Aerosol Optical Properties over the Northwestern European Seas

Aerosol Optical Properties over the Northwestern European Seas

Floutsi, A.A.

Biskos, G. (mentor)
Riva, R.E.M. (mentor)

Civil Engineering and Geosciences

Geoscience and Remote Sensing

Master Applied Earth Sciences

2017-03-01

Atmospheric particulate matter (aerosols), originating from both natural and anthropogenic sources, is affecting the regional and global climate through direct, indirect, and semi-direct effects on the radiative energy budget of the Earth-atmosphere system. In order to quantify these effects it is necessary to determine the load of aerosol particles in the atmosphere. An effective way to do this is by measuring the aerosol optical depth (AOD). The higher the AOD values the greater the aerosol load. Along with AOD, the Fine mode Fraction (contribution of particles smaller than 1 μm to the total AOD, FF) is an effective parameter for the characterization of the aerosol, providing a rough proxy for the size of the particle present in a region at a particular time. In this study, I investigate the spatiotemporal variability of the AOD, FF, fine and coarse mode AOD over the Northwestern European Seas (that extend from 43° N to 67° N and from 10° W to 31° E), where the presence of both natural and anthropogenic particles is significant. Anthropogenic particles (both primary and secondary aerosols, mostly fine mode) originate from ship activity, or from urban-industrial and fossil fuel and biomass burning processes. The natural, coarse mode particles are primarily originated either from the oceans (sea salt particles) or from the desserts (dessert dust particles). In the present study I use mean daily aerosol data (Collection 006 Level-3) from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that is on board Aqua satellite. These data are available in 1° × 1° resolution (ca. 100 km × 100 km). The study period extends from 2002 until 2014. A significant spatial variability of the aerosol load is observed over the study region. On annual level, the highest AOD values (up to 0.32) are observed over the English Channel and the coasts of the Netherlands and Germany. The highest FF values (values up to 0.77) are observed over the same regions, indicating that a large contribution of the aerosol load is from anthropogenic particles. Offshore (at remote regions), both AOD and FF are lower compared to coastal regions, thus indicating the predominance of maritime aerosols (sea salt particles). The data also show a clear seasonal cycle, with larger aerosol load observed during spring and summer period (AOD up to 0.60), and lower during autumn and winter period (AOD up to 0.30). A similar pattern is observed only for the FF, implying a larger contribution of anthropogenic particles during spring and summer period compared to autumn and winter period. The highest FF values (up to 0.80- 0.85) are observed during summer over the Baltic Sea, while year-round the lowest values are observed in remote maritime areas, mostly in the northern part of the study region, accentuating the predominance of maritime/sea salt particles. The AOD experiences an overall decreasing trend over most of the study region (slope range between -0.18 to 0.05 per decade). Over the northwestern ocean parts of the study region positive values are observed (sea salt particles are dominating), while over most of the rest study region parts the slope is of the order of -0.02 to -0.05 per decade. These decreasing AOD trends are associated with a reduction of mostly the fine mode AOD. Therefore it can be assumed that the decrease of the aerosol load over the study region is mainly due to the reduction of the anthropogenic emissions.

AOD
AOT
Fine mode AOD
Coarse mode AOD
Fine Fraction
Aerosol optical properties
Northwestern European Seas
aerosol load

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Student theses

student report

(c) 2017 Floutsi, A.A.