[1] Breaking waves on the ocean surface produce bubbles that, upon bursting, inject seawater constituents into the atmosphere. Nascent aerosols were generated by bubbling zero-air through flowing seawater within an RH-controlled chamber deployed at Bermuda and analyzed for major chemical and physical characteristics. The composition of feed seawater was representative of the surrounding ocean. Relative size distributions of inorganic aerosol constituents were similar to those in ambient air. Ca 2+ was significantly enriched relative to seawater (median factor = 1.2). If in the form of CaCO 3 , these enrichments would have important implications for pH-dependent processes. Other inorganic constituents were present at ratios indistinguishable from those in seawater. Soluble organic carbon (OC) was highly enriched in all size fractions (median factor for all samples = 387). Number size distributions exhibited two lognormal modes. The number production flux of each mode was linearly correlated with bubble rate. At 80% RH, the larger mode exhibited a volume centroid of $5-mm diameter and included $95% of the inorganic sea-salt mass; water comprised 79% to 90% of volume. At 80% RH, the smaller mode exhibited a number centroid of 0.13-mm diameter; water comprised 87% to 90% of volume. The median mass ratio of organic matter to sea salt in the smallest size fraction (geometric mean diameter = 0.13 mm) was 4:1. These results support the hypothesis that bursting bubbles are an important global source of CN and CCN with climatic implications. Primary marine aerosols also influence radiative transfer via multiphase processing of sulfur and other climate-relevant species.Citation: Keene, W. C., et al. (2007), Chemical and physical characteristics of nascent aerosols produced by bursting bubbles at a model air-sea interface,

Abstract. We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. In both cases dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation we used the fully online coupled model WRF-chem.The results show that increased aerosol concentrations due to the presence of mineral dust can enhance the formation of ice crystals. This leads to slight shifts of the spatial and temporal precipitation patterns compared to scenarios where dust was not considered to act as ice nuclei. However, the total amount of precipitation did not change significantly. The only exception occurred when dust entered into an area of orographic ascent, causing glaciation of the clouds, leading to a local enhancement of rainfall. The impact of dust particles acting as giant cloud condensation nuclei on precipitation formation was found to be small. Based on our simulations the contribution of dust to the CCN population is potentially significant only for warm phase clouds. Nevertheless, the dust-induced differences in the microphysical structure of the clouds can contribute to a significant radiative forcing, which is important from a climate perspective.

<p><strong>Abstract.</strong> The Middle East and particularly the Arabian Gulf region are characterised by highly favourable conditions for O₃ formation in summer. We investigated the role of meteorological conditions in O₃ formation using the WRF-chem model. The dispersion of air pollutants strongly depends on local wind patterns, in particular the persistent low-level north-westerly flow known as the summer Shamal, and recurrent land-sea breeze circulation systems. <br><br> A general finding from our simulations is that extreme pollution events, with O₃ mixing ratios exceeding 150 nmol mol⁻¹, can occur regularly over the Arabian Gulf, however, their location and magnitude can vary widely. O₃ mixing ratios are highest when the outflow of the regions with major anthropogenic emissions along the coast is advected over the Gulf, where pollution plumes are captured in the shallow and stable marine boundary layer allowing little ventilation. The sea-breeze circulation often causes onshore advection of the pollution in the afternoon, affecting the densely populated coastal regions along the western shoreline of the Gulf. <br><br> When the pollution is transported deeper over land, O₃ mixing ratios are generally lower due to rapid dilution of precursor gases in the very deep convective boundary layer over the desert.</p>

Abstract. Organic material from the ocean's surface can be incorporated into sea salt aerosol particles often producing a surface film on the aerosol. Such an organic coating can reduce the mass transfer between the gas phase and the aerosol phase influencing sea salt chemistry in the marine atmosphere. To investigate these effects and their importance for the marine boundary layer (MBL) we used the one-dimensional numerical model MISTRA. We considered the uncertainties regarding the magnitude of uptake reduction, the concentrations of organic compounds in sea salt aerosols and the oxidation rate of the organics to analyse the possible influence of organic surfactants on gas and liquid phase chemistry with a special focus on halogen chemistry. By assuming destruction rates for the organic coating based on laboratory measurements we get a rapid destruction of the organic monolayer within the first meters of the MBL. Larger organic initial concentrations lead to a longer lifetime of the coating but lead also to an unrealistically strong decrease of O 3 concentrations as the organic film is destroyed by reaction with O 3 . The lifetime of the film is increased by assuming smaller reactive uptake coefficients for O 3 or by assuming that a part of the organic surfactants react with OH. With regard to tropospheric chemistry we found that gas phase concentrations for chlorine and bromine species decreased due to the decreased mass transfer between gas phase and aerosol phase. Aqueous phase chlorine concentrations also decreased but aqueous phase bromine concentrations increased. Differences for gas phase concentrations are in general smaller than for liquid phase concentrations. The effect on gas phase NO 2 or NO is very small (reduction less than 5%) whereas liquid phase NO 2 concentrations increased in some cases by nearly 100%. We list suggestions for further laboratory studies which are needed for improved model studies.