Polymers, including natural proteins (such as DNA) and artificial materials (such as nylon and polyester), are examples of macromolecules. materials scientist Someone who studies the ways in which the atomic and molecular structure of a material relates to its overall properties.
Emission standards for engines and vehicles, including emission standards for greenhouse gas (GHG) emissions, are established by the US Environmental Protection Agency (EPA).The EPA authority to regulate engine emissionsâand the air quality in generalâis based on the Clean Air Act (CAA), most recently amended in 1990.ther states have a choice to either implement the federal emission standards, or else to adopt California requirements (CAA section 177).
For air pollution indices in general, see Air quality index. The Pollutant Standards Index, or PSI, is a type of air quality index, which is a number used to provide the public with an easily understandable indicator of how polluted the air is. Initially PSI was based on five air pollutants, but since 1 April 2014 it has also included fine particulate matter (PM 2.5).