Number Of Coarse Particles Research Articles

The study of radionuclide activities in the sediments of deep areas of Skagerrak and Southern Baltic

This study investigates the activities of radionuclides (137Cs, 210Pb, 214Pb, 239,240Pu, and 40K), carbon isotopes (δ13C and 14C), and grain size compositions in surface bottom sediments across the southern Baltic and Skagerrak Strait. Our findings reveal significant connections between these parameters and their dependence on sediment transport dynamics. The distribution patterns of natural and artificial radionuclides were studied to understand the factors influencing their transport to the deep areas. The results show that 137Cs activity in surface bottom sediments (0–5 cm) ranges from 8 to 11 Bq/kg in the Skagerrak area and reaches 220 Bq/kg in the southern Baltic, closer to the vicinity of river discharges. The activity ranges of 239,240Pu are similar between the study areas, but the mean value at the Skagerrak site is higher at 1.6 Bq/kg. The transport of 210Pbex to the bottom is mainly dependent on the number of fine particles (0–20 μm) in the water column, while the transport of 137Cs primarily driven by scavenging by marine organics from the water column. In the southern Baltic, a strong correlation indicates that a significant share of 137Cs most likely originates from fluvial input. The particle size distribution reflects calm conditions in the deep waters, while in the Curonian Lagoon reference areas there are pronounced contrasts between stations with strong and calm hydrodynamic conditions. The δ13C values in the surface bottom sediments decrease towards river discharge areas, reflecting an increased terrestrial component of the organic fraction, and the number of coarse particles also increases.

Exploring debris flow deposit morphology in river valleys: Insights from physical modeling experiments

A comprehensive understanding of the deposit morphodynamics of debris flows in river valleys is crucial for disaster prevention and mitigation in mountainous areas. However, debris flows in river valleys are complex and variable, and the influence of the composition and terrain on deposit mechanisms and morphology remains unclear. In this study, a series of laboratory experiments were conducted to investigate the impact of the water content, slope, and grain size distribution on the deposit morphology of debris flows in river valleys. In the experiments, debris flows form narrow and elongated shuttle-shaped deposits upon entering river valleys. Increased water content and slope enhance the mobility of debris flows, resulting in wider deposit widths, gentler deposit slopes, and larger deposit areas. An increase in the gravel fraction partially facilitates the movement and deposition of debris flows. However, a large number of coarse particles may increase internal friction within the debris flow, hindering the spread of deposits and resulting in a relatively concentrated deposit with a steeper morphology. Furthermore, the debris flow regime shifts from friction to collision as the water content, slope, and gravel fraction increase. Debris flows dominated by collision forces exhibit higher mobility and a wider impact area, potentially leading to more severe disaster consequences. Compared with unconfined debris flows, the deposit area of debris flows in the river valley is smaller, and the deposit width to height ratio is larger. There is a power function relationship between deposition area and Savage number in river valleys. Additionally, particle sorting and flow regime transformation during the movement and deposition of debris flows can significantly impact the morphology and internal structure of the deposits in river valleys and then affect the development of debris flow dam breaching. In summary, this study utilized experiments to simulate natural debris flows, offering fresh insights into the depositional behavior of debris flows in river valleys.

Structural evolution of bed drainage channels under the shear effect of the whole process of tailings thickening

Cemented paste backfill (CPB) technology has the advantages of safety, environmental friendliness, economics, and efficiency. This method offers assurances for practical underground mining and tailings pond management. The bed drainage channel structure and coarse particles with diameters above 45 μm were reconstructed and quantitatively characterized in 3D by computed tomography (CT) for the whole tailings thickening process. The spherical pore diameter evolution trends, stick throat channel radius and throat channel length were analyzed with and without shear using the pore network model (PNM). The functional relationship between the average spherical pore diameter and bed pressure is given, and the boundary values between the bed’ primary and secondary drainage channels are clarified. The ratio of throat length to diameter (Tw) is proposed to measure the difficulty of throat channel structure on the water discharge in the bed. The effects of the volume and number of coarse particles with diameters above 45 μm on the bed porosity and pore connectivity were analyzed. The range of particle diameters that significantly affect the bed porosity and pore connectivity was clarified. The results show that the spherical pore diameter, throat channel radius, and throat channel length decrease with increasing bed pressure with and without shear. Moreover, the average spherical pore diameter in the bed has a power-law relationship with the bed pressure. The spherical pore diameter, throat channel radius, and throat channel length with shear were lower than without shear, and the slurry concentration was higher than without shear. The main drainage channels of the bed with and without shear consisted of large pore structures with diameters of not less than 433.3 μm and 329.8 μm, respectively. The throat channel structure parameter Tw increases with the increase of bed pressure. When Tw is higher than 8.7, the discharge of water in the bed is hindered, making it challenging to improve the slurry concentration. The porosity and pore connectivity of the bed decreases with increasing volume and number of coarse particles. Among them, coarse particles in the diameter 150–300 μm range significantly reduce the bed porosity and pore connectivity. This study guides the preparation of high-concentration paste filling slurry, which is helpful to improve the efficient mining capacity of mines and have fewer tailings ponds.

