Large biogenic contribution to boundary layer O3-CO regression slope in summer

Modeling analysis suggests that the contribution from biogenic isoprene oxidation to the observed O-3-CO regression slope is as large as that from primary anthropogenic CO emissions. As a result of decrease of anthropogenic primary CO emissions during the past decades, biogenic CO from oxidation of isoprene is increasingly important. Consequently, observed and simulated O-3-CO regression slopes can no longer be used directly with an anthropogenic CO emission inventory to quantify anthropogenic O-3 production over the United States.

The consistent enhancement of O-3 relative to CO observed in the boundary layer, as indicated by the O-3-CO regression slope, provides a useful constraint on model photochemistry and emissions.