Bulk and molecular-level composition of primary organic aerosol from wood, straw, cow dung, and plastic burning

Abstract

Abstract. During the past decades, the source apportionment of organic aerosol (OA) in ambient air has been improving substantially. The database of source retrieval model-resolved mass spectral profiles for different sources has been built with the aerosol mass spectrometer (AMS). However, distinguishing similar sources (such as wildfires and residential wood burning) remains challenging, as the hard ionization of the AMS mostly fragments compounds and therefore cannot capture detailed molecular information. Recent mass spectrometer technologies of soft ionization and high mass resolution have allowed for aerosol characterization at the molecular formula level. In this study, we systematically estimated the emission factors and characterized the primary OA (POA) chemical composition with the AMS and the extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for the first time from a variety of solid fuels, including beech logs, spruce and pine logs, spruce and pine branches and needles, straw, cow dung, and plastic bags. The emission factors of organic matter estimated by the AMS and hydrocarbon gases estimated by the total hydrocarbon analyzer are 16.2 ± 10.8 g kg−1 and 30.3 ± 8.5 g kg−1 for cow dung burning, which is generally higher than that of wood (beech, spruce, and pine), straw, and plastic bag burning (in the range from 1.1 to 6.2 g kg−1 and 14.1 to 19.3 g kg−1). The POA measured by the AMS shows that the f60 (mass fraction of m/z 60) varies from 0.003 to 0.04 based on fuel types and combustion efficiency for wood (beech, spruce, and pine) and cow dung burning. On a molecular level, the dominant compound of POA from wood, straw, and cow dung is C6H10O5 (mainly levoglucosan), contributing ∼ 7 % to ∼ 30 % of the total intensity, followed by C8H12O6 with fractions of ∼ 2 % to ∼ 9 %. However, as they are prevalent in all burning of biomass material, they cannot act as tracers for the specific sources. By using the Mann–Whitney U test among the studied fuels, we find specific potential new markers for these fuels from the measurement of the AMS and EESI-TOF. Markers from spruce and pine burning are likely related to resin acids (e.g., compounds with 20–21 carbon atoms). The product from the pyrolysis of hardwood lignins is found especially in beech log burning. Nitrogen-containing species are selected markers primarily for cow dung open burning. These markers in the future will provide support for the source apportionment.

Reply on RC1

“…Generally, the total fraction of nitrogen-containing species (CxHyN and CxHyOzN) is significantly higher in the primary NMOGs emitted from open burning of cow dung (18.8%) compared to the other fuels (2.1% to 7.3%). This trend is consistent with both our results from aerosol composition measurement and previous literature (Stewart et al, 2021b;Zhang et al, 2023;Loebel Roson et al, 2021). Generally, nitrogen containing compounds in cow dung consist mainly of one nitrogen atom and have a wide range of carbon numbers between 2 and 7 (Figure 2).…”

“…In this study, the mixing ratio relative contribution for more than 1500 species from six different fuels for all 28 test burns was quantified by using Vocus. To identify the characteristic compounds of emissions from different fuels, we implemented the Mann-Whitney U test (Mann and Whitney, 1947;Wilcoxon, 1945) in MATLAB®, which has been applied in the selection of aerosol markers (Zhang et al, 2023). It is a nonparametric test and is used for between-group comparisons when the dependent variable is ordinal or continuous and not assumed to follow a normal distribution.…”

“…Specifically, cow dung exhibits a slightly lower fraction of high O/C compared to other fuels studied. (Zhang et al, 2023).…”

Impact of Biomass Burning on Arctic Aerosol Composition

“…As the size of the particles plays a role for wet removal it is also possible that the BC is incorporated in the larger particles (prevalent in E1–E3, E6, and E7, see Section ) and the levoglucosan in the smaller particles (prevalent in E4 and E5, see Section ), which results in a more efficient removal of BC and a less efficient removal of levoglucosan in the summer (E4 and E5) . However, other factors could have influenced the observed ratios as well, such as the type of fuel burnt and if the fire was smoldering or flaming. , As such, the higher contribution of organic material in form of levoglucosan during E4 and E5 could indicate smoldering fires, whereas during the remaining events the larger contribution of eBC might suggest flaming fires . As our observations are quite far away from the potential source region of the fires (Section ), the air mass for each event might have experienced different atmospheric conditions during transport, which include varying amounts of oxidants to which the air mass was exposed during the time of transport and could explain the different ratios as well.…”

“… 72 However, other factors could have influenced the observed ratios as well, such as the type of fuel burnt and if the fire was smoldering or flaming. 73 , 74 As such, the higher contribution of organic material in form of levoglucosan during E4 and E5 could indicate smoldering fires, whereas during the remaining events the larger contribution of eBC might suggest flaming fires. 74 As our observations are quite far away from the potential source region of the fires ( Section 3.6 ), the air mass for each event might have experienced different atmospheric conditions during transport, which include varying amounts of oxidants to which the air mass was exposed during the time of transport and could explain the different ratios as well.…”