What is Ozone?
Ozone is a gas found naturally in the Earth’s upper atmosphere. This “good” ozone makes up the ozone layer and is found in the stratosphere where it protects life on Earth from the sun’s harmful ultraviolet rays. Ozone located in the stratosphere forms when one oxygen molecule (O₂) breaks up due to the presence of ultraviolet radiation. The separated atoms combine with an oxygen molecule to produce an ozone molecule (O₃) which will eventually form the ozone layer.
The troposphere is found closest to the Earth’s surface and extends six miles. Ozone found here, at ground level, is considered an air pollutant. This “bad” ozone can harm health and the environment. Breathing ozone can trigger or exacerbate health problems such as chest pain, cough, throat irritation, bronchitis, asthma, and emphysema. Ground level ozone also damages vegetation and ecosystems leading to reduced agricultural crops, decreased commercial forest yields, reduced growth and survivability of seedlings, and damage to foliage of trees and other plants.
What is ground-level ozone and why is it important?
Ground level ozone is not emitted directly into the air. Instead, it is created by a chemical reaction when volatile organic compounds (VOCs) and nitrogen oxides (NOx) react in the presence of sunlight. The major source of VOCs and NOx are emissions from industrial facilities, electrical utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents.
Ozone is particularly likely to reach unhealthy levels on hot sunny days in urban environments and is a major component of urban smog. However, even rural areas can experience high ozone levels when ozone is transported by the wind.
As summer approaches, ground-level ozone is more of a concern due to the high heat and low precipitation that occur during this time. Ground-level ozone forms when Nitrogen Oxide (NOx) and Volatile Organic Compounds (VOCs) react in the presence of sunlight and heat. To help keep us “in-attainment,” we must target NOx emissions to prevent ozone from forming. By removing either VOCs, NOx, sunlight, or heat, ground-level ozone cannot form. Since VOCs are produced largely from vegetation, the only element we have some control over is the amount of NOx being emitted.
What is air pollution?
The presence or introduction of gases, dust, fumes, or odors in amounts which could be harmful to the health or comfort of humans and animals and/or which could cause damage to plants and materials.
What are pollutants?
A pollutant is a substance introduced into the environment that has undesired effects. Pollutants emitted directly from a source are called primary pollutants. Examples include nitrogen oxides (NOx) and volatile organic compounds (VOCs) emissions from vehicles. When primary pollutants in the atmosphere undergo chemical reactions the resulting compounds are called secondary pollutants. Ground level ozone is an example.
What is the Air Quality Index?
The AQI is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.
How Does the AQI Work?
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.
An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.
Understanding the AQI
The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories. Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:
|Air Quality Index Levels of Health Concern||Numerical Value||Meaning|
|Good||0 to 50||Air quality is considered satisfactory, and air pollution poses little or no risk.|
|Moderate||51 to 100||Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.|
|Unhealthy for Sensitive Groups||101 to 150||Members of sensitive groups may experience health effects. The general public is not likely to be affected.|
|Unhealthy||151 to 200||Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.|
|Very Unhealthy||201 to 300||Health warnings of emergency conditions. The entire population is more likely to be affected.|
|Hazardous||301 to 500||Health alert: everyone may experience more serious health effects.|
- Respiratory diseases-asthma, lung function changes
- Cardiovascular diseases
- Adverse pregnancy outcomes
- In 2013, the World Health Organization concluded that outdoor air pollution is carcinogenic to humans.
Who is most at risk from ozone pollution?
Ozone can affect anyone, but it bothers some people more than others. People most likely to experience health effects caused by ozone include:
- People with asthma or other lung diseases
- Older adults
- People of all ages who exercise or work hard outside
- Babies and children
How is ozone pollution controlled?
Ozone is one of the six common air pollutants identified in the Clean Air Act. EPA calls these “criteria air pollutants” because their levels in outdoor air need to be limited based on health criteria.
There are national ambient air quality standards (NAAQS) for each of the criteria pollutants. These standards apply to the concentration of a pollutant in outdoor air.
After working with the states and tribes and considering the information from air quality monitors, EPA “designates” an area as attainment or nonattainment with national ambient air quality standards. If the air quality in a geographic area meets or does better than the national standard, it is called an attainment area; areas that don’t meet the national standard are called nonattainment areas.
In order to improve air quality, states must draft a plan known as a state implementation plan (SIP) to improve the air quality in nonattainment areas. The plan outlines the measures that the state will take in order to improve air quality. Once a nonattainment area meets the standards, EPA will designate the area as a “maintenance area.”
What rules or regulations help reduce ozone pollution?
EPA’s national and regional rules to reduce emissions of pollutants that form ground level ozone will help state and local governments meet the Agency’s national air quality standards. Actions include vehicle and transportation standards, regional haze and visibility rules, and regular reviews of the NAAQS.