Gas/particle partitioning and global distribution of polycyclic aromatic hydrocarbons – A modelling approach

The global atmospheric distribution and long-range transport (LRT) potential of three polycyclic aromatic hydrocarbons (PAH) - anthracene, fluoranthene and benzo[a]pyrene - are studied. The model used is a global aerosol-chemistry-transport-model, which is based on an atmospheric general circulation model. The model includes an in-built dynamic aerosol model coupled to two-dimensional surface compartments. Several parameterisations of gas/particle partitioning and different assumptions of degradation in the aerosol particulate phase were tested. PAHs are mostly distributed in the source regions but reach the Arctic and the Antarctic. The Canadian Arctic is predicted to be significantly less affected by mid-latitude PAH emissions than the European Arctic. Re-volatilisation is significant for semivolatile PAHs. Accumulation of semivolatile PAHs in polar regions, however, is not indicated. The model study suggests that gas/particle partitioning in air drastically influences the atmospheric cycling, the total environmental fate (e.g. compartmental distributions) and the LRT potential of the substances studied. A parameterisation which calculates the gas/particle partitioning assuming absorption into organic matter and adsorption to black carbon (soot) agrees best with the observations at remote sites. The study provides evidence that the degradation in the particulate phase must be slower than that in the gas-phase. The predicted concentrations of the semivolatile PAHs anthracene and fluoranthene in near-ground air at remote sites in mid and high northern latitudes are in line with measured concentrations, if adsorption of the substances to soot combined with absorption in particulate organic matter is assumed to determine gas/particle partitioning, but cannot be explained by adsorption alone (Junge-Pankow parameterisation of gas/particle partitioning). The results suggest that PAHs absorbed in the organic matrix of particulate matter is shielded from the gas-phase. (C) 2009 Elsevier Ltd. All rights reserved. [References: 42

Anreicherung persistenter organischer Schadstoffe in den Polargebieten - Untersuchungen mit Modellwerkzeugen

tmospharische Transporte vermogen Stoffe zwar innerhalb weniger Tage von mittleren in hohe Breiten zu verfrachten. Die globale Verteilung chemisch sehr unterschiedlicher mittelfluchtiger organischer Stoffe wird aber durch Multikompartimentprozesse kontrolliert. Fur die Untersuchung von grosraumiger Verfrachtung in die, und Verbleib von Spurenstoffen in den Polargebieten eignen sich komplexe Modelle, die die naturraumlichen Gegebenheiten und die Chemodynamik auflosen. Es wurde ein auf einem sog. Klimamodell aufbauendes Multikompartiment-Chemie-Transport-Modell entwickelt und zur Untersuchung grosraumigen Stoffausbreitungs- und -verteilungsverhaltens angewandt. Tatsachlich wird gefunden, dass das Ferntransportpotenzial mittelfluchtiger Stoffe aufgrund mehrerer Emissions-Transport- Depositions-Zyklen erhoht ist (sog. Grashupfer-Effekt oder Multi-hopping). Das Modellexperiment sagt eine Anreicherung von ƒÁ-HCH (nicht aber von DDT) in der Arktis und Antarktis jedoch auch ohne den Grashupfer-Effekt voraus, d.h. allein aufgrund des Transports in der Atmosphare, der einer Erstemission folgt. Offenbar ist die Anreicherung der mittelfluchtigen und schwer abbaubaren Stoffe in den Polargebieten nicht notwendigerweise auf Multi-hopping zuruckzufuhren, sondern kann auch meteorologisch bedingt sein

FEBUKO and MODMEP: Field measurements and modelling of aerosol and cloud multiphase processes

An overview of the two FEBUKO aerosol–cloud interaction field experiments in the Thüringer Wald (Germany) in October 2001 and 2002 and the corresponding modelling project MODMEP is given. Experimentally, a variety of measurement methods were deployed to probe the gas phase, particles and cloud droplets at three sites upwind, downwind and within an orographic cloud with special emphasis on the budgets and interconversions of organic gas and particle phase constituents. Out of a total of 14 sampling periods within 30 cloud events three events (EI, EII and EIII) are selected for detailed analysis. At various occasions an impact of the cloud process on particle chemical composition such as on the organic compounds content, sulphate and nitrate and also on particle size distributions and particle mass is observed. Moreover, direct phase transfer of polar organic compound from the gas phase is found to be very important for the understanding of cloudwater composition. For the modelling side, a main result of the MODMEP project is the development of a cloud model, which combines a complex multiphase chemistry with detailed microphysics. Both components are described in a fine-resolved particle/drop spectrum. New numerical methods are developed for an efficient solution of the entire complex model. A further development of the CAPRAM mechanism has lead to a more detailed description of tropospheric aqueous phase organic chemistry. In parallel, effective tools for the reduction of highly complex reaction schemes are provided. Techniques are provided and tested which allow the description of complex multiphase chemistry and of detailed microphysics in multidimensional chemistry-transport models

Global fate and distribution of polycyclic aromatic hydrocarbons emitted from Europe and Russia, Atmos. Environ. 41 (2007) 8301-8315

The long-range atmospheric transport (LRT) of polycyclic aromatic hydrocarbons (PAHs) is not fully understood and has hardly been addressed by model studies. By model experiments the LRT of PAH emissions into air from Europe and Russia is studied testing several scenarios of gas–particle partitioning and degradability by reaction with ozone and the hydroxyl and nitrate radicals for two PAHs, benzo[a]pyrene (BAP) and fluoranthene (FLT). The model used is the atmosphere general circulation model ECHAM5 with a dynamic modal aerosol sub-model, HAM, ozone and sulfur species chemistry and bidirectional mass exchange on 2D marine (ocean surface mixed layer) and terrestrial surfaces (top soil layer and vegetation surfaces). After 5 years the substances are found to be mostly distributed to the soil compartment (64–97% as the global mean, varying with substance and season), which after 10 years is still filling; 1–5% are found in air and 2–33% in ocean. It is found that the lifetime and vertical distribution of the substances in the atmosphere and the LRT potential are all significantly influenced by the partitioning and degradation scenario. The total environmental burden is higher when sorption to organic matter and black carbon are considered to determine gas–particle partitioning rather than adsorption to the surface of particulate matter. The effect is þ20% for BAP but sevenfold for FLT. Concentrations in Arctic air are mostly underestimated by the model, which is partly explained by emissions not considered in the simulation. The comparison shows, however, that degradation of the sorbed BAP and FLT molecules should be significantly slower than the respective gaseous molecules and that absorptive partitioning is necessary to explain the LRT potential of FLT

Dégradation photochimique sous irradiation UV des liquides ioniques en solution aqueuse

International audienc

Dégradation photochimique sous irradiation UV des liquides ioniques en solution aqueuse

International audienc