Gaseous, PM<sub>2.5</sub> Mass, and Speciated Emission Factors from Laboratory Chamber Peat Combustion

Abstract

<p><strong>Abstract.</strong> Peat fuels representing four biomes of boreal (western Russia and Siberia), temperate (northern Alaska, U.S.A.), subtropical (northern and southern Florida, U.S.A), and tropical (Borneo, Malaysia) regions were burned in a laboratory chamber to determine gas and particle emission factors (EFs). Tests with 25 % fuel moisture were conducted with predominant smoldering combustion conditions (average modified combustion efficiency [MCE] = 0.82 ± 0.08). Average fuel-based EFCO<sub>2</sub> (carbon dioxide) are highest (1400 ± 38 g kg<sup>−1</sup>) and lowest (1073 ± 63 g kg<sup>−1</sup>) for the Alaskan and Russian peats, respectively. EFCO (carbon monoxide) and EFCH<sub>4</sub> (methane) are ~12 %‒15 % and ~0.3 %‒0.9  % of EFCO<sub>2</sub>, in the range of 157‒171 g kg<sup>−1</sup> and 3‒10 g kg<sup>−1</sup>, respectively. EFs for nitrogen species are at the same magnitude of EFCH<sub>4</sub>, with an average of 5.6 ± 4.8 and 4.7 ± 3.1 g kg<sup>−1</sup> for EFNH<sub>3</sub> (ammonia) and EFHCN (hydrogen cyanide); 1.9 ± 1.1 g kg<sup>−1</sup> for EFNO<sub><i>x</i></sub> (nitrogen oxides); as well as 2.4 ± 1.4 and 2.0 ± 0.7 g kg<sup>−1</sup> for EFNO<sub><i>y</i></sub> (reactive nitrogen) and EFN<sub>2</sub>O (nitrous oxide). An oxidation flow reactor (OFR) was used to simulate atmospheric aging times of ~2 and ~7 days to compare fresh (upstream) and aged (downstream) emissions. Filter-based EFPM<sub>2.5</sub> varied by >4-fold (14‒61 g kg<sup>−1</sup>) without appreciable changes between fresh and aged emissions. The majority of EFPM<sub>2.5</sub> consists of EFOC (organic carbon), with EFOC/EFPM<sub>2.5</sub> ratios in the range of 52 %‒98 % for fresh emissions, and ~15 % degradation after aging. Reductions of EFOC (~7‒9 g kg<sup>−1</sup>) after aging are most apparent for boreal peats with the largest degradation in organic carbon that evolves at <140 °C, indicating the loss of high vapor pressure semi-volatile organic compounds upon aging. The highest EFLevoglucosan is found for Russian peat (~16 g kg<sup>−1</sup>), with ~35 %‒50 % degradation after aging. EFs for water-soluble OC (EFWSOC) accounts for ~20 %‒62 % of fresh EFOC. The majority (>95 %) of the total emitted carbon is in the gas phase with 54 %‒75 % CO<sub>2</sub>, followed by 8 %‒30 % CO. Nitrogen in the measured species explains 24 %‒52 % of the consumed fuel nitrogen with an average of 35 ± 11 %, consistent with past studies that report ~one- to two-thirds of the fuel nitrogen measured in biomass smoke. The majority (>99 %) of the total emitted nitrogen is in the gas phase, with an average of 16.7 % fuel N emitted as NH<sub>3</sub> and 9.5 % of fuel N emitted as HCN. N<sub>2</sub>O and NO<sub><i>y</i></sub> constituted 5.7 % and 2.9 % of consumed fuel N. EFs from this study can be used to refine current emissions inventories.</p>

Changes in PM<sub>2.5</sub> peat combustion source profiles with atmospheric aging in an oxidation flow reactor

“…Group comparisons between fresh and aged samples (Panel A of Table 2) show statistical differences for all but Putnam (FL1) peat (P > 0.94). This is consistent with Watson et al (2019) where atmospheric aging (7 d) reduced organic carbon EFs (i.e., EF OC ) by ∼ 20 %-33 % for all but Putnam (FL1) peats (EF OC remained within ±0.5 %). As OC is a major component of PM 2.5 , no apparent changes in OC and carbon fraction abundances may dictate the lack of statistical differences between the fresh and aged profiles.…”

“…5, most of the NH 3 rapidly diminished after 2 d, with increasing particle-phase NH + 4 and NO − 3 after 7 d. The highest NH 3 -to-PM 2.5 ratios are found for fresh Everglades (FL2) peat profiles (51 %-64 %), ∼ 2-8fold higher than other peats. These high and low NH 3 /PM 2.5 ratios are consistent with the nitrogen contents in peat fuel: 3.93 ± 0.08 % for Everglades and 1.50 ± 0.52 % for Russian peats (Watson et al, 2019).…”

“…The highest OM / OC ratios are found for Russian peat, ranging from 1.6 to 1.7 for fresh profiles and increasing to 2.1-2.2 for aged profiles, consistent with formation of lowvapor-pressure oxygenated compounds in the OFR. Watson et al (2019) report that the Russian peat fuel contains the lowest carbon (44.20 ± 1.01 %) and highest oxygen (38.64 ± 0.78 %) contents among the six peats. The low carbon contents in peat fuel and source profiles are consistent with the lowest sum of species found in Russian peat, with 62 %-64 % and 50 %-52 % of PM 2.5 mass for the fresh and aged profiles, respectively.…”

“…Peatland fires produce long-lasting thick smoke that leads to adverse atmospheric, climate, ecological, and health impacts. Smoke from Indonesian and Malaysian peatlands is a major concern in the countries of southeastern Asia (Wiggins et al, 2018) and elsewhere; it is transported over long distances. Aged peat smoke profiles are likely to differ from fresh emissions, as well as among the different types of peat in other parts of the world.…”

“…Laboratory peat combustion EFs for gaseous carbon and nitrogen species corresponding with the profiles described here, as well as PM 2.5 mass and major chemical species (e.g., carbon and ions), are reported by Watson et al (2019). The PM 2.5 speciated source profiles derive from six peat fuels collected from Odintsovo, Russia; Pskov, Siberia; northern Alaska and Florida, USA; and Borneo, Malaysia, representing boreal, temperate, subtropical, and tropical climate regions.…”