There are many, many different environmental science fair projects that can be carried out in a large variety of settings with a similar large variety of organizations and goals. After all, the environment is our surroundings and our surroundings have millions of different aspects and attributes.
One such project is to test the pH level in acid rain; you can also test the pH level of snow, if it is winter. For this experiment, you will need a pH indicator, such as pH paper or a garden soil pH testing kit, and a few test tubes to put the rain water or snow into. These pH indicators contain a chemical that changes color when it comes into contact with acids or bases. You can further this experiment by testing the effects of acid rain on plant growth.
Another idea for an environmental science fair project is to look at the causes of, and solutions to, pollution. Pollution can be in the form of chemical substances, or energy like noise, heat or light. There are forms of pollution control out there controlling emissions and effluents that go into our air, water and soil. Without pollution control, waste products would degrade our environment, but even better than pollution control would be pollution prevention that actually reduces the amount of pollution put out by vehicles or industrial businesses. It is never the wrong time to teach children about how they can affect the natural world around them in both positive and negative ways.