Charged particle activation studies on the surface of LDEF spacecraft

High energy proton induced nuclear reaction products are examined using seven elements, namely, Aluminum, Silicon, Nickel, Copper, Zirconium, Tantalum, and Tungsten. The samples were in the form of plates, 2 x 2 x 1/8 inches. Activities due to Na-22 from Al, Co-56 and Co-57 from Ni, Co-58 from Cu, and Y-88 from Zr targets were detected. No induced activity was observed in Si, Ta, and W, most probably due to the long cooling times. Only the Zr sample contained a weak Be-7 peak, although Ta and W were also located at the leading edge of the spacecraft. Gamma-rays of individual isotopes were measured using high-resolution Ge(Li) solid state detector coupled to 4096-multichannel analyzer. Activities were calculated for Co-56 (846 keV) and Co-57 (122 and 136 keV's) at the time of the entry of the spacecraft and found to be 0.014 plus or minus 0.005 c/sec. g, 0.018 plus or minus 0.002 c/sec. g, and 0.0024 plus or minus 0.0007 c/sec. g, respectively

Particle bioturbation in Massachusetts Bay: Preliminary results using a new deliberate tracer technique

To better understand temporal and particle size-dependent bioturbation processes, we conducted a study of sediment mixing in Massachusetts Bay using a newly developed deliberate tracer technique. Sediments from a 32-m, fine-grained site were collected and the 38–62 (“silt”) and 63–125 (“sand”) μm fractions isolated. These particle-size fractions were labeled with two different noble metals (Au: silt & Ag: sand) using a thermal diffusion technique. Mixtures of the tracers were spread onto the seafloor in April and July 1992 by divers and were tube-cored (3 replicates) ˜ 80 d later in each case. Vertical profiles of the tracers were measured at μg/g (Ag) and ng/g (Au) levels by instrumental neutron activation analysis. During the spring experiment, Au (silt) was mixed to depths \u3e 15 cm and displayed multiple subsurface maxima, whereas Ag (sand) was confined to the upper 5 cm of the bed and showed a near monotonic decrease in concentration with depth. In the fall experiment, the tracers displayed more congruent down-core profiles consisting of near-surface maxima and several subsurface peaks. Two nonlocal bioturbation modes are suggested by the tracer data: reverse conveyor-belt transport and head-down deposit feeding or excavation. A particle caching strategy by an unidentified macrofaunal species is postulated to explain the subsurface peaks, but remains conjectural without better species-level natural history information regarding solid-phase bioturbation

Al and Fe in PM 2.5 and PM 10 suspended particles in South-Central Florida : The impact of the long range transport of African mineral dust

Abstract. Aluminum and iron were measured in daily samples collected at urban and rural sites near Ft. Myers, Florida, in 1995–1996 using a dichotomous sampler. Al and Fe concentrations were low during most of the year but they increased dramatically during summer when African dust was advected into Florida. The ratio of fine (less than 2.5 m diameter) to coarse (2.5–10 m) Al and Fe is relatively constant in African dust events with the fine accounting for a third to a half of the total. Also the mass ratio of Al-to-Fe is relatively constant at 1.8, a value similar to average crustal material. In contrast, in non-African dust the fine-to-coarse and Al-to-Fe ratios are extremely variable and generally much lower than those during African events when dust concentrations ranged up to 86 g m−3. The timing and magnitude of the Ft. Myers dust peaks closely matched those measured concurrently in Miami, 200 km to the southeast. Large areas of the eastern United States are fre-quently impacted by African dust every summer. Although dust concentrations can reach very high values it seems unlikely that African dust events alone will cause a violation of the Environmental Protection Agency’s standards for PM 2.5 or PM 10. However, African dust in conjunction with emissions from local and regional sources could conceivably present a problem with compliance. The probability of such an occurrence is heightened by the fact that dust concentrations are highest in the summer when pollution levels are often at a maximum in the eastern states

Physical and Chemical Characterization of Atmospheric Ultrafine Particles in the Los Angeles Area

