Tropical peat fire emissions: 2019 field measurements in Sumatra and Borneo and synthesis with previous studies

Abstract

Abstract. Peat fires in Southeast Asia are a major source of trace gases and particles to the regional-global atmosphere that influence atmospheric chemistry, climate, and air quality. During the November 2015 record-high Ocean Niño Index (ONI, 2.6) our mobile smoke sampling team made the first, or rare, field measurements of numerous trace gases, aerosol optical properties, and aerosol chemistry and mass emissions for fires burning only peat in the Indonesian province of Central Kalimantan (on the island of Borneo). The measurements used Fourier transform infrared spectroscopy (FTIR), whole air sampling (WAS), photoacoustic extinctiometers (PAX, 401 and 870 nm), and detailed off-line analyses of particulate matter (PM) collected on filters. In September–November 2019 we measured peat fire trace gas emissions again, using WAS only, under El Niño–Southern Oscillation (ENSO)-neutral conditions (ONI, 0.3) in more remote areas of Central Kalimantan and also the Indonesian provinces of Riau, Jambi, and South Sumatra, all on the island of Sumatra. The 2019 measurements significantly expanded the geographic range and climate conditions sampled. This paper presents the 2019 results and synthesizes them with the previous fieldwork to converge on more robust regional average emission factors (EFs; grams of compound per kilogram of biomass burned) for authentic peat fires. In addition, samples of peat imported from Indonesia were burned in US laboratories, and the EFs and optical properties were characterized in more detail than in the field by a larger suite of instrumentation. We use the improved knowledge of regional emissions based on the expanded field measurements to select the most representative lab data and compute a synthesized, more “chemically complete” set of EFs and aerosol optical properties for tropical peat fires. The modified combustion efficiency (MCE) values for the peat smoke sampled in 2019 were within the range of MCEs sampled in 2015, but with a lower average in 2019 (0.718±0.021, range 0.687–0.736) than 2015 (0.772±0.035, range 0.693–0.835). Averaging the new and older data together suggests an updated MCE for tropical peat fires of ∼0.76. Despite the difference in MCE, the study-average methane emission factors (EF CH4) were remarkably similar across the 2 years probing different regions: 9.42±2.51 g kg−1 in 2019 and 9.51±4.74 g kg−1 in 2015. When parsing the 2019 samples by province, the EFs for non-methane organic gases (NMOGs) were about 3 times higher in South Sumatra and Central Kalimantan than in Jambi and Riau, but the overall 2019 study average was only ∼15 % higher than the 2015 study average. South Sumatra peat fires emitted higher amounts of carbonyl and dimethyl sulfide, suggesting a volcanic or marine influence or effects of agricultural chemicals. The lab and fieldwork taken together provide EFs for 230 trace gases including CO2 (1544 g kg−1), CO (315 g kg−1), and CH4 (9.8 g kg−1). These are significant adjustments to IPCC-recommended EFs, −9 %, +50 %, and −53 %, respectively. We also report EFs for numerous NMOGs, 46 N-containing compounds, and 14 sulfur- or halogen-containing species. The use of high-resolution mass spectrometry in the lab allowed measurement of 82 % more NMOG mass than in the field. Gravimetrically measured EF PM2.5 in the field in 2015 (17.3±5.8 g kg−1) was ∼20 % lower than the average from lab studies (22.4±10.4 g kg−1), perhaps due to higher field temperatures. Taken together the lab and field data show that the single-scattering albedo (SSA) was largely independent of wavelength and MCE in the visible (∼0.998), but lower at low MCE at 401 and 405 nm with a value of 0.958 at the study-average MCE. The absorption Ångström exponent (AAE) at the average MCE was 5.7. By far the largest PM component was weakly absorbing insoluble organic carbon.

Neutralization of Anthropogenic Acidic Particles by NH3 From Wildfire Over Tropical Peatland

“…These figures demonstrate that peatland fire in Sumatra and Kalimantan islands served as intense point sources of NH 3 during the haze periods. It should be noted that emission factor of NH 3 in GFED (1.33 g kg −1 ) is a few times lower than that has been estimated by recent field observations, meaning that NH 3 emission shown in Figure S3 of Supporting Information may be underestimating the actual emission (Stockwell et al., 2016; van der Werf et al., 2010; Yokelson et al., 2022).…”

“…Wildfire in Indonesia was dominantly occurring during July‐October, associated with the seasonal cycle in precipitation of the region (Kuwata et al., 2021; Latif et al., 2018; Reid et al., 2012). Wildfire activity in Indonesia was intense in 2015 and 2019, as El Niño occurred in the corresponding years (Budisulistiorini et al., 2017; Crippa et al., 2016; Yokelson et al., 2022). In fact, the fire activity over Indonesia in 2015 was the most intense fire event in 2010s’ (Field et al., 2016; Latif et al., 2018).…”

“…Both in situ and remote sensing observations demonstrated that combustion of peat emits pronounced amount of basic gas species such as NH 3 and amines (Stockwell et al., 2014; Yokelson et al., 2022). For instance, an in situ observation at Central Kalimantan in Indonesia demonstrated that emission factor of NH 3 from peatland fire was 2.86 ± 1 g kg −1 (Stockwell et al., 2016).…”

Detecting the sensitivity of water content and deficiency rainfall during positive Indian Ocean Dipole events

“…The gas emission factor for non-methane organic in South Sumatra and Central Kalimantan was three times higher than in Jambi and Riau. In general, the average study in 2019 was only 15 % higher than the average study in 2015 [11]. The raised combustion vulnerability was predominantly initiated when the groundwater table dropped less than 40 cm and flamed when lower than 60 cm [12].…”

Emissions and Atmospheric Chemistry of Furanoids from Biomass Burning: Insights from Laboratory to Atmospheric Observations

“…observations for a wide variety of fuels described in Table . Similarly, GC-MS has been deployed on ground and mobile platforms to quantify furan, furanaldehydes, methylated furanoids, and benzofurans. ,,,,,,,− …”