旅游活动和区域大气污染对九寨沟湿沉降的影响研究

Jiuzhaigou World Natural Heritage site (hereafter Jiuzhaigou) is one of the most popular tourist destinations in China, with over 3.6 million tourist arrivals in 2012. Intensive tourist activities bring about tremendous impacts, economically, environmentally, and ecologically. In recent decade, remarkable aquatic and forest changes have been observed in Jiuzhaigou, such as tufa degradation, increasing biomass of green algae in surface water, and dieback of trees. Based on our studies, acid rain and elevated reactive nitrogen deposition are important causes of the aquatic and forest changes, and reactive nitrogen deposition is mainly from wet deposition. To develop relative strategies to well manage and protect Jiuzhaigou, it is imperative to understand the sources of acid rain and reactive nitrogen deposition. Both local tourist activities and regional air pollutant emissions would be the important sources, but their contributions have not been quantified. In this study, we will quantify and distinguish the impacts of local tourism and regional emissions on the acidity and chemical composition of wet deposition in Jiuzhaigou. To achieve this goal, we will compare the acidity and chemical composition of wet deposition between a tourism-impacted site and a background site. Based on the results of wet deposition monitoring, using the HYSPLIT model, we will determine the sources of air masses of acid rain. In addition, we will develop air pollutant emission inventory for the tourism region of Jiuzhaigou. Furthermore, using the Community Multi-scale Air Quality Model (CMAQ) and the source-orient CMAQ model, we will simulate the fluxes of wet SO42-, NO3-, and NH4+ deposition and quantify the contributions of different regions/sources to wet SO42-, NO3-, and NH4+ deposition. The expected results of this study would be helpful: (1) to develop relative strategies to manage and protect Jiuzhaigou, (2) to understand the impact of regional emissions of air pollutants on remote subalpine regions in southwestern China, and (3) for China’s environmental diplomacy.

世界自然遗产地九寨沟是我国最具吸引力的旅游目的地之一。保护九寨沟生态环境具有重要的社会意义和经济意义。近十多年来，九寨沟出现了明显的生态变化和景观退化。酸雨和活性氮沉降量增加是导致这些问题的重要原因之一，九寨沟活性氮沉降主要来自湿沉降，因此有必要深入研究九寨沟酸雨和活性氮湿沉降的来源，本项目将开展相关的定性和定量研究。通过监测，将比较湿沉降酸度及化学组成在旅游景区和不受旅游活动影响的背景点之间的差异；建立景区的大气污染物排放清单；使用HYSPLIT模型模拟酸雨气团的来源；使用CMAQ模型和source-orient CMAQ模型模拟不同地区和不同类型污染源对九寨沟及其周边地区SO42-、NO3-和NH4+湿沉降通量的贡献。研究结果有助于我国自然保护区和世界自然遗产地的管理和景观可持续开发，也有助于认识我国区域大气污染物排放对西南边远亚高山地区的污染程度，还可能有助于我国环境外交。

世界自然遗产地九寨沟的钙华湿地及彩林具有重要的生态、经济与遗产价值。但是，近十多年来，九寨沟钙华湿地出现退化，彩林出现受害症状，这些都可能与大气污染，特别是酸沉降和过量养分氮沉降有关。酸沉降与活性氮和硫沉降有关，九寨沟氮和硫沉降主要来自湿沉降。因此，项目组开展了大气湿沉降监测和模式模拟，以揭示:（1）旅游活动对九寨沟景区内湿沉降的影响程度，即认识旅游活动是否加剧了九寨沟景区内酸雨的发生， 是否显著增加了SO42-、 NO3-和 NH4+的湿沉降通量；（2）区域大气污染物排放对九寨沟地区湿沉降的影响程度，即认识哪些地区和哪些类型污染源对九寨沟地区湿沉降的酸度及化学组成有重要影响。为达到以上研究目的，项目组在景区和背景点同时开展了湿沉降监测；采用Positive Matrix Factorization (PMF)模型、Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT)模型、Source-oriented Community Multiscale Air Quality Modeling (CMAQ)和Weather Research Forecasting (WRF) 模式研究了氮和硫干湿沉降通量的来源；估算了旅游观光车对氮湿沉降的贡献。研究结果显示：（1）旅游活动未加剧景区内酸雨的发生，旅游活动对九寨沟湿沉降中氮和硫的浓度有一定贡献（p<0.05），但氮和硫的湿沉降通量主要还是受区域大气污染物排放和降水量的影响；（2）九寨沟流域的氮和硫湿沉降主要来自人为源大气污染物的跨区域传输，SO42- 和NO3-的湿沉降主要来自工业、火电厂和生活源；NH4+湿沉降主要来自农业；九寨沟当地及周边3个县对九寨沟流域SO42-和NO3-湿沉降通量的贡献低于10%，约70%以上的NH4+湿沉降通量来自其它地区；（3）与其他西南监测点类似，2010-2016年九寨沟湿沉降中SO42-和NO3-浓度与通量呈降低趋势，这与我国SO2和NOx减排相关；（4）九寨沟NH4+湿沉降加剧，可能与当地旅游观光车NH3排放有关；（5）结合大气监测与模拟、地表水监测与模拟，项发现大气污染物跨区域传输增加了九寨沟氮和硫湿沉降，进而成为钙华景观退化的原因之一。研究结果有助于未来制订区域大气污染防治和生态保护措施。