南昌市大气NH_(x)干沉降及其氮同位素昼夜变化特征  

Nyctohemeral variations of atmospheric NH_(x) deposition and nitrogen isotopic compositions in Nanchang

作　　者：尤子昇 孔露静 张永运 王小嫚 张浩然 刘敏 罗笠 YOU Zisheng;KONG Lujing;ZHANG Yongyun;WANG Xiaoman;ZHANG Haoran;LIU Min;LUO Li(School of Water Resources and Environmental Engineering,East China University of Technology,Nanchang 330013,Jiangxi,China;Jiangxi Environmental Monitoring Center Station,Nanchang 330013,Jiangxi,China;State Key Laboratory of Marine Resources Utilization in South China Sea,Haikou 570228,Hainan,China)

机构地区：[1]东华理工大学水资源与环境工程学院,江西南昌330013 [2]江西省环境监测中心站,江西南昌330013 [3]海南大学南海海洋资源利用国家重点实验室,海南海口570228

出　　处：《地球化学》2022年第2期233-242,共10页Geochimica

基　　金：国家自然科学基金项目(41763001);江西省教育厅科技项目(GJJ160580);东华理工大学博士科研启动基金项目(DHBK2016105)联合资助。

摘　　要：NH_(x)(NH_(3)和NH_(4)^(+))是大气中主要的碱性物质,NH_(x)干沉降是大气中NH_(x)移除的重要途径之一。本研究于2019年8月11日至31日在江西省南昌市东华理工大学分昼夜采集了大气NH_(x)干沉降样本(包括颗粒铵(NH_(4)^(+)(p))和气态氨(NH_(3(g)))),测定了干沉降样本的NH_(4)^(+)离子浓度、δ15N-NH_(4)^(+)和pH,基于干沉降样品中NH_(x)浓度估算了大气中NH_(x)干沉降通量。结果显示,白天NH_(x)干沉降通量(0.2~25.9μg/(m^(2)·h),均值14.2±10.0μg/(m^(2)·h))低于夜晚(0.9~50.2μg/(m^(2)·h),均值23.1±10.4μg/(m^(2)·h)),与昼夜温度变化趋势相反,表明NH_(x)干沉降通量昼夜差异与NH_(3)在不同温度下的溶解度有关。此外,NH_(x)干沉降通量与pH值的昼夜变化一致,说明干沉降样本中NH_(4)^(+)浓度对溶液的pH有影响。干沉降样本中,δ^(15)N-NH_(4)^(+)值在白天(−14.62‰~17.54‰,均值3.56‰±8.49‰)高于夜晚(−20.07‰~−0.25‰,均值−8.97‰±5.80‰),这种差异可能与气态NH_(3)和离子态NH_(4)^(+)之间的氮同位素分馏有关,也可能与昼夜氨气排放源不同有关。基于不同排放源δ^(15)N-NH_(3)特征值和氮同位素分馏效应,南昌市夏季白天大气中NH_(x)主要来源于化石燃料燃烧,晚上主要受控于农业肥料挥发与动物排泄。NH_(x)(NH_(3) and NH_(4)^(+))is the main alkaline substance in the atmosphere,and its dry deposition is one of the important ways to remove NH_(x) from the atmosphere.To investigate NH_(x) dry deposition fluxes and explore the possible sources of atmospheric NH_(x),dry deposition samples were collected between August 11-31,2019,at East China University of Technology,Nanchang.Concentrations of ammonium(NH_(4)^(+)),values ofδ^(15)N-NH_(4)^(+),and pH values of dry deposition samples were analyzed.NH_(x) dry deposition fluxes during daytime(0.2 to 25.9μg/(m^(2)·h)),with an average of 14.2±10.0μg/(m^(2)·h),were lower than those during the night(0.9 to 50.2μg/(m^(2)·h)),with an average of 23.1±10.4μg/(m^(2)·h).Deposition fluxes showed similar pH value patterns,indicating that NH_(4)^(+)levels can regulate the pH values of dry deposition samples.Values ofδ15N-NH_(4)^(+)during daytime(−14.62‰to 17.54‰,with an average of 3.56‰±8.49‰)were higher than those during the night(−20.07‰to−0.25‰,with an average of−8.97‰±5.80‰).The diurnal variations ofδ^(15)N-NH_(4)^(+)values may be related to the nitrogen isotopic fractionation between the gas phase NH_(3) and ionic NH_(4)^(+),and between NH_(3) emission sources during the day and night.Based on theδ^(15)N-NH_(3) values from different NH_(3) emission sources and nitrogen isotopic fractionation between the gas phase NH_(3) and ionic NH_(4)^(+),NH_(x) in dry deposition samples may be mainly sourced from fossil fuel combustion during the daytime and predominately from agricultural fertilizer volatilization and animal excretion during the night.An opposite trend with diurnal temperature suggests that high NH_(x) deposition fluxes during the night may be related to the high solubility of ammonia at low temperatures.

关 键 词：NH_(x)干沉降通量 氮同位素 南昌市 

分 类 号：X142[环境科学与工程—环境科学]