United States Department of Transportation - Federal Highway AdministrationFHWA HomeFeedback
OHPI LogoOffice of Highway Policy Information

Air Quality

National Emission Trends

Bar chart illustrating National Emission Trends

Source: Environmental Protection Agency's "National Emission Inventory, Air Pollutant Emission Trends" Office of Air Quality Planning and Standards, Federal Highway Administration http://www.epa.gov/ttn/chief/trends/index.html

Most of the reduction in emissions can be attributed to reductions from motor vehicles. Emission controls for cars and trucks have significantly reduced their emissions of carbon monoxide and volatile organic compounds (a primary ingredient of ozone) since 1970, even though travel more than doubled over the past 24 years. Emissions of these pollutants from other sources have fallen only slightly. At the same time, motor vehicle nitrogen oxide emissions, nitrogen oxide emissions, which contribute to ozone, have held about their 1970 levels, while those from all other sources have increased slightly.

Air Quality Trends

Line Chart illustrating Air Quality Trends

Source: 1975-1995 data were tabulated from individual monitor records in EPA Aerometric Information Retrieval Service (AIRS) database. These are for the subset of monitors having complete data for at least 15 of the 21 years included in that period. Supplemental 1994-2000 data were tabulated from EPA AIRSDATA Monitor Trends Report which can be found on the Internet at: http://www.epa.gov/airsdata/montrnd.htm.

Residents of the Nation's urban areas are breathing easier these days. Atmospheric levels of ozone and car monoxide (CO) have declined consistently for several decades. Violations of the National Standards for Carbon Monoxide have been virtually eliminated. Controlling ground-level ozone (or "smog") has proven more challenging, but violations of the Federal 1-hour ozone standard have also been sharply reduced.

Previous | Back to ONH page | Next

FHWA Home | OHPI Home | Products & Publications | Feedback


United States Department of Transportation - Federal Highway Administration