2013年夏季华北乡村站点固城大气氨变化特征

Characteristics of Atmospheric Ammonia at Gucheng,a Rural Site on North China Plain in Summer of 2013

利用2013年6—8月河北省定兴县固城站的NH_3连续高时间分辨率观测数据,分析了NH_3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NH_3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PM_(2.5)中NH_4^+平均质量浓度为(19.77±33.24)μg·m^(-3)。2013年夏季固城站NH_3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NH_3和NH_4^+质量浓度水平显著提高。夏季NH_3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SO_2和NH_3转化为SO_4^(2-)和NH_4^+的速率较大。华北地区应加大对由农业活动造成的NH_3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 emissions from fertilizer use and animal production in surrounding areas. Ammonia and other trace gases are observed by DLT-100 Ammonia Analyzer and a set of commercial instruments during summer of 2013. Hourly concentrations 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 concentrations of SO2, NO2 and 03 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. NH2 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 concentration. 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 SO24- and NH3 to NH＋. The dependence of inorganic PM2. 5 on NH3 levels suggest that controlling NHa emission from agricultural sources could be an efficient way to reduce secondary inorganic particle pollution on North China Plain.