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

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Forest Ecology

Background:

• Increasing surface ozone (O3) concentrations in China raise concerns about potential negative impacts on forest ecosystems.
• Understanding O3 exposure risks is crucial for forest health assessment and conservation efforts in the region.

Purpose of the Study:

• To estimate the risks of O3 exposure to forest health across China.
• To quantify source contributions to O3 exposure in key forest regions.
• To identify priority areas for future O3 impact assessments.

Main Methods:

• Calculated several O3 exposure indices (M7, M24, N100, SUM60, W126, AOT40f) for 2013.
• Utilized a source-oriented Community Multiscale Air Quality (CMAQ) model to quantify source contributions.
• Compared calculated O3 exposure levels with established critical loads for ecosystems and plant species.

Main Results:

• 85% and 75% of China's forests exceed critical loads for O3 (SUM60 and W126, respectively).
• 90% of forest areas surpass the AOT40f critical load.
• Higher O3 exposure observed in the western Sichuan Basin, southern Qinghai-Tibetan Plateau, Yunnan, and North China Plain.
• Southeast Asian transport impacts spring O3 in Yunnan and SQTP; industrial and transport sectors contribute significantly in WSCB and NCP.
• O3 production is primarily driven by nitrogen oxides (NOx) over volatile organic compounds (VOCs).

Conclusions:

• Significant portions of Chinese forests are exposed to harmful levels of O3, exceeding critical loads.
• Specific regions like WSCB, SQTP, Yunnan, and NCP require prioritized field investigations.
• Reducing NOx emissions from industries, transportation, and international sources is the most efficient strategy to mitigate O3 risks to forests.