Study Using Machine Learning Approach for Novel Prediction Model of Liquid Limit

The liquid limit (LL) is considered the most fundamental parameter in soil mechanics for the design and analysis of geotechnical systems. According to the literature, the LL is governed by different particle sizes such as sand content (S), clay content (C), and silt content (M). However, conventional methods do not incorporate the effect of all the influencing factors because traditional methods utilize material passing through a # 40 sieve for LL determination (LL40), which may contain a substantial number of coarse particles. Therefore, recent advancements suggest that the LL must be determined using material passing from a # 200 sieve. However, determining the liquid limit using # 200 sieve material, referred to as LL200 in the laboratory, is a time-consuming and difficult task. In this regard, artificial-intelligence-based techniques are considered the most reliable and robust solutions to such issues. Previous studies have adopted experimental routes to determine LL200 and no such attempt has been made to propose empirical correlation for LL200 determination based on influencing factors such as S, C, M, and LL40. Therefore, this study presents a novel prediction model for the liquid limit based on soil particle sizes smaller than 0.075 mm (# 200 sieve) using gene expression programming (GEP). Laboratory experimental data were utilized to develop a prediction model. The results indicate that the proposed model satisfies all the acceptance requirements of artificial-intelligence-based prediction models in terms of statistical checks such as the correlation coefficient (R2), root-mean-square error (RMSE), mean absolute error (MAE), and relatively squared error (RSE) with minimal error. Sensitivity and parametric studies were also conducted to assess the importance of the individual parameters involved in developing the model. It was observed that LL40 is the most significant parameter, followed by C, M, and S, with sensitivity values of 0.99, 0.93, 0.88, and 0.78, respectively. The model can be utilized in the field with more robustness and has practical applications due to its simple and deterministic nature.

Characterization and Elemental Analysis of Particulate Matter in a Chemical Digestion Laboratory

Particulate matter (PM) may constitute health-threatening substances that are classified as carcinogens. In laboratories, common PM-emitting activities include chemical processing and electronic equipment utilization. Thus, workers run the risk of inhaling possible contaminants into their respiratory systems and affecting their overall health. In this study, PM10 and PM2.5 sampled from a chemical digestion laboratory were analyzed based on the size distribution and elemental composition. Samples were collected using a cascade impactor coupled with an air pump for 7 h per sampling day. Size distribution showed variation in the number of coarse particles, which was mainly attributable to activities that occurred during sampling. Elemental analysis by scanning electron microscope with energy dispersive X-ray identified 23 elements. Some of the highest obtained concentrations belonged to the elements O, Si, Na and Ba with 41, 21, 10 and 10% in weight percentages, respectively. Possible PM sources included indoor dust, laboratory reagents, mechanical abrasions of buildings, crustal material and combustion emission. Furthermore, six elements from the identified PM constituents, namely Ba, Cl, Al, F, Mn and Cr were determined as inhalation contaminants based on toxicological reports from the Agency for Toxic Substances and Disease Registry.

Effects of deformation temperature on second-phase particles and mechanical properties of multidirectionally-forged 2A14 aluminum alloy

Age-hardenable 2A14 aluminum alloy was subjected to multidirectional forging (MDF) at different temperatures (380, 430, 480 °C) and then treated with solid-solution and T6 aging. The effect of the MDF temperature on the evolution and distribution of second-phase particles and mechanical properties was examined. The results showed that many coarse particles adopted a network distribution when the sample was MD-forged at a lower temperature. This induced large stress concentrations that acted as crack initiation sites, resulting in a decrease in the mechanical properties. Upon increasing the MDF temperature, the number of coarse particles decreased and became more spherical. Correspondingly, the solubility of solute atoms and the atomic diffusion rate increased, which enhanced the precipitation ability, density, and uniformity of the precipitated phases. Thus, upon increasing the MDF temperature, the mechanical properties of the 2A14 alloy were enhanced, while the uniformity was improved in all three directions. The best mechanical properties in all three directions were obtained at an MD-forging temperature of 480 °C, with room-temperature UTS values of 484 MPa, 450 MPa, and 448 MPa; YS values of 365 MPa, 357 MPa, and 356 MPa; and EL values of 11.0%, 10.5%, and 8.0%.

