Pay Extra for Nitrogen?

Today I finally had time to replace the worn tires on my car. My Firestones had more than 60,000 miles on them. Given the fact my driveway has 10 layers of ice on it, I want the best traction I can get. I stopped at Wright Tire to get some new ones. I think I got a good deal on the tires. I paid less than I thought I would. The cost was $160 less than what the car dealer quoted me. I was asked if I wanted to pay an extra $20 ($5 each tire) to have them filled with nitrogen. I was told nitrogen has larger molecules and fewer molecules will escape through the tire. I will have less of a difference in tire pressure as the seasons change from winter to summer. As the sales clerk was talking, my mind went back to the diagrams of the nitrogen cycle we were shown in my master naturalist class. Do I want more nitrogen? Do I want to pay extra to have nitrogen in my tires? Will this be bad for the environment? Nitrogen is an ingredient in fertilizer. Lightening adds nitrogen to the environment. Leaving the roots of bean plants in the garden keeps the trapped nitrogen in the soil. Wait a minute, isn't there nitrogen in our air already? My mind is racing a thousand ways while the clerk is waiting for an answer. I pass on the nitrogen filled tires. When I got home I looked it up on the Internet - the source of all correct information, right? Yes, our air is composed of 78% nitrogen. According to a popular mechanics article, the benefits are less moisture inside the tire (keeping the rim corrosion free) and consistent tire pressure resulting in slightly better mileage and lower tire maintenance costs. Good information to have. I wish I had it a little sooner so I could have made a more informed decision.