Field measurements of trace gases and aerosols emitted by peat fires in Central Kalimantan, Indonesia, during the 2015 El Nino

Abstract. Peat fires in Southeast Asia have become a major annual source of trace gases and particles to the regional–global atmosphere. The assessment of their influence on atmospheric chemistry, climate, air quality, and health has been uncertain partly due to a lack of field measurements of the smoke characteristics. During the strong 2015 El Niño event we deployed a mobile smoke sampling team in the Indonesian province of Central Kalimantan on the island of Borneo and made the first, or rare, field measurements of trace gases, aerosol optical properties, and aerosol mass emissions for authentic peat fires burning at various depths in different peat types. This paper reports the trace gas and aerosol measurements obtained by Fourier transform infrared spectroscopy, whole air sampling, photoacoustic extinctiometers (405 and 870 nm), and a small subset of the data from analyses of particulate filters. The trace gas measurements provide emission factors (EFs; grams of a compound per kilogram biomass burned) for up to  ∼  90 gases, including CO2, CO, CH4, non-methane hydrocarbons up to C10, 15 oxygenated organic compounds, NH3, HCN, NOx, OCS, HCl, etc. The modified combustion efficiency (MCE) of the smoke sources ranged from 0.693 to 0.835 with an average of 0.772 ± 0.053 (n  =  35), indicating essentially pure smoldering combustion, and the emissions were not initially strongly lofted. The major trace gas emissions by mass (EF as g kg−1) were carbon dioxide (1564 ± 77), carbon monoxide (291 ± 49), methane (9.51 ± 4.74), hydrogen cyanide (5.75 ± 1.60), acetic acid (3.89 ± 1.65), ammonia (2.86 ± 1.00), methanol (2.14 ± 1.22), ethane (1.52 ± 0.66), dihydrogen (1.22 ± 1.01), propylene (1.07 ± 0.53), propane (0.989 ± 0.644), ethylene (0.961 ± 0.528), benzene (0.954 ± 0.394), formaldehyde (0.867 ± 0.479), hydroxyacetone (0.860 ± 0.433), furan (0.772 ± 0.035), acetaldehyde (0.697 ± 0.460), and acetone (0.691 ± 0.356). These field data support significant revision of the EFs for CO2 (−8 %), CH4 (−55 %), NH3 (−86 %), CO (+39 %), and other gases compared with widely used recommendations for tropical peat fires based on a lab study of a single sample published in 2003. BTEX compounds (benzene, toluene, ethylbenzene, xylenes) are important air toxics and aerosol precursors and were emitted in total at 1.5 ± 0.6 g kg−1. Formaldehyde is probably the air toxic gas most likely to cause local exposures that exceed recommended levels. The field results from Kalimantan were in reasonable agreement with recent lab measurements of smoldering Kalimantan peat for “overlap species,” lending importance to the lab finding that burning peat produces large emissions of acetamide, acrolein, methylglyoxal, etc., which were not measurable in the field with the deployed equipment and implying value in continued similar efforts. The aerosol optical data measured include EFs for the scattering and absorption coefficients (EF Bscat and EF Babs, m2 kg−1 fuel burned) and the single scattering albedo (SSA) at 870 and 405 nm, as well as the absorption Ångström exponents (AAE). By coupling the absorption and co-located trace gas and filter data we estimated black carbon (BC) EFs (g kg−1) and the mass absorption coefficient (MAC, m2 g−1) for the bulk organic carbon (OC) due to brown carbon (BrC). Consistent with the minimal flaming, the emissions of BC were negligible (0.0055 ± 0.0016 g kg−1). Aerosol absorption at 405 nm was  ∼  52 times larger than at 870 nm and BrC contributed  ∼  96 % of the absorption at 405 nm. Average AAE was 4.97 ± 0.65 (range, 4.29–6.23). The average SSA at 405 nm (0.974 ± 0.016) was marginally lower than the average SSA at 870 nm (0.998 ± 0.001). These data facilitate modeling climate-relevant aerosol optical properties across much of the UV/visible spectrum and the high AAE and lower SSA at 405 nm demonstrate the dominance of absorption by the organic aerosol. Comparing the Babs at 405 nm to the simultaneously measured OC mass on filters suggests a low MAC ( ∼  0.1) for the bulk OC, as expected for the low BC/OC ratio in the aerosol. The importance of pyrolysis (at lower MCE), as opposed to glowing (at higher MCE), in producing BrC is seen in the increase of AAE with lower MCE (r2 =  0.65)

