It’s important to keep indoor humidity at an optimum level (45 to 65 percent). Dry air in the winter  is one the main causes of sinus infections and sore throats. You can use a mechanical humidifier to add moisture to the air, but these devices require constant cleaning to prevent the growth of microorganisms.

An easier way to add humidity to a room, is to put a few areca palms in it. These palms release copious amounts of water into the air, and remove chemical toxins too. They are consistently rated among the best houseplants for removing all indoor toxins tested. According to B. C. Wolverton, author of How To Grow Fresh Air, a six foot (1.8 m) areca palm transpires approximately 1 quart (1 litre) of water every 24 hours. So if you put three in your bedroom, the palms will be release three quarts of water per day — not bad!

Author B.C. Wolverton originally began his research to investigate creating a breathable environment for a NASA lunar habitat. What came of that research was the discovery that houseplants are the most efficient filters of common pollutants such as ammonia, formaldehyde and benzene. (See our list of the top plants for cleaning the air).

In this well laid-out book, Wolverton presents 50 plants that are ranked on removal of chemical vapors, ease of maintenance, resistance to insect infestation, and transpiration rate. Each plant gets a two-page spread — one page discusses the plant’s ideal environment, sunlight conditions, care, and general information about the plant along with a full photo of it. The next page has a zoomed-in full-page photo of the leaves and/or flowers so the reader gets a feel for what the plant looks like.

How To Grow Fresh Air is available from Amazon for $12.24.