H.-W. Georgii

An experimental investigation of the absorption of sulphur dioxide by water drops containing heavy metal ions

SO2 absorption by 2 mm dia. droplets of dilute heavy metal solutions (concentration 10−6−10−4 m) exposed to trace concentration of SO2 in air (10–1000 ppb) was measured at 25 and 8°C. Manganese and iron ions were effective catalysts of SO2 oxidation in acidic solutions but copper ions were not. Results indicate that the manganese ion Mn2+ formed complexes [Mn2+(SO32−)3]−4 before taking part in the oxidation reaction. The rate of SO2 absorption by a droplet of catalyst solution decreased with decreasing pH. Decreasing the temperature of a manganese solution from 25 to 8°C caused a five- to ten-fold decrease in SO2 absorption rate. The addition of iron ions (Fe2+ or Fe3+) to solutions of Mn2+ not only increased the rate of SO2 oxidation but also reduced the dependence of absorption rate on temperature. A quantitative estimate of the rate of SO2 removal by a typical urban cloud led to SO2 removal rates between 0.08 and 2.0% h−1 depending on temperature and the heavy metal content of the cloud water.

LARGE SCALE SPATIAL AND TEMPORAL DISTRIBUTION OF SULFUR COMPOUNDS

Abstract The paper contains new results on the large-scale distribution of SO 2 , H 2 S and sulfate-aerosols. Recently developed analytical methods permit the measurement of SO 2 in the upper troposphere and lower stratosphere as well as first measurements of the background-concentration of H 2 S. Measurements of H 2 S close to the ground and in relation to the air-temperature above the ground shows a temperature-dependence of H 2 S-release from the soil by biogenic activity. The measurement of sulfateaerosols over the ocean clarified the picture of the formation of maritime sulfate-aerosols and explained the existence of excess sulfate in the maritime atmosphere. Decay of SO 2 and transformation of SO 2 to sulfate was also studied in a meso-scale study over the continent which supplied further information on the influence of anthropogeneous SO 2 sources on the large-scale sulfur budget. Vertical profiles of SO 2 resulting from aircraft measurements over the continent and the Atlantic ocean are compared They are of importance to evaluate the transport and decay of SO 2 over long distances and also indicate the sink function of the ocean surface for the uptake of SO 2 .

The Kleiner Feldberg Cloud Experiment 1990. An overview

An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 November 1990. The experiment was carried out by numerous European research groups as a joint effort within the EUROTRAC-GCE project in order to study the interaction of cloud droplets with atmospheric trace constituents. After a description of the observational site and the measurements which were performed, the general cloud formation mechanisms encountered during the experiment are discussed. Special attention is given here to the process of moist adiabatic lifting. Furthermore, an overview is given regarding the pollutant levels in the gas phase, the particulate and the liquid phase, and some major findings are presented with respect to the experimental objectives. Finally, a first comparison attempts to put the results obtained during this campaign into perspective with the previous GCE field campaign in the Po Valley.

The size-dependent chemical composition of cloud droplets

Abstract Size-dependent cloud droplet solute concentrations were measured using a two-stage fog water impactor at the summit station of Great Dun Fell (GDF) in the north of England. The measurements showed mostly higher concentrations in the small-droplet fraction. During one cloud event, however, higher solute concentrations were found in the larger-droplet fraction. In order to identify the factors governing the size dependence of cloud droplet solute concentrations, sensitivity studies by means of a diffusional growth model were performed. The time available for the droplets to grow was identified to be of great importance for the size dependence of solute concentrations. In cases when higher solute concentrations were found in the fraction containing the bigger droplets, the cloud droplets were relatively young having been formed by orographic lifting of the air at the GDF summit. For the other events the evidence indicates that the cloud was already formed far upwind from the summit site. Our experimental and model results imply that, after an initially strong decrease of solute concentrations with droplet size we would observe: • ⊎|increasing solute concentrations with increasing diameters during the initial stage of a cloud, e.g. near cloud base where the droplets have just been formed. The primary factors contributing to this behaviour are high peak supersaturations, large numbers of coarse aerosol particles, and high solubility of the aerosol particles. • ⊎|decreasing solute concentrations with increasing diameters in aged cloud parcels, such as those which can be observed high above the cloud base in cumuliform clouds or are advected to the observation point in the case of stratiform clouds. The primary factors contributing to this behaviour are low peak supersaturations, low numbers of coarse particles, and low solubility of the aerosol particles.

