There are some important air pollution topics that do not fit the flow of the previous twelve chapter well. They are grouped into the last chapter of this book. In my opinion, an environmental professional should be familiar with these topics because they are relevant. Visibility and odor problems are usually not considered health-related (actually some odorants are very toxic). They are often considered as aesthetic issues. However, visibility impairment is mainly caused by particulate matters in the air and many of them originated from anthropogenic sources. In the meantime, presence of odor can be a good indicator that other air pollutants may also be present. We spend more time indoor than outdoor. Although EPA does not regulate indoor air quality, we need to have good indoor air quality in our homes, schools, and offices. Lead is one of the six criteria pollutants, but it seems to be neglected in most of the discussions.