Probing key organic substances driving new particle growth initiated by iodine nucleation in coastal atmosphere

Abstract

Abstract. Unlike the deep understanding of highly oxygenated organic molecules (HOMs) driving continental new particle formation (NPF), little is known about the organics involved in coastal and open ocean NPF. On the coastline of China we observed intense coastal NPF events initiated by iodine nucleation, but particle growth to cloud condensation nuclei (CCN) sizes was dominated by organic compounds. This article revealed a new group of C18,30HhOoNn and C20,24,28,33HhOo compounds with specific double bond equivalents and oxygen atom numbers in sub-20 nm coastal iodine new particles by using ultrahigh resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS). We proposed these compounds are oxygenated or nitrated products of long chain unsaturated fatty acids, fatty alcohols, non-protein amino acids or amino alcohols emitted mutually with iodine from coastal biota or biological-active sea surface. Group contribution method estimated that the addition of −ONO2, −OH and −C = O groups to the precursors reduced their volatility of by 2~7 orders of magnitude and thus made their products condensable onto iodine new particles in the coastal atmosphere. Non-target MS analysis also provided a list of 440 formulas of iodinated organic compounds in size-resolved aerosol samples during the iodine NPF days, which facilitates the understanding of unknown aerosol chemistry of iodine.

Butene Emissions From Coastal Ecosystems May Contribute to New Particle Formation

“…A negative lag time, which means that particle components are being driven by nucleation rates, reflects the fact that particles need to grow to larger diameters to be detected by the c‐ToF‐AMS, whose detection efficiency is rather poor below 50 nm (see Section 2.5). Contrarily to previous studies at higher latitudes (Allan et al., 2015; Baccarini et al., 2020; Mäkelä et al., 2002; McFiggans et al., 2010; Wan et al., 2020; Yu et al., 2019), a clear link between iodine species and NPF events was not observed during the AEROCLO‐sA campaign (example correlation with the I + fragment measured by the c‐ToF‐AMS shown in Table S4 in Supporting Information ). However, NPF event of the 9 September (Figure 3a) occurs hours after a spike of the iodide ion, locally produced in the morning (Figure 3f), which may be driving nucleation even if it is only a minor contributor to aerosol mass at the size range detectable by the c‐ToF‐AMS.…”