Nitrogen Oxide Emissions by Vehicle Type at Different Speeds

IELTS Academic Writing Task 1 - Line Graph

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IELTS Writing Task 1 Question

The given graph shows the nitrogen oxide emissions produced by four vehicles. Summarise the information by selecting and reporting the main features and make comparisons where relevant

47-Nitrogen Oxide Emissions by Vehicle Type at Different Speeds

Common Questions for the Line Graph

1. Graph Type: Line Graph

2. Title: Nitrogen Oxide Emissions by Vehicle Type at Different Speeds

3. What are the units of measurement?: Grams per kilometer (g/km)

4. Who: Four vehicle types (buses, lorries, diesel cars, petrol cars)

5. When: Not specified

6. Where: Not specified

7. Topic: Comparison of nitrogen oxide emissions based on vehicle type and speed

Comparison Showing and Trends Any change over time (such as an increase or a decrease) is a trend.

Comparison 1: Buses (Highest Emissions)

Details:

1.Emit 40 g/km at 10 kph, the highest among all vehicles.

2. Emissions decrease as speed increases to 60 kph, reaching around 25 g/km.

3. Beyond 60 kph, emissions rise again, exceeding 40 g/km at 130 kph.

Comparison 2: Lorries (Similar Pattern to Buses)

Details:

1. Emissions are slightly lower than buses but follow a similar trend.

2. Emissions decrease until 90 kph, then increase beyond this speed

Comparison 3: Diesel and Petrol Cars (Lowest Emissions)

Details:

1.Emissions remain relatively constant across speeds.

2. Diesel cars emit the least (around 5 g/km), while petrol cars emit around 10 g/km.

Sample Answer

The line graph compares the nitrogen oxide emissions of four vehicle types—buses, lorries, diesel cars, and petrol cars—at various speeds.

Overall, buses and lorries produce higher emissions with a clear pattern of decrease and increase at different speeds, while diesel and petrol cars show consistently low and stable emissions.

At a low speed of 10 kph, buses emit 40 g/km, the highest among all vehicles. As speed increases to 60 kph, their emissions decrease steadily to around 25 g/km. However, emissions begin to rise again beyond this speed, exceeding 40 g/km at 130 kph. Lorries show a similar pattern but produce slightly lower emissions. Their emissions decrease until 90 kph and then start to rise, mirroring the trend seen in buses.

Diesel and petrol cars emit far less nitrogen oxide than buses and lorries. Diesel cars consistently produce the least emissions, hovering around 5 g/km regardless of speed. Petrol cars emit slightly more at approximately 10 g/km and show minimal variation across speeds.

Top 26 Vocabularies

Vocabulary	Type	Meaning	Synonyms	Examples
Emission	Noun	The release of gas or substance into the air	Discharge, Release	The emissions from buses were the highest at 10 kph.
Pattern	Noun	A repeated or consistent trend	Trend, Arrangement	Buses and lorries follow a similar emission pattern.
Decrease	Verb/Noun	To reduce the amount	Decline, Drop	Emissions decrease as bus speed increases to 60 kph.
Hover	Verb	To remain around a specific value	Float, Stay	Emissions from diesel cars hover around 5 g/km.
Variation	Noun	A change or difference	Fluctuation, Change	Diesel and petrol cars show minimal variation in emissions.
Compare	Verb	To examine differences and similarities	Contrast, Relate	“The line graph compares emissions from different vehicle types.”
Consistently	Adverb	In a reliable or unchanging manner	Uniformly, Steadily	“Diesel cars consistently produce the least emissions.”
Stable	Adjective	Remaining unchanged or steady	Constant, Steady	“Petrol cars showed stable emissions across various speeds.”
Fluctuation	Noun	Irregular changes in level or value	Variance, Oscillation	“Lorries exhibit some fluctuation in their emissions.”
Peak	Verb/Noun	To reach the highest point	Summit, Climax	“Bus emissions peaked at 40 g/km at high speeds.”
Significant	Adjective	Large or important enough to be noticed	Notable, Substantial	“There is a significant difference between diesel and bus emissions.”
Trend	Noun	A general direction in which something is developing	Pattern, Movement	“The graph highlights a trend in emissions reduction at lower speeds.”
Decline	Verb/Noun	A gradual decrease in value	Reduction, Drop	“Bus emissions show a decline at moderate speeds.”
Steady	Adjective	Happening in a regular, continuous manner	Stable, Gradual	“There is a steady decrease in emissions from buses as speed increases.”
Exceed	Verb	To go beyond a certain limit	Surpass, Overtake	“Bus emissions exceed 40 g/km at high speeds.”
Proportion	Noun	A part or share in relation to a whole	Percentage, Ratio	“Buses emit the largest proportion of nitrogen oxides at low speeds.”
Contrast	Noun/Verb	A noticeable difference between two or more things	Difference, Distinction	“The graph contrasts emissions from buses and diesel cars.”
Level	Noun/Verb	A specific value or point	Rate, Position	“The emissions level from lorries starts to rise at higher speeds.”
Rise	Verb/Noun	An increase in quantity or level	Increase, Surge	“Bus emissions rise beyond 60 kph.”
Moderate	Adjective	Average in amount, intensity, or degree	Medium, Reasonable	“Lorries show moderate emissions compared to buses.”
Maintain	Verb	To keep in the same state or condition	Sustain, Preserve	“Diesel cars maintain low emissions regardless of speed.”
Noticeable	Adjective	Easy to see or observe	Visible, Distinct	“The difference in emissions becomes noticeable at higher speeds.”
Mirror	Verb	To reflect or show similarities	Resemble, Echo	“Lorry emissions mirror the trend of buses at higher speeds.”
Recover	Verb	To return to a normal or improved state	Rebound, Improve	“Lorry emissions recover slightly after a sharp decrease.”
Consistent	Adjective	Remaining the same over time	Steady, Regular	“Diesel cars show consistent emission levels throughout.”
Highlight	Verb	To emphasize or draw attention to	Emphasize, Underline	“The graph highlights the significant differences between vehicle types.”

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