Measurements of gaseous lead alkyls in polluted atmospheres

Abstract The gaseous lead alkyls in ambient air were collected by enrichment in an adsorption tube at liquid air temperature. The desorbed lead alkyls were analyzed by atomic adsorption spectrometry. The measured concentrations of the gaseous lead alkyls vary between 0.001 μm −3 in the environment of Frankfurt/Main and 0.2μgm −3 in a city-street with high traffic-density. Paniculate lead was simultaneously measured. The ratio of gaseous organic lead to particulate lead varies with time and space between 1 and 20%. Within a street canyon particulate lead concentrations decrease more rapidly with altitude than the gaseous lead compounds. Chromatographie separation of lead alkyl samples showed that the more volatile and chemically more stable tetra-methyl-lead (TML) represents roughly 3 4 of gaseous lead in urban atmosphere.

Contributions of H2S to the atmospheric sulfur cycle

H2S is a most important biogenic sulfur compound with regard to the atmospheric sulfur cycle. Our present knowledge of the spatial and temporal distribution of this trace gas is rather incomplete owing to unreliable analytical methods. Therefore, a new method for the analysis of H2S in the μg-range was applied. This paper deals with the results of ground- and aircraft measurements of H2S in unpolluted air over swamps and tidal flats. Based on the measured vertical distributions a removal coefficient of 2.3×10−5 sec−1 and an average lifetime of 12 hours were calculated. Some conclusions of the contribution of H2S to the atmospheric sulfur budget are added.

Deposition of acidic components and heavy metals in the Federal Republic of Germany for the period 1979–1981

Abstract The paper discusses the results of the measurement of wet and dry deposition of sulfate, nitrate, chloride and heavy metal aerosols which were obtained from a network established in the Federal Republic of Germany during 1979 to 1981. The results characterize the deposition-pattern with respect to time and space.

A. TWO-STAGE IMPACTOR FOR FOG DROPLET COLLECTION: DESIGN AND PERFORMANCE

A two-stage fog water impactor was designed for the measurement of size-dependent cloud droplet solute concentrations. The instrument achieves isokinetic sampling conditions by using a variable inlet as well as by using a rotating stand in connection with a wind vane to keep the impactor aligned with the actual mean wind direction. These features are important for reliable results, especially at the high wind velocities which frequently occur at mountain stations. The instrument operated successfully during the Great Dun Fell Cloud Experiment in spring 1993. The results of field measurements, as well as of cloud chamber experiments to test the performance of the instrument are presented.

Design and Operation of a Two-Stage Fogwater Collector

A sampling device has been developed, which allows to separate the fog droplet spectrum into two size fractions. The first stage collects droplets down to a diameter of 4 μm using a string collector technique. The second stage with a calculated 50 % cut-off diameter of 2 μm was constructed under application of numerically developed and experimentally proven design criteria. Depending on the actual liquid water content, the collector has been operated with a time resolution of 60–120 minutes during several fog events under different conditions. The samples have been analyzed for pH and total conductivity as well as for the major ions by Ion Chromatography. Concentration values in smaller droplets were found to be up to 14 times higher than the corresponding concentrations in larger droplets.

Biogenic Sulfur Compounds in Seawater and the Marine Atmosphere

Dimethyl Sulfide (DMS), Carbonyl Sulfide (COS) and Carbon Disulfide (CS2) were determined in surface water and the overlying atmosphere during a cruise between Bremerhaven, FRG (52°N) and Rio Grande do Sul, Brasil (32°S) on board the polar research vessel ‘Polarstern’. The cruise track included both oligotrophy and coastal waters, the air samples included both remote marine air and air masses influenced by terrestrial or coastal inputs. The ranges of measured atmospheric concentrations for all samples were 5 –100 pptv DMS, 420 – 670 pptv COS and <3 –160 pptv CS2. Both atmospheric DMS and CS2 in the marine boundary layer were characterized by a significant spatial variability, in particular an increase of DMS and a rapid decrease of CS2 with distance from land has been found. Due to its long tropospheric lifetime COS was distributed fairly homogeneous along the cruise track showing a mean of 550 pptv. With respect to atmospheric DMS, COS and CS2 seawater was found to be supersaturated with dissolved Dimethyl Sulfide, Carbonyl Sulfide and Carbon Disulfide. The results show DMS to be the dominant sulfur gas in all the waters examined, with less amounts of COS and CS2. Our measurements reveal daytime maxima in dissolved COS and CS2 concentrations, indicating photochemical influenced sources of these sulfur compounds in seawater.