利用2013年6—8月河北省定兴县固城站的 NH3连续高时间分辨率观测数据，分析了 NH3体积分数水平、变化特征和影响因素。结果表明：2013年夏季固城站 NH3小时平均体积分数变化范围为0．9×10－9～862．9×10－9，平均体积分数为43．9×10－9±65．9×10－9。观测期间 PM2．5中 NH ＋4平均质量浓度为（19．77±33．24）μg· m－3。2013年夏季固城站 NH3和 NH ＋4质量浓度有较好的相关性，且浓度明显高于华北地区城市站点，说明由于农业施肥等活动导致固城站大气 NH3和 NH ＋4质量浓度水平显著提高。夏季 NH3体积分数有明显日变化且呈单峰特征。2013年夏季固城站硫氧化率和氨转化率较高，说明 SO2和 NH3转化为 SO2－4和 NH ＋4的速率较大。华北地区应加大对由农业活动造成的 NH3排放的控制力度，以降低区域二次气溶胶污染。%In-situ measurement of ambient ammonia (NH3 )and water-soluble ions in PM2.5 is conducted at Gucheng,a rural site,from June to August in 2013.Gucheng is an integrated experiment site on ecological and meteorological observation belonging to Chinese Academy of Meteorological Sciences.This station is influenced by high NH3 e-missions from fertilizer use and animal production in surrounding areas.Ammonia and other trace gases are ob-served by DLT-100 Ammonia Analyzer and a set of commercial instruments during summer of 2013.Hourly con-centrations of the water-soluble inorganic ions in PM2.5 are also measured with the Ambient Ion Monitor (URG 9000 Series,USA).Concentrations of NH3 at Gucheng range from 0.9×10-9 to 862.9×10-9 ,with the average of 43.9×10-9 ±65.9×10-9 .In summer,high temperatures favor ammonia volatilization from fertilizer applied to the cropland.NH3 concentrations increase sharply after fertilizer application in July for summer maize.Mean con-centrations of SO2 ,NOX and O3 are 4.3×10-9 ±5.5×10-9 ,13.2×10-9 ±6.8×10-9 and 42.4×10-9 ±31.5× 10-9 during the sampling period.The ammonia shows a significant diurnal variation during the sampling period. NH3 concentration maximum occurs at 0900 BT and the minimum at 1900 BT.The sulfate,ammonium and nitrate are dominant ions in PM2.5 with their average concentration being (20.46±13.62),(19.77±33.24)μg·m-3 and (11.34±9.14)μg·m-3 ,respectively.Ammonium shows significant positive correlations with NH3 concentra-tion.To understand the relationship between particulate ions and their respective precursors,sulfur oxidation ratio (SOR),nitrogen oxidation ratio (NOR)and ammonia conversion ratio (NHR)are investigated.SOR and NOR represent the oxidation ratio of sulfate and nitrate,and NHR represents the conversion ratio of ammonium.Higher SOR and NHR have important effects on the conversion of SO2 to SO2-4 and NH3 to NH+4 .The dependence of in-organic PM2.5 on NH3 levels suggest that controlling NH3 emission from agricultural sources could be an efficient way to reduce secondary inorganic particle pollution on North China Plain.
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