An emission measured at a stack or other source does not remain at that concentration once it enters the atmosphere. Wind, temperature, turbulence, terrain, buildings and atmospheric conditions influence where it travels and what concentrations may occur downwind.
Pollutants do not always remain chemically unchanged after release. Atmospheric reactions, sunlight, water, surfaces and biological processes can transform substances into new forms whose environmental behaviour may differ from that of the original emission.
Airborne pollutants do not remain in the atmosphere indefinitely. They can be transferred to soil, vegetation and water through dry deposition or precipitation, creating environmental pathways beyond inhalation.
Environmental contaminants can move between air, soil, water and living systems. A credible food-chain claim requires evidence across each stage of that pathway, not merely the detection of a hazardous substance somewhere in the environment.
Stack monitoring tells us what leaves a source. Ambient monitoring tells us what is present in the surrounding environment. Neither, on its own, establishes the complete causal pathway between a facility and population exposure.