Indoor air versus outdoor: Which is cleaner?

The surprising answer is that the air outside your home is probably healthier than the air inside.

Indoor air can be two to five times more polluted than outdoor air even in the largest and most industrialized cities, according to the Environmental Protection Agency.

Even in smoggy Los Angeles? Yes.

Martin Wolfe, Seventh Generation's "Scienceman," measured pollution levels in several Los Angeles locations including the side of a freeway, behind a natural-gas powered bus, inside private homes, and more. The result: The outside air in LA is twice as good for you as the air inside your home.

You can see the testing process for yourself in the entertaining video below.

We spend about 90 percent of our time indoors, so it's worth making small changes to improve the air whenever you can. Below are some tips to help you breathe easier when you're at home.

Think twice about what you bring into your home:

• Air out dry-cleaned clothes before hanging them in your closet.
• Stay away from commercial air fresheners. Many contain synthetic fragrances that can aggravate allergies and asthma. Instead, find the source of the odor and fix it.
• Switch to less toxic household cleaning products or follow in grandma's footsteps and use items right out of your pantry. For example, use Alka Seltzer to clean your toilet, glass baking dishes, and more.
• Choose low-VOC paints, sealants, and glue. A wide variety of affordable options that work well are available at most home improvement stores.
• Replace a vinyl shower curtain with one made from a natural material such as cotton or linen.
• Minimize carpeting and look for formaldehyde-free pressed wood furniture and supplies when decorating.

Maintain and clean your house regularly:

• Wet-mop or vacuum with a high-efficiency particulate (HEPA) air filter often to limit the chemicals that can accumulate in household dust.
• Fix leaks to help avoid formation of molds.
• Change your furnace's filters regularly and maintain other fuel-burning appliances.

Keep track of potential pollutants:

• Install battery-operated carbon monoxide detectors in your bedroom and other places where you spend a lot of time. Make sure you place detectors in spots where you can hear them, and change the batteries regularly.
• Buy a simple radon test kit to determine if radon levels in your home are too high. Radon is a naturally occurring gas that's found in the ground, and it can accumulate in a basement and make its way into your living area.

Let the fresh air in

When it comes to ventilation, there are several options from opening your windows on a windy day to using kitchen and bathroom exhaust fans to employing a whole-house mechanical system. You can ask a knowledgeable professional to explain how you can bring in enough outdoor air to dilute the pollutants in your house and circulate some of them outside.

Environmental journalist Lori Bongiorno shares green-living tips and product reviews with Yahoo! Green's users. Send Lori a question or suggestion for potential use in a future column. Her book, Green Greener Greenest: A Practical Guide to Making Eco-smart Choices a Part of Your Life is available on Yahoo! Shopping and Amazon.com.