D.T. Jost

Heterogeneous production of nitrous acid on soot in polluted air masses

Polluted air masses are characterized by high concentrations of oxidized nitrogen compounds which are involved in photochemical smog and ozone formation. The OH radical is a key species in these oxidation processes. The photolysis of nitrous acid (HNO2), in the morning, leads to the direct formation of the OH radical and may therefore contribute significantly to the initiation of the daytime photochemistry in the polluted planetary boundary layer. But the formation of nitrous acid remains poorly understood: experimental studies imply that a suggested heterogeneous formation process involving NO2 is not efficient enough to explain the observed night-time build-up of HNO2 in polluted air masses. Here we describe kinetic investigations which indicate that the heterogeneous production of HNO2 from NO2 on suspended soot particles proceeds 105 to 107 times faster than on previously studied surfaces. We therefore propose that the interaction between NO2 and soot particles may account for the high concentrations of HNO2 in air masses where combustion sources contribute to air pollution by soot and NOx emissions. We believe that the observed HNO2 formation results from the reduction of NO2 in the presence of water by C–O and C–H groups in the soot. Although prolonged exposure to oxidizing agents in the atmosphere is likely to affect the chemical activity of these groups, our observations nevertheless suggest that fresh soot may have a considerable effect on the chemical reactions occurring in polluted air.

The epiphaniometer, a new device for continuous aerosol monitoring

A new device is described, which allows continuous monitoring of aerosols of any kind. Air is continuously pumped through a closed chamber containing short-lived 211Pb atoms delivered by a 227Ac source. These atoms attach onto the aerosol particles. After transportation through a thin capillary to a filter and counting station the particles are detected by means of an α-detector for measuring the decay of 211Pb (via 211Bi). Due to the relatively short half-life of 211Pb, the system allows continuous monitoring of aerosols without changing or transporting the filter. The measured signal is proportional to the exposed Fuchs surface of the aerosol particles. In the case of environmental applications, the device is therefore most sensitive to particles contained in the accumulation mode. Due to its high sensitivity it also works well at the lowest particle concentrations of less than 100 ng m−3 with gas flow rates as low as 1 l min−1.

Chemical properties of element 106 (seaborgium)

The synthesis, via nuclear fusion reactions, of elements heavier than the actinides, allows one to probe the limits of the periodic table as a means of classifying the elements. In particular, deviations in the periodicity of chemical properties for the heaviest elements are predicted as a consequence of increasingly strong relativistic effects on the electronic shell structure. The transactinide elements have now been extended up to element 112 (ref. 8), but the chemical properties have been investigated only for the first two of the transactinide elements, 104 and 105 (refs 9,10,11,12,13,14,15,16,17,18,19). Those studies showed that relativistic effect render these two elements chemically different from their lighter homologues in the same columns of the periodic table (Fig. 1). Here we report the chemical separation of element 106 (seaborgium, Sg) and investigations of its chemical behaviour in the gas phase and in aqueous solution. The methods that we use are able to probe the reactivity of individual atoms, and based on the detection of just seven atoms of seaborgium we find that it exhibits properties characteristic of the group 6 homologues molybdenum and tungsten. Thus seaborgium appears to restore the trends of the periodic table disrupted by relativistic effects in elements 104 and 105.

The Jungfraujoch high-alpine research station (3454 m) as a background clean continental site for the measurement of aerosol parameters

The first annual data set of climatically important aerosol parameters, measured at the Jungfraujoch (JFJ) high-alpine research station (3454 m, Switzerland) from an ongoing field campaign since July 1995, is presented. Analysis of diurnal variations in continuous measurements of the total and backward hemispheric scattering coefficients (σSP, σBSP), the absorption coefficient (σAP, from aethalometer data), condensation nuclei (CN) concentration, and epiphaniometer signal (related to surface area (S) concentration) established the diurnal period 0300 – 0900 as being representative of the free tropospheric background aerosol. The annual data set was then edited to omit (1) the period 0900–0300 (i.e., 18 hours), taken to represent possible planetary boundary layer influenced conditions and (2) in-cloud conditions using a cloud liquid-water monitor. The seasonal aerosol cycle exhibited a July maximum and a December minimum in most aerosol parameters. Typical monthly median values for the free troposphere exhibit the following seasonal maxima and minima, respectively: σSP (550 nm) ∼ 16.1 and 0.43 × 10−6 m−1, σBSP (550 nm) ∼ 2.10 and 0.09 × 10−6 m−1, σAP (550 nm) ∼ 10.4 and 0.76 × 10−7 m−1 (≈ 104 and 7.6 ng m−3 black carbon), CN concentration ∼ 670 and 280 cm−3, and epiphaniometer signal ∼ 9.26 and 0.67 counts s−1 (S concentration ≈24.1 and 1.7 μm2 cm−3). Aerosol parameters were found to be comparable in magnitude to other NOAA baseline and regional stations and suggest that a clean continental designation for the JFJ site is applicable, when removing the planetary boundary layer influenced period.

