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.

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We propose using a wireless network to facilitate communications between sensors/switches and control units located within a vehicle. In a typical modern vehicle, the most demanding sensor will require a latency of approximately less than 1 msec with throughput of 12 kbps. Further, the network will need to support about 15 sensors with this requirement. The least demanding sensor will require a latency of approximately 50 msec with data throughput rate of 5 bps and will need to support about 20 of these types of devices. Initial part of this paper gives an overview of the issues spanning several layers of the protocol stack. Then, we focus on the Medium access control (MAC) layer and derive necessary design parameters based on given network requirements. We evaluate the IEEE 802.15.4 standard with respect to its suitability for use in a prospective intra-vehicle wireless sensor network.

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The assessment of human health and ecological risks at chemically contaminated sites often includes the use of models to assess chemical transport, fate, and exposure/toxicity. These models require input data on a variety of physical and chemical properties for each compound of concern. Small changes in some of these parameters may result in significant differences in estimated human health or ecological risks and in the extent of required remediation efforts. The octanol-water partition coefficient (K ow ) for hydrophobic organic compounds is one such parameter, particularly because it is often used to estimate additional partitioning and bioaccumulation parameters. Unfortunately, there is considerable variability among tabulated K ow values for many compounds of concern. This paper assesses the implications of using various values of K ow to calculate health-protective polychlorinated biphenyl (PCB) sediment quality objectives (SQOs) in a case study using a simplified food chain model and the range of K ow values available from or recommended by the U. S. EPA. For the site and K ow values considered in this study, which are a snapshot of values available in the spring of 2004, the SQOs differ by as much as a factor of 5. This range of SQOs is estimated to correspond to a difference in remediation costs of $48 million.