Table 32.3 - Importance of precursor changes for various oxidising and acidic compounds and visibility

Source: Grennfelt et al, 1993

Precursors Episodic ozoneAverage ozoneAverage OHAverage H2O2SO2/SO42=NOx/NO3­NH3/NH4+ Visibility
CH4 + +++ ­ ­ ­ +++ weak medium 0 +
CO + + ­ ­ ­ +++ weak medium 0 +
NMVOC* +++ + weak weak ++ medium 0 ++
NOx strong(+/­) +++ +++ ­ ­ ++ strong medium ++
SO2 0 0 0 ­ strong 0 strong strong
NH3 0 0 0 0 weak weak strong weak

Notes:

* NMVOC = non-methane VOC.

The sign of the relationship is indicated by +/­ meaning that, when the precursor emission increases, the concentration of the different compounds or visibility increases/decreases.