Atmospheric aerosols are subject to extensive research, due to their effect on air quality, human health and ecosystems, and hold a pivotal role in the Earth’s climate. The first focus of this study is to improve the modelling of aerosol emissions and its dispersion in the atmosphere, in different spatial and temporal scales, and secondly, to integrate the dispersion modelling with
population activity data to estimate exposure metrics. The mathematical models used in this study are fully or partially developed by the Finnish Meteorological Institute: a regional-to-global scale chemical transport model SILAM, a local-scale point/line-source dispersion model, UDM/CAR-FMI, and a human exposure and intake fraction assessment model, EXPAND.
One of the outcomes of this work was the refinement of the emission modelling for the mesoscale dispersion model. A new parameterisation for bubble-mediated sea salt flux has been developed, taking in to account the effects of wind speed and seawater salinity and temperature. The parameterization is valid for low-to-moderate wind speed, seawater salinity ranging
between 0 and 33 ‰, seawater temperature ranging between -2 and 25 °C, and can be applicable to particles with dry diameters raging between 0.01 and 10 μm. The near-real time fire estimation system, IS4FIRES, based on Fire Radiative Power (FRP) measured by the remote sensing instrument MODIS, was refined to reduce the overestimation of particulate matter (PM) emissions by including more vegetation types, improving the diurnal variation, removing misattributed fires from the FRP data, and recalibrating the emission factors. Applying dynamic emission modelling brought more insight to the spatial distribution of these emissions, their contribution to the atmospheric budget, and possible impact on air quality and climate. The modelling shows that sea salt can be transported far over land and contribute up to 6 μg m-3 to PM10 (at annual level). It also indicates that the Mediterranean Sea has sharp gradients of concentration, becoming an interesting area to analyse regarding the feedbacks to the regional climate. According to the predictions, upward scattering by SSA, at TOA, can be up to 0.5 W m-2, and there will be an overall cooling in the future for the North of Europe and warming for the South, due to SSA. The simulations for wildland fires show how the system improves after calibration and the importance vegetation type for the intensity of the emissions. By including misattributed fires, there will be up to 80% overestimation in aerosol optical depth, close to the misattributed sources.
The emissions for Helsinki Metropolitan Area (HMA) were revised to bring up-to-date the emissions for traffic and energy sectors, for urban-scale applications. The EXPAND model was revised to combine concentrations and activity data in order to compute parameters such as population exposure or intake fraction. EXPAND includes improvements of the associated
urban emission and dispersion modelling system, time use of population, and infiltration coefficients from outdoor to indoor air. This refinement showed that PM2.5 in HMA is mainly originated from long-range transport, with the largest local contributors being vehicular and shipping (at harbours and its vicinity) emissions. At annual level, the population is mostly exposed to PM2.5 indoors (home and work), but the population is acutely exposed while commuting
