Abundant Biogenic Oxygenated Organic Aerosol in Atmospheric Coarse Particles: Plausible Sources and Atmospheric Implications

Abstract

Secondary organic aerosol (SOA) is a key component in atmospheric aerosols, strongly influencing air quality and climate. Most previous studies focused on SOA formation in the fine aerosol mode, and little is known about SOA formation across a broader size range, especially for the coarse aerosol mode. In this study, we coupled radiocarbon analysis and the offline aerosol mass spectrometric method to characterize water-soluble organic matter in size-segregated samples between 0.056 and 18 μm collected in urban Shenzhen, China. For the first time, detailed size distributions of different types of oxygenated organic aerosols (OOAs) are obtained. Fossil fuel OOA was mostly distributed in fine particles, and biogenic OOA occurred mostly in coarse particles. Organic composition and correlation analyses suggested that the major source of the coarse-mode OOA was more plausible to be heterogeneous reactions of biogenic volatile organic compounds (VOCs) on soil dust rather than primary biological materials. If so, this mechanism would complement the missing sinks of biogenic VOCs, significantly influence the regional and global organic aerosol budgets, and thus should be considered in air quality and climate models. This study highlights the urgent need for laboratory simulations of heterogeneous reactions of various VOCs on soil dust.

Particle size-dependent fluorescence properties of water-soluble organic compounds (WSOC) and their atmospheric implications on the aging of WSOC

“…PARAFAC results showed that HULIS was rich in fine particles and protein-like compounds were rich in coarse particles among both seasons, which were accordant with former research (Chen et al, 2019;Huang et al, 2020). In winter, the wavelength of HULIS-1 was slightly higher than HULIS-2 and their EEM spectra were similar to the PARAFAC results of highly oxygenated species and less oxygenated species in Chen et al (2016b)'s study on the chromophoric WSOC.…”

“…FRI Ⅳ (microbial related species) peaked between 1.4 to 2.5 µm and showed little variations with particle size increase. Almost the same size distributions of protein-like (and microbial species) and HULIS fluorophores were also obtained by the isotopic method (Huang et al, 2020).…”

“…Peak T/Peak C peaked at coarse mode in both seasons indicating that fluorescent biogenic organics were likely to exist in larger atmospheric particles. Former researchers also found that biogenic oxygenated organics are more inclined to sink in coarse mode (Huang et al, 2020). Stokes shift is the energy loss of fluorophore relaxation which might associate with the π-conjected system and electron cloud density (Lakowicz, 2006).…”

“…Table 1 showed the size-segregated concentrations of WSIN, WSOC, OC, and their ratios at a rural site in Beijing for winter and summer. WSOC showed monomodal in winter and bimodal features in summer, respectively, with a dominant mode between 0.26 to 0.44 µm, or having a small secondary mode in particles larger than 1 µm, indicating that carbonaceous species were mainly rich in fine particles (Huang et al, 2020). Contemporary researchers observed bimodal distribution of organic matter in Shenzhen, China, and Gwangju, Korea (Yu et al, 2016;Huang et al, 2020).…”

“…Utilization of exquisite mass spectroscopy like electrospray ionization mass spectrometry (ESI-MS), ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and proton transfer reaction mass spectrometry sees increasing owing to the requirement of further insight into organics in particulate matter (Cai et al, 2020;Mayorga et al, 2021). Isotopic ratio mass spectroscopy (IRMS) and accelerate mass spectroscopy (AMS) are always used to distinguish fossil combustion sources and biogenic sources by carbon isotopic (Masalaite et al, 2018;Zhao et al, 2019;Huang et al, 2020). Although having various advantages, the expanding application of formerly mentioned instruments is limited by sampling requirements or expensive costs.…”