Metal Powder Recyclability in Binder Jet Additive Manufacturing

The recyclability of 316L stainless steel powder in the binder jetting process has been determined. The powder characterization results demonstrated a 22% increase in the number of coarse particles (> 30 µm) and an 18.2% reduction in the number of small particles (< 10 µm) after recycling up to 16 times. A few elongated and irregular-shaped particles were found after recycling, possibly due to particle agglomeration during handling and sieving. A negligible increase in the oxygen content by 0.036% was detected in the recycled powder. The density of sintered parts produced using recycled powder was approximately 1.5% lower than when using fresh powder due to the changes in the particle size distribution and the flowability of the powder caused by the changes in morphology. Final parts built using fresh and recycled powder showed similar hardness (155 ± 3 HV and 165 ± 9 HV) and yield strength (206 ± 16 MPa and 192 ± 10 MPa), respectively.

Long-Term Aerosol Trends and Variability over Central Saudi Arabia Using Optical Characteristics from Solar Village AERONET Measurements

Natural and anthropogenic aerosols over the Kingdom of Saudi Arabia (KSA) play a major role in affecting the regional radiation budget. The long-term variability of these aerosols’ physical and optical parameters, including aerosol optical depth (AOD) and Ångström exponent (α), were measured at a location near central KSA using the Solar Village (SV) AERONET (Aerosol Robotic Network) station during the period December 1999–January 2013. The AERONET measurements show an overall increase in AOD on an annual basis. This upward trend is mainly attributed to a prolonged increase in the monthly/seasonal mean AOD during March–June and during August–September. In contrast, lower AOD values were observed during November–December. This can be attributed to a low frequency of dust outbreaks and higher precipitation rates. An overall, weak declining trend in α was observed, except during the summer. The spring and summer seasons experienced a pronounced increase in the number of coarse particles (~2 µm) during April 2006–January 2013 as compared to December 1999–March 2006, suggesting an increase in natural aerosol loadings. Using the HYSPLIT model, it was found that the March 2009 dust storm contributed to the mixing of long-transported dust with anthropogenic local emissions near the SV. The results suggest that extensive industrial activity contributed to the increase of anthropogenic emissions over KSA during the period April 2006–January 2013.

Relationship of particle stimulated nucleation, recrystallization and mechanical properties responding to Fe and Si contents in hot-extruded 7055 aluminum alloys

The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt% Fe and 0.024 wt% Si increasing to 0.272 wt% Fe and 0.134 wt% Si were investigated. The particle stimulated nucleation (PSN) behaviors for different kind of coarse particles were detailly analyzed by EBSD. Moreover, the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated. With increasing Fe and Si contents, the size and number density of coarse η/S particles are reduced, while the number densities of coarse Al7Cu2Fe and Mg2Si particles are both increased and the coarse Al7Cu2Fe particles transform from rod-like to irregular. More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al7Cu2Fe and Mg2Si particles, because a higher degree of local non-uniform deformation is produced. The rod-like Al7Cu2Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio, but the shape also restricts the area of particle deformation zone (PDZ) resulting in fewer PSN recrystallized grains. The irregular η/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures. Consequently, despite the number and size of coarse η/S particles are reduced, the proportion of high angle grain boundaries (HAGBs) is increased and the extruded fiber textures are weakened with Fe and Si contents increasing, because of the increased Al7Cu2Fe and Mg2Si particles. The strength is slightly declined by the weakened <111>//ED (extrusion direction) fiber texture, while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.

