posted on 2024-03-13, 20:29authored byYuyang Li, Xiaoxiao Li, Runlong Cai, Chao Yan, Guangjie Zheng, Yiran Li, Yijing Chen, Yusheng Zhang, Yishuo Guo, Chenjie Hua, Veli-Matti Kerminen, Yongchun Liu, Markku Kulmala, Jiming Hao, James N. Smith, Jingkun Jiang
New particle formation and growth greatly influence air
quality
and the global climate. Recent CERN Cosmics Leaving OUtdoor Droplets
(CLOUD) chamber experiments proposed that in cold urban atmospheres
with highly supersaturated HNO3 and NH3, newly
formed sub-10 nm nanoparticles can grow rapidly (up to 1000 nm h–1). Here, we present direct observational evidence
that in winter Beijing with persistent highly supersaturated HNO3 and NH3, nitrate contributed less than ∼14%
of the 8–40 nm nanoparticle composition, and overall growth
rates were only ∼0.8–5 nm h–1. To
explain the observed growth rates and particulate nitrate fraction,
the effective mass accommodation coefficient of HNO3 (αHNO3) on the nanoparticles in urban Beijing needs
to be 2–4 orders of magnitude lower than those in the CLOUD
chamber. We propose that the inefficient uptake of HNO3 on nanoparticles is mainly due to the much higher particulate organic
fraction and lower relative humidity in urban Beijing. To quantitatively
reproduce the observed growth, we show that an inhomogeneous “inorganic
core–organic shell” nanoparticle morphology might exist
for nanoparticles in Beijing. This study emphasized that growth for
nanoparticles down to sub-10 nm was largely influenced by their composition,
which was previously ignored and should be considered in future studies
on nanoparticle growth.