海陆风相互作用下中国南海海域的大气化学和气象特征研究

The interaction between continental air pollution and the maritime atmosphere have long been a focus of global tropospheric chemistry and climate change research. On the one hand, human activities can significantly affect tropospheric O3 levels over oceanic regions, the exchanges of trace gases across the air-sea interface, and the interaction of chemical species originating from continents with those released from oceans. On the other hand, the cyclic behavior of the land-sea breeze can significantly aggravate air pollution in coastal urban environments like the Pearl River Delta (PRD) region. Since 1980s, the rapid economic development in the PRD of southern China has led to a tremendous increase of energy consumption, which has resulted in regional air pollution. Although many air pollution studies have been carried out in the subtropical PRD region, all of these studies were undertaken on the continent, which may not truly reflect the interaction between continental anthropogenic emissions and the marine boundary layer of the SCS. Our knowledge on some key scientific issues in this region-such as sources of high SO2 levels over the SCS, photochemistry of air pollutants (such as O3, dimethyl sulfide (DMS) and isoprene downwind of the SCS), concentration gradients of main air pollutants over the SCS, long-range transport of air pollution to SCS and the PRD region from the East China Sea, and the association between mesoscale recirculation (land-sea breeze) and air pollutants over the SCS and subtropical continental region-is still unclear. Therefore, there is an urgent need to characterize the interaction between continental anthropogenic emissions and marine environment over the SCS and subtropical continental regions in southern China. .The proposed research will be undertaken in two stages. First, based at a coastal site and an oceanic site in the SCS, an intensive field campaign will measure atmospheric air pollutants (e.g. SO2, O3, nitrogen oxides, hydrocarbons, aerosols) and their evolution and gradient over the SCS. This will be followed by thorough data analysis using a combination of statistical analyses of field observations, mesoscale meteorological simulations, an observation-based box model, an emission-based model, and chemical transport models. By the end of this study, our knowledge of the transport pathways of continental emissions to the SCS, photochemical reactivity over the marine environment, the interaction of meteorology and air pollutants, and the impact of oceanic and ship emissions on the marine chemical composition will be significantly improved. This will contribute to our overall knowledge of the atmospheric chemistry in the marine boundary and have wide implications for other subtropical coastal regions. The scientific findings will have direct policy implications for reducing O3 pollution and visibility degradation in subtropical southern China.

陆地空气污染和海洋大气之间的相互作用一直是对流层大气化学和气候变化研究的重点。虽然在珠江三角洲已经开展了许多有关空气污染的研究，但是这些研究主要是针对陆地进行的，而针对南方陆上人为排放和南海海洋环境之间的相互作用及其特征研究则较少涉及。本项目通过在沿海陆地和南海海区内分别设立采样点进行连续、长期的野外采样，获得大气污染物（如臭氧，二氧化硫，氮氧化物，烃类化合物和气溶胶等）浓度及其在南海区域内的演变和梯度分布；基于观测的箱型模式，排放模式和化学输送模式,结合中尺度气象模拟，对实测数据进行深入的统计和分析。通过该研究，有关污染物从陆地到南海的传输路径、海洋环境中的光化学反应、气象条件和大气污染物之间的相互作用，以及海洋和船舶排放对海洋化学成分的影响等方面的认知将会得到大幅度的提升。同时也有助于系统地了解海洋边界层内的大气化学，为中国南部地区制定减少臭氧污染和提高能见度的政策提供依据。

陆地空气污染和海洋大气之间的相互作用一直是对流层大气化学和气候变化研究的重点。虽然珠江三角洲陆地空气污染的研究已较为成熟，但针对陆上人为排放和南海海洋环境之间的相互作用及其特征研究则较少涉及。本项目在沿海陆地（香港东涌）和南海海域（珠海大万山岛）设站开展了4个月的一系列典型污染物的同步连续观测，获得了海-陆大气污染物的浓度水平及其季节和日变化特征，并通过多种数值模拟进行了深入分析。.观测数据显示,万山站的一次污染物浓度（CO，NOx，SO2和VOC等）显著低于靠近人为源排放的东涌站，而二次污染物O3的浓度则要高于东涌（约79%）。一方面是因为海上NO浓度较低，故因滴定反应而损失的O3更少。另一方面箱式模型模拟发现海上的光化学反应较陆地更为强烈，有利于O3生成。研究O3与其前体物的关系表明，在非O3事件日海上O3生成对NOx较为敏感，而在高O3事件日则转变为类似城区一样，即对VOC敏感，说明内陆污染物的传输会改变海上的光化学反应模式，从而影响海上大气化学组成。.两站点污染物浓度分布受到海-陆气团之间的相互作用影响较大。首先，夏季气团主要来自海上，污染物浓度较低；当秋冬季东北季风主导时，两站点气团主要来自于内陆及沿海地区，污染物浓度较高。其次，通过天气研究和预报模型在两站之间捕捉到了中尺度环流，即海陆风现象，对海陆之间的污染物分布产生了影响。此外，采样期间受到七次热带气旋的不同影响，沿海地区气流较为凝滞，内陆污染物缓慢传输到海上，形成了两站点的高O3事件日。.此外本项目对万山站VOC来源进行了解析，确定了其中有超过50%是来自于沿海地区机动车和船舶排放。同时，本项目研究了东涌站近10年污染物的变化趋势，发现O3浓度正逐年上升，本地生成和区域传输对O3的贡献有明显的季节差异，且本地O3的生成对VOC越来越敏感。.总之，通过海-陆站点同步采样及长期数据分析，本项目提升了人们对沿海地区污染物特征的认知，同时也为中国南部地区制定减少O3污染提供了政策依据。