氯化铁细粒子对苯二次有机气溶胶化学组分和光学性质的影响

Influence of ferric chloride fine particles on the chemical components and optical properties of benzene secondary organic aerosol

铁离子是大气气溶胶中常见的重金属离子,它能够影响二次有机气溶胶(SOA)的化学组分和光学性质.本文利用烟雾腔系统研究氯化铁细粒子对苯SOA化学组分和光学性质的影响.与无细粒子条件相比,氯化铁细粒子存在时,苯SOA粒子的激光解吸附电离质谱出现m/z=164的离子峰,提取液的紫外可见吸收光谱在396 nm和700 nm附近存在吸收峰,电喷雾电离质谱含有m/z=234和272的质谱峰.综合这些谱图信息表明,苯光氧化产生的邻苯二酚等气相产物在细粒子表面与铁离子发生络合、氧化还原反应,产生苯醌类产物和二氯邻苯二酚合铁(Ⅲ)离子和二邻苯二酚合铁(Ⅲ)离子等金属有机物络合离子.这些产物具有较强的吸光能力,导致苯SOA粒子在200~1000 nm范围内的平均质量吸收系数(<MAC>)值明显增大,并随着氯化铁细粒子浓度的增大而逐渐增大.这为重金属细粒子存在下金属有机络合物的形成机理和光学性质研究提供了实验依据.

Iron ion is the common heavy metal ion in atmospheric aerosol,which can affect the chemical components and optical properties of secondary organic aerosol(SOA).The influence of ferric chloride fine particles on the constituents and optics of benzene SOA are investigated using smog chamber system in this study.Compare with the condition without fine particles,the laser desorption ionization mass spectra of benzene SOA particles in the presence of ferric chloride fine particles show the ion peak of m/z=164,and the UV-Vis absorption spectra of SOA particles extraction solution have the absorption peaks near 396 nm and 700 nm,and the electrospray ionization mass spectra contain mass peaks at m/z=234 and 272.Based on these spectrogram information,it is demonstrated that the gaseous catechol formed from the photooxidation of benzene may react with iron ion on the surface of fine particles by complexing and oxidation-reduction,resulting in benzoquinone products and metallo-organic complex ions such as dichloride catechol−Fe(Ⅲ)complex ion,binuclear catechol−Fe(Ⅲ)complex ion.These products have strong light absorption ability,resulting in the increase of the mass absorption coefficient averaged over 200~1000 nm(<MAC>)of benzene SOA,and gradually increase with the increasing concentration of ferric chloride fine particles.These provide the experimental basis for studying the formation mechanism and optical properties of metallo-organic complex in the presence of heavy metal fine particles.