Future ozone air quality and radiative forcing over China owing to future changes in emissions under the Representative Concentration Pathways (RCPs)

Abstract

We apply the nested grid version of the Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to assess 2000–2050 changes in O3 air quality and associated radiative forcing in China owing to future changes in emissions under the Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). Changes in surface layer O3 concentrations, numbers of O3 exceedance days (days with maximum daily 8h average (MDA8) O3 exceeding 74.7 ppbv), and tropospheric O3 radiative forcing (RF) are simulated for 2000–2050. Over China, RCP8.5 is the worst scenario for near future (2020–2030) and RCP6.0 is the worst scenario over 2040–2050; the maximum increases in annual mean surface layer O3 concentrations of 6–12 ppbv relative to present day (year 2000) are found over southern China in 2020 and 2030 under RCP8.5 and in 2040 and 2050 under RCP6.0. The numbers of MDA8 O3 exceedance days are simulated to be 10, 0, 0, and 2 days over Beijing-Tianjin-Tanggu (BTT), Yangtze River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SCB), respectively, in the present day (year 2000). No exceedance days are simulated in year 2050 for all the four regions under RCP2.6 and RCP4.5, but extremely high numbers of exceedance days are found in 2050 under RCP6.0 (with 102, 75, 57, and 179 days in BTT, YRD, PRD, and SCB, respectively) and in 2030 under RCP8.5 (with 94, 60, 34, and 162 days in BTT, YRD, PRD, and SCB, respectively). The tropospheric O3 RF in 2050 relative to 2000 averaged over eastern China (18°–45°N, 95°–125°E) is simulated to be 0.11, 0.0, 0.01, and 0.14 W m2 under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. When we consider both the health and climate impacts of tropospheric O3 over China in 2050, RCP2.6 is a significantly improving scenario for both air quality and climate, RCP4.5 is a significantly improving scenario for air quality but has small consequences for climate, RCP6.0 is a significantly worsening scenario for air quality and a slightly worsening scenario for climate, and RCP8.5 is a slightly worsening scenario for air quality and a significantly worsening scenario for climate. These results indicate that to simultaneously abate air pollution and climate warming induced by O3 in China, both the anthropogenic emissions of NOx, CO, nonmethane volatile organic compounds (NMVOCs), and global CH4 levels should be reduced, as represented by RCP2.6.