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Air Quality Basics

Key Issues

Environmental and Health Impacts

Reduce idling, reduce pollution. Vehicles emit a variety of pollutants including fine particles, volatile organic compounds, toxic chemicals, and greenhouse gases. These pollutants can contribute to increased rates of cancer, asthma, and other respiratory illnesses. To protect public health, the Environmental Protection Agency (EPA) establishes air quality standards to ensure the air we breathe is safe. Decreased idling activity can further reduce concentrations of fine particles and ozone in the air.

During high levels of pollution, active children and adults, and people with lung disease, such as asthma, or heart disease, should avoid prolonged or heavy exertion outdoors.

See EPA’s Guide to Air Quality and Your Health for more information on health effects.

EPA Air Quality Guide
The Air Quality Index provides guidelines to protect your health when ozone and particulate matter levels rise.

What is Ozone?

Ozone is a colorless, odorless gas and is the primary ingredient of smog. It is a form of oxygen with three oxygen atoms (O3) in every molecule instead of the two atoms in the oxygen (O2) molecules we need to live. This extra atom makes the gas highly reactive, enabling it to damage tissues and materials. Ozone occurs naturally above the earth in the stratosphere to provide a protective layer against ultraviolet radiation. At ground level, it is increasingly harmful to breathe as concentrations rise. Ozone is not emitted directly into the air, but is formed by gases called nitrogen oxides (NOx) and volatile organic compounds (VOCs), which, in the presence of heat and sunlight, react to form ozone. NOx + VOCs (with sunlight) = O3.

Ground-level ozone forms readily in the atmosphere in hot, sunny weather. This is why high levels of ozone are more likely to occur in the summer months.

What is Particulate Matter?

Particulate matter consists of solid particles and liquid droplets found in the air. Particulate matter 2.5 microns in diameter or smaller is referred to as “fine” particles or “PM2.5”. Fine particles can be formed when combustion gases are chemically transformed into particles. Individually, these particles are invisible to the human eye. (For comparison, a human hair has a diameter of 70 microns.) Collectively, however, they can appear as clouds or fog-like haze.


Particulate matter larger than 2.5 microns in diameter is referred to as “coarse” particles. Coarse particles have many sources, including wind-blown dust, vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations.


Long-term exposure to particulate matter may increase the rate of respiratory and cardiovascular illness and reduce life span.

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