Dear EarthTalk: Is using nitrogen to inflate my car's tires really better for the environment than using air? And if so, how? -- Roger Mawdsley, Abbotsville, BC

Dear EarthTalk: How can I measure -- and then improve -- my overall "carbon footprint?" What are the major areas of one's daily life that one measures? -- Andy Fusco, Passaic, NJ

With global warming dominating so many headlines today, it's no surprise that many of us are looking to reduce the amount of carbon dioxide and other greenhouse gases our activities produce.

Dear EarthTalk: What's the deal nowadays with aerosol spray cans? I thought that the ozone-depleting chemicals used in them were eliminated back in the 1970s. Is this true? If so, what is now used as a propellant? Are aerosols still bad for the ozone layer? -- Sheila, Abilene, TX

Dear EarthTalk: I am considering solar panels for my roof to provide heat for my hot water and possibly to do more than that. Are there some kinds of solar panels that are better than others? How do I find a knowledgeable installer? --Elise, Watertown, MA

Dear EarthTalk: How often do I really need to change my car's oil? Conventional wisdom has always put it at every 3,000 miles to prevent engine wear, but isn't changing oil that frequently wasteful and unnecessary? Also, what is the "greenest" and longest-lasting oil I should use?
-- Vic Roberts, Lincoln, MA

Dear EarthTalk: I've read that plastic bottles are not always safe to reuse over and over as harmful chemicals can leach out into the contents. I'm wondering if the same issues plague Tupperware and other similar plastic food storage containers. -- Sylvie, Dawson City, Yukon, Canada

Dear EarthTalk: What's going on with all the cases of autism cropping up and no one seems to know why? It stands to reason it must be something (or some things) environmental, yet every study allegedly turns up no conclusion? What are the possible causes? -- Jessica W., Austin, TX

Dear EarthTalk: What green-friendly lawn and garden pesticides are available today? I'm particularly interested in options that won't harm my cats.
-- Nancy Blanchard, via email

Pesticides have greatly boosted agricultural yields over the last half-century, so it is no wonder, given the commercial availability of many of these synthetic chemicals, that American homeowners apply 100 million pounds of the stuff each year to make their own gardens grow bigger and faster, too.

Dear EarthTalk: What are the environmental pros and cons of corn-based plastic as an alternative to conventional petroleum-based plastic?
—Laura McInnes, Glasgow, Scotland