城市土壤气态亚硝酸（HONO）排放特征及影响机制

Gaseous nitrous acid (HONO) plays an important role in atmospheric chemistry study and influences atmospheric oxidation capacity, haze and air quality. HONO emissions from soil can be acted as a source of atmospheric HONO and is also international research hot spot. However, only few papers published in this field, and the key factors and influencing mechanisms of soil HONO emission are still under discussion. Current research mainly focus on natural ecosystems, such as farmland, forest and grassland, but urban ecosystem has not been reported. This project will study urban soils in Shanghai, analysis the spatial variation of HONO emissions in urban soil using field sampling method and measuring HONO flux by dynamic chamber system; quantifying the effects of light, temperature, soil moisture and nitrogen deposition by laboratory incubation experiments; determining the contributions of physiochemical, microbiological nitrification and denitrification processes on HONO emissions from soil by absorption-desorption experiments, isotopic 15N labeling and microbial functional genes of amoA, haoA, napA, narG and nirS. We hope the results can provide scientific guidance for urban soil safety and nitrogen management.

气态亚硝酸（HONO）是大气化学研究中的重要物质，直接影响大气氧化能力、灰霾的形成和空气质量等。土壤HONO排放是大气HONO的直接来源，也是国际上研究的热点。然而，目前相关研究偏少，土壤HONO排放的影响因素和机理尚有争议。且研究多集中在农田、森林、草地等自然生态系统，城市生态系统尚未见报道。本项目以上海城市土壤为研究对象，通过室外土壤样品采集和室内动态箱系统测定，解析城市土壤HONO排放的空间变异特征；通过耦合环境因子和室内培养实验，定量光照、温度、土壤湿度和氮沉降等因素在城市土壤HONO排放过程中的作用；通过吸附解吸附实验、同位素15N标记和定量amoA、haoA、napA、narG和nirS等功能性基因，阐明物理、化学和微生物硝化反硝化过程对土壤HONO排放的贡献，为城市土壤安全及氮素管理提供科学依据。

气态亚硝酸（HONO）是城市空气污染的典型代表物，影响大气氧化能力和空气质量等。土壤HONO排放是大气HONO的重要来源，然而城市土壤HONO的排放量、驱动因素和影响机制尚不清楚。本研究1）采用Teflon材料、扩散管和动态箱等技术手段，构建了测定土壤HONO和NOx排放需要的动态箱系统，为开展土壤HONO排放通量测定提供了技术支持。2）以上海市土壤为研究对象，通过室外土壤样品采集和室内动态箱系统测定等，解析了城市土壤HONO排放的空间变异特征和影响因素。结果表明，上海城市土壤HONO的排放通量为3.7~288.2 ng N m−2 s−1；农田、森林、城市绿地和草地的土壤HONO最大排放通量分别为48.6 ± 17.4、50.3 ± 30.1、44.2 ± 9.5和27.7 ± 15.6 ng N m⁻2 s⁻1（平均值±标准差）。基于相关性分析，发现上海市土壤HONO排放峰值与土壤NO2−-N、NO3−-N、NO3−-N/NH4+-N及总碳含量等显著正相关，与TOC/NO3−-N显著负相关。基于ArcGIS空间插值发现，上海市土壤HONO的排放强度呈现中心城区和崇明地区高，而西南地区低，由中心城区及闵行区向城市其他地区浓度逐渐降低的规律。同时，采用“干湿交替法”估算的上海市土壤HONO的年排放量为329 (284~375)吨，其中约57%源于氮肥的施用。3）发现了高含水量土壤HONO气体排放过程（“湿峰”），其最大排放通量为5~190 ng N m−2 s−1，是“干峰”最大排放量的10%~90%。通过室内培养、灭菌实验等，表明土壤“湿峰”HONO排放与微生物硝酸盐还原有关。通过微生物纯菌培养、敲除功能基因实验等，解析了其驱动机制是亚硝态氮累积造成的氮素代谢过程。上述研究结果为定量城市大气HONO来源及其对空气质量的影响等提供科学依据和决策参考。