A colorless gas that can that can bother the lungs. It is formed when fossil fuels that contain sulfur are burned. It is also given off when volcanoes erupt.

The layer of air surrounding the earth.

A body's system for breathing, including the nose, throat, and lungs.

Areas such as tidal flats or swamps covered by shallow water, or where the water table is at or near the surface.

The upper level of groundwater.

The area drained by a given stream.

The addition of enough harmful or objectionable material to damage water quality.

Any substance that evaporates at low temperature.

Atmospheric air circulation determined by wind speed and mixing height. The degree of ventilation is an indication of how well air pollution will be dispersed.

Storm water from city streets, usually carrying litter and organic wastes.