Other studies, primarily with laboratory animals, suggest that the chemical composition5 and surface areas of the particles may be more important than particle mass. Scientists are continuing to study the health effects of particles and are developing better methods for measuring the important constituents. It may be possible in the near future to more accurately assess the effects of inhaled particles on human health. Nitrogen Oxides Nitrogen oxides are produced during most combustion processes. Mobile sources and power plants are the major contributors in Southern California. About 80 percent of the immediately released nitrogen oxide.
