Polar Semivolatile Organic Compounds in Biomass-Burning Emissions and Their Chemical Transformations During Aging in an Oxidation flow Reactor
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Atmos. Chem. Phys., 20, 8227–8250, 2020 https://doi.org/10.5194/acp-20-8227-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Polar semivolatile organic compounds in biomass-burning emissions and their chemical transformations during aging in an oxidation flow reactor Deep Sengupta, Vera Samburova, Chiranjivi Bhattarai, Adam C. Watts, Hans Moosmüller, and Andrey Y. Khlystov Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA Correspondence: Vera Samburova ([email protected]) Received: 20 December 2019 – Discussion started: 23 January 2020 Revised: 7 May 2020 – Accepted: 18 May 2020 – Published: 16 July 2020 Abstract. Semivolatile organic compounds (SVOCs) emit- 350 g mol−1 decreased after OFR aging, while abundances ted from open biomass burning (BB) can contribute to chem- of low-MW compounds (e.g., hexanoic acid) increased. This ical and physical properties of atmospheric aerosols and indicated a significant extent of fragmentation reactions in also may cause adverse health effects. The polar fraction of the OFR. Methoxyphenols decreased after OFR aging, while SVOCs is a prominent part of BB organic aerosols, and thus a significant increase (3.7 to 8.6 times) in the abundance of it is important to characterize the chemical composition and dicarboxylic acids emission factors (EFs), especially maleic reactivity of this fraction. In this study, globally and region- acid (10 to 60 times), was observed. EFs for fresh and ratios ally important representative fuels (Alaskan peat, Moscow from fresh-to-aged BB samples reported in this study can be peat, Pskov peat, eucalyptus, Malaysian peat, and Malaysian used to perform source apportionment and predict processes agricultural peat) were burned under controlled conditions occurring during atmospheric transport. using the combustion chamber facility at the Desert Re- search Institute (DRI). Gas- and particle-phase biomass- burning emissions were aged in an oxidation flow reactor (OFR) to mimic 5–7 d of atmospheric aging. Fresh and OFR- aged biomass-burning aerosols were collected on Teflon- 1 Introduction impregnated glass fiber filters (TIGF) in tandem with XAD resin media for organic carbon speciation. The polar fraction Biomass burning (BB), including both wildfires and pre- extracted with dichloromethane and acetone was analyzed scribed burns, is a major source of carbonaceous aerosols in with gas chromatography mass spectrometry (GC-MS) for the atmosphere (Penner et al., 1991) and can contribute up 84 polar organic compounds – including mono- and dicar- to 75 % of total atmospheric aerosol mass loading (Andreae boxylic acids, methoxylated phenols, aromatic acids, anhy- and Merlet, 2001; Park et al., 2007). These carbonaceous drosugars, resin acids, and sterols. For all these compounds, aerosols have a significant impact on both regional and global fuel-based emission factors (EFs) were calculated for fresh radiative forcing (Ramanathan and Carmichael, 2008). BB and OFR-aged samples. The carbon mass of the quanti- emissions also can cause adverse health effects (Arbex et fied polar compounds was found to constitute 5 % to 7 % al., 2007; Regalado et al., 2006) because of the toxicolog- of the total organic compound mass. A high abundance of ical properties of particle-bound organic compounds (Chen methoxyphenols (239 mg kg−1 for Pskov peat; 22.6 % of to- et al., 2017; Pardo et al., 2020; Pavagadhi et al., 2013; Sigs- tal GC-MS characterized mass) and resin acids (118 mg kg−1 gaard et al., 2015; Yang et al., 2010). Therefore, the compre- for Alaskan peat; 14.5 % of total GC-MS characterized mass) hensive, molecular-level characterization of BB emissions is was found in peat-burning emissions (smoldering combus- essential for understanding health effects. Such a molecular tion). The concentration of some organic compounds (e.g., characterization of BB carbonaceous aerosols in the atmo- tetracosanoic acid) with a molecular weight (MW) above sphere, however, is challenging, as these aerosols are com- Published by Copernicus Publications on behalf of the European Geosciences Union. 