Under provisions of the Clean Air Act Amendment (CAAA), the 2015 Cincinnati ozone area includes portions of the Ohio counties of Butler, Clermont, Hamilton, and Warren; and the Kentucky counties of Boone, Campbell, and Kenton. Ozone is formed through photochemical reactions created when sunlight reacts with volatile organic compounds, or VOCs, and oxides of nitrogen (NOx). VOCs and NOx occur from incomplete combustion of fossil fuels.
How is Environment defined?
On June 9, 2022, The U.S. Environmental Protection Agency (EPA) found that the Cincinnati, Ohio area had attained 2015 ozone National Ambient Air Quality Standard (NAAQS) and have been redesignated to a maintenance area. On November 7, 2022, EPA reclassified the Kentucky portion of the Cincinnati area to moderate nonattainment. With those new designations the OKI region is still required to maintain 2015 ozone standards and complete air quality conformity for both the Transportation Improvement Program (TIP) and the Metropolitan Transportation Plan (MTP).
How is the OKI region doing?
Following progress in reducing fine particle pollution, the region has attained the annual particulate matter 2.5 (PM2.5) standards. The area must continue to maintain the standards, keep previous regulatory commitments, and continue to demonstrate transportation conformity. PM2.5 refers to a complex mixture of fine particulates, primarily from fossil fuel combustion. It is emitted directly and will also form indirectly through reactions with precursor emissions, especially NOx. A primary contributor to transportation-related PM2.5 is diesel emissions.
The U.S. Environmental Protection Agency (EPA) requires the monitoring of six air pollutants due to their harmful effect on human health. These “criteria” pollutants include ozone, particulate matter (fine and course particulates), carbon monoxide, sulfur dioxide, nitrogen dioxide and lead. Monitors have recorded high concentrations of ozone and particulates, which have frequently caused the OKI region to exceed the health-based standards. The good news: Ozone concentrations in the OKI region have dropped 14% and fine particulates (PM2.5) have decreased 40% since 2000. In comparison, ozone and PM2.5 concentrations in the U.S. have dropped 16% and 37%, respectively.
Ozone Concentration Levels 2000-2021
Fine Particulates (PM2.5) Concentration Levels ug/m3 2000-2021
Pollutant emissions from motor vehicles can be a major contributor to poor air quality. In the OKI region, motor vehicle emissions account for about one-third of carbon dioxide (CO2) equivalent, and fine particulate emissions. Motor vehicles account for up to half of emissions that, when combined with sunlight, form harmful ozone. The “ozone-precursor” emissions include volatile organic compounds (VOC) and oxides of nitrogen (NOx). The tables below show county-level motor vehicle emissions in tons per year (NOx and VOC) and million metric tons per year (CO2) through 2050, as estimated by OKI’s activity-based model.