Exploring car emissions data

Uses this dataset. Car makers with less than 10 examined vehicles have not been included.

There is at least one surprising result here. Although the median value of the CO emissions for one car maker is among the smallest observed, the amount of emissions increases dramatically when all three categories are considered. This suggests that measuring only CO can give an imprecise picture about the emissions of a car.

We must consider that not all emissions are equally harmful to the environment. Instead of taking the sum of emissions, it would have been more appropriate to take a weighted sum if we know how much harm a given particle does once released. In the past some people suggested that some other particles could be up to 20x more harmful than CO2.

Although there were scandals with manipulated measurements, we can see that the cars of some of the affected companies are not emitting that much, at least when it comes to this dataset. On the other side, car makers that were not discussed at all are showing relatively high emitting rates.

These emission rates might seem small, but we must not forget that they are per km (and measured only on vehicles driven in 2016). If we took the median for all emissions (425.0mg/km) and multiplied it by 100 thousand cars that are driven for 150000km on average, this would result in 6375 tons of emissions that come in the air that we then breathe. But the cars in use are much more than 100 thousand (yet, another factor to multiply with).

As expected, the list of the most expensive cars to drive is dominated by expensive brands like Ferrari, Lamborghini, Bentley, Rolls Royce and Aston Martin. In the list of least expensive cars to drive we see many models. Interestingly, Tesla with its model S already appears on the list.

But, for instance, for the least expensive cars, we can examine which of them have the smallest sum of emissions. Unfortunately, this data is unavailable for most of these cars on the list. But the second Bmw, i Series, From November 2013 has only 59mg/km—the smallest among the values we can actually calculate. Toyota, Prius Plug-In, MY2012 came at 144mg/km, while Toyota, Prius, 2016 came at 181mg/km. Audi A3 Sportback released 74mg/km, while Hyundai, i20 released 542mg/km. Since these values are (mostly) below, but in one case also above the median value, we cannot easily conclude that driving more cheaply is always connected with releasing less particles in the atmosphere.

Combined emissions by engine capacity

We could also divide the combined emissions by the engine capacity, once we normalize both values. The intuition is that we want to find the strongest engine that pollutes the least. The smaller this number, the closer we are to this goal. Here are the results we obtain:

The models on this list tend to appear in groups. This is because the measurements have been made on multiple cars having the same manufacturer and model. For each group the values appear to be approximately the same, which raises the question whether we could detect the type of the car simply from the measurement...

Emissions by model

Sometimes it is useful to compare the emissions of different models from the same manufacturer. But we should not blindly trust these results, since only few cars from a given model could have been included in the data. Use these results only as an orientation and check them against other information sources you come across.