On the use of aerosol optical properties and satellite-retrieved trace gases in regional air quality modelling
Licentiate thesis, 2015
The effects of anthropogenic pollutants in the lower atmosphere (troposphere) have been shown, historically and scientifically, to have a deleterious effect on both plant and animal life. Pollutants such as near-surface ozone and soot (black carbon) are two notorious examples with clear anthropogenic sources. Consequently, laws controlling emissions and future projections of air quality, especially around large cities worldwide, are critical to the vibrancy and sustainability of life.
The main purpose of this thesis is to summarise two studies involving the regional chemical transport model MATCH and its simulations of carbon monoxide (CO), ozone (O3) and aerosols. The core question addressed in the first study is how the long-range transport representation of carbon monoxide and ozone can be evaluated. Simulating the long-range transport in regional models is important to get a well represented vertical distribution of the long lived (relative to modelling time and domain) species, a category to which the aforementioned gases belong. A methodology for evaluating lateral boundary conditions (LBCs) is tested for LBCs derived from the global EMEP MSC-W model. First, the method directly evaluates the LBCs at the model boundaries with satellite retrievals from MOPITT (CO) and OMI (O3). The second part of the method uses the new LBC to drive MATCH model. MATCH is compared to satellite-retrieved data from the AIRS sensor and ground based observations from the GAW-network. The method of evaluating LBCs highlights the need for better evaluation techniques, rather than only using a direct evaluation at the lateral boundaries. The use of combined ground-based and satellite measurements, especially close to the model boundaries, needs to be further exploited.
A similar study, where aerosols concentrations fields are confronted with satellite retrievals, instead of trace gases, cannot be made without the use of an aerosol optics model. An optics model simulates the corresponding radiometric properties as retrieved from satellite measurements. Therefore, the focus of the second study involves the simulation of aerosol optical properties using a new, stand-alone, aerosol optics model. Simulated aerosol fields are provided by using MATCH. The new optics model simulates radiometric properties from particles whose morphology is based on more realistic assumptions. Special consideration is given to fractal aggregates of externally mixed soot and inhomogeneous internally mixed soot. The latter part mixes solid soot with liquid hydrophilic substances, where parts of the soot particle are confined as a solid spherical core and parts of the soot is mixed into a liquid phase coating of for example sulphate or nitrate. The simulations of the new optics model resulted in large impacts on the radiometric properties, comparable to the effects of using aerosol dynamics. This is an important finding since most climate and remote sensing applications, today, use rather coarse and simple models to retrieve aerosol optical properties.