How much pollution is created by an airplane taking off?
To provide more detail, let's look at some actual numbers. Without knowing where you got this information, the term "air pollution" is especially vague. But let's see what we can do. I'll compare CO (carbon monoxide) emissions since I could find that for both cars and jet engines.

The new 747-8 uses the GEnx-2B67 engine. The older 747-400 has a few engine options, one of which is the CF6-80C2B5F. Emissions information about these engines is available from EASA tests, and available for the GEnx and CF6. More info about the tests is here.

Based on that information the two engines have the following CO emissions at takeoff, reported as grams per kg of fuel burned:


CF6: .05 g/kg CO
GEnx: .17 g/kg CO


The fuel burn rates at takeoff for the engines are reported as:


CF6: 2.685 kg/s fuel
GEnx: 2.451 kg/s fuel


To find a value of comparison for cars, the EPA standards are here, in units of g/mi. Let's assume that we are using a recent model year, certified to the ULEV (Ultra-Low Emission Vehicles) standard.


ULEV: 1.7 g/mi CO


Now we need a way to compare these values. Let's use your initial value of 5 miles as the comparison distance. The jet engines will remain at takeoff thrust over these 5 miles, and the cars will meet the ULEV standard.

So how long will it take the 747 to cover those 5 miles? Let's look at the whole takeoff run, from a complete stop. This means that it will take about 40 seconds to cover the first mile down the runway. After that, lets assume it averages 160 knots, or 185 mph, over the next 4 miles. This means it will take 78 seconds to cover the rest of the distance, for a total of 118 seconds.

Computing the emissions for the takeoff:

CF6:

$$\begin{align*}
2.685\,\mathrm{kg/s} \times 0.05\,\mathrm{g/kg} &amp;= 0.13\,\mathrm{g/s}\text{ CO}\\
0.13\,\mathrm{g/s}\times 118\,\mathrm{s} &amp;= 15.84\,\mathrm{g} \text{ CO per engine}\\
15.84\,\mathrm{g}\times 4\text{ engines} &amp;= 63.4\,\mathrm{g}\text{  CO per takeoff.}\end{align*}$$

GEnx:

$$\begin{align*}
2.451\,\mathrm{kg/s} \times 0.17\,\mathrm{g/kg} &amp;= 0.42\,\mathrm{g/s}\text{ CO}\\
0.42\,\mathrm{g/s}\times 118\,\mathrm{s} &amp;= 49.17\,\mathrm{g}\text{ CO per engine}\\
49.17\,\mathrm{g}\times 4\text{ engines} &amp;= 196.7\,\mathrm{g}\text{ CO per takeoff.}\end{align*}$$

The car will be easier to compute:

$$5\,\mathrm{mi}\times 1.7\,\mathrm{g/mi} = 8.5\,\mathrm{g}\text{ CO per car.}$$

The 747-400 holds 416 people, and the 747-8 holds 467 (3-class configuration). Let's assume each car will carry 4 people. 

$$\begin{align*}
416/4 &amp;= 104\text{ cars}\\
467/4 &amp;= 116.75\text{ cars.}
\end{align*}$$

We'll split the difference between cramming the three extra people into other cars and adding another car, and just leave it as 116.75 cars. Totaling the emissions from all cars:

$$\begin{align*}
104\text{ cars}\times 8.5\,\mathrm{g/car} &amp;= 884\,\mathrm{g}\text{ CO}\\
116.75\text{ cars}\times 8.5\,\mathrm{g/car} &amp;= 992\,\mathrm{g}\text{ CO.}\end{align*}$$

So comparing the 747 and the cars:


747-400: 63.4 g CO
104 cars: 884 g CO
747-8: 197 g CO
116.75 cars: 992 g CO


So a 747-400 is equivalent to about 7.5 cars, and a 747-8 is equivalent to 23.2 cars, comparing the takeoff run with average vehicle emissions.

I found this pretty surprising. It would be more fair to compare a takeoff with a drag race or a 0-60 test on the cars, which is probably not what the emissions test requires.

If anyone has more info or sees an issue with this please let me know.