Abstract
Abstract. Unlike the deep understanding of highly oxygenated organic molecules (HOMs) driving continental new particle formation (NPF), little is known about the organic compounds 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 reveals a new group of C18,30HhOoNn and C20,24,28,33HhOo compounds with specific double-bond equivalents and oxygen atom numbers in new sub 20 nm coastal iodine 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, nonprotein amino acids or amino alcohols emitted mutually with iodine from coastal biota or biologically active sea surface. Group contribution method estimated that the addition of –ONO2, –OH and –C=O groups to the precursors reduced their volatility by 2–7 orders of magnitude and thus made their products condensable onto new iodine particles in the coastal atmosphere. Nontarget 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.
Highlights
Atmospheric new particle formation (NPF) contributes over half of global cloud condensation nuclei (CCN) (Merikanto et al, 2009) and influences cloud properties and Earth’s radiation budget (Metzger et al, 2010)
The classification of I-NPF event, continental NPF (C-NPF) event or non-NPF was based on particle number size distributions (PNSDs) between 2 and 750 nm monitored from January to May 2018 by a scanning mobility particle spectrometer (SMPS; TSI DMA3081 and CPC3775; scanning range: 40–750 nm) and a neutral cluster air ion spectrometer (NAIS; scanning range: 2–42 nm)
Each set of nano-MOUDI samples was collected continuously for 72 h, during which NPF occurred on a daily basis, so that particle chemical composition of different event types can be obtained from offline analyses
Summary
Atmospheric new particle formation (NPF) contributes over half of global cloud condensation nuclei (CCN) (Merikanto et al, 2009) and influences cloud properties and Earth’s radiation budget (Metzger et al, 2010). By deploying a highresolution chemical ionization mass spectrometer, recent laboratory and field studies have identified a group of highly oxygenated multifunctional organic molecules (HOMs) with high O/C ratios and low volatility from the reactions of volatile organic compounds (VOCs) such as monoterpenes (Ehn et al, 2014), sesquiterpenes (Richters et al, 2016) and alkenes (Mentel et al, 2015) with a hydroxyl radical (OH), ozone (O3), nitrate radicals (NO3) and chlorine atoms (Wang et al, 2020) These HOMs play an important role in particle nucleation and growth of continental NPF, as well as in the formation of secondary organic aerosols. Wan et al.: Key organic substances driving coastal new particle growth
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