大气PM2.5中水溶性离子在线观测技术的应用研究

为了解北京大气PM2.5污染状况,评估大气细颗粒物快速捕集-化学成分在线分析系统(RCFP-IC)在追踪污染生成-消散过程中的适用性,于2011年3月对北京PM2.5中NO3-、SO24-、NH4+和Cl-这4种污染型水溶性离子浓度变化进行了连续高时间分辨率观测,并结合同期气象要素的变化,探讨了污染过程形成的原因.结果表明,一个月的观测期内捕捉到了5次较为明显的污染过程,4种水溶性离子的浓度变化趋于一致,并呈现出典型的"慢积累、快清除"的锯齿型污染物浓度时间序列变化特征.NO3-和NH4+在典型污染事件中峰值浓度是清洁时期浓度的10倍以上,而SO24-和Cl-污染峰值浓度仅为清洁时期的2～4倍.停暖后4种离子浓度较采暖期下降了15%～60%.RCFP-IC与高分辨率飞行时间气溶胶质谱(HR-TOF-AMS)同期观测结果变化趋势具有高度的一致性,但RCFP-IC定量水溶性离子浓度更为准确.

On-Line Measurement of Water-Soluble Composition of Particulate Matter in Beijing

Concentrations of NO₃^-, SO₄², NH₄⁺ and Cl^- were measured in Beijing during March, 2011, at a time resolution of 15 minutes using the system for rapid collection of fine particles and ion chromatography (RCFP-IC). Meteorological parameters were recorded concurrently to investigate the formation processes of typical pollutants. Five pollution episodes were observed in one month during the study period. All measured ions had similar temporal distributions showing saw-tooth cycle variations with slow accumulation and relatively rapid clearing. The peak concentrations of NO₃^- and NH₄⁺ in typical pollution episodes were observed to be about an order of magnitude higher than the background levels while the maximum concentrations of SO₄^2- and Cl^- were only 2-4 times as high as the background values. Two episodes were observed during and after the home heating period. Compared to those during the home heating period, concentrations of the four ions after the home heating period were 15%-60% lower, implying that the home heating affected the concentration of ions. Measurements of ionic concentrations from RCFP-IC and those from the high time resolution of flight aerosol mass spectrometry (HR-TOF-AMS) during the study period were compared. The comparison results suggested the RCFP-IC was more reliable for the measurements of water soluble species.