One source of valley air pollution and risk to groundwater safety is spilled fuel at filling stations. One cause is the practice of many customers who insist on "topping off" their fuel tank either to get the cost amount to an even figure or in an attempt to get more fuel into their tank. Neither reason has any justification, but in all cases when a contemporary fuel nozzle used on a contemporary automobile in proper repair shuts off, the tank is full and there is no more room for additional fuel.
The only result they gain is limiting the function of their emissions controls, spilled fuel and general waste, to say nothing about the waste of time including the time of customers waiting their turn. Unfortunately, old habits die hard and many people continue to do this even though it's a practice with a number of downsides, and no benefit.
Our poor air quality has many causes and this is only one, but by attacking bad practices one at a time we can make a difference. All it takes is a change in mindset to make a better choice. In the interest of clean air, fuel conservation and, in general, more bang for the buck, those who have been doing this should show consideration for themselves and others, stop and not make further attempts to add what at best could be a tiny amount of fuel.