Ozone value refers to the concentration of ozone gas present in the air, typically measured in parts per million (ppm) or parts per billion (ppb). The significance of this value depends heavily on where the ozone is located.
Ground-Level Ozone: A Pollutant
Ground-level ozone, also known as tropospheric ozone, is a harmful air pollutant. The primary National Ambient Air Quality Standard (NAAQS) for ozone in the United States is 0.070 parts per million (ppm) averaged over eight hours (annual fourth-highest daily maximum 8-hour concentration, averaged over three years). [Source: Ozone Pollutant Reference]. Concentrations above this level are considered unhealthy and contribute to smog. Ground-level ozone forms from emissions of pollutants reacting in sunlight and causes serious health problems, aggressively attacking lung tissue. [Source: US EPA Ground-level Ozone Pollution, American Lung Association Ozone]. Agencies like the EPA and state-level organizations monitor ozone levels and issue air quality advisories when levels become dangerous. [Source: US EPA Ground-level Ozone Basics, Wisconsin DNR Ozone].
Various organizations provide current ozone level data, often presented as an Air Quality Index (AQI). The AQI incorporates ozone along with other pollutants like particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. [Source: Air Quality Index (AQI) Basics].
Stratospheric Ozone: Protective Layer
In contrast to ground-level ozone, stratospheric ozone is beneficial. It forms a protective layer in the upper atmosphere that absorbs harmful ultraviolet (UV) radiation from the sun. The amount of stratospheric ozone is often measured in Dobson Units (DU). A column ozone level of less than 220 DU over Antarctica, for instance, indicates significant ozone loss due to chlorine and bromine. [Source: NASA Ozone Watch]. This depletion is a separate environmental concern not directly related to ground-level ozone values.
Examples of Ozone Value Reporting:
- EPA: Reports 8-hour averages in ppm to determine compliance with NAAQS.
- State Agencies: May provide real-time ozone data in ppb, often visualized on maps showing current concentrations at various monitoring sites. [Source: Current Ozone 1-Hour Levels]
- AQI Reports: Express ozone levels indirectly through an AQI value, combining ozone data with other pollutants to give a single air quality score. [Source: NCTCOG Current Ozone Activity]
- Historical Data: Some agencies provide long-term average ozone values for specific regions. [Source: NC DEQ Ozone Average Values].
In summary, the "value" of ozone depends entirely on its location. Ground-level ozone is a dangerous pollutant, with established standards for safe levels. Stratospheric ozone, conversely, is crucial for protecting life on Earth.
