大气HONO来源探究——畜禽粪便的排放

Nitrous acid (HONO) has been regarded as one important source of OH radicals in the troposphere, and plays key roles in removal of atmospheric pollutants and formation of secondary pollutants. Although various possible sources of atmospheric HONO have been recognized, it is still unable to explain the relatively high HONO concentrations during daytime based on the model simulation of these known sources, revealing that it still remains unknown daytime sources for atmospheric HONO. Our preliminary results have found that HONO emission fluxes from pig manure in process of stacking can reach up to about 16mg kg-1 h-1 under the low temperature condition during the wintertime, so we speculate that livestock manure may be an important unknown source of atmospheric HONO. Therefore, HONO emission fluxes from the prevailing livestock manure (pig manure, chicken manure and cattle manure) in the North China Plain (NCP) in the process of stacking during the different seasons will be comprehensively measured by using twin dynamic chambers, which would be used to obtain seasonal variations and impact factors of HONO emission from livestock manure. The exchange fluxes of NO, N2O and NH3 are measured simultaneously for exploring the key formation and emission mechanism of atmospheric HONO from livestock manure. Finally, based on the obtained HONO emission fluxes and the total amount of livestock manure in the NCP, the total HONO emission from livestock manure will be rationally evaluated in the region.

大气亚硝酸（HONO）是对流层OH自由基的主要来源之一，在大气污染物去除以及二次污染物形成方面扮演着重要角色。尽管人们已经认识到大气HONO的多种可能来源，但这些来源仍无法解释白天观测到的高HONO浓度，表明大气中仍存在未认知的HONO重要来源。申请者初步研究发现猪粪在堆放过程中HONO的排放通量在冬季低温条件下可高达约16mg kg-1 h-1，因此推测畜禽粪便可能为大气HONO一种尚未认知的重要来源。为此，本项目拟选择华北地区主流的养殖业畜禽粪便（猪粪、鸡粪和牛粪）为研究对象，采用双动态箱法测定不同粪便在四个季节堆放过程中HONO的排放通量，获得畜禽粪便HONO排放的季节变化特征及影响因素；同步测定其它含氮气体（NO、N2O及NH3）的交换通量，探究畜禽粪便HONO形成及排放的关键机制；基于所测HONO的排放通量以及华北地区畜禽粪便总量，估算该地区畜禽粪便HONO的排放总量。

大气亚硝酸（HONO），作为对流层OH自由基的主要来源，在大气污染物去除以及二次污染物形成方面扮演着重要角色。尽管人们已经认识到大气HONO的多种可能来源，但这些来源仍无法解释白天观测到的高HONO浓度，表明大气中仍存在未认知的HONO重要来源。基于此，本项目利用双动态箱法对华北地区主流的养殖业畜禽粪便（猪粪和鸡粪）在堆放过程中HONO的排放通量进行了综合测定。结果表明，畜禽粪便被发现是大气HONO一种尚未认知的重要来源，其排放强度随着温度的升高而显著抬升。同时，鸡粪在堆放过程中HONO的排放通量要明显高于猪粪，这主要是因为鸡粪中含有丰富的有机氮成分；然而，由于鸡粪中较高含量的水分抑制了亚硝酸根向大气HONO的转化，故使得其HONO的排放通量峰值出现较晚。此外，在猪粪和土壤混合处理下较高的HONO排放通量也验证了土壤的确也是大气HONO一种重要来源。最后，基于我国的畜禽粪便年总量（约38亿吨），可以估算出其在堆放过程中排放的年HONO总量约为0.14 Tg，说明畜禽粪便在堆放过程中对大气HONO的贡献不容忽视。