Sozialhilfe - ein Ueberblick: rechtliche Grundlagen und empirische Entwicklung

Available from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel W 158 (N.F.42) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Modeling heterogeneous sulphate production in maritime stratiform clouds

A size-resolved droplet physico chemical model linked to a Lagrangian parcel framework was developed and used to study the heterogeneous sulphate production process in marine stratiform clouds. This model study provides a rigorous approach to cloud chemistry processing by treating the effects of non ideal chemistry on both aqueous phase equilibration and droplet growth using the Pitzer method to overcome many of the shortcomings of alternative thermodynamic methods. In addition, the current study uses a multi modal representation of sea-salt aerosol, rather than the single mode used in most previous work. The results of the model simulations showed a distribution of sulphate production across the aerosol size range that was non linear and that a significant fraction ((Minus tilde sign)75-90%) of the sulphate was produced in droplets formed on sea-salt aerosol particles. The number of sea-salt particles affected both the total amount of sulphate produced and the fraction produced on cloud droplets formed around non-sea-salt sulphate aerosol. Dissolved ozone and hydrogen peroxide were both important as oxidant species, although the ozone-driven oxidation pathway was dominant in droplets formed on sea-salt aerosol particles. The rate of sulphate production was found to be a non linear function of the gaseous sulphur dioxide concentration at cloud base and only very weakly dependent on sulphate nuclei concentration. A comparison of sulphate production in cloud and below cloud indicates that sulphate production in sea-salt nuclei is not limited by the carbonate buffer and that in-cloud production can exceed, many times, that of cloud-free production due to the "virtual" buffering capacity of the cloud. The use of non ideal solution effects appear important, particularly for clean-to-moderately polluted SO2 concentrations (< 500 parts per trillion) and when sea-salt nuclei are present, resulting in at least 40% lower sulphate production when compared to ideal solution simulations

Evolution of the vertical profile and flux of large sea-salt particles in a coastal zone

Journal of Geophysical Research, Vol. 106, No. D11, pp. 12,039 - 12,053, June 16, 2001.In the vicinity of the North Carolina Outer Banks we observed both steady onshore flow conditions and a continental air mass transition into a marine boundary layer. Using the CIRPAS Twin Otter aircraft, we measuredc hangesin the columnb urden of sea salt as the air mass was advected out to sea. We also measured the flux of whitecap-generatesde a-saltp articlesi n neutrallys tablea tmospherea t wind speedso f 4, 8, and1 2r n s- •. Productioonf saltp articleass s malla s0 .27/•mi n diametewr aso bserved. Furthermore,w e measureds alt particle size distributionsa t variousw ind speedsd uring alongs horew ind and near steadys tate conditionsU. sing thesem easurementsa s a frame of reference,w e discussth e very large differencesi n the reported size and flux of sea salt presentedi n the literature. The disagreemenitn reported salt fluxesi s larger for smallersizedp articles( almosta n order of magnitude)a nd is most likely due to assumptionms ade when the fluxesw ere computed,e speciallyt he particle dry depositionv elocitya nd air mass history.H owever,f or giant salt particlesw ith short atmosphericli fetimes (>-10/•m in diameter),t here is generala greementb etweenf luxesa nd size distributionsm easuredi n this studya nd previouso nes.R eported salt particle size distributionsin the literature also vary considerablyu nder similar steadyw ind and stability conditions.F rom these and our results it is clear that no more than half of the variance in salt particle concentration can be explainedb y wind speeda lone, suggestingth at the idea of "steadys tate" in the marine boundary layer rarely exists at midlatitudes

Biogenic sulphur emissions and inferred non-sea-salt-sulphate cloud condensation nuclei in and around Antarctica.

Accumulation mode aerosol properties and biogenic sulphur emissions over the South Atlantic and Antarctic Oceans are examined. Two contrasting air masses, polar and maritime, each possessing distinct aerosol properties, were encountered during the summer months. By examining aerosol volatile properties, polar air masses arriving from the Antarctic continent were shown to consist primarily Of H2SO4 in the accumulation mode size range, with inferred NH+ 4 to SO= 4 molar ratios close to zero. By comparison, air masses of temperate maritime origin were significantly neutralized with molar ratios of ≈1. These results suggest a deficit of ammonia in polar air masses compared with that in maritime air masses. Dimethyl sulphide (DMS) exhibited no correlation with its putative aerosol oxidation products, although spatial coherence in atmospheric concentrations of DMS, methane sulphonic acid (MSA), and non-sea-salt (nss)-sulphate mass was observed. Volatility analysis, used to infer nss-sulphate cloud condensation nuclei (nss-sCCN) active at a supersaturation of ≈0.2%, indicates that nss-sCCN mass and number concentration were best correlated with MSA mass (r≈0.63). Aerosol volatility identified the presence of MSA in submicron non-sea-salt aerosol; however, its contribution to the aerosol mass was small relative to the contribution of sulphuric acid and ammonium bisulphate/sulphate aerosol. The marine sulphur cycle appears strongly coupled to the sea-salt cycle with, typically, 80–90% of nss-sulphate thought to be internally mixed with sea-salt aerosol. During the austral Summer of 1992/1993, a period of strong biological productivity in the Weddell Sea and sub-Antarctic Ocean, particularly during ice-melt, the cruise-average DMS flux of 61 μg m−2 d−1 corresponded to a very modest average nss-sCCN concentration of 21 cm−3. Observed peak values of DMS flux and inferred nss-CCN concentrations during the cruise were 477 μg m−2 d−1 and 64 cm−3, respectively. Events of new particle formation were identified in the Weddell Sea and occurred under conditions of high DMS flux and low aerosol surface area