8228 D. Sengupta et al.: Emissions and fates of polar SVOCs from laboratory BB experiments posed of tens of thousands of compounds (Goldstein and pected to be different mechanistically from individual com- Galbally, 2007). pounds. This necessitates the need for studies of the evolu- The simulation of natural fires in a laboratory environment tion of organic compounds through the bulk molecular-level using a BB chamber is one way to characterize the chemical characterization of BB emissions. Recently, Fortenberry et composition of BB emissions (Yokelson et al., 2003). A num- al. (2018) characterized the chemical fingerprints of aged ber of studies characterizing the molecular composition of biomass-burning aerosols (leaf and hardwood of white oak) combustion emissions from fuels that represent different ge- by performing oxidation in a potential-aerosol-mass oxida- ographical regions have been completed: temperate conifers tion flow reactor (PAM-OFR) and chemical analysis with a (Oros and Simoneit, 2001a), deciduous trees (Oros and Si- thermal desorption aerosol gas chromatograph aerosol mass moneit, 2001b), grasses (Oros et al., 2006), and peats (Sam- spectrometer (TAG-AMS). In this study, denuders were used burova et al., 2016; Iinuma et al., 2007). Akagi et al. (2011) to remove gases, and particles were introduced to the OFR compiled fuel-based emission factors (EFs) from different to evaluate only the changes in particulate BB emissions dur- fuels from throughout the world, including the peatlands of ing OFR oxidation. However, the presence of both gas- and southern Asia, and found that burning condition (flaming and particle-phase emissions in real BB emissions and the parti- smoldering) can influence the EFs of individual compounds. tioning of organic compounds in such a complex mixture can These data have been used for modeling work in predicting affect the reactivity inside the OFR and hence the fate of or- ozone-forming potential and other air quality impacts (Al- ganic compounds during OFR aging. Bertrand et al. (2018) varado et al., 2015). Very few studies (e.g., Samburova et analyzed 71 organic compounds in BB emissions, sampled al., 2016) have focused on peat emissions. However, the im- from a smog chamber, with high-resolution time of flight portance of investigating the combustion products from burn- mass spectrometry (HR-ToF-AMS). This study confirms that ing peat soils is multifaceted. Peat soils, comprised predom- nitroaromatic compounds are formed after OFR oxidation inantly of partially decomposed organic material, represent and that they can be used as a tracer of secondary organic one fourth to one third of global terrestrial carbon and are un- aerosol (SOA). However, this study was focused on con- der threat of increased fire activity in both boreal and tropical trolled wood (pellet) burning that is substantially different latitudes, areas of widespread peatland occurrence (Turetsky from wildland BB emissions. There is still a lack of under- et al., 2015). In addition to the implications of peat fires for standing, however, regarding (1) major organic compounds the global C cycle, local impacts from the burning of peat- emitted from BB (especially from peat fuels), (2) their roles lands include problems of public health and safety from de- in atmospheric photochemical reactions, and (3) what com- graded air quality and the reduction of surface albedo upon pounds are responsible for the light absorption of fresh and peat smoke deposition on snow surfaces (Beres et al., 2020), aged BB emissions. as well as ecological changes due to altered surface hydrol- In this study, emissions from the laboratory combustion ogy in low-relief areas (Watts et al., 2015). Most source ap- of six globally important fuels (Alaskan peat, Moscow peat, portionment studies, however, focused on the characteriza- Pskov peat, eucalyptus, Malaysian peat, and Malaysian agri- tion of fresh emissions and emissions of either particle-phase cultural peat; Watts et al., 2020) were quantitatively analyzed or gas-phase compounds. for more than 250 individual organic species, and the anal- Significant changes in organic aerosol composition during ysis of 84 polar organic species is presented in this paper. atmospheric transport have been reported (Liu et al., 2017; BB emissions generated in a combustion chamber were run Decker et al., 2019). These changes can impact local and re- though the OFR, mimicking approximately 5 to 7 d of at- gional air quality. Also, the role of Siberian peat burning in mospheric oxidation (Bhattarai et al., 2018), and the OFR haze formation in the Korean Peninsula (Jung et al., 2016) output was analyzed to characterize aged BB emissions. demonstrates the global impact of BB emissions and their at- BB emissions were collected on filter and XAD media to mospheric transport on regional air quality. Some laboratory identify the distribution of organic species between the gas studies found an increase in the mass of organic aerosol (OA) and particle phases. For the polar fraction of collected or- after photochemical aging (Ortega et al., 2013; Grieshop et ganic compounds, we quantitatively analyzed a total of 84 al., 2009), while others observed a modest decrease (Bhat- compounds (methoxyphenol derivatives, dicarboxylic acids, tarai et al., 2018). There are still limited data on the evolu- monocarboxylic acids, aromatic acids, resin acids, and anhy-