Biogenic sources contribute a large portion of emissions of volatile organic compounds (VOCs), a precursor to tropospheric ozone (O3). These emissions are difficult to control and are affected by land-use and climate. A sensitivity analysis was performed using an emissions scenario with a 100% increase in biogenic emissions and another scenario with an additional 100% increase in motor vehicle emissions. Meteorological and air pollution models were used to generate hourly ozone estimates for a case study high ozone episode. Resulting concentration estimates correspond to the total effect of changes from emissions, incorporating the interaction between anthropogenic and biogenic emissions.
Biogenic VOCs had a greater impact than a comparable percent increase in motor vehicle emissions of ozone precursors, in this case study. The 100% increase in biogenic VOC emissions raised ozone levels, with an estimated maximum 1-h concentration 30% higher than that of the baseline scenario. The additional emissions of ozone precursors from motor vehicles raised the maximum 1-h concentration 40% over that of the baseline. The largest increases in ozone concentrations occurred near peak values. Urban areas had larger increases in ozone levels than rural regions. Both adjusted emissions scenarios resulted in ozone concentrations lower than that of the baseline for some estimates. These reductions occurred near low ozone levels however and were generally small.
This research demonstrates the importance of biogenic VOC emissions in ozone formation for this region and of biogenic emissions inventories. Results also imply that climate change-induced increases in biogenic VOC emissions could significantly impact ozone concentrations.