Federal emissions regulations are set by the U.S. Environmental Protection Agency (EPA) to regulate the emissions of stationary and mobile engines. These standards restrict the amount of known pollutants — greenhouse gases like carbon monoxide, methane, and formaldehyde — that are released into the air. The aim of such limits is to reduce pollution and the greenhouse effect. In addition to setting such regulations, the EPA also monitors air quality.
Carbon monoxide and methane contribute to pollution that may manifest itself as poor air quality and smog. These and other greenhouse gases can also build up in the Earth’s atmosphere and create a barrier that traps heat, often called the greenhouse effect. Some people theorize that the resulting rise in temperature causes global warming because, over time, the planet grows warmer. Such temperature changes are thought to affect climate, weather, crops and disease.
In 1970, U.S. president Richard Nixon created the EPA. The Clean Air Act, legislation which gave the EPA the authority to set federal emissions standards for all vehicles and equipment, was enacted that same year. Soon after, the EPA began to enforce federal emissions standards, when it required U.S. auto manufacturers to install a catalytic converter in every car.
A catalytic converter is a device that reduces the toxic emissions of unburned hydrocarbons, or fuel, from internal combustion engines. The EPA catalytic converter requirement reduced the output of unburned hydrocarbons by 85%. Since the 1970s, there have been more laws made to control emissions.
In June 1991, an amendment to the Clean Air Act was approved. This change to the act sought to strengthen federal emissions standards through a program called the National Low Emission Vehicle Standards (NLEV). These standards seek to further curtail automobile emissions through the implementation of regulations in three steps or tiers.
Tier one, which was implemented between 1994 and 1999, based allowable emissions on a vehicle’s weight. Tier two took effect from 2004 to 2009 and graded vehicles according to an emission standard chart. Cars with a low rating on this chart were deemed clean, while those with high ratings were typically removed from use due to unacceptable emission levels.
Tier three of the federal emissions standards is scheduled to take effect from 2010 to 2016. It will incorporate the state of California's strict emissions standards into the national regulations. California was given the authority to set its own emissions regulations due, in part, to the state's poor air quality and its need for measures even more stringent than that set forth by the EPA.