The given graph illustrates the nitrogen oxide emissons produced by four type of cars: Buses, Lorries, Petrol car and Diesel car.
Overall, it is clear that Buses and Lorries released much more nitrogen oxide at high speed, while Petrol and Diesel cars showed relatively stable emissions.
In the detailed way, at 10 kph Buses produced 40 g/km, which was higher indicator, while Lorries showed 33 g/km relatively. Then both type of vehicles saw a slighly decline, when at 20 kph Buses and Lorries production of nitrogen were 36 and 30 g/km respectively. Therefore, The lower point of Buses was 26 g/km at 60 kph, whereas Buses indicator was about 19 g/km at 100 kph. After, Lorries showed development, with small dump at 120 kph, where production was 24 g/km. Meanwhile, Buses production only increase and the highest point was 43 g/km relatively at 130 kph.
To contrast, Petrol and Diesel car emissions were 10 and 6 g/km respectively at 10 kph. Diesel car produstion decreases to 5 g/km at 20 kmp, and this indicator was constant until the maximum speed. The situation with Petrol car was quite similar, that the level of emission was constant in the beginning with negligible increasement that was 12 g/km at 130kph.