Sensitivity of biogenic secondary organic aerosols to future climate change at regional scales: An online coupled simulation

Biogenic emissions and secondary organic aerosols (SOA) are strongly dependent on climatic conditions. To understand the SOA levels and their sensitivity to future climate change in the United States (U.S.), we present amodelingworkwith the consideration of SOA formation from the oxidation of biogenic emissions with atmospheric oxidants (e.g., OH, O3, and NO3). The model simulation for the present-day climate is evaluated against satellite and ground-based aerosol measurements. Although the model underestimates aerosol concentrations over thenorthwesternU.S. due to the lackoffireemissions in themodel simulations, overall, the SOA results agree well with previous studies. Comparing with the available measurements of organic carbon (OC) concentrations, we found that the amount of SOA in OC is significant, with the ratio ranging from0.1 to 0.5/0.6. The enhancedmodeling systemdriven byglobal climatemodel outputwas also applied for two three-year one-month simulations (July, 2001e2003 and 2051e2053) to examine the sensitivity of SOA to future climate change. Under the future two emissions scenarios (A1B and A2), future temperature changes arepredicted to increase everywhere in theU.S., butwithdifferent degrees of increase in different regions. As a result of climate change in the future, biogenic emissions are predicted to increase everywhere, with the largest increase (w20%) found in the southeastern and northwestern U.S. under the A1B scenario. Changes in SOA are not identical with those in biogenic emissions. Under the A1B scenario, the biggest increase in SOA is found over Texas,with isoprene emissions being themajor contributor to SOA formation. The range of change varies from 5% over the southeast region to 26% over Texas. The changes in either biogenic emissions or SOA under the two climate scenarios are different due to the differences in climatic conditions. Our results also suggest that future SOA concentrations are also influenced by several other factors such as the partitioning coefficients, the atmospheric oxidative capability, primary organic carbon aerosols and anthropogenic emissions. 2010 Elsevier Ltd. All rights reserved.