深圳大气中含黑碳气溶胶化学组分特征及其生成机制研究

Chemical composition characteristics and formation of black carbon-containing aerosols in the atmosphere in Shenzhen

为了探究黑碳(BC)老化过程其表面不同化学组分变化特征及其生成机制,本研究于2021年9月19日-10月8日在深圳市开展了为期20 d的观测,利用黑碳气溶胶质谱仪(SP-AMS)对含黑碳气溶胶化学组分的质量浓度进行了现场测量.结果表明:在观测期间,BC核质量浓度约为(0.8±0.5)μg·m^(-3),仅占整个黑碳颗粒质量的24%.包裹物中有机物(OA_(BC))的占比最高,其次为硫酸盐(SO_(4BC)^(2-))、硝酸盐(NO^(-)_(3BC))、铵盐(NH_(4BC)+)和氯盐(Cl^(-)_(BC)).使用PMF对黑碳表面有机物来源进行解析,得到4种不同的因子,分别为含碳簇有机因子(BC-rich_(BC))、还原性有机因子(HOA_(BC))、氧化程度较低的二次因子(LO-OOA_(BC))和氧化程度较高的二次因子(MO-OOA_(BC)).二次组分主导了黑碳的老化,尤其是二次有机物.分析不同二次组分的生成机制发现,光化学氧化过程促进了LO-OOA_(BC)的生成,但对MO-OOA_(BC)生成的作用非常有限.对于二次硝酸盐来说,光化学氧化主导了清洁天硝酸盐的生成,而污染天主要与液相反应有关.

In order to explore the characteristics and formation of different chemical components that encapsulate on black carbon(BC)aerosol,this study carried out a 20-day observation in Shenzhen from September 19 to October 8,2021,using a soot particle aerosol mass spectrometer(SP-AMS)to measure the mass concentrations of chemical components on BC.The results show that the mass concentration of the BC cores was(0.8±0.5)μg·m^(-3),which accounted for 24%of the mass of the whole BC particles.The most abundant coating component was organics(OA_(BC)),followed by sulfate(SO^(2-)_(4BC)),nitrate(NO^(-)_(3BC)),ammonium(NH+_(4BC))and chloride(Cl^(-)_(BC)).The source apportionment of organics on BC was analyzed by the Positive Matrix Factorization(PMF)model,and four different factors were determined,which were BC-rich OA_(BC)(BC-rich_(BC)),hydrocarbon-like OA_(BC)(HOA_(BC)),less-oxidized oxygenated OA_(BC)(LO-OOA_(BC))and more-oxidized oxygenated OA_(BC)(MO-OOA_(BC)).The aging of BC is dominated by secondary components,especially secondary organics.The formation of different secondary components on BC was further analyzed,and it was found that photochemical oxidation promoted the formation of LO-OOA_(BC),but it had very limited effect on MO-OOA_(BC).For NO^(-)_(3BC),photochemical oxidation dominated the formation in clean days,while the formation in polluted days was mainly related to liquid-phase heterogeneous reactions.