Comment by defrost

  If gasoline engines burned their fuel as efficiently as possible, they would produce three by-products: water vapor (H2O), carbon dioxide (CO2) and nitrogen (N2). 

  Unfortunately, engines do not run perfectly, and as a result, they also produce three by-products commonly referred to as the "terrible trio" of automotive pollutants. This trio includes the following:

  *  Carbon monoxide (CO) – An odorless, tasteless, poisonous gas, carbon monoxide can cause a variety of health problems and even death. Many urban areas experience critically high levels of carbon monoxide, especially during the cold winter months when engines take longer to warm up and run cleanly

  *  Unburned hydrocarbons (HC) – Responsible for causing a variety of respiratory problems, unburned hydrocarbons can also cause crop damage and promote the formation of smog

  *  Oxides of nitrogen (NOX) – Like unburned hydrocarbons, oxides of nitrogen cause respiratory problems and promote the formation of smog

* https://www.walkerexhaust.com/support/exhaust-101/exhaust-ga...