University of Helsinki, Department, of Physics, P.O. Box 64, FI-00014, Finland.
Faraday Discuss. 2017 Aug 24;200:271-288. doi: 10.1039/c6fd00257a.
In terms of the global aerosol particle number load, atmospheric new particle formation (NPF) dominates over primary emissions. The key for quantifying the importance of atmospheric NPF is to understand how gas-to-particle conversion (GTP) takes place at sizes below a few nanometers in particle diameter in different environments, and how this nano-GTP affects the survival of small clusters into larger sizes. The survival probability of growing clusters is tied closely to the competition between their growth and scavenging by pre-existing aerosol particles, and the key parameter in this respect is the ratio between the condensation sink (CS) and the cluster growth rate (GR). Here we define their ratio as a dimensionless survival parameter, P, as P = (CS/10 s)/(GR/nm h). Theoretical arguments and observations in clean and moderately-polluted conditions indicate that P needs to be smaller than about 50 for a notable NPF to take place. However, the existing literature shows that in China, NPF occurs frequently in megacities such as in Beijing, Nanjing and Shanghai, and our analysis shows that the calculated values of P are even larger than 200 in these cases. By combining direct observations and conceptual modelling, we explore the variability of the survival parameter P in different environments and probe the reasons for NPF occurrence under highly-polluted conditions.
就全球气溶胶粒子数负荷而言，大气新粒子形成（NPF）超过了初级排放。量化大气 NPF 重要性的关键是要了解在不同环境中，粒径小于几纳米的气体到粒子转化（GTP）是如何发生的，以及这种纳米 GTP 如何影响小团簇存活并生长到更大的尺寸。生长团簇的存活概率与它们的生长和被预先存在的气溶胶粒子清除之间的竞争密切相关，在这方面的关键参数是凝结阱（CS）和团簇生长速率（GR）之间的比值。在这里，我们将它们的比值定义为一个无量纲的生存参数 P，即 P = (CS/10 s)/(GR/nm h)。在清洁和中度污染条件下的理论论证和观测表明，要发生显著的 NPF，P 需要小于约 50。然而，现有文献表明，在中国，像北京、南京和上海这样的特大城市经常发生 NPF，我们的分析表明，在这些情况下，计算得到的 P 值甚至大于 200。通过结合直接观测和概念模型，我们探讨了不同环境中生存参数 P 的可变性，并探讨了在高度污染条件下发生 NPF 的原因。
