北京郊区秋季灰霾天气下细颗粒物化学成分及其混合特征研究

Chemical composition and mixing state of single particles during the haze period at a Beijing suburb site

于2014年11月在北京郊区利用单颗粒气溶胶质谱仪(SPAMS)高时间分辨率观测了大气中细颗粒物的化学成分。通过Art-2a对单颗粒化学成分进行分类,主要包括8类颗粒物:有机碳(OC)、元素碳(EC)、元素碳有机碳(ECOC)、钾二次颗粒(K-Sec)、钠钾二次颗粒(NaK-Sec)、矿尘颗粒(Dust)、左旋葡聚糖颗粒(Lev)、含铅颗粒(Pb)。清洁期(2014年11月5日15:00至2014年11月15日0:00, PM_(2.5)平均质量浓度27.4μg/m^3)和灰霾期(2014年11月19日0:00至2014年11月30日10:00, PM_(2.5)平均质量浓度116.4μg/m^3)对比研究发现,清洁期OC颗粒占比最高,占总颗粒数的33.0%,其次是EC和ECOC颗粒,分别占总颗粒数的29.7%和16.4%;灰霾期OC颗粒物显著增加,比例高达46.1%,其次是ECOC,增至22.4%,而EC颗粒降至18%。此外,灰霾期二次组分HSO_4~–、NO_3~–的信号强度与二次组分数浓度均大于清洁期,表明灰霾期无机盐(HSO_4~–、NO_3~–)在颗粒物中的贡献增大。通过分析相对湿度与SO_2、NO_x和含硫酸盐、硝酸盐颗粒之间的关系,发现含硫酸盐和硝酸盐颗粒数浓度随环境湿度增加而增加,表明液相反应对硫酸盐生成有促进作用,同时相对湿度的增加可能对硝酸盐的形成有一定的贡献。混合状态分析表明,含碳气溶胶与HSO_4~–和NO_3~–的混合程度较强,与铵盐混合程度较弱。研究结果反映二次气溶胶形成特别是有机物颗粒的增加对于北京市灰霾形成具有重要的贡献。

The chemical composition of fine particulates in the atmosphere was observed at a high temporal resolution using single particle aerosol mass spectrometry (SPAMS) in the Beijing suburbs in November 2014. The single particles were clustered to eight types from the Art-2a method: particles consisting of organic carbon (OC),elemental carbon (EC), elemental carbon organic carbon (ECOC), K-Sec, NaK-Sec, dust, levoglucosan (Lev), and Pb. The percentages of each type of particle were compared between the clean period (from 15: 00 on the 5th to 00: 00 on the 15th of November 2014 the average concentration of PM2.5 was 27.4 μg/m^3) and the haze period (from 00: 00 on the 19th to 10: 00 on the 30th of November 2014 the average concentration of PM2.5 was 116.4 μg/m^3). During the clean period, the OC-type particles accounted for 33.0% of the total particles, followed by those of EC and ECOC which accounted for 29.7% and 22.4%, respectively. The OC particles increased to 46.1% during the haze period, followed by ECOC (22.4%) and EC (18%). In addition, the signal intensity and secondary component concentration of HSO4^– and NO3^– during the haze period were higher than those during the clean period, indicating that the contribution of inorganic salts (HSO4^–, NO3^–) to particulate matter during the haze period increased. The relationship among relative humidity (RH), SO2, NOx, and sulfate- and nitrate-containing particles showed that the sulfate- and nitrate-containing particles increased with RH, indicating that aqueous phase chemistry favors sulfate production. At the same time, the increase in RH may have contributed to nitrate formation. Carbonaceous-type particles were found to contain more sulfate and nitrate than ammonium. The current work shows that the increase in secondary organic aerosols importantly contributed to haze formation in Beijing.