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The main sources of aerosols in the remote Marine Boundary Layer (MBL) are sea salt sources, non sea salt sources, and entrainment of free tropospheric aerosols. Non sea salt aerosols are mainly sulphate derived from the oxidation of gaseous DiMethyl Sulphide (DMS) produced in surface water.1 DMS is produced by phytoplankton and is estimated to account for approximately 25% of the total global gaseous sulphur released into the atmosphere.2 DMS can either be dissolved into aqueous-phase aerosols or oxidised to other gas-phase species which can contribute to aerosol formation, e.g. SO2, H2SO4, DiMethyl SulphOxide (DMSO), DiMethyl SulphOne (DMSO2), MethaneSulfInic Acid (MSIA) and Methane Sulphonic Acid (MSA). It has therefore been postulated3 that DMS emission from the oceans can produce new condensation nuclei and eventually Cloud Condensation Nuclei (CCN). Thus, DMS may have significant influence on the Earth’s radiation budget. In this paper, this DMS-postulate has been investigated for MBL conditions using the Chemistry-Aerosol-Cloud (CAC) model.4 The CAC model is a box model where the following processes are solved:

Persistent organic pollutants (POPs) are a group of chemical compounds with mainly anthropogenic origin; they are semi-volatile, hydrophobic, they bioaccumulate, they have toxic effects on human and wildlife and they display low degradation rates in the environment (Jones and de Voogt, 1999). POPs are emitted to the atmosphere either from industrial production, as by-products from combustion, or intentionally as pesticides used on crops or for insect control. A number of POPs are banned or subject to regulation, e.g. under the UNEP Stockholm convention for POPs and emissions of them have decreased during the last decades (Jones and de Voogt, 1999). However, due to the great persistence large amounts are still cycling in the environment. The volatility of POPs is temperature dependent, which can lead to several consecutive deposition and re-emission events named multi-hop or grasshopper transport (Wania and Mackay, 1996). To contribute to the understanding of these processes several models are developed. The environmental fate of POPs is traditionally studied with box models (e.g. Wania et al., 1999). Recently, atmospheric transport models with high spatiotemporal resolution are also developed to address these issues (e.g. Koziol and Pudykiewicz, 2001; Hansen et al., 2004).

A one year PM10 and its major components measurement campaign in, and around, Berlin has been carried out from September 2001 to September 2002. The most important challenge was to improve the knowledge about the contribution of anthropogenic urban sources and of long term transports of anthropogenic and natural constituents of air to local concentrations in order to give advice to authorities to elaborate reduction strategies for PM10 concentrations. The validation of the chemical transport model (CTM) REM_Calgrid (Stern et al, 2003) by means of the sampled data was propaedeutic to any further use of it in determining possible sources of air pollution.

Atmospheric aerosols play a major role in the global climate system. Many researchers have conducted studies on the radiative forcing of aerosols for recent years. Aerosol particles are known to cool or warm the atmosphere directly by absorption, scattering and emission of solar and terrestrial radiation and indirectly by changing the albedo and the life time of clouds by acting as cloud condensation nuclei (Charlson et al., 1992).

Atmospheric particulate matter (PM) is a complex mixture of anthropogenic and natural airborne particles. Particulate matter in ambient air has been associated consistently with excess mortality and morbidity in human populations (e.g., Brunekreef, 1997; Hoek et al., 2002). The European air quality standards currently focus on all particles smaller than 10 μm in diameter (PM10), which covers the inhalable size fraction of PM. Mass and composition of PM10 tend to divide into two principal groups: coarse particles, mostly larger than 2.5 μm in aerodynamic diameter, and fine particles, mostly smaller than 2.5 μm in aerodynamic diameter. The fine particles contain secondary aerosols, combustion particles and condensed organic and metal vapours. The larger particles usually contain sea salt, earth crust materials and fugitive dust from roads and industries. Although adverse health effects are associated with elevated levels of both PM10 and PM2.5, these health effects were most strongly and consistently associated with particles derived from fossil fuel combustion (e.g. Hoek et al. 2002), which mostly occur in the PM2.5 size range.

Diseases of the respiratory system due to aeroallergens, such as rhinitis and asthma, are major causes of a demand for healthcare, loss of productivity and an increased rate of morbidity. The overall prevalence of seasonal allergic rhinitis (allergic reactions in the upper respiratory system) in Europe is approximately 15%; the asthma rates vary from 2.5%–10%; etc.. Pollenosis accounts for 12–45% of all allergy cases. The sensitisation to pollen allergens is increasing in most European regions.

The interaction of gases and aerosol particles with clouds entails a number of key environmental processes. On the one hand, they directly influence the life cycles of trace constituents and facilitate conversions of these trace constituents. On the other hand, multiphase transformations strongly influence cloud formation. Over a long time, the complexities of the cloud processes involved have discouraged investigators from simultaneously treating all aspects of multiphase chemistry and microphysics with equal rigor. Many recently available models focus either on complex multiphase chemistry only in a few aggregated drop classes (Ervens et al., 2003; Herrmann et al., 2000), or detailed microphysics for strongly simplified chemical mechanisms (Bott, 1999).

The inorganic species of sulfate, nitrate and ammonium constitute a major fraction of atmospheric aerosols. The behavior of nitrate is one of the most intriguing aspects of inorganic atmospheric aerosols because particulate nitrate concentrations depend not only on the amount of gas-phase nitric acid, but also on the availability of ammonia and sulfate, together with temperature and relative humidity. Particulate nitrate is produced mainly from the equilibrium reaction between two gas-phase species, HNO3 and NH3.

Most of the parameters commonly used to describe the turbulence in the atmospheric boundary layer represent conditions of atmospheric turbulence near the ground and therefore have a small footprint. For a mast of 10 meters above ground the footprint is few hundred meters. A 40-50 meter mast looks over some kilometers in upwind direction. The height of the convective boundary layer is typically 1-2 kilometers in middle latitudes and reflects the conditions several tens of kilometers upwind. The footprint of meteorological characteristics is essentially dependant on atmospheric stability and wind speed (Gryning and Batchvarova, 1999; Kljun et al., 2003).

Almost every country has adopted modeling systems to forecast the consequences of atmospheric dispersion at various scales. In particular long range transport and dispersion (LRTD) models are used to forecast the dispersion of large emissions of harmful pollutants from point sources such as, for example, atmospheric dispersion of radioactive gasses from NPP or other sources. The comparison of state-of-the-art model results with observations (e.g. Draxler, 1983; Klug ., 1992; Girardi ., 1998) has shown unequivocally that among the various approaches to atmospheric dispersion modeling, none is systematically performing better than others. Two are the main sources of uncertainty in the model results: one connected to the atmospheric circulation forecast and one dependent on the way in which atmospheric dispersion has been modeled. Therefore none of the models evaluated can be identified as “the model” to be used. On the other hand, model results are used for the assessment or forecast of conditions that may involve adoption of countermeasures for the protection of the population, for which a high level of accuracy is required.