Effects of deformation temperature on second-phase particles and mechanical properties of 2219 Al-Cu alloy

In this study, an age-hardenable 2219 Al–Cu alloy was severely deformed by multidirectional forging (MDF) at 360–510°C, followed by solution treatment and T8 aging treatment. The evolution of the second-phase Al2Cu particles and the mechanical properties of the T8-aged samples were examined. The results indicated that a higher volume fraction and a more disperse distribution of the fragmented coarse particles were obtained for the sample deformed at low temperatures. The fragmented coarse particles were still difficult to sufficiently dissolve in the Al matrix in the subsequent solution treatment and could act as crack initiation sites, thereby reducing the mechanical properties of the alloy. With increasing the temperature of MDF, the number of coarse particles was gradually decreased, and the particles exhibited a more spheroidized shape after MDF. Correspondingly, more Cu atoms were dissolved in the Al matrix in the subsequent solution treatment, and the uniformity and density of the precipitates after T8 aging were improved. Thus, the mechanical properties of the T8-aged forgings were improved with increasing the temperature of MDF. The optimal mechanical properties were obtained when the deformation temperature was 510°C, with ultimate tensile strength of 431.2MPa, yield strength of 341.3MPa, and elongation of 6.5% at room temperature.

Observations of aerosol color ratio and depolarization ratio over Wuhan

The aerosol color ratio, depolarization ratio and aerosol optical depth (AOD) were measured by a two-wavelength-depolarization lidar at Wuhan, China during the period from May 2015–July 2016. The annual average AOD at Wuhan was about 0.33 during the period 2015–2016. The seasonal average AOD is small (0.26 ± 0.25) during the winter (December–February) season and large (0.4 ± 0.1) during the summer (June–August) season. The monthly average color ratio is small (0.23 ± 0.09) in January and large (0.76 ± 0.21) in August with an annual average value 0.54. The maximum monthly mean depolarization ratio (0.2 ± 0.07) occurred in the month of October, while the minimum (0.06 ± 0.02) occurred in the month of September, and the annual mean depolarization ratio was about 0.17. An analysis of temporal variations of color ratio and depolarization ratio suggests the presence of coarse and non-spherical particles during the autumn. The aerosol color ratio between 0.3 and 2.0 km was large (0.65), suggesting a large number of coarse particles in this range. The vertical distribution of the depolarization ratio is uniform. Finally, the spatial aerosol distribution under different weather conditions and its relationship with the color ratio is investigated in detail. The color ratio value of 0.74 could be used as a threshold for distinguishing polluted weather from clean weather. The aerosol optical and physical properties are investigated to provide a comprehensive understanding of aerosol radiative forcing and environmental problems in this region.

Thermal crystallization of sputter-deposited amorphous Ge films: Competition of diamond cubic and hexagonal phases

Following our previous studies on crystallization induced by electron irradiation, we have investigated the crystallization of sputter-deposited amorphous germanium films by heat treatments. On continuous heating, samples aged for 3 days and 4 months at room temperature crystallized at 500°C to form coarse spherical particles of a hexagonal structure, of about 100 nm in diameter, whereas samples aged for 7 months turned to homogeneous nanograins of the diamond cubic structure at 600°C. When the films aged for 4 months at room temperature were annealed at 350°C for 2 h and then heated, they crystallized at 550°C to form a mixture of the two microstructures, and those annealed at 350°C and further at 500°C for 1 h crystallized at 600°C mostly to nanograins. Crystallization by electron irradiation at 350°C to 4-month-aged samples has also been studied. With increasing annealing time at 350°C, coarse particles of a hexagonal structure ceased to appear, and were replaced by fine nanograins of the diamond cubic structure. These observations can be understood in terms of structural instability of sputter-deposited amorphous films. Medium-range ordered clusters must initially be present in the films and serve as nuclei of the metastable hexagonal phase. They are unstable, however, and are eliminated by annealing, resulting in the reduction in size and number of coarse particles with a metastable structure.

Crystallization of sputter-deposited amorphous Ge films by electron irradiation: Effect of low-flux pre-irradiation

We investigated the effect of low-flux electron irradiation with 125 keV to sputter-deposited amorphous germanium on the amorphous structure and electron-induced crystallization microstructure by TEM following our previous study on the effect of aging at room temperature. In samples aged for 3 days, coarse, spherical particles about 100 nm in diameter appear dominantly. By low-flux pre-irradiation to the samples, a reduction in the size and number of coarse particles, embedded in the matrix with fine nanograins of the diamond cubic structure, was noted with the increase in fluence. The crystal structure of these coarse particles was found to be not cubic but hexagonal. In samples aged for 4 months, a similar tendency was observed. In samples aged for 7 months, on the other hand, the homogeneous diamond cubic structured nanograins were unchanged by pre-irradiation. These results indicate that pre-irradiation as well as aging modifies the amorphous structure, preventing the appearance of a hexagonal phase. The elimination of a certain amount of medium-range ordered clusters by pre-irradiation, included in as-deposited samples and the samples aged for 4 months, apparently gives rise to a reduction in the size and number of coarse particles with a metastable hexagonal structure.

