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- ItemSignificant increase of aerosol number concentrations in air masses crossing a densely trafficked sea area(Amsterdam : Elsevier, 2015) Kecorius, Simonas; Kivekäs, Niku; Kristensson, Adam; Tuch, Thomas; Covert, David S.; Birmili, Wolfram; Lihavainen, Heikki; Hyvärinen, Antti-Pekka; Martinsson, Johan; Sporre, Moa K.; Swietlicki, Erik; Wiedensohler, Alfred; Ulevicius, VidmantasIn this study, we evaluated 10 months data (September 2009 to June 2010) of atmospheric aerosol particle number size distribution at three atmospheric observation stations along the Baltic Sea coast: Vavihill (upwind, Sweden), Utö (upwind, Finland), and Preila (downwind, Lithuania). Differences in aerosol particle number size distributions between the upwind and downwind stations during situations of connected atmospheric flow, when the air passed each station, were used to assess the contribution of ship emissions to the aerosol number concentration (diameter interval 50–400 nm) in the Lithuanian background coastal environment. A clear increase in particle number concentration could be noticed, by a factor of 1.9 from Utö to Preila (the average total number concentration at Utö was 791 cm−3), and by a factor of 1.6 from Vavihill to Preila (the average total number concentration at Vavihill was 998 cm−3). The simultaneous measurements of absorption Ångström exponents close to unity at Preila supported our conclusion that ship emissions in the Baltic Sea contributed to the increase in particle number concentration at Preila.
- ItemSPARTA – Solver for Polarized Atmospheric Radiative Transfer Applications: Introduction and application to Saharan dust fields(Amsterdam : Elsevier, 2016) Barlakas, Vasileios; Macke, Andreas; Wendisch, ManfredNon-spherical particles in the atmosphere absorb and scatter solar radiation. They change the polarization state of solar radiation depending on their shape, size, chemical composition and orientation. To quantify polarization effects, a new three-dimensional (3D) vector radiative transfer model, SPARTA (Solver for Polarized Atmospheric Radiative Transfer Applications) is introduced and validated against benchmark results. SPARTA employs the statistical forward Monte Carlo technique for efficient column-response pixel-based radiance calculations including polarization for 3D inhomogeneous cloudless and cloudy atmospheres. A sensitivity study has been carried out and exemplarily results are presented for two lidar-based mineral dust fields. The scattering and absorption properties of the dust particles have been computed for spheroids and irregular shaped particles. Polarized radiance fields in two-dimensional (2D) and one-dimensional (1D) inhomogeneous Saharan dust fields have been calculated at 532 nm wavelength. The domain-averaged results of the normalized reflected radiance are almost identical for the 1D and 2D modes. In the areas with large spatial gradient in optical thickness with expected significant horizontal photon transport, the radiance fields of the 2D mode differ by about ±12% for the first Stokes component (radiance, I) and ±8% for the second Stokes component (linear polarization, Q) from the fields of the 1D mode.
- ItemModeling the multiphase processing of an urban and a rural air mass with COSMO-MUSCAT(Amsterdam : Elsevier, 2014) Schrödner, R.; Tilgner, A.; Wolke, R.; Herrmann, H.A reduced version of the complex aqueous phase mechanism CAPRAM3.0i (C3.0RED) was used in the regional chemistry transport model COSMO–MUSCAT in a 2-D application. Besides sulfate and nitrate production, the mechanism treats a complex HOx-chemistry, transition metal ion chemistry and organic species up to C4. The effects of the cloud chemistry on the chemical composition of air and particles were investigated. Sensitivity studies were conducted for an urban and a rural air mass. For this purpose simulations with C3.0RED were compared to ones with a simple inorganic aqueous phase mechanism (INORG) and without aqueous phase chemistry. A reduction of the gas phase concentrations of major oxidants was observed especially in the urban environment. Compared to INORG, C3.0RED is always more acidic leading to shifts in several chemical subsystems, (e.g. production of sulfate). Using C3.0RED instead of INORG, differences in sulfate mass of 3% to −15% occurred. The modeled O/C-ratio tends to be higher than observations as C3.0RED does not consider the whole population of organics and no insoluble organic mass. Nevertheless, the modeled concentration of glyoxalic acid is in the range of atmospheric measurements in both environments, whereas oxalic acid and pyruvic acid are underestimated in the urban case.
- ItemEstimating the contribution of photochemical particle formation to ultrafine particle number averages in an urban atmosphere(Amsterdam : Elsevier, 2015) Birmili, W.Ultrafine particles (UFPs, diameter < 100 nm) have gained major attention in the environmental health discussion due to a number of suspected health effects. Observations of UFPs in urban air reveal the presence of several, time-dependent particle sources. In order to attribute measured UFP number concentrations to different source type contributions, we analyzed observations collected at a triplet of observation sites (roadside, urban background, rural) in the city of Leipzig, Germany. Photochemical new particle formation (NPF) events can be the overwhelming source of UFP particles on particular days, and were identified on the basis of characteristic patterns in the particle number size distribution data. A subsequent segmentation of the diurnal cycles of UFP concentration yielded a quantitative contribution of NPF events to daily, monthly, and annual mean values. At roadside, we obtained source contributions to the annual mean UFP number concentration (diameter range 5–100 nm) for photochemical NPF events (7%), local traffic (52%), diffuse urban sources (20%), and regional background (21%). The relative contribution of NPF events rises when moving away from roadside to the urban background and rural sites (14 and 30%, respectively). Their contribution also increases when considering only fresh UFPs (5–20 nm) (21% at the urban background site), and conversely decreases when considering UFPs at bigger sizes (20–100 nm) (8%). A seasonal analysis showed that NPF events have their greatest importance on UFP number concentration in the months May–August, accounting for roughly half of the fresh UFPs (5–20 nm) at the urban background location. The simplistic source apportionment presented here might serve to better characterize exposure to ambient UFPs in future epidemiological studies.