质子转移反应质谱在线测量大气挥发性有机物及来源研究——以深圳夏季为例

含氧挥发性有机物(OVOCs)在光化学烟雾形成过程中起到重要作用,其分析技术在近些年才有突破性发展.为了解深圳大气中含氧挥发性有机物和NMHCs的组成和浓度的演变规律与来源特征,2011年夏季在深圳利用先进的质子转移反应质谱技术对①生物质燃烧示踪物、②生物源排放挥发性有机物、③芳香烃类以及④含氧挥发性有机物等4类VOCs进行了为期4个月的观测.结果显示,深圳OVOCs和NMHCs浓度水平普遍高于国外,且本地甲苯、甲醇和异戊二烯有较强排放,它们的浓度分别为(3.86±5.85)、(16.06±13.88)和(0.75±1.12)ppbv(parts per billion by volume:10-9),主要受本地的溶剂使用挥发以及夏季高温高日照的影响;不同类VOCs有不同的月际变化,但大部分VOCs浓度5月份最高,6月份最低,分析表明这是气象条件和排放源源强变化的综合作用结果;通过研究OVOCs的日变化曲线发现OVOCs不仅来源于一次源的排放,还源于NMHCs的二次转化,其中甲醇和丙酮可能还源于生物质燃烧,乙醛和MEK还受生物源排放的影响;最后结合反向轨迹发现深圳夏季源于洋面的气团对苯乙烯和C9芳香烃的传输作用较大,源于内陆的气团对MEK、乙醛和甲苯的传输作用较大,而甲醇、丙酮、苯等主要受本地源排放的控制.

On-line measurements and source analysis of VOCs in the atmosphere using Proton Transfer Reaction-Mass Spectrometry:Case study in summer of Shenzhen

Oxygenated VOCs (OVOCs) play an important role in atmospheric photochemical processes.Their measurement,however,was significantly improved just in recent years.In order to obtain the information of the composition and concentrations of ambient OVOCs and Non-methane hydrocarbons (NHMCs) and to identify their sources,the continuous measurement of VOCs (including a biomass burning tracer,biogenic VOCs,aromatics,and OVOCs) was performed in Shenzhen in Summer 2011,using Proton Transfer Reaction-Mass Spectrometry (PTR-MS).Results showed that the VOC pollution in Shenzhen was more serious than that in foreign countries,especially for methanol,toluene,and isoprene,with the mean concentrations of (3.86±5.85),(16.06±13.88),and (0.75±1.12) ppbv,respectively.Such high levels of pollutants may come from the local solvent evaporation.Although different classes of VOCs had different monthly variation patterns,most of the VOCs showed the highest concentrations in May and the lowest in June as a combined result of the weather conditions and the emission variations.The OVOCs were found not only from the primary sources,but also from the photochemical reactions of NMHCs.By analyzing the diurnal profiles,methanol and acetone were attributed to biomass burning emissions and acetaldehyde and methyl ethyl ketone (MEK) was found from biogenic emissions.With the analysis of air mass back-trajectories,the impact of pollution transport on OVOCs and aromatics was discussed.The air mass from the ocean had an effect on styrene and C9 aromatics,while MEK,acetaldehyde,and toluene were significantly influenced by the inland air mass.Methanol,acetone,and benzene were found to be mainly controlled by local sources.