Why are pollutant emissions measured in g/km?

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In summary, there is a debate about the most appropriate unit to measure emissions from internal combustion engines in vehicles. While the common unit is grams per kilometre, the speaker argues that measuring in grams per second or per minute would be more accurate and useful. This is because it is easier to set and measure emissions targets when using mass flow rate units. However, it is unclear if vehicle manufacturers and regulatory agencies use mass/distance units for simplicity and ease of comparison for consumers. Additionally, it is pointed out that in some countries, pollution is also measured in units of time, taking into account factors such as idling at intersections.
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ksio89
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When we read about how much carbon dioxide (or any other air pollutant) an internal combustion engine in a certain vehicle produces, the measure unit employed is grams per kilometre, it is, mass per unit of distance. However, in my understanding, it would make much more sense to measure emissions in grams per second or per minute, it is, to use mass flow rate units. One of the reasons is that I believe it is much easier to set an emissions target and to measure it if the unit chosen is in mass per unit of time.

Correct me if I'm wrong, but stating how much CO2 an engine produces per kilometre does not make any sense at all, because we don't know how the gas production rate has variated. It seems more intuitive and useful to know how much pollutant gas is produced per unit of time, considering some additional parameters such as engine rpm or gasoline octane rating.

Do vehicle manufacturers and regulatory agencies stating emissions in units mass/distance for simplification? I I mean, does it make easier for consumers to compare emissions between different models?
 
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Since the normal purpose of a vehicle to transport someone from one location to another, then emissions and efficiency are rated versus distance instead of versus time.

In the USA and some other countries, pollution versus unit time is also taken into account, such as a car idling while stopped at an intersection.
 
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1. Why are pollutant emissions measured in g/km?

Pollutant emissions are measured in grams per kilometer (g/km) because it is a standard unit of measurement that allows for easy comparison between different vehicles. It represents the amount of pollutants emitted by a vehicle for every kilometer it travels.

2. How are pollutant emissions measured in g/km?

Pollutant emissions can be measured in g/km through various methods such as using emissions testing equipment, calculating emissions based on fuel consumption and engine efficiency, or using mathematical models based on vehicle specifications.

3. Why is it important to measure pollutant emissions in g/km?

Measuring pollutant emissions in g/km is important because it helps us understand the environmental impact of vehicles and their contribution to air pollution. It also allows for the development and implementation of regulations to control and reduce emissions.

4. Are all types of pollutants measured in g/km?

No, not all pollutants are measured in g/km. Typically, g/km is used to measure carbon dioxide (CO2) emissions, as this is the primary greenhouse gas emitted by vehicles. Other pollutants such as nitrogen oxides (NOx) and particulate matter (PM) may be measured in different units, such as grams per horsepower-hour (g/hp-hr).

5. How do g/km emissions standards differ between countries?

G/km emissions standards can vary between countries depending on their environmental regulations and policies. Some countries may have stricter standards, while others may have more lenient ones. These standards are often based on the average emissions of vehicles in a certain fleet, and may also vary depending on the type of vehicle (e.g. passenger cars vs. heavy-duty trucks).

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