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Air Pollution from Vehicle Emissions

December 1, 2021
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WRITTEN BY Gabe Hamburg

Air pollution from motor vehicle emissions (i.e., exhaust) can lead to negative public health and environmental impacts that disproportionately impact children, seniors, urban residents and people with existing lung and heart problems. The United States Environmental Protection Agency (EPA) sets standards for allowable levels of certain air pollutants (e.g., carbon monoxide, ozone) through the National Ambient Air Quality Standards (NAAQS). When a particular air quality control region exceeds any portion of the NAAQS, the home state must either submit a plan to reduce pollution or accept EPA sanctions such as highway funding restrictions and/or emission offset requirements. In 2007, Missouri established the Gateway Vehicle Inspection Program (GVIP) in response to NAAQS nonattainment in the St. Louis Region (City of St. Louis; St. Louis, St. Charles, Franklin and Jefferson Counties). House Bill 661, passed during the 2021 regular session and vetoed by the Governor, would have removed the GVIP inspection and maintenance requirements for Franklin, Jefferson, and St. Charles Counties.3,4 In October 2021, the Missouri Department of Natural Resources proposed a rule change that would remove Franklin County from GVIP requirements due to emissions reductions in the St. Louis region that offset higher emissions within Franklin County.


Science Highlights

  • Pollutants from vehicle exhaust can cause a range of negative health consequences, including lung and heart disease. 
  • Air pollutants regulated through the NAAQS are also known to cause harm to plants and animals located in the polluted region. 
  • The St. Louis region is currently designated an NAAQS nonattainment area by the EPA, which is attributed to the large number of vehicles and miles traveled in the area.
  • Vehicle inspection and maintenance (I/M) programs allow regions to monitor and respond to air pollutants released by cars. However, the frequency of emission testing can lead to increased costs for individuals and businesses.
    • In Missouri, the emissions testing fee cannot exceed $24, and the safety inspection fee cannot exceed $12.
  • I/M programs in some states (e.g., AK, NJ) have been rescinded due to reduced levels of NAAQS air pollutants. However, it is difficult to discern how much of this improvement is due to I/M programs compared to other contemporaneous offset strategies and the increasing prevalence of newer, lower emission cars over time. 



  • Total reductions in regional emissions due to I/M have been overestimated in some cases due to inappropriate modeling. At this point, there is not enough evidence to understand how I/M programs impact larger health and environmental outcomes.
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