Why are automobile exhaust and farm runoff difficult to control through environmental regulation?

Automobile exhaust and farm runoff are challenging to regulate primarily because they are classified as dispersed sources (or nonpoint sources) of pollution.1

Unlike point sources, such as industrial pipes or sewerage systems, which collect waste at a single, treatable location, dispersed sources enter the environment from broad, unconfined areas.1

• Farm Runoff: Because agricultural runoff enters water bodies from vast, diffuse landscapes, it cannot be easily captured or conveyed to a treatment facility. This makes it a persistent contributor to water pollution despite advancements in waste disposal technology.1
• Automobile Exhaust: While individual vehicle emissions are managed through stringent emission controls like catalytic converters and fuel injection, the sheer volume of vehicles—driven trillions of miles annually—creates a massive, mobile, and decentralized source of air pollution that is difficult to mitigate entirely. Furthermore, urban stormwater runoff containing petroleum residues from cars is also considered a dispersed source, complicating efforts to protect local water quality.21