What about local problems with high SOx and NOx levels?

It should be clarified that NOx and SOx trading define a method of abatement and does not disqualify regulators from addressing local situations. In the American schemes, federal standards for SO2, NOX, ozone, and particulate matter require facility-by-facility emission limits, if necessary, that cannot be exceeded.

US EPA reports that the NOx and SOx schemes have decreased the overall depositions of nitrogen and sulphur oxides to such an extent, that hot spots are not longer an issue. SOx and NOx emissions are elemental and tend not to deposit nearby but to travel further in the atmosphere, where they remain for a period of time until they deposit to the earth, in average some thousand kilometers away from the chimney. Within one geographical area, there is a diverse spectrum of industries participating in a credit based trading scheme; some by over-reducing their emissions and some by purchasing these over-reductions.

Within a given area, reducing SOx and NOx emissions overall, may also diminish hot spots problem that is otherwise difficult to control.