Continuous background aerosol monitoring with the epiphaniometer

Abstract For the first time, continuous monitoring of background aerosols in the Alps, at altitudes up to 4450 m a.s.l. was performed. As a measuring device, the newly developed epiphaniometer was used, which measures the exposed Fuchs surface of the aerosol particles. High concentration ranges of more than four orders of magnitude were found, with the lowest concentrations corresponding to about 2 ng m −3 . The results show that in winter the highest sites in the Alps are not reached by polluted air masses from lower regions, whereas in the other seasons the planetary boundary layer can extend to as high as 4450 m.

IVO, a device for in situ Volatilization and On-line detection of products from heavy ion reactions

Abstract A new gaschromatographic separation system to rapidly isolate heavy ion reaction products in the form of highly volatile species is described. Reaction products recoiling from the target are stopped in a gas volume and converted in situ to volatile species, which are swept by the carrier gas to a chromatography column. Species that are volatile under the given conditions pass through the column. In a cluster chamber, which is directly attached to the exit of the column, the isolated volatile species are chemically adsorbed to the surface of aerosol particles and transported to an on-line detection system. The whole set-up was tested using short-lived osmium (Os) and mercury (Hg) nuclides produced in heavy ion reactions to model future chemical studies with hassium (Hs, Z =108) and element 112. By varying the temperature of the isothermal section of the chromatography column between room temperature and −80°C, yield measurements of given species can be conducted, yielding information about the volatility of the investigated species.

Cold fusion reactions with 48Ca

Abstract Fusion reactions of 48 Ca projectiles with 180 Hf, 184 W, 197 Au, 208 Pb and 209 Bi targets were studied. Highest cross sections were found in the 208 Pb( 48 Ca,2n) 254 No channel with σ max 3.2 ± 0.3 μb. The results of the heavier systems are discussed in terms of the extra — push model. For the lighter systems missing cross section is observed if compared to estimates made by the evaporation code HIVAP.

OLGA II, an on-line gas chemistry apparatus for applications in heavy element research☆

Abstract OLGA II is a device which performs on-line gas phase separations of volatile compounds of atoms produced in nuclear reactions. Reaction products are attached to aerosol particles and transported in a gas-jet to a heated quartz column and stopped in a quartz wool plug kept at 900 to 1000°C. Volatile compounds are formed by the addition of reactive gases. The volatile compounds are transported along a cooler, isothermal part of the column by the gas flow. The retention time in the isothermal part of the column is related to the enthalpies of adsorption of the compounds on the quartz surface. Separated atoms leaving the column are attached to new aerosol particles and transported through a second gas-jet to a detection system. This apparatus consists of a modified tape system. In a first collecting chamber the products are deposited on the surface of a stepwise moving tape. At preset times the deposited activity is moved past a series of six counting chambers equipped with charged particle or high-purity germanium detectors for α, spontaneous-fission, X- and γ-ray counting. Data acquisition is performed event-by-event which allows to detect also correlated events. The system can be used for nuclides with half-lives longer than about 10 s. Correlated events can be resolved for times ⩾ 150 μs between consecutive decays.

Radon and thoron decay product and 210Pb measurements at Jungfraujoch, Switzerland

Abstract During one year, the atmospheric activity concentrations of the short-lived “radon” (222Rn) and “thoron” (220Rn) decay products were measured at Jungfraujoch (3450 m a.s.l.). The measurements were performed using a modified epiphaniometer, with a time resolution of 1 h. In addition, also the long-lived radon decay product 210Pb was measured with a time resolution of one month. Strong seasonal variations of all activity concentrations were found, the average summer values being a factor of ten higher than the average winter values. During summer time the activity concentrations of the radon and thoron decay products showed. pronounced diurnal variations. During winter these diurnal variations were absent, and the activity concentrations were close to free tropospheric background values. From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time of aerosol particles in the atmosphere of about six days could be estimated. The average activity concentrations of the radon and thoron decay products at Jungfraujoch were found to be related to the regional soil temperatures at a near-by low altitude Swiss Midland site and to the static stability of the air mass between this Midland site and the Jungfraujoch. Furthermore, a significant correlation was found between the radon and thoron decay product activity concentrations and synoptic situations with higher than average activity concentrations for air flours from NE to SW and lower than average concentrations for air flows from W to N.

Trajectory Analysis of High-Alpine Air Pollution Data

The EUROTRAC subproject ALPTRAC (High Alpine Aerosol and Snow Chemistry Study) is devoted to the investigation of air and snow pollution at high Alpine sites. The aerosol surface concentration is continuously recorded at Jungfraujoch (3450 m a.s.1., 7° 59’E, 46° 32’N) in the Swiss Alps and Sonnblick (3106 m a.s.1, 12° 57’E,47° 03’N) in the Austrian Alps with a time resolution of 30 min with an epiphaniometer (Gaggeler et al., 1989; Baltensperger, et al. 1991). The measurements showed a pronounced seasonal cycle with mean summer concentrations more than one order of magnitude higher than mean winter concentrations, and the occurrence of episodes with especially high or low concentrations (Seibert et al., 1993). While the seasonal cycle is mainly to be explained by the atmospheric stability, the short-term variations are caused by synoptic-scale transports. These have been investigated using isobaric back trajectories at 700 hPa with a length of 72 h, computed twice daily for a period of three years (July 1990 - June 1993). Due to technical problems at Sonnblick, only 925 trajectories were available for the analysis; most of the missing data fall on winter.