Ozone and haze pollution weakens net primary productivity in China
Xu Yue1, Nadine Unger2, Kandice Harper3, Xiangao Xia4, Hong Liao5, Tong Zhu6, Jingfeng Xiao7, Zhaozhong Feng8, and Jing Li91Climate Change Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 2College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QE, UK 3School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, Connecticut 06511, USA 4Laboratory for Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 5School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China 6State Key Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China 7Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA 8Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 9Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
Received: 17 Nov 2016 – Accepted for review: 13 Dec 2016 – Discussion started: 15 Dec 2016
Abstract. Atmospheric pollutants have both beneficial and detrimental effects on carbon uptake by land ecosystems. Surface ozone damages leaf photosynthesis by oxidizing plant cells, while aerosols promote carbon uptake by increasing diffuse radiation and exert additional influences through concomitant perturbations to meteorology and hydrology. China is currently the world's largest emitter of both carbon dioxide and short-lived air pollutants. The land ecosystems of China are estimated to provide a carbon sink, but it remains unclear whether air pollution acts to inhibit or promote carbon uptake. Here, we employ Earth system modeling and multiple measurement datasets to assess the separate and combined effects of anthropogenic ozone and aerosol pollution on net primary productivity (NPP) in China. In the present day, air pollution reduces annual NPP by 0.4 Pg C (9 %), resulting from a decrease of 0.6 Pg C (14 %) by ozone damage, and an increase of 0.2 Pg C (5 %) by aerosol direct effects. The enhancement by aerosols is a combination of diffuse radiation fertilization, reduced canopy temperatures, and reduced evaporation leading to higher soil moisture. However, precipitation inhibition from combined aerosol direct and indirect effects reduces annual NPP by 0.2 Pg C (4 %), leading to a net air pollution suppression of 0.8 Pg C (16 %). Our results reveal strong dampening effects of air pollution on the land carbon uptake in China today. Following the current legislation emission scenario, this suppression will not alleviate by the year 2030, mainly due to a continuing increase in surface ozone. However, the maximum technically feasible reduction scenario could drastically relieve the current level of NPP damage by 70 % in 2030, offering protection of this critical ecosystem service and the mitigation of long-term global warming.
Yue, X., Unger, N., Harper, K., Xia, X., Liao, H., Zhu, T., Xiao, J., Feng, Z., and Li, J.: Ozone and haze pollution weakens net primary productivity in China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1025, in review, 2016.