Intercomparison of aerosol optical depth measurements in the UVB using Brewer Spectrophotometers and a Li-Cor Spectrophotometer

The first Iberian UV radiation intercomparison was held at “El Arenosillo”-Huelva station of the Instituto Nacional de Técnica Aeroespatial (INTA) from September 1 to 10, 1999. During this campaign, seven Brewer spectrophotometers and one Li-Cor spectrophotometer measured the total column aerosol optical depth (AOD) at 306, 310, 313.5, 316.75 and 320 nm. The AOD calibration of one Brewer was transferred to all other Brewers using one day of intensive measurements. The remaining days were used to observe the stability and reproducibility of the AOD measurements by the different instruments. All Brewer spectrophotometers agreed to within an AOD of 0.03 during the whole measurement campaign. The differences in AOD between the Li-Cor spectrophotometer and the Brewer spectrophotometers were between −0.07 and +0.02 at 313.5, 316.75, and 320 nm. This investigation demonstrates the possibility of using the existing worldwide Brewer network as a global UV aerosol network for AOD monitoring.The first Iberian UV radiation intercomparison was supported by the CICYT, project CLI97- 0345-C05-05 under the coordination of INM

An Approximation for the rp-Process

Hot (explosive) hydrogen burning or the Rapid Proton Capture Process (rp-process) occurs in a number of astrophysical environments. Novae and X-ray bursts are the most prominent ones, but accretion disks around black holes and other sites are candidates as well. The expensive and often multidimensional hydro calculations for such events require an accurate prediction of the thermonuclear energy generation, while avoiding full nucleosynthesis network calculations. In the present investigation we present an approximation scheme applicable in a temperature range which covers the whole range of all presently known astrophysical sites. It is based on the concept of slowly varying hydrogen and helium abundances and assumes a kind of local steady flow by requiring that all reactions entering and leaving a nucleus add up to a zero flux. This scheme can adapt itself automatically and covers situations at low temperatures, characterized by a steady flow of reactions, as well as high temperature regimes where a $(p,\gamma)-(\gamma,p)$-equilibrium is established. In addition to a gain of a factor of 15 in computational speed over a full network calculation, and an energy generation accurate to more than 15 %, this scheme also allows to predict correctly individual isotopic abundances. Thus, it delivers all features of a full network at a highly reduced cost and can easily be implemented in hydro calculations.Comment: 18 pages, LaTeX using astrobib and aas2pp4, includes PostScript figures; Astrophysical Journal, in press. PostScript source also available at http://quasar.physik.unibas.ch/preps.htm

Air pollutants in office environments and emissions from electronic equipment: a review

The aim of this review is to evaluate the existing knowledge on the presence of indoor air contaminants in office buildings. The most commonly found chemicals are aromatic compounds (BTEX), linear and cyclic alkanes (hexane, nonane, methyl-cyclohexane, terpenes (α-pinene, limonene), carbonyl compounds (formaldehyde, acetaldehyde) and particulate matter. Concentrations of volatile organic compounds (VOC) in office buildings in Europe and North America are in the range of 0.1-1000 μg/m3, with average concentrations being in most cases <100 μg/m3. Higher concentrations (up to 1600 μg/m3) were measured in Asiatic countries. Thus, concentrations of benzene and toluene in European countries range from 2 to 11.2 and from 4.3 to 43.1 μg/m3, respectively, while, in non-European countries, concentrations range from 3.4 to 87.1 and from 52.8 to 287.3 μg/m3, respectively. Emission rates of chemicals from office equipment (including fax machines, laser jet printers, ink-jet printers, scanners, and photocopying machines) were studied in test chambers. Highest emission rates were obtained for toluene, ethylbenzene, m,p-xylene, and styrene, as these compounds are normally used as solvent in toner for printers. Emissions from desktop computers using CRT or TFT screens include aromatic hydrocarbons, alkanes, alcohols, ketones and aldehydes, particularly formaldehyde, with emission rates up to 103 μg/h per unit. For particles, the PM levels measured in European offices range from 7 to 180 μg/m3 (for PM10) and 5 to 60 μg/m3 (for PM2.5). Indoor/Outdoor ratios ranged from 0.34-0.88 (for PM2.5) and 0.46-1.7 (for PM10). Significant PM levels are generally found during operation of printers, copy machines and multi-functional devices.JRC.I.1-Chemical Assessment and Testin

Constraining the astrophysical origin of the p-nuclei through nuclear physics and meteoritic data

A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-processes. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called γ-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the γ-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiencies remain. An increasing number of processes and sites has been studied in recent years in search of viable alternatives replacing or supplementing the massive star models. A large number of unstable nuclei, however, with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may also bear considerable uncertainties. The current status of astrophysical models, nuclear input and observational constraints is reviewed. After an overview of currently discussed models, the focus is on the possibility to better constrain those models through different means. Meteoritic data not only provide the actual isotopic abundances of the p-nuclei but can also put constraints on the possible contribution of proton-rich nucleosynthesis. The main part of the review focuses on the nuclear uncertainties involved in the determination of the astrophysical reaction rates required for the extended reaction networks used in nucleosynthesis studies. Experimental approaches are discussed together with their necessary connection to theory, which is especially pronounced for reactions with intermediate and heavy nuclei in explosive nuclear burning, even close to stability.Peer reviewe