Atmospheric ultrafine particles (diameter < 0.1 μm) are under study by inhalation toxicologists to determine whether they pose a threat to public health, yet, little is known about the chemical composition of ultrafine particles in the atmosphere of cities. In the present work, the number concentration, size distribution, and chemical composition of atmospheric ultrafine particles is determined under wintertime conditions in Pasadena, CA, near Los Angeles. These experiments are conducted using a scanning differential mobility analyzer, laser optical counter, and two micro-orifice impactors. Samples are analyzed to create a material balance on the chemical composition of the ultrafine particles. The number concentration of ultrafine particles in the size range 0.017 < d_p < 0.1 μm, analyzed over 24-h periods, is found to be consistently in the range 1.3 × 10^4 ± 8.9 × 10^3 particles cm^(-3) air. Ultrafine particle mass concentrations are in the range 0.80−1.58 μg m^(-3). Organic compounds are the largest contributors to the ultrafine particle mass concentration. A small amount of sulfate is present in these particles, at concentrations too low to tell whether it exists as unneutralized sulfuric acid. Iron is the most prominent transition metal found in the ultrafine particles. These data may assist the health effects research community in constructing realistic animal or human exposure studies involving ultrafine particles

Physical and Chemical Characterization of Atmospheric Ultrafine Particles in the Los Angeles Area

Atmospheric ultrafine particles (diameter < 0.1 μm) are under study by inhalation toxicologists to determine whether they pose a threat to public health, yet, little is known about the chemical composition of ultrafine particles in the atmosphere of cities. In the present work, the number concentration, size distribution, and chemical composition of atmospheric ultrafine particles is determined under wintertime conditions in Pasadena, CA, near Los Angeles. These experiments are conducted using a scanning differential mobility analyzer, laser optical counter, and two micro-orifice impactors. Samples are analyzed to create a material balance on the chemical composition of the ultrafine particles. The number concentration of ultrafine particles in the size range 0.017 < d_p < 0.1 μm, analyzed over 24-h periods, is found to be consistently in the range 1.3 × 10^4 ± 8.9 × 10^3 particles cm^(-3) air. Ultrafine particle mass concentrations are in the range 0.80−1.58 μg m^(-3). Organic compounds are the largest contributors to the ultrafine particle mass concentration. A small amount of sulfate is present in these particles, at concentrations too low to tell whether it exists as unneutralized sulfuric acid. Iron is the most prominent transition metal found in the ultrafine particles. These data may assist the health effects research community in constructing realistic animal or human exposure studies involving ultrafine particles

Atmospheric trace elements in Ankara Turkey 1 factors affecting chemical composition of fine particles

Fine and coarse aerosol samples were collected between February and June 1993, in Ankara, Turkey using a stack filter unit (SFU). Collected samples were analyzed for approximately 40 trace elements and major ions using a combination of instrumental neutron activation analysis, atomic absorption spectromerty and ion chromatography. Particle sizing characteristics of the SFU was tested against dichotomous sampler and the sampler was found to be a good alternative for more expensive particle sizing devices. Fossil fuel combustion was found to be the main source of anthropogenic elements in aerosols, including the ones with well-known industrial sources. Atmospheric loading and seasonal variations in the concentrations of crustal elements are determined by the variations in wind speed and moisture of the soil. Short-term episodes in the concentrations of all elements are governed by local meteorology, particularly by the wind speed and mixing height. Concentrations of elements with anthropogenic origin have fairly similar concentrations in all wind sectors as they are distributed uniformly over the city and its suburbs due to low annual average wind speed. However, these elements showed directional preferences in samples which correspond to wind speeds higher than 2.5 m s(-1). Change in the concentrations of anthropogenic elements in Ankara atmosphere is consistent with the history of regulatory actions taken to reduce air pollution. Moreover, an unexpected decrease in the concentrations of crustal elements between 1975 and 1993 is related to reduction in exposed earth surface due to rapid urban developments. (C) 2000 Published by Elsevier Science Ltd. All rights reserved