双通道大气汞监测方法研究厦门气态活性汞分布特征

Characteristics of reactive gaseous mercury in Xiamen based on dual channel atmospheric mercury monitoring method

大气汞的形态转化及其影响因素是汞研究领域的热点之一,目前有关低对流层大气光化学过程对大气活性汞的影响研究仍十分有限.本研究将双级阳离子交换膜(CEM)与Tekran 2537汞监测仪相结合,搭建了双通道大气汞监测系统,并对沿海城市厦门2023年5—9月的大气气态汞浓度开展了观测.结果表明,观测期间厦门地区气态元素汞(GEM)和气态活性汞(RGM)平均浓度分别为(2.10±0.74)ng·m^(-3)和(218±131)pg·m^(-3).RGM月均浓度表现为7月>8月>6月>9月>5月,其主要原因是夏季较高的温度和太阳辐射促进了GEM向RGM的转化,同时高温不利于RGM由气相向颗粒相的分配.厦门7—8月GEM浓度相对较高,这可能与台风的频繁影响有关.在日变化特征上,厦门GEM和RGM均在清晨达到最高值,在傍晚下降到最低值,表现出边界层厚度变化驱动的特征.研究期间经常监测到极高的RGM浓度,其中一些持续了数天.F0AM模型模拟结果显示,在RGM高浓度事件过程中,RGM受到来自本地或外来光化学氧化的影响相比大气传输和人为源排放更为重要.

The transformation of atmospheric mercury species and its influencing factors are a prominent subject in mercury research.However,limited studies have examined the impacct of photochemical processes on reactive gaseous mercury(RGM),particularly in the lower troposphere.This study developed a dual-channel atmospheric mercury monitoring system by combining a two-stage cation exchange membrane(CEM) sampler with a Tekran 2537 analyzer.Using this method,we investigated the atmospheric gaseous mercury concentration in Xiamen,a coastal city,from May to September 2023.Throughout the observation period,the average concentrations of gaseous elemental mercury(GEM) and reactive gaseous mercury(RGM) in Xiamen were(2.10±0.74) ng·m^(-3) and(218±131) pg·m^(-3),respectively.RGM concentrations in Xiamen displayed a seasonal variation with the highest levels in July,followed by August,June,September,and May.This pattern can be attributed to the elevated temperature and solar radiation in summer,which promote the conversion of GEM to RGM,while the high temperature hindered the distribution of RGM from the gas phase to the particulate phase.Notably,higher concentrations of GEM were observed from July to August,potentially due to the influence of typhoons.In terms of diurnal patterns,both GEM and RGM concentrations in Xiamen reached their peaks in the early morning and decreased to a minimum in the evening,likely influenced by changes in boundary layer height.High concentrations of RGM were frequently detected during the study,with some lasting for several days.A chemical box model F0AM simulation showed that during high RGM concentration events,the influence of local or transported photochemical oxidations on RGM was more significant than that of atmospheric transport and anthropogenic emissions.