They run on inefficient two and four-stroke engines that emit several dangerous gasses and chemicals including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxide (NOx), and particulate matter (PM)sup> 56/sup>sup> ,/sup> yet are not monitored in any way by the EPA. While ATV sales outnumber those of other off-road vehicles, two-stroke snowmobiles are much more polluting and contribute more air