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

Abstract

Abstract. New particle formation processes contribute significantly to the number concentration of ultrafine particles (UFP), and have great impacts on human health and global climate. Iodine oxoacids (HIOx, including iodic acid, HIO3 and iodous acid, HIO2) have been observed in pristine regions and proved to dominate NPF events at some sites. However, the knowledge of HIOx in polluted urban areas is rather limited. Here, we conducted a long-term comprehensive observation 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 HIOx to UFP number concentration in urban environments. HIO3 concentration is highest in summer, up to 2.85×106 cm-3 and 2.78×106 cm-3 in Beijing and Nanjing, respectively, and is lowest in winter, with a more prominent seasonal variation than H2SO4. HIO3 concentration shows a clear diurnal pattern at both sites with a daily maximum at around noontime, similar to the atmospheric temperature, radiation and ozone (O3) levels. HIO2 concentration has the same diurnal and seasonal trend as HIO3 but is overall about one order of magnitude lower than HIO3 concentration. Back trajectory analysis suggests that the sources for inland iodine species could be a mix of marine and terrestrial origins, both having peak iodine emission in warm seasons. While the contribution of HIO2 to particle growth is marginal in Beijing and Nanjing, our results demonstrate that HIO3 enhances the particle survival probability of sub-3 nm particles by about 40 % (median) and occasionally by more than 100 % in NPF events, suggesting HIOx are non-negligible contributor to UFPs in polluted urban areas. As the growth contribution from HIO3 and H2SO4 is similar on a per-molecule basis, we propose that the sum of HIO3 and H2SO4 could be used to estimate sub-3 nm particle growth of inorganic acid origin, in the polluted atmospheres with a significant amount of HIOx.

Modeling the Formation of Organic Compounds across Full Volatility Ranges and Their Contribution to Nanoparticle Growth in a Polluted Atmosphere

“…For instance, a potentially influential process is coagulation, wherein large particles can grow by scavenging small particles . Meanwhile, other inorganic vapors including iodine oxoacid (HIO 3 ), nitric acid (HNO 3 ), and ammonia (NH 3 ) may also promote nanoparticle growth under specific environments, − but their influence on the growth of 4–40 nm particles is limited in most cases. , Besides, heterogeneous reactions may also slightly impact nanoparticle growth by either increasing or decreasing the particle-phase species . Observed GRs may also have some uncertainty due to instrument, sampling, or computational errors, affecting the validation of simulation GRs. − However, our purpose here is not to comprehensively describe all the detailed mechanisms relevant to nanoparticle growth but rather to find out the main species and processes that contribute to nanoparticle growth and establish a prediction method for GRs.…”

Enhancement of Atmospheric Nucleation Precursors on Iodic Acid-Induced Nucleation: Predictive Model and Mechanism

“…A recent study based on long-term observations found that [IA] can reach about 2.8 × 10 6 cm −3 in the polluted urban atmosphere in Beijing and Nanjing. 23 As shown in Figure 6B, DEA with a ppt level can lead to notable J values (>10 cm −3 s −1 ) when [IA] is about 10 6 cm −3 . In fact, DEA at ppt levels has been detected in polluted urban atmospheres, including Beijing.…”

“…18 However, the current knowledge may not well predict IA-induced nucleation under all circumstances, especially in chemically complex polluted and semi-polluted environments. As the presence of iodine species in polluted environments has been unambiguously revealed, 14,23 it is necessary to investigate the enhancing potential of other compounds on IA-induced nucleation, with special attention to compounds with stronger enhancing potential compared to HIO 2 .…”

“…It should be noted that S-atom-containing acids also bind strongly with amines and O-atom-containing OAs. 57,74−77 Since iodine oxoacids, Satom-containing acids, O-atom-containing OAs, and amines coexist in the polluted atmosphere, 23 the synergistic nucleation of multi-components (e.g., ternary IA-SA/HMSA/MSIA-HIO 2 /OAs/amines, quaternary IA-HIO 2 -SA/HMSA/MSIA-OAs, IA-HIO 2 -SA/HMSA/MSIA-amines, etc.) may occur.…”

Temperature, humidity, and ionisation effect of iodine oxoacid nucleation

“…32 This simple and efficient production pathway of HIO 3 may help explain the ubiquitous presence of HIO 3 globally, 16 even including inland polluted cities such as Beijing and Nanjing. 33 The CLOUD experiment has also revealed that HIO 3 alone is not able to explain iodine particle formation and HIO 2 is needed to form the initial clusters together with HIO 3 (termed the iodine oxoacid nucleation mechanism). 16 Recent theoretical work utilising quantum chemical calculations and kinetic simulations further uncovered the critical role of HIO 2 in stabilising HIO 3 clusters because HIO 2 exhibits strong alkalinelike behaviour.…”