洞庭湖PM2.5重污染期水溶性离子污染特征和来源

于2017年9—12月在我国中部大气背景点洞庭湖采集PM2.5,分析水溶性离子成分,以研究其组成、分布特征及来源等。结果表明,采样期间洞庭湖PM2.5浓度平均值超过日均一级标准限值,主要成分是水溶性离子,其中NO3-、SO42-、NH4+在总离子浓度中分别占42.7%、27.4%、23.7%。NO3-、SO42-的摩尔浓度与NH4+拟合度较好,NH4+的量比酸性离子略占优势,说明NO3-和SO42-基本被NH4+中和。线性拟合表明NH4+与NO3-和SO42-主要以NH4NO3和NH4HSO4的形式存在。硫氧化率和氮氧化率说明SO42-和NO3-主要来自SO2和NOx的二次转化。二次转化受气象条件的影响;冬季比秋季更加有利二次转化,尤其是NO3-和NH4+的生成。后向轨迹气团分析发现,采样期间大气污染主要受中部地区和局地区域气团的影响,从山东半岛附近传输的气团对洞庭湖区域可能会产生海源的影响。本研究可为中部地区尤其是农业区域的大气污染成因和治理措施提供理论基础。

Characteristics and sources of water soluble ions in PM2.5 during severe pollution in Dognting Lake

In this study, PM2.5 was sampled in the Dongting Lake, a background site for Central China, from September to December in 2017. Water-soluble ions were analyzed to investigate their composition, distribution, and sources. The results showed that, the averaged PM2.5 during the sample period in Dongting Lake exceeded the limit of daily average level 1. Water-soluble ions were the main component in PM2.5, with NO3-, SO42-, and NH4 accounting for 42.7%, 27.4%, and 23.7% of the total ions, respectively. The sum of NO3- and SO42- fitted with NH4 , and the mole of NH4 was more than acidic ions, suggesting that NO3- and SO42- were neutralized by NH4 completely. NH4 , NO3-, and SO42- mainly existed in the form of NH4NO3 and NH4HSO4. The sulfur oxidation ratio and nitrogen oxidation indicated that NO3- and SO42- were mainly converted from SO2 and NOx, respectively. Such conversion was affected by meteorological factors. Winter was more conducive to the formation of secondary ions (especially NO3- and NH4 ) than autumn, due to the meteorological factors. The backward trajectory suggested that the air pollution was mainly affected by the air mass from the Central China and the local area, and to a less extent, the air mass with marine source from the vicinity of the Shandong Peninsula. This study will be useful to understand the causes as well as put forward control measures for atmospheric pollution in Central China, especially the agricultural region.