO42− (nss‐SO42−), with the bulk of the NH4+ present on particles in the 0.43–1.1 μm diameter range. Although nss‐SO42− was primarily found in the submicron size range, a substantial fraction (≥25%) was found in the supermicron range for all three cases. Chloride was depleted on average 25% in aerosols and 13% in precipitation with respect to sea‐salt aerosols, with the deficit greatest for particles in the 1.1–3.3 μm and 9.0–25 μm diameter ranges.