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Staff (Retired)

Secondary Ozone Standard

Secondary Ozone Standard


Christine Wu, James Kniffen, Elena Beckman and Steven Crenshaw, NC State University

The Clean Air Act established two types of national ambient air quality standards for the major air pollutants.  Primary standards protect public health, while secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings.  In 2006, EPA proposed a new metric as a possible secondary ozone standard based on a cumulative peak-weighted index to protect vegetation versus the daily maximum 8-hour average health-related metric (current primary standard).  In 2008, the EPA Administrators recommended the secondary ozone standard be the same as the primary ozone standard; however, the secondary ozone standard is now being proposed as a separate standard.

     This project performed exploratory analysis on the cumulative peak-weighted index to determine whether the monthly cumulative index varies during the year and whether three-month cumulative index varies from year to year.  In addition, we looked into the locations of higher value trends and investigate whether elevation, latitude, or longitude has an impact on the values collected.  Moreover, we studied meteorological conditions that may be conducive to high values.  Analysis is done using three levels (7, 15, or 21ppm-hour) of proposed values for secondary ozone standards to examine the impact at each of the proposed levels.  A comparison will be made between the proposed primary and secondary standards using the percentage of reduction needed for sites violating the primary and/or secondary standard to achieve standard levels.  Our initial results show those sites that exceeded the proposed 21 ppm-hour level are located between 35 degrees and 40 degrees North across the United States.  This may be due to a longer growing season and suggests that the secondary standard should be adjusted to account for different growing seasons.  A possible solution would be to adopt different secondary standards for different growing seasons, based upon latitude.

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