The graph illustrates the amount of nitrogen oxide which was emitted by four vehicles, namely, Diesel cars, Petrol cars, lorries, and buses.
Overall, a significantly downward trend applied to the amount of nitrogen oxide produced by lorries, while the amount of nitrogen oxide which was emitted by buses witnessed a slight increase. Additionally, the amount of nitrogen oxide produced by Petrol cars was subject to a marginal fluctuation, whereas the nitrogen oxide emitted by Diesel cars saw a slight decrease in this period.
As can be seen from the graph, at the speed of 10 kph, buses emitted the highest amount of nitrogen oxide, at 40 g/km, which was nearly fourfold the nitrogen oxide emitted by Petrol cars, at 11 g/km. Meanwhile, the amount of nitrogen oxide which was emitted by lorries was the second highest, at 33 g/km. In addition, the amount of nitrogen oxide which was emitted by Diesel cars was the lowest, at 7 g/km.
From 10 kph to 90 kph, the amount of nitrogen oxide which was emitted by buses suddenly dropped before rising again to nearly 35 g/km at the speed of 90 kph. Besides, the nitrogen oxide emitted by lorries dramatically decreased to about 16 g/km. In addition, the amount of nitrogen oxide which was emitted by Petrol cars and Diesel cars saw a fluctuation but slightly decreased to about 10 g/km and 5 g/km, respectively.
Between 90 kph and 130 kph, the nitrogen oxide emitted by buses and lorries continued to rocketed and reached a peak of 42 g/km and 24 g/km. Similarly, the amount of nitrogen oxide which was emitted by Petrol cars saw a marginal rise to about 11 g/km. Meanwhile, the amount of nitrogen oxide produced by Diesel cars remained stable at 5 g/km from 90 kph to 130 kph. 
The graph illustrates the  
amount
 of nitrogen oxide which was  
emitted
 by four vehicles,  
namely
,  
Diesel
  cars
,  
Petrol
  cars
,  
lorries
, and buses. 
Overall
, a  
significantly
 downward trend applied to the  
amount
 of nitrogen oxide produced by  
lorries
, while the  
amount
 of nitrogen oxide which was  
emitted
 by buses witnessed a slight increase.  
Additionally
, the  
amount
 of nitrogen oxide produced by  
Petrol
  cars
 was subject to a marginal fluctuation, whereas the nitrogen oxide  
emitted
 by  
Diesel
  cars
  saw
 a slight decrease in this period.
As can be  
seen
 from the graph, at the speed of 10 kph, buses  
emitted
 the highest  
amount
 of nitrogen oxide, at 40 g/km, which was  
nearly
 fourfold the nitrogen oxide  
emitted
 by  
Petrol
  cars
, at 11 g/km. Meanwhile, the  
amount
 of nitrogen oxide which was  
emitted
 by  
lorries
 was the second highest, at 33 g/km.  
In addition
, the  
amount
 of nitrogen oxide which was  
emitted
 by  
Diesel
  cars
 was the lowest, at 7 g/km.
From 10 kph to 90 kph, the  
amount
 of nitrogen oxide which was  
emitted
 by buses  
suddenly
 dropped  
before
 rising again to  
nearly
 35 g/km at the speed of 90 kph.  
Besides
, the nitrogen oxide  
emitted
 by  
lorries
  dramatically
 decreased to about 16 g/km.  
In addition
, the  
amount
 of nitrogen oxide which was  
emitted
 by  
Petrol
  cars
 and  
Diesel
  cars
  saw
 a fluctuation  
but
  slightly
 decreased to about 10 g/km and 5 g/km,  
respectively
.
Between 90 kph and 130 kph, the nitrogen oxide  
emitted
 by buses and  
lorries
 continued to rocketed and reached a peak of 42 g/km and 24 g/km.  
Similarly
, the  
amount
 of nitrogen oxide which was  
emitted
 by  
Petrol
  cars
  saw
 a marginal rise to about 11 g/km. Meanwhile, the  
amount
 of nitrogen oxide produced by  
Diesel
  cars
 remained stable at 5 g/km from 90 kph to 130 kph.