Many types of engineering fields impact improving the cleanliness of our air and water. Civil engineers work on the big infrastructure that transports water and treats water. Chemical engineers might develop new kinds of membranes to clean water. Materials engineers work with chemical engineers to develop new kinds of materials that improve the efficiency of the membranes for cleaning air and water or with civil engineers to make longer lasting infrastructure. Materials engineers also develop new materials for scrubbing the air (for example catalytic converters have new materials in them). Materials engineers are also finding replacements for synthetic materials (for example, natural replacements for styrofoam – see www.ecovativedesign.com) in order to reduce the impact of some materials on the environment.
The difference between materials engineering and other engineering disciplines is that materials engineers relate the structure and the processing of the material to the properties and performance. Here are two web sites that might help you understand the materials profession better.