Particulate matter in the indoor and outdoor air of a gymnasium and a fronton.

An indoor/outdoor monitoring programme of PM10 was carried out in two sports venues (a fronton and a gymnasium). Levels always below 50 μg m(-3) were obtained in the fronton and outdoor air. Due to the climbing chalk and the constant process of resuspension, concentrations above 150 μg m(-3) were registered in the gymnasium. The chalk dust contributed to CO3 (2-) concentrations of 32 ± 9.4 μg m(-3) in this sports facility, which represented, on average, 18 % of the PM10 mass. Here, the carbonate levels were 128 times higher than those registered outdoors. Much lower concentrations, around 1 μg m(-3), were measured in the fronton. The chalk dust is also responsible for the high Mg(2+) concentrations in the gym (4.7 ± 0.89 μg m(-3)), unfolding a PM10 mass fraction of 2.7 %. Total carbon accounted for almost 30 % of PM10 in both indoor spaces. Aerosol size distributions were bimodal and revealed a clear dependence on physical activities and characteristics of the sports facilities. The use of climbing chalk in the gymnasium contributed significantly to the coarse mode. The average geometric mean diameter, geometric standard deviation and total number of coarse particles were 0.77 μm, 2.79 cm(-3) and 28 cm(-3), respectively.

Dispersion of carbon black by a media mill and correlation of its rate constant with beads impact energy

We investigated the dispersion of a carbon black sample by a bead mill under wet conditions and assessed the correlation of its rate constant with the bead impact energy. The carbon black used in the experiment is fine powder of less than 100nm diameter, dispersed in solvent by a bead mill under different milling conditions. The degree of dispersion was defined by a normalized number of coarse particles of carbon black in the slurry; it was correlated with dispersion time, representing an empirical equation. As for the bead impact energy, we simulated the motion of the beads in the mill under wet conditions in different conditions using the Discrete Element Method (DEM). The impact energy of the beads was determined from the bead velocities in different conditions. Results show that the dispersion rate constant of the carbon black sample in the mill is fairly correlated with the impact energy of the beads. It is well correlated with the impact energy of the beads is based on the normal impact energy.

The Influence of Temperature and Oxidation Time on the Preparation of Graphite Oxide

Graphite oxide samples with different oxidation levels were prepared by the oxidation of natural flake graphite based on a modified Hummers method, using different reaction temperatures and oxidation times followed by ultrasonication then centrifugation to obtain the corresponding graphene oxide nanosheet suspensions. The samples were characterized by XRD and AFM. The results show that the oxidation level of graphite oxide samples can be increased by increasing either the reaction temperature or the oxidation time. Well-dispersed suspensions of the graphite oxide samples can be formed in alkaline solution after ultrasonication, especially for samples with higher oxidation levels. A number of coarse particles are observed in the suspensions, particularly those derived from graphite oxide samples with lower oxidation levels, due to the lower degree of exfoliation in these samples, which is influenced by the oxidation level. Rapid sedimentation of these coarse particles can be achieved by high-speed centrifugation, yielding homogenous suspensions of graphite oxide comprising a mass of monolayer graphene oxide nanosheets with lateral dimensions of several hundred nanometers to several micrometers and thickness of ~1.0–1.4 nm.

A 600-year flood history in the Yangtze River drainage: Comparison between a subaqueous delta and historical records

Based on grain size analysis and high-resolution elemental scanning of core YD0901, taken from the subaqueous Yangtze River delta, a 600-year flood history was reconstructed for the Yangtze River drainage system. Zr/Rb ratios were chosen as a proxy for Yangtze River floods. Zr resides mainly in the coarse-grained minerals, and Rb is found in the fine-grained minerals. When floods occur, the discharge of the Yangtze River increases, which carries more coarse-grained minerals into the East China Sea. Therefore, deposition of coarse-grained minerals significantly increases relative to fine-grained minerals on the subaqueous delta, and subsequently the Zr/Rb ratios also increase. The higher the Zr/Rb peaks, the greater number of coarse particles deposited by saltation processes. Zr/Rb peaks correlate very well with historical records for Yangtze River floods. Especially at about AD 1870, the Zr/Rb ratio reached a maximum value over the last 600 years, which is consistent with “the extreme flood event” in the upper and middle reaches of the Yangtze River in AD 1870, as indicated in the historical records. Results show that floods have occurred at a relatively high frequency over the last 600 years, which is consistent with historical records when, during the Ming-Qing Dynasty, floods occurred once every 4 years. In addition, spectral analysis of the Zr/Rb ratio showed that there is close link between the Yangtze River floods and ENSO intensity.

