Gas-powered lawnmowers are notorious polluters. According to the US Environmental Protection Agency, running a new gas mower for one hour produces as much air pollution as would be generated by 11 typical automobiles being driven for the same amount of time. Switching to an electric or reel mower is certainly one option, but for those applications where it's gotta be gasoline, a team of engineering students from the University of California, Riverside are developing another: an attachment that they claim reduces noxious emissions by over 90 percent.

Known as UCR NOx-Out, the device takes the form of an L-shaped stainless steel pipe, that replaces an existing mower's muffler. It cleans up the exhaust via a three-step process.

First, a stainless steel filter removes the bulk of the particulate matter. Next, a fine spray of urea is released into the exhaust stream. Finally, that urea reacts with a copper zeolite catalyst to convert the exhaust's nitrogen oxide and ammonia content into innocuous nitrogen gas and water, which are released into the air. That catalyst also converts the carbon monoxide into carbon dioxide.

The device with its filter (top left) and catalyst (bottom left)

NOx-Out was initially developed by another team last year, and will likewise be further developed by a third team next year. All of the students have been (or will be) advised by Dr. Kawai Tam, Prof. David Cocker, and Assistant Professor Phillip Christopher.

The previous version of the device was reportedly shown to reduce carbon monoxide content by 87 percent, nitrogen oxides by 67 percent, and particulate matter by 44 percent. In the current version, the figure for particulate matter removal jumps to 93 percent.

Other improvements introduced by the most recent team include the longer-lasting steel filter (it was formerly made of quartz), a honeycomb-structured solid catalyst (which previously took the form of a powder that could get blown out), a less obtrusive one-piece design, and the addition of a noise-reducing muffler.

The device is about to be trialled on the lawnmowers used to maintain the campus grounds. Once commercialized in an estimated four to five years, it is estimated that NOx-Out should be available for about US$30. Dr. Tam tells us that an 8-oz (237-ml) container of urea should be good for approximately 10 to 13 weeks of use, in cases where an average-sized lawn is being mowed for around one hour per week.

Sources: UC Riverside, UCR NOx-Out