NOx and PM
Emissions limits cover in particular nitrogen oxides (NOx) and particulate matter (PM) which pose the most serious health problems. NOx can lead to respiratory illnesses and contributes to acid rain. Particulate matter can come from many sources. Generally, any activity which involves burning of materials or any dust generating activities is a source of PM. Vehicles of all types produce particulates. PM can be found in the air in a whole spectrum of different sizes, but most air quality measurements focus on particles up to 10 microns in diameter (PM 10) or fine particles of up to 2.5 microns in diameter (PM 2.5). The latter are particularly harming for the human body as they are small enough to get deep into the lungs.
PM can alter the body's defence systems against foreign materials, damage lung tissues, and aggravate existing respiratory and cardiovascular disease. PM of 100nm (0.1 microns)and less can pass from the lung into the blood supply and other organs.
Diesel and Petrol
Diesel cars emit significantly less carbon dioxide (CO2) than petrol cars due to their fuel efficiency. However, emissions of NOx and PM from diesel vehicles are currently higher than those for petrol vehicles, therefore they are at the core of emissions control development.
To comply with new legislation, car manufacturers are working on technologies to optimise diesel engines for higher fuel economy and to diminish NOx and PM levels. Emissions vary depending on several technical factors, including the diesel fuel quality, engine type and engine tuning as well as the workload demand on the engine.