The given graph reports the emission of nitrogen oxide from four vehicles (diesel car, petrol car, lorries and buses) and how much they produce the gas at different speeds.
As shown, buses and lorries tend to produce the most nitrogen oxide out of all the vehicles. The buses emit at 40 grams per kilometer at 10 kph with lorries coming in at about 33 grams per kilometer at the same speed. On the other hand, cars that run on diesel or petrol only produce about 11 and 6 grams per kilometer respectively at the same rate.
As much gas as buses can produce however, these vehicles seem to dip in the emissions as they accelerate, leading to a decline in production till about 26 grams per kilometer at 60 kph, and only start to increase again later maxing up the emissions to 42 grams per kilometer at 130 kph. Similarly, lorries also tend to experience fluctuations with varying speeds. It decreases its manufacture of nitrogen oxide way below to about 16 grams per kilometer at 90 kph, only increasing again up to about 24 grams per kilometer at 130 kph. Compared to these two, diesel and petrol motors don’t experience any dramatic changes in their share of pollution. They both produce the same respective amounts, with slight changes as the speed increases. Petrol cars just stagger a little up to about 11 grams per kilometer at 130 kph while diesel cars remain the same at a perfect 5 grams per kilometer at the same speed.