Investigating the contribution of grown new particles to cloud condensation nuclei with largely varying pre-existing particles – Part 1: Observational data analysis

Abstract

Abstract. This study employed multiple techniques to investigate the contribution of grown new particles to the number concentration of cloud condensation nuclei (CCN) at various supersaturation (SS) levels at a rural mountain site in North China Plain from 29 June to 14 July 2019. On eight new particle formation (NPF) days, the total particle number concentrations (Ncn) were 8.4±6.1 ×103 cm-3, which were substantially higher compared to 4.7±2.6 ×103 cm-3 on non-NPF days. However, the Nccn at 0.2 %SS and 0.4 %SS on the NPF days were significantly lower than those observed on non-NPF days (P<0.05). This was due to the lower cloud activation efficiency of pre-existing particles resulting from organic vapor condensation and smaller number concentrations of pre-existing particles on NPF days. A case-by-case examination showed that the grown new particles only yielded a detectable contribution to Nccn at 0.4 % SS and 1.0 % SS during the NPF event on 1 July 2019, accounting for 12±11 % and 23±12 % of Nccn, respectively. The increased Nccn during two other NPF events and at 0.2 % SS on 1 July 2019 were detectable, but determined mainly by varying pre-existing particles rather than grown new particles. In addition, the hygroscopicity parameter values, concentrations of inorganic and organic particulate components, and surface chemical composition of different sized particles were analyzed in terms of chemical drivers to grow new particles. The results showed that the grown new particles via organic vapor condensation generally had no detectable contribution to Nccn, but incidentally did. However, this conclusion was drawn from a small size of observational data, leaving more observations, particularly for long-term observations and the growth of pre-existing particles to the CCN required size, needed for further investigation.