Vehicle emissions standards are regulations set by governments to limit the amount of pollutants that cars and trucks can emit into the atmosphere. These standards aim to reduce harmful substances like carbon monoxide, nitrogen oxides, and particulate matter, which can contribute to air pollution and health problems. By establishing specific limits for different types of vehicles, such as passenger cars and heavy-duty trucks, these standards encourage manufacturers to develop cleaner technologies. Compliance with these regulations is often monitored through testing, ensuring that vehicles meet the required emissions levels before they can be sold or operated on the roads.