Iodine oxoacids and their roles in sub-3 nm particle growth in polluted urban environments

Zhang, Ying; Li, Duzitian; He, Xu-Cheng; Nie, Wei; Deng, Chenjuan; Cai, Runlong; Liu, Yuliang; Guo, Yishuo; Liu, Chong; Li, Yiran; Chen, Liangduo; Li, Yuanyuan; Hua, Chenjie; Liu, Tingyu; Wang, Zongcheng; Xie, Jiali; Wang, Lei; Petäjä, Tuukka; Bianchi, Federico; Qi, Ximeng; Chi, Xuguang; Paasonen, Pauli; Liu, Yongchun; Yan, Chao; Jiang, Jingkun; Ding, Aijun; Kulmala, Markku

New particle formation contributes significantly to the number concentration of ultrafine particles (UFPs, inline-formuladinline-formula≤ 100 nm) and has a great impact on human health and global climate. Iodine oxoacids (HIOinline-formulax, including iodic acid, HIOinline-formula3, and iodous acid, HIOinline-formula2) have been observed in pristine regions and proved to dominate new particle formation (NPF) at some sites. However, the knowledge of HIOinline-formulax in polluted urban areas is rather limited. Here, we conducted a long-term measurements of gaseous iodine oxoacids and sulfuric acid in Beijing from January 2019 to October 2021 and also in Nanjing from March 2019 to February 2020 and investigated the contribution of HIOinline-formulax to UFP number concentration in both urban environments. HIOinline-formula3 is highest in summer, up to 2.85 inline-formula× 10inline-formula6 and 2.78 inline-formula× 10inline-formula6 cminline-formula−3 in Beijing and Nanjing, respectively, and is lowest in winter by 96 % and 75 %, respectively. HIOinline-formula3 exhibits more prominent variation than Hinline-formula2SOinline-formula4 in both urban sites. HIOinline-formula3 concentration shows a clear diurnal pattern at both sites with a daily maximum at around noontime, similar to the atmospheric temperature, solar radiation, and ozone (Oinline-formula3) levels. HIOinline-formula2 concentration has the same diurnal and seasonal trend as HIOinline-formula3 but is overall about an order of magnitude lower than HIOinline-formula3 concentration. Back trajectory analysis suggests that the sources for inland iodine species could be a mix of marine and terrestrial origins, with both having peak iodine emission in warm seasons. While the contribution of HIOinline-formula2 to particle growth is marginal in Beijing and Nanjing, our results demonstrate that HIOinline-formula3 enhances the particle survival probability of sub-3 nm particles by about 40 % (median) and occasionally by more than 100 % in NPF events, suggesting HIOinline-formulax are significant contributor to UFPs in polluted urban areas. As the growth contribution from HIOinline-formula3 and Hinline-formula2SOinline-formula4 is similar on a per-molecule basis, we propose that the sum of HIOinline-formula3 and Hinline-formula2SOinline-formula4 could be used to estimate sub-3 nm particle growth of inorganic acid origin in polluted atmospheres with a significant amount of HIOinline-formulax.

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Zhang, Ying / Li, Duzitian / He, Xu-Cheng / et al: Iodine oxoacids and their roles in sub-3 nm particle growth in polluted urban environments. 2024. Copernicus Publications.

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