Researchers in Steve Pacala’s group have been investigating the impact of recent changes in both natural and anthropogenic precursors on surface ozone smog. Drew Purves’ work has shown that a combination of forest regrowth on abandoned farmland and increases in plantation forests in the Eastern US caused rapid increases in biogenic volatile organic compound (VOC) emissions between the 1980s and 1990s. The average increase in heatwave emissions of biogenic VOC was three times greater than the decrease in anthropogenic VOC over this time period. This result implies that forest re-growth and plantation forestry cancelled out some or all of the ozone improvements achieved via legislative reduction of VOC.

Arlene Fiore is applying chemical transport models to examine the implications of the recent changes in biogenic VOC found by Purves. Fiore’s simulations show that the increases in isoprene in the southeastern United States reported by Purves could actually decrease ozone concentrations. This result calls into question the conventional wisdom in air quality management, that increases in VOC should either increase ozone (if sufficient NOx is available) or have little impact on ozone (in low-NOx settings). Fiore’s findings, along with those of other groups, imply that the expected isoprene emission increases in a warmer future climate may not raise surface ozone concentrations as much as might be anticipated from the strong correlation of ozone pollution events with temperature, particularly if more stringent controls on anthropogenic NOx emissions are implemented.