Road transport is responsible for large quantities of nitrogen oxides (NO\({}_{\rm x}\)), particulate matter (PM\({}_{2.5}\)), and volatile organic compounds (VOCs) emitted in the atmosphere (EEA's Transport and Environment Reporting Mechanism [7]), and therefore for the poor air quality, especially in traffic hotspots in urban areas, through primary and secondary air pollutants such as PM, ozone (O\({}_{3}\)), and secondary aerosols (SA). Transport emissions harm our health and need to be drastically reduced without delay [8]. Although these emissions have decreased, they have declined less than foreseen over the last 20 years [7]. This could be explained by the fact that the reduction of NO\({}_{\rm x}\) emissions by diesel cars has shown to be more challenging, due to the difference between real-world NO\({}_{\rm x}\) emissions and certification limits under Euro 4 and 5 [9]. Since 1970, road transport activities increased in Europe by 1.7 times when compared to nowadays (2018) and increased by more than 30% over the past two decades. Despite the increase of fuel combustion in this sector, most air pollutant emissions have decreased over the past two decades (with the exception of NH\({}_{3}\)) thanks to the implementation of emission control technologies. Recent studies by [10; 11] found that in 2017, emissions from road transport were lower than in the previous year. In particular, emissions of nitrogen oxides decreased at a faster rate when compared to the decreased activity in [12], specifically by 3%, and PM\({}_{10}\) and PM\({}_{2.5}\) decreased by 1.4% and 3.6%, respectively [5] thanks, among others, to the implementation of the latest emission control technologies in new light-duty vehicles as they entered EU vehicle fleets. However, several countries did not meet the reduction targets set by the National Emission reduction Commitments Directive (NECD) for 2020 [13]. Therefore, more action is required to meet the air quality standards [14]. Aiming at reducing the emissions from the transport sector, passenger cars, and light-commercial vehicles, the EU has introduced since the 1990s a series of directives and regulations, commonly known as Euro standards (Euro 1 to Euro 6). The most recent regulatory steps within Euro 6 standard, Euro 6d-TEMP and Euro 6d, require emission tests of light-duty vehicles over a combination of on-road routes and laboratory tests. These have resulted in an important decrease of tailpipe NO\({}_{\rm x}\) emissions for diesel vehicles and for ultrafine particle emissions from direct injection gasoline cars equipped with gasoline particulate filters [15; 16; 17; 18; 19], whereas the results for ammonia (NH\({}_{3}\)) and carbon monoxide (CO) emissions of some diesel and gasoline vehicles showed elevated emissions for these compounds [17; 20; 21]. It is important to note that some of these pollutants remain either non-regulated for light-duty vehicles (NH\({}_{3}\)) or not covered by the Real Driving Emissions legislation (CO and VOCs). Vehicles meeting the Euro 6d-TEMP/6d standard constitute however, only a small part of the European fleet. While the traditional exhaust emissions (e.g., NO\({}_{\rm x}\), PM) are well known and documented, several recent studies [15; 16; 17; 18] point out the need of controlling ammonia (NH\({}_{3}\)) emissions in vehicle exhaust, as they contribute to secondary aerosol formation. The objective of this work was to study the contribution of NMVOCs, PM, NO\({}_{\rm x}\), and NH\({}_{3}\) emitted by vehicles to NO\({}_{2}\) concentrations and to the formation of secondary aerosol (SA) and ozone, which are major contributors to urban pollution in Europe. This is achieved by changing the emission characteristics of passenger cars and light-commercial vehicles in dedicated model simulations to represent different emission reduction scenarios.