Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China; Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Finland; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Finland.
Sci Total Environ. 2021 Jan 20;753:142207. doi: 10.1016/j.scitotenv.2020.142207. Epub 2020 Sep 14.
Secondary aerosol formation in the aging process of primary emission is the main reason for haze pollution in eastern China. Pollution evolution with photochemical age was studied for the first time at a comprehensive field observation station during winter in Beijing. The photochemical age was used as an estimate of the timescale attributed to the aging process and was estimated from the ratio of toluene to benzene in this study. A low photochemical age indicates a fresh emission. The photochemical age of air masses during new particle formation (NPF) days was lower than that on haze days. In general, the strongest NPF events, along with a peak of the formation rate of 1.5 nm (J) and 3 nm particles (J), were observed when the photochemical age was between 12 and 24 h while rarely took place with photochemical ages less than 12 h. When photochemical age was larger than 48 h, haze occurred and NPF was suppressed. The sources and sinks of nanoparticles had distinct relation with the photochemical age. Our results show that the condensation sink (CS) showed a valley with photochemical ages ranging from 12 to 24 h, while HSO concentration showed no obvious trend with the photochemical age. The high concentrations of precursor vapours within an air mass lead to persistent nucleation with photochemical age ranging from 12 to 48 h in winter. Coincidently, the fast increase of PM mass was also observed during this range of photochemical age. Noteworthy, CS increased with the photochemical age on NPF days only, which is the likely reason for the observation that the PM mass increased faster with photochemical age on NPF days compared with other days. The evolution of particles with the photochemical age provides new insights into understanding how particles originating from NPF transform to haze pollution.
二次气溶胶在一次排放物老化过程中的形成是中国东部霾污染的主要原因。本研究首次在北京冬季综合野外观测站研究了光化学年龄对污染演变的影响。光化学年龄被用作老化过程时间尺度的估计，并根据甲苯与苯的比值进行估计。低光化学年龄表明是新鲜排放物。新粒子形成（NPF）期间空气团的光化学年龄低于霾天。一般来说，当光化学年龄在 12 至 24 小时之间时，会观察到最强的 NPF 事件，以及 1.5nm（J）和 3nm 粒子（J）的生成速率峰值，而当光化学年龄小于 12 小时时，很少发生 NPF。当光化学年龄大于 48 小时时，会发生霾，并且抑制 NPF。纳米颗粒的源和汇与光化学年龄有明显的关系。研究结果表明，在光化学年龄为 12 至 24 小时范围内，凝结汇（CS）呈低谷状，而 HSO 浓度随光化学年龄无明显变化趋势。空气团内前体蒸气的高浓度导致持续成核，光化学年龄在 12 至 48 小时范围内，冬季也是如此。巧合的是，在此光化学年龄范围内也观察到 PM 质量的快速增加。值得注意的是，仅在 NPF 日，CS 随光化学年龄增加，这可能是 NPF 日 PM 质量随光化学年龄增加比其他日更快的原因。颗粒物随光化学年龄的演变提供了对理解 NPF 产生的颗粒物如何转化为霾污染的新认识。
