Implications of RCP emissions on future concentration and direct radiative forcing of secondary organic aerosol over China.

This study applies the nested-grid version of Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to examine future changes (2000-2050) in SOA concentration and associated direct radiative forcing (DRF) over China under the Representative Concentration Pathways (RCPs). The projected changes in SOA concentrations over 2010-2050 generally follow future changes in emissions of toluene and xylene. On an annual mean basis, the largest increase in SOA over eastern China is simulated to be 25.1% in 2020 under RCP2.6, 20.4% in 2020 under RCP4.5, 56.3% in 2050 under RCP6.0, and 44.6% in 2030 under RCP8.5. The role of SOA in PM2.5 increases with each decade in 2010-2050 under RCP2.6, RCP4.5, and RCP8.5, with a maximum ratio of concentration of SOA to that of PM2.5 of 16.3% in 2050 under RCP4.5 as averaged over eastern China (20°-45°N, 100°-125°E). Concentrations of SOA are projected to be able to exceed those of sulfate, ammonium, and black carbon (BC) in the future. The future changes in SOA levels over eastern China are simulated to lead to domain-averaged (20°-45°N, 100°-125°E) DRFs of +0.19 W m-2, +0.12 W m-2, - 0.28 W m-2, and -0.17 W m-2 in 2050 relative to 2000 under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. Model results indicate that future changes in SOA owing to future changes in anthropogenic precursor emissions are important for future air quality planning and climate mitigation measures.