Summer is on the horizon, and the environmentally conscious person might wonder: How can I make my backyard barbeque carbon-neutral?

Let’s start with the barbeque itself.

For the tree-hugging grill-master, a gas grill is the best bet. Gas grills have a carbon footprint about a third of the size of a charcoal grill, according to Swiss researcher Eric Johnson.

“What you find is that far and away, the major impact comes from the actual production and burning of the fuel itself,” Johnson told National Public Radio in 2009.

Charcoal is made by slowly heating wood in a limited-oxygen environment, which gets rid of most of the liquid in the material and leaves you with a lump of nearly pure carbon. The more familiar lozenge- or pillow-shaped briquettes are made by compressing charcoal with other wood by-products like sawdust. There’s often other additives packed in, too, like borax, sodium nitrate and limestone.

Grilling with charcoal takes the carbon from the wood and puts it directly in the air, minus whatever goes into cooking your burgers. Plus, we often use charcoal pretty inefficiently, with a big bag of briquettes being used to cook just a few burgers and hot dogs.

If you’re already planning to fire up a charcoal grill this Memorial Day, “the most helpful thing you could do is when you're done, if you could shut down your grill and try to reuse what coals are there,” Johnson told NPR. “Some grills are actually relatively easy to shut down, but a lot of them are quite difficult. But still, you know, pour some water on it and use them again, because you're really wasting it when the rest of it just goes up in the air.”

Before the guests arrive, you might want to mow your lawn. But engine-powered lawnmowers expel carbon emissions, much like their souped-up cousins the car and the truck. The U.S. Environmental Protection Agency has regulations limiting the amount of exhaust emissions from gasoline-powered lawnmowers, and California has already passed even tighter restrictions. Air quality officials in Southern California have even encouraged people to exchange their gas mowers for electric ones at a reduced price.

But if you’re insistent on keeping the gas-powered lawnmower, you might be able to turn it into a greener machine, thanks to some college students.

A team of University of California, Riverside, students has invented a device that attaches to a lawnmower’s muffler port and helps reduce the machine’s emissions. The principle is similar to the catalytic converter used on most modern automobiles.

The invention, called the NOx-Out, is made of a glass jar filled with urea solution, a filter and a modified lawnmower muffler containing a chemical catalyst. The filter captures particles, while urea combines with the gaseous part of the exhaust to prime it for a reaction with the catalyst in the muffler. Exhaust goes in; nitrogen gas and water come out.

Testing showed that the NOx-Out cut carbon monoxide emissions from a lawnmower by 87 percent, nitrogen oxide emissions by 67 percent and particulate matter pollution by 44 percent. The students say the device could sell for about $30.