Adsorption of benzoic acid and hydroquinone by organically modified bentonites

Two organobentonites (ODTMA-B, HDTMA-B) were synthesized using hexadecyltrimethyle ammonium bromide (HDTMAB) and octadecyltrimethyle ammonium bromide (ODTMAB). Synthesized organobentonites were characterized by X-ray diffraction particle size, and surface area analysis. Particle size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. While the basal spacings of the organobentonites increased organic cation, the surface area decreased. To evaluate the potential use of two modified bentonites in removing organic pollutants such as benzoic acid and hydroquinone from water, adsorption experiments were performed under conditions of varied pH (3, 6 and 11) and temperatures(298 and 313 K). Experimental results showed that the sorption capacities increase with decreasing pH value and increasing temperature. The adsorption equilibrium of benzoic acid and hydroquinone on organobentonites was described by the Langmuir and Dubinin–Radushkevich (D–R) models. It was concluded that the isotherm shapes were not affected by pH and temperature. Adsorption capacity of ODTMA-B for benzoic acid was higher compared to that of HDTMA-B at various pH and temperatures.

Adsorption of Aromatic Hydrocarbons on BTEA–Bentonites

Organobentonites were synthesized using benzyltrimethyl-ammonium bromide (BTEA) with five different exchange degrees. At low concentrations, the amounts of BTEA exchanged did not reach the value of the cation-exchange capacity (CEC) of the bentonite. To obtain full displacement, it was necessary to add an amount of BTEA four-times greater than the CEC. Synthesized organobentonites were characterized by X-ray diffraction, particlesizeanalysis and infrared spectroscopy. The basal spacings of the organobentonites increased slightly with increasing amounts of BTEA cations. Particle-size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. Toluene and xylenes were used as solutes to determine the adsorption properties of the BTEA–bentonites. The 4BTEA–bentonite was evaluated as an adsorbent of water-soluble aromatic hydrocarbons including toluene and xylenes.

Correlations in the chemical composition of rural background atmospheric aerosol in the UK determined in real time using time-of-flight mass spectrometry.

An aerosol time-of-flight mass spectrometer (ATOFMS) was used to determine, in real time, the size and chemical composition of individual particles in the atmosphere at the remote inland site of Eskdalemuir, Scotland. A total of 51,980 particles, in the size range 0.3-7.4 microm, were detected between the 25th and 30th June 2001. Rapid changes in the number density, size and chemical composition of the atmospheric aerosol were observed. These changes are attributed to two distinct types of air mass; a polluted air mass that had passed over the British mainland before reaching Eskdalemuir, interposed between two cleaner air masses that had arrived directly from the sea. Such changes in the background aerosol could clearly be very important to studies of urban aerosols and attempts at source apportionment. The results of an objective method of data analysis are presented. Correlations were sought between the occurrence of: lithium, potassium, rubidium, caesium, beryllium, strontium, barium, ammonium, amines, nitrate, nitrite, boron, mercury, sulfate, phosphate, fluorine, chlorine, bromine, iodine and carbon (both elemental and organic hydrocarbon) in both fine (d < 2.5 microm) and coarse (d > 2.5 microm) particle fractions. Several previously unreported correlations were observed, for instance between the elements lithium, beryllium and boron. The results suggest that about 2 in 3 of all fine particles (by number rather than by mass), and 1 in 2 of all coarse particles containing carbon, consisted of elemental carbon rather than organic hydrocarbon (although a bias in the sensitivity of the ATOFMS could have affected these numbers). The ratio of the number of coarse particles containing nitrate anions to the number of particles containing chloride anions exceeded unity when the air mass had travelled over the British mainland. The analysis also illustrates that an air mass of marine origin that had travelled slowly over agricultural land can accumulate amines and ammonium.