生物源挥发性有机物对大气氮沉降的响应及其对臭氧分布格局的影响

In recent years, regional ozone(O3) pollution is becoming more and more severe over China. With the effective control of anthropogenic emissions, the contribution of biogenic volatile organic compounds (BVOCs) to O3 formation is increasingly prominent. However, high uncertainties of the accurate estimation of natural emissions and the assessment of their environmental effects are still existed, in which, the neglect of the effects of atmospheric nitrogen deposition is one of the key uncertainty sources. In view of the insufficient consideration of the impacts of atmospheric nitrogen deposition on the simulation of BVOCs emissions, environmentally controlled plant growth chamber experiment is conducted to reveal the potential influences of atmospheric nitrogen deposition on BVOCs emissions over China, further to establish a parameterization scheme in the response relationship between BVOCs emissions and atmospheric nitrogen deposition. Secondly, upscaling model is developed to extrapolate the response of BVOCs emissions to atmospheric nitrogen deposition at the regional scale, and the two-way feedback between BVOCs emissions and atmospheric nitrogen deposition is achieved. Thirdly, the influence of BVOCs emissions on the distribution pattern of surface O3 over China is explored through sensitivity studies. This study is expected to enhance the characterization capability of the dynamic exchange processes between BVOCs emissions and atmospheric nitrogen deposition, and to deepen the understanding of the effects of BVOCs emissions on O3 formation, which could potentially provide scientific evidences for the prevention and control of regional O3 pollution, and the improvement of air quality.

近年来我国区域臭氧(O3)污染态势严峻。在人为源排放有效控制的背景下，生物源挥发性有机物(BVOCs)对O3生成的贡献日益突出，然而当前BVOCs排放的准确估算及其环境效应评估仍然具有很大不确定性，其中忽略大气氮沉降的影响是其不确定的重要来源之一。针对BVOCs排放估算考虑大气氮沉降影响不足的问题，本项目拟开展环境控制植物生长室实验，揭示大气氮沉降对BVOCs排放的影响，并建立树种尺度的BVOCs-大气氮沉降响应关系参数化方案；进一步构建升尺度模型，推算区域尺度BVOCs排放对大气氮沉降的响应，实现WRF/Chem-MEGAN数值模式BVOCs排放-大气氮沉降的双向反馈模拟；最后通过开展敏感性实验，阐明中国BVOCs排放对近地面O3分布格局的影响。项目有望提升BVOCs排放和大气氮沉降动态交换过程的表征能力，深化BVOCs排放对O3生成的认识，为区域O3污染防治和空气质量改善提供科学依据。

近年来我国臭氧(O3)浓度仍处于高位，阻碍了空气质量的持续改善。近十年一系列减排措施的出台有效遏制了O3人为前体物排放不断上升的势头，然而生物源排放对近地面O3生成的贡献愈发凸显。然而当前生物源排放的准确模拟及其对二次污染格局的影响仍具有很高不确定性。针对此问题，本项目通过收集多源数据，对生物源估算模式MEGAN的输入资料本地化更新，包括植被功能类型、排放因子、叶面积指数；同时考虑大气氮沉降和氮肥施用的影响，改进土壤NO排放机制，从而在WRF/Chem-MEGAN模式实现天然源排放与大气氮沉降在线耦合模拟，大幅提升天然源排放模拟能力，其中BVOCs模拟偏差从68%降至21%，土壤NO排放平均偏差从-25.4降低到-6.4 ngN·m-2·s-1。基于改进模式，结合近地面污染物浓度观测数据，通过建立O3浓度与温度之间的关系，明确了2013-2019年全国清洁季节和污染季节的背景O3浓度分别为35-40和50-55 ppbv；与清洁季节相比，BVOCs排放是污染季节背景O3增加的主要原因，BVOCs排放使得污染季节背景O3浓度平均增加了8 -16 ppbv；2013-2019年期间，污染季节背景O3以0.6–8.0 ppbv·yr-1的速度增长，揭示了不断上升的区域背景O3浓度水平需要对人为排放进行更严格的控制。敏感性实验发现，需要额外减少 2–16%的人为 VOCs 排放才能将2018-2019年O3浓度降低到2013-2017年期间浓度水平。基于改进的WRF/Chem-MEGAN模式进一步发现，在充足的BVOCs排放的情况下，土壤NO排放(SNO)可有效促进 BVOCs 的大气化学反应过程及O3生成过程。BVOCs和SNO 排放的协同作用超过各自贡献之和，其中夏季中国东部地区平均达到10-20 ug·m-3。相对于BVOCs或SNO对O3生成的单独作用，为了抵消天然源排放BVOCs和SNO协同作用对O3生成的影响，人为VOCs排放量需要增加1.76倍。本项目通过改进WRF/Chem-MEGAN模式，提升天然源表征能力，准确量化天然源排放及其对近地面O3形成的协同影响，对于评估大气化学过程和有效制定O3污染控制政策具有重要意义。