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  • atom: everything around you is made up of atoms. Atoms are so tiny that it takes a very powerful microscope to see them. The atoms join together to make elements, and the elements join together to make compounds, and so on ... until everything is joined together to make - YOU! (Back to Hot Summer Days)

  • chimney: a device used to light a charcoal grill. It's about the size and shape of a coffee can, and it has little air holes cut in the side near the bottom. The air holes help the flame from the match concentrate on lighting the charcoal and paper in the grill. Chimneys take the place of lighter fluid. (Back to Hot Summer Days)
  • compound: a compound is made up of two or more elements combined after a chemical reaction. The salt on your kitchen table is a compound. It is made out of sodium, which is a silvery metal, and chlorine, which is a greenish gas. But salt is not silver or green, and it's not a metal or a gas. The little white crystals of salt were made when sodium and chloride chemically reacted with each other and changed into something completely new - salt! (Back to Hot Summer Days)
  • ecosystem: an ecosystem is made up of all the plants and animals that live in an area and depend on each other to survive. Ecosystems also include things like rocks and streams that are used by the plants and animals. (Back to Hot Summer Days)
  • emit: to release something into the air or the environment. For instance, smelly fumes are emitted from the tailpipe of a car. (Back to Hot Summer Days)
  • fossil fuel: fossil fuels (coal, oil, and natural gas) make up the biggest part of our sources of energy. They are called fossil fuels because they were formed over millions of years from dinosaur bodies and from prehistoric plants. When fossil fuels are burned, they produce pollution. Also, it takes a long time to form new fossil fuels - millions of years - and we're using up the existing ones before new ones can form. (Back to Hot Summer Days)
  • ground-level ozone: ozone that is formed in the troposphere when chemicals produced by cars, power plants, factories, and other pollutants are baked in the hot sun. Ground-level ozone makes it hard for us to breathe, and is harmful to the leaves of plants and trees. (Back to Hot Summer Days)
  • nitrogen oxides (NOx): nitrogen and oxygen combine to form different varieties of this compound. Each variety has a different number of oxygen atoms that have joined together with a nitrogen atom. (The 'x' at the end of NOx can stand for 1, 2, 3 or more oxygen atoms. That's why it's an 'x' and not a number.) When NOx is baked with VOCs in the hot summer sun, ground-level ozone is created. (Back to Hot Summer Days)
  • nonattainment areas: regions of the United States where air pollution (including ground-level ozone) has been measured at unhealthy levels. These regions are required by the Clean Air Act to reduce the amount of pollution in order to protect the health of people, plants and animals. (Back to Hot Summer Days)
  • pollutant: A pollutant is something that makes our environment dirty or harmful. Ozone is a pollutant because it makes the air unhealthy to breathe. (Back to Hot Summer Days)
  • react: to undergo a chemical change. For instance, flames from a fire react with the wood to form smoke, and eventually you are left with ash or charcoal instead of wood. This is a chemical change that happened because the wood reacted with the fire. NOx and VOCs react to form ozone. Ozone can react in a similar way with rubber, plants, and our lungs to cause them to break down. (Back to Hot Summer Days)
  • secondary pollutant: a pollutant created when two or more pollutants are mixed together and a chemical reaction happens to turn them into a new pollutant. Ground-level ozone is a secondary pollutant because it is formed when two other types of pollutants, NOx and VOCs, get baked by the sun. (Back to Hot Summer Days)
  • stratosphere: the layer of the atmosphere that is found 6 to 30 miles above the ground. It contains stratospheric ozone. (Back to Hot Summer Days)
  • stratospheric ozone: ozone found in the stratosphere. Stratospheric ozone is the same chemical as ground-level ozone, but because it is high above the Earth (instead of close down, where we could breathe it), stratospheric ozone is helpful, not harmful. It protects us by blocking the most harmful rays of the sun - ultraviolet rays - which can cause skin cancer. (Back to Hot Summer Days)
  • tissue: these tissues aren't the kind you blow your nose on. Our bodies are made up of cells. Cells are so tiny that we can't see them without using a microscope. These cells get together to form tissues, and tissues get together to form organs, like our lungs and heart. (Back to Hot Summer Days)
  • troposphere: the layer of the atmosphere reaching from the ground up to 6 miles. (Back to Hot Summer Days)
  • tropospheric ozone: tropospheric ozone is also known as ground-level ozone. See ground-level ozone for more information. (Back to Hot Summer Days)
  • ultraviolet, or UV: Have you ever gotten a sunburn? (ouch!) You can thank ultraviolet light. The beams of the sun are rays of light. Light rays can be divided into three main groups: visible light, ultraviolet light, and infrared light. Visible light is what humans can see. We can't see ultraviolet light and infrared light, but they are present in sunlight, and can have an effect on us, like sunburns. Although sunlight is good for us, too much ultraviolet light can cause skin cancer or other health problems. (Back to Hot Summer Days)
  • unstable: when a chemical is unstable it means that the chemical can change into other chemicals easily, or react with other substances. Ozone is unstable and it can react with our lungs to damage the tissues. (Back to Hot Summer Days)
  • volatile organic compound (VOC): In chemistry, organic means something containing carbon. Volatile means 'easily evaporated' - like water boiling away in a kettle. It can also mean explosive. And a compound is something that is made up of two or more other elements. If you put it all together, then a volatile organic compound is a carbon substance that is made up of two or more elements, is easily evaporated, and may be explosive. (Back to Hot Summer Days)
  • voluntary: voluntary actions are things that people do without being made to do them, or without being paid to do them. Volunteering to walk or bike to the store on an Ozone Action! Day is a good example of this. The benefit you get from doing this is not money or toys, but something better - clean air and exercise. (Back to Hot Summer Days)
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