基于差分光学吸收光谱法的大气甲醛和乙二醛研究

基于差分光学吸收光谱法的大气甲醛和乙二醛研究

沈仕亮;王珊珊;周斌

【摘要】介绍了一种基于差分光学吸收光谱技术对上海城市大气中 HCHO 和CHOCHO 进行高时间分辨率的测定方法。针对 HCHO 和 CHOCHO 的不同吸收结构,选择适当的光谱分析波段,扣除干扰气体的吸收,有效降低残差,得到了用于反演目标气体的光学厚度,并进一步获得2013年10月 HCHO 与 CHOCHO 的浓度变化特征。HCHO,CHOCHO 平均浓度分别为(4.0±1.6)和(3.4±1.2)μg·m-3。受人为源的影响, HCHO 工作日平均浓度高于假期平均浓度,而 CHOCHO 的浓度相差不大。两者浓度的日变化趋势相似,早晨06：00—07：00出现最大值后迅速下降,到09：00左右出现最小值后又缓慢上升,并在夜间至日出前保持相对稳定的浓度水平。为探索大气 HCHO 可能的来源和生成过程,选取夜间稳态阶段,早高峰阶段,光化学反应阶段和晚高峰阶段等四个典型时段对 HCHO 的来源进行解析。NO2作为 HCHO 的一次源指示物；同时作为光化学反应的中间产物,HCHO 和CHOCHO 生成机理具有相似性,因此以 CHOCHO 作为解析HCHO 的二次源指示物,利用线性回归模型来源解析结果所得 HCHO 浓度与实际观测值具有较好的相关性,相关系数 r 为0.60~0.81,分析得出上海城区二次来源对环境 HCHO 浓度的贡献约为三分之一。%This paper proposes a method to monitor atmospheric HCHO and CHOCHO with high temporal resolution based on differential optical absorption spectroscopy (DOAS)in Shanghai urban area.Based on the characteristic absorbing structure of HCHO and CHOCHO,different fitting intervals were chosen for spectral analysis in order to avoid the absorption of interfering gases and reduce the residuals of spectral analysis.The resulting optical thickness of the target gas is used to obtain

HCHO and CHOCHO concentrations,which were averaged at (4.0±1.6)and (3.4±1.2)μg·m-3 in October 2013,respectively.The av-eraged concentrations of HCHO in workdays were higher than those in holidays due to the impacts of its anthropogenic emission sources,while no obvious differences of averaged CHOCHO concentrations between workdays and holidays were observed.Di-urnal patterns of HCHO and CHOCHO were alike.In the early morning,both the HCHO and CHOCHO concentrations peaked at 06:00—07:00,and then decreased rapidly to the minimum around 09:00.Afterwards,the concentrations increased continu-ously until sunset and kept in a relatively stable level in the evening.To explore the possible emission source and formation mechanism of atmospheric HCHO,four typical periods,i.e.steady-state stage at night,morning rush hours,photochemical re-action stage and evening rush hours,were classified for source apportionment.NO2 is regarded as the indicator for primary source of ambient HCHO.As the intermediate products of photochemical reactions,HCHO has a similar formation mechanism in common with CHOCHO.Therefore,it is reasonable to use CHOCHO as an indicator for secondary source of ambient HCHO. The linear regression analysis showed a good agreement between modeled and observed HCHO concentrations,the correlation coefficients R 2 ranged from 0.60 to 0.81.Secondary sources of HCHO were estimated to contribute to one third of ambient HCHO concentrations in Shanghai urban area.

【期刊名称】《光谱学与光谱分析》