Abstract
Livestock housing, especially poultry and pigs, are major sources of particulate matter (PM). High ambient concentrations of PM can threaten human and animal health and welfare, as well as the environment. The best approach to reduce PM emissions from livestock houses seems to be to prevent it from being generated. Controlling PM at source not only reduces emissions but also improves inside air quality. Furthermore, data on particle morphology and chemical composition are essential to evaluate the likely exposure to PM on the one hand, and on the other hand, to develop control measures to reduce it. The research aim of this thesis was to acquire knowledge on where PM comes from in various livestock housing systems and to evaluate abatement techniques on reducing PM in relation with other pollutants. 
This thesis is composed of four research studies and a review of the state-of-the-art of PM in and from livestock production systems, which is the background of this thesis. Firstly, known sources of PM were collected from different housing systems for poultry and pigs and experimentally aerosolized in a laboratory dust generator to collect fine and coarse PM samples. These samples were analyzed i) using scanning electron microscopy with X-ray microanalysis to develop comprehensive morphological and chemical source profiles; and ii) with optical particle counter to determine source particle-size distribution. Secondly, the developed source profiles from known sources as well as particle morphological characteristics extracted with digital image analysis software were used to investigate which particle characteristics were best to distinguish amongst specific sources. Thirdly, the previous information was used to quantify the contribution of the different sources to fine and coarse airborne on-farm PM emissions from livestock houses using two source apportionment models (expert systems and multivariate linear regression models). To do this, we sampled airborne on-farm fine and coarse PM at 14 different livestock locations for poultry (including broilers, laying hens in floor, and aviary system and turkey production) and pigs (including piglets, growing-finishing pigs, and dry-pregnant sow housings). Finally, the potential of air ionization for reducing PM concentrations and emissions from a pilot-scale broiler farm was evaluated and its effect on particle properties and other pollutants was assessed. 
Our results indicated that the sources that contribute to PM are specific to livestock housing system and livestock species and that housing systems and livestock species determine particle diversity and heterogeneity. The laboratory dust generation process was successfully applied to develop comprehensive morphological and chemical source profiles for feathers, feed, manure, hair, skin, wood shavings, and outside source. The developed source profiles and presented particle-size distributions are valuable to compare similarities and differences in particle types and will allow faster and more accurate qualitative and semi-quantitative estimations of source contributions in future studies. Our results also indicated that to apply source apportionment models in livestock houses, it is necessary to obtain not only particle chemical characteristics, but also morphological particle characteristics because they can make additional value to using only chemical characteristics when sources show distinctive and well defined individual particle morphology or differ in size. On average 69% of particles belonging to a mixture of sources from poultry and pig houses can be correctly assigned to their source based on the combinations of chemical and morphological characteristics in fine and coarse PM, and based on our results, it is the recommended approach to apportion all individual sources to PM in livestock houses. In the surveyed poultry houses, source contributions vary amongst poultry housing systems, but most particles originate from feathers (ranging from 4 to 43% in fine and from 6 to 35% in coarse PM) and from manure (ranging from 9 to 85% in fine and from 30 to 94% in coarse PM). In the surveyed pig houses, source contributions vary amongst pig housing systems, but most particles originate from manure (ranging from 70 to 98% in fine and from 41 to 94% in coarse PM). When expressed in mass, big particles from wood shavings and especially skin gain relative importance compared with number of particles. Finally, air ionization proved to effectively and significantly reduce total PM10 mass emission by 36% and PM2.5 mass emissions by 10% in broiler production, but it had no effect on airborne micro-organisms, odor or ammonia emissions. Overall, the studies presented in this thesis have provided new knowledge for better and more efficient designing of PM reduction measures at source and for predicting how different techniques will work.