Towards operational data assimilation of satellite-based aerosol observations in a chemical transport model for air quality monitoring

Kurzfassung

Aerosol monitoring is of growing interest due to the impact of aerosol particle concentration on human health and the global climate. Additionally, increased attention is spent from the economic viewpoint towards aerosol-induced variations in surface solar irradiance which is the resource for solar electricity generation and a driver for electricity consumption in general. Air quality models as the EURopean Air pollution Dispersion model EURAD offer a continuous and operational monitoring and forecasting of the aerosol load in sufficient temporal and spatial resolution. But they fail in case of episodic emissions which are not covered by the underlying emission data bases used to describe aerosol sources. Also, emission data bases are in general still not sufficient in terms of accuracy, long term trends and temporal-spatial resolution. On the other hand, satellite-based measurements as available from the European Environmental Satellite ENVISAT offer global measurements of aerosol optical depth and type both over land and ocean. These measurements distinguish between different aerosol components as sulphate/nitrate, soot, water insoluble erosion-based or industrial particles, sea salt and long-range transported mineral aerosols. Such observations can be used to learn about and to overcome the restrictions of current emission data bases in air quality modelling. There is the need to couple model and observational information to achieve an optimum estimate of the atmospheric state by means of data assimilation. The work presented will show a first validation and impact analysis of ENVISAT component-wise aerosol optical depth measurements assimilated into the EURAD model using a variational assimilation scheme. The scheme proposed holds also the potential to be used for the MODIS instrument onboard the TERRA and AQUA platforms and the GOME-2 and AVHRR instruments onboard the METOP satellite series. Special focus is laid on the link between the typical model output giving mass concentrations of different chemical aerosol species and the optical perspective of satellites which deliver optical parameters as aerosol optical depth. Assumptions needed e.g. for the mapping of model aerosol species on satellite-typical aerosol components or the optical properties of modelled aerosol species will be discussed. Additionally, an update of the existing OPAC (Optical Properties of Aerosols and Clouds) data base based on recent field campaigns and aerosol chamber measurements will be presented.