These can be journal articles, books, book chapters, dissertations, or reports of government agencies. Letters and short notes printed in journals are also usually primary sources. These publications exist to provide a formal, authoritative, credible means of communication between specialists in the scholarly community. Some synthesis of previously-published material published is expected. In other words, primary sources almost always have a bibliography of more than just a couple of cited works.
Secondary sources are generally writings about environmental issues.
These include articles in popular magazines, news items in popular or scientific publications, interviews, encyclopedia articles, some textbooks, etc. Secondary sources report new developments or applications, synthesize or popularize the work of Environmental Scientists or Policy experts. The audience for these publications may be the general public, or the scientific community at various levels of expertise. References to other published articles are not always necessary. Keep this in mind as you try to find sources that present various aspects of your chosen topic.