The Clean Air Act and related legislation and regulations have played a major role in improving air quality through reduced on-road motor vehicle emissions, despite increases in population and in personal and freight travel. Technological innovations, cleaner fuels, and highway and transit programs have reduced emissions significantly in the past 20 years, and this trend is projected to continue. New measures taking effect in the next few years will intensify the clean air trends. This article looks closely at some of these trends, such as the following: from 1990 to 1999, only 9% of metropolitan areas had an upward trend in 1-hr ozone concentrations, only 1% of metropolitan areas had an upward trend of PM10 (particulate matter 10 micrometers in diameter or smaller) concentrations, and no metropolitan areas had an upward trend of carbon monoxide concentrations.

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  • Authors:
    • Jensen, G
  • Publication Date: 2003-7


  • English

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 4-9
  • Serial:
    • TR News
    • Issue Number: 227
    • Publisher: Transportation Research Board
    • ISSN: 0738-6826

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Filing Info

  • Accession Number: 00962801
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Sep 8 2003 12:00AM