Spatial-temporal variations and source contributions to forest ozone exposure in China

摘要

As surface ozone (O-3) concentrations have significantly increased in many regions of China, it is concerned that O-3 may cause negative impacts on forests in the country. To estimate the risks of O-3 exposure to forest health, several frequently used O-3 exposure indices (M7, M24, N100, SUM60, W126, and AOT40f) were calculated for the entire year of 2013 and the source contributions to exposure in April and August were quantified using a source-oriented version of the Community Multiscale Air Quality (CMAQ) model. Critical loads for natural ecosystems (12 ppm-h for SUM60) and for moderately sensitive plant species (23.8 ppm-h for W126) are exceeded in 85% and 75% of the forest areas in China, respectively. About 90% of the forest areas have AOT40f higher than the critical load of 10 ppm-h. Forests in the western rim of the Sichuan Basin (WSCB), parts of the southern rim of the Qinghai-Tibetan Plateau (SQTP), Yunnan Province, and the North China Plain (NCP) have higher O-3 exposure than that of other areas. In spring, transport of O-3 and precursors from Southeast Asia have significant contributions to O-3 exposure for forests in Yunnan, SQTP and to a less extent in WSCB. In both spring and summer, industries and transportation sectors have large contributions to O-3 exposure along the WSCB and in the NCP. A higher priority in future field investigations to assess O-3 impacts on forests in China should be given to these regions. The results also suggest that O-3 production in China is much more due to nitrogen oxides (NOx) than due to volatile organic compounds (VOCs). In order to protect China's forest from O-3, it would be most efficient to reduce NOx emissions from industries, transportation, and other countries in general. (C) 2019 Elsevier B.V. All rights reserved.