Υποστήριξη Διδακτορικής Διατριβής - Γεωργία Θεοδωρίτση

The chemical transport model PMCAMx was extended to investigate the effects of transport and photochemical aging of biomass burning gaseous and particulate emissions. The new source-resolved model, PMCAMx-SR, simulates separately from the rest of the pollutants the emissions and their corresponding products from biomass burning. The model uses the latest result of laboratory experiments for the description of the emissions and of the corresponding physicochemical processes. PMCAMx-SR was applied in both Europe and the US during characteristic summer, winter, spring and fall periods. For Europe, the PMCAMx-SR simulations showed that residential biomass burning is one of the most important sources of air pollution during the wintertime. For the US, the simulations indicated the importance of the processes of production of secondary organic particulate matter from the organic vapors emitted during fires. These chemical processes can double the concentrations of the corresponding particles far away from the fires and can expand their area of influence to over one thousand kilometers.

                In the next phase of this work the role of prescribed burning on air quality was investigated. These controlled fires are set intentionally by the corresponding land management agencies in an effort to reduce the probability of large wild fires. Prescribed burning activities were limited in the US during the summer months due to the prevailing weather conditions. However, there were significant such activities during the spring and the summer contributing 20-40% of the total biomass burning emissions in the US.  Locally these prescribed fires lead to increased levels of particulate matter leading to exceedances of the corresponding limits. However, the average concentration of the corresponding organic particulate matter for the whole country is small. Our simulations indicated that the levels of secondary organic aerosol from prescribed burning even 500-700 km away from the fire can reach 2 μg m^-3, underlying this way the spatial extent of the influence of biomass burning. The air quality effects of these prescribed burns are a lot smaller than those of large wildfires.

In the final stage of this work, the importance of intermediate volatility organic vapors emitted during biomass burning as a source of secondary particulate matter was investigated. An alternative biomass burning module was added to PMCAMx-SR based on recent laboratory experiments. PMCAMx-SR using both the base and the alternative schemes was applied to the US. The analysis of the model results demonstrated the importance of the assumed volatility distribution of biomass burning emissions and of the chemical aging processes. The oxidation of the intermediate volatility organic compounds can increase the concentrations of secondary aerosol from biomass burning by a factor of 5 to 10. The use of the alternative scheme lead to a small improvement of the predictions of PMCAMx-SR during spring, but in overprediction of the organic aerosol concentration during summertime and during periods of intense photochemistry. Additional study of the reactions leading to the production of secondary organic aerosol from biomass burning in different meteorological periods is recommended for future work.