Internal combustion engine vehicles' air pollution can be reduced by using: 

When fuel is burned in an internal combustion engine and air/fuel residuals are emitted through the vehicle tailpipe, carbon monoxide, nitrogen oxides, and hydrocarbons are released. Gasoline vapours escape into the atmosphere during refuelling as well as when fuel vaporises from engines and fuel systems as a result of vehicle operation or hot weather. Pollutants in vehicle emissions are known to harm lung tissue and can cause or worsen respiratory diseases such as asthma.

Motor vehicle pollution also contributes to acid rain formation and the greenhouse gas emissions that cause climate change. Pollutants emitted directly from vehicles aren't the only thing to be concerned about.

On hot, sunny days, hydrocarbons react with nitrogen oxides to produce ozone, a secondary pollutant. Motor vehicles are the single largest contributor to ground-level ozone, a common component of smog, in many urban areas. Ozone causes coughing, wheezing, and shortness of breath, and it can cause permanent lung damage, making it a major public health concern. As a result, CNG gas is used to reduce air pollution. CNG, or compressed natural gas, is natural gas under pressure that is clear, odourless, and non-corrosive. Although natural gas can be used in vehicles as a liquid or a gas, most vehicles use the gaseous form compressed to high pressures.