Thesis (Master's)--University of Washington, 2016-03Forest operations in the Pacific Northwest produce a large amount of harvest residues, known as harvest slash, commonly collected, piled and burned in prescribed fires. These prescribed slash burns provide a source of emissions, which affect local and regional air quality with potential negative impacts on human health. While most environmental assessments of biofuels are focused on the impact on global warming, very few studies have considered the impact on local air quality related to human health impacts as a result of slash pile burning. Alternative solutions have been proposed to recover woody biomass residues for the production of biofuels. The aim of this study is to calculate the avoided impact on human health as a result of recovering biomass instead of burning it in prescribed fires. The thesis project is structured in five main sections: i) evaluation of biomass supply, through the Washington State Biomass Calculator; ii) piles modeling, including sizes, shapes and distributions; iii) calculation of slash pile emissions through Bluesky Playground online tool; iv) evaluation of pollutants concentrations in air, based on AIRPACT chemical transport and interaction models, and v) calculation of the potential human intake and impacted populations and comparison of the concentrations with the EPA and WHO air quality standards. The area of study is represented by three timbersheds in Southwestern Washington and the burn period is 29 days. The results show a deterioration in air quality in the direct vicinity of the pile burns mainly caused by PM2.5 and PM10. On some of the burn days, depending on the amount of slash burned and the weather conditions, particulate matter emitted from the slash burns, travel great distances away from the burn locations reaching densely populated areas such as Seattle and Tacoma, in addition to impacting smaller communities. The results also demonstrate, that as a result of the pile burns the particulate matter concentrations in the air exceeded critical air quality thresholds on some of the days, surpassing EPA’s “very unhealthy” air quality standards. Additionally, results show that existing poor air quality and specific weather conditions significantly contributed to deterioration of the air quality, as a result of slash burns. On a day with poor weather conditions, the air pollution resulting from similar volume of slash pile burns can get magnified several times, leading to 10 to 100 times increase in adverse human health impact
