Mass spectral characterization of submicron biogenic organic particles in the Amazon Basin

Abstract

[1] Submicron atmospheric particles in the Amazon Basin were characterized by a high-resolution aerosol mass spectrometer during the wet season of 2008. Patterns in the mass spectra closely resembled those of secondary-organicaerosol (SOA) particles formed in environmental chambers from biogenic precursor gases. In contrast, mass spectral indicators of primary biological aerosol particles (PBAPs) were insignificant, suggesting that PBAPs contributed negligibly to the submicron fraction of particles during the period of study. For 40% of the measurement periods, the mass spectra indicate that in-Basin biogenic SOA production was the dominant source of the submicron mass fraction, contrasted to other periods (30%) during which out-of-Basin organic-carbon sources were significant on top of the baseline in-Basin processes. The in-Basin periods had an average organic-particle loading of 0.6 mg m À3 and an average elemental oxygen-to-carbon (O:C) ratio of 0.42, compared to 0.9 mg m À3 and 0.49, respectively, during periods of out-of-Basin influence. On the basis of the data, we conclude that most of the organic material composing submicron particles over the Basin derived from biogenic SOA production, a finding that is consistent with microscopy observations made in a concurrent study. This source was augmented during some periods by aged organic material delivered by long-range transport. Citation: Chen, Q., et al.

A simplified description of the evolution of organic aerosol composition in the atmosphere

“…The aerosols sampled at Riverside exhibit a limited range of composition, which likely reflects predominantly anthropogenic sources of OA, both primary and secondary, transported from the center of the Los Angeles basin. Aerosol loadings at the AMAZE-08 site, are substantially lower [Chen et al, 2009] which may explain the higher degree of scatter on the elemental ratios. OA in this clean, forested environment exhibits a wide range of oxygen content, with more oxidized aerosol than observed at Riverside.…”

Aircraft-based observations of isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region

“…These two ions are important tools to identify the photochemical aging of organic aerosol components in the atmosphere. Organic aerosol can be grouped into oxygenated 20 organic aerosol (OOA) and hydrocarbon-like organic aerosol (HOA), whereby OOA is further classified into low-volatile OOA (LV-OOA) and semi-volatile OOA (SV-OOA) (e.g., Alfarra et al, 2004;Zhang et al, 2005;Canagaratna et al, 2007;Zhang et al, 2007;Jimenez et al, 2009;Ng et al, 2011;Ortega et al, 2016). The difference between these two sub-components is represented by the two ions at m/z 43 and m/z 44.…”

“…These two ions, or more specifically f 43 and f 44 , change during photochemical aging of organic aerosol, leading to higher f 44 and lower f 43 values for LV-OOA than SV-OOA. With increasing photochemical aging, organic aerosol of different origins become more similar in terms of chemistry (Jimenez et al, 2009). …”

“…Volatile organic compounds (VOCs) emitted by vegetation can lead to the formation of secondary organic aerosol (SOA) 10 through atmospheric oxidation and further chemical processes (e.g., Zhang et al, 2007;Jimenez et al, 2009;Hallquist et al, 2009;Shrivastava et al, 2017). One important VOC is isoprene (C 5 H 8 , 2-methyl-1,3-butadiene), the most abundant nonmethane hydrocarbon with a global emission rate of~500 Tg y −1 , with a large contribution coming from the Amazon rain forest (Guenther et al, 2012).…”

“…The submicron aerosol particles were found to be dominated by secondary organic mate-15 rial (Chen et al, 2009). From positive matrix factorization (PMF) analysis one factor was associated with the reactive uptake of IEPOX to acidic haze, fog or cloud droplets (Chen et al, 2015).…”