9.1 Background9.2 Size Fractions9.3 Which Pollution Particle Sizes Are Important?9.4 What Health Outcomes Are Associated with Exposure to Air Pollution?9.5 Sources of Atmospheric Aerosols9.6 Particle Deposition in the Lungs9.7 Aerosol Interaction Mechanisms in the Human Body9.8 Human Respiratory Outcomes and Aerosol Exposure9.9 Cardiovascular Outcomes and Aerosol Exposure9.10 Conclusions and RecommendationsReferences