What’s measured This section spotlights on-road vehicular emissions of nitrogen oxides (NOx) in the 14-county region. States are required by the EPA to collect and report emissions data every three years. Data for this indicator are from the North Carolina Department of Environment and Natural Resources, and the South Carolina Department of Health and Environmental Control. The most recently published data are for 2002, with 2005 data anticipated in 2008. Data for prior time periods were defined and collected differently, precluding comparison to current data. Population data are from U.S. Census inter-censal population estimates. Why it’s measured Because volatile organic compounds (VOCs) are in plentiful supply due to vegetation and other sources, NOx is the limiting agent in the formation of ground-level ozone in the region, meaning that the amount of NOx determines how much ozone is produced. Moreover, NOx emissions are something over which the region can exert some control. Although non-mobile point sources (for example, smokestacks) are important emitters of NOx, mobile on-road sources (cars, trucks, vans, etc.) are more directly affected by individual decisions. Ground-level ozone has been the chief cause of the EPA’s 2005 designation of Non-Attainment for much of the region. This designation will have an economic impact if not addressed. Indicator results In 2002, NOx on-road vehicular emissions for the 14-county region averaged 82.8 pounds per person. By county, a high degree of variability exists in per-person measures of NOx emissions from on-road vehicles. Iredell had the highest figure at 167.9 pounds per person in 2002, based on 10,952 tons emitted and a population of 130,495. Union, York and Lancaster counties have the lowest per capita emissions at 58.2, 58.3 and 60.6 pounds per person, respectively. Union and York each have roughly half of Iredell’s emissions, with populations slightly higher than Iredell’s. Lancaster has about one-fifth the emissions and about half the population of Iredell. Mecklenburg has the highest actual emissions at 27,967 tons, but it also has the highest population at 735,194. Those numbers yield a rate of 76.1 pounds per person. Evaluation It is potentially misleading to emphasize individual county results when examining air pollutants from any source. Air pollutants shift downwind from their source, and in the case of on-road emissions, the presence of interstate highways in predominantly rural counties tends to elevate the per capita rate. For example, Iredell’s high per capita measure of on-road emissions is in part attributable to the location of Interstates 40 and 77 within its borders. The regional trend will be the more critical indicator to monitor once 2005 data are released. Connections As the region’s population continues to grow, controlling contributions to ground-level ozone formation from sources such as on-road vehicular NOx emissions will be increasingly critical to public health and thus to workplace productivity and the region’s attractiveness as a place to live and work. Failing to control growth in per capita NOx emissions will increase the difficulty of controlling ground-level ozone formation, which in turn will increase the difficulty and cost of returning the region to compliance with the Clean Air Act. |