Gaseous, PM2.5 Mass, and Speciated Emission Factors from Laboratory Chamber Peat Combustion

Peat fuels representing four biomes of boreal (western Russia and Siberia), temperate (northern Alaska, USA), subtropical (northern and southern Florida, USA), 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 EFCO2 (carbon dioxide) are highest (1400 +/- 38 g kg(-1)) and lowest (1073 +/- 63 g kg(-1)) for the Alaskan and Russian peats, respectively. EFCO (carbon monoxide) and EFCH4 (methane) are similar to 12 %15 % and similar to 0.3 %0.9 % of EFCO2, in the range of 157171 and 310 g kg(-1), respectively. EFs for nitrogen species are at the same magnitude as EFCH4, with an average of 5.6 +/- 4.8 and 4.7 +/- 3.1 g kg(-1) for EFNH3 (ammonia) and EFHCN (hydrogen cyanide); 1.9+/-1.1 g kg(-1) for EFNOx (nitrogen oxides); and 2.4+/-1.4 and 2.0 +/- 0.7 g kg(-1) for EFNOy (total reactive nitrogen) and EFN2O (nitrous oxide). An oxidation flow reactor (OFR) was used to simulate atmospheric aging times of similar to 2 and similar to 7 d to compare fresh (upstream) and aged (downstream) emissions. Filter-based EFPM2.5 varied by \u3e 4-fold (1461 g kg(-1)) without appreciable changes between fresh and aged emissions. The majority of EFPM2.5 consists of EFOC (organic carbon), with EFOC / EFPM2.5 ratios in the range of 52 %98 % for fresh emissions and similar to 14 %23 % degradation after aging. Reductions of EFOC (similar to 79 g kg(-1)) after aging are most apparent for boreal peats, with the largest degradation in low-temperature OC1 that evolves at \u3c 140 degrees C, indicating the loss of high-vapor-pressure semivolatile organic compounds upon aging. The highest EFLevoglucosan is found for Russian peat (similar to 16 g kg(-1)), with similar to 35 %50 % degradation after aging. EFs for water-soluble OC (EFWSOC) account for similar to 20 %62 % of fresh EFOC. The majority (\u3e 95 %) of the total emitted carbon is in the gas phase, with 54 %75 % CO2, 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 similar to 1/3 to 2/3 of the fuel nitrogen measured in biomass smoke. The majority (\u3e 99 %) of the total emitted nitrogen is in the gas phase, with an average of 16.7 % as NH3 and 9.5 % as HCN center dot N2O and NOy constituted 5.7 % and 2.9 % of consumed fuel nitrogen. EFs from this study can be used to refine current emission inventories

Multi year aerosol characterization in the tropical Andes and in adjacent Amazonia using AERONET measurements

This work focuses on the analysis of columnar aerosol properties in the complex geophysical tropical region of South America within 10-20 South and 50-70 West. The region is quite varied and encompasses a significant part of Amazonia (lowlands) as well as high mountains in the Andes (highlands,~4000 m a.s.l.). Several AERONET stations were included to study the aerosol optical characteristics of the lowlands (Rio Branco, Ji Parana and Cuiaba in Brazil and Santa Cruz in Bolivia) and the highlands (La Paz, Bolivia) during the 2000-2014 period. Biomass-burning is by far the most important source of aerosol in the lowlands, particularly during the dry season (August-October). Multi-annual variability was investigated and showed very strong burning activity in 2005, 2006, 2007 and 2010. This resulted in smoke characterized by correspondingly strong, above-average AODs (aerosol optical depths) and homogeneous single scattering albedo (SSA) across all the stations (~0.93). For other years, however, SSA differences arise between the northern stations (Rio Branco and Ji Parana) with SSAs of ~0.95 and the southern stations (Cuiaba and Santa Cruz) with lower SSAs of ~0.85.Such differences are explained by the different types of vegetation burned in the two different regions. In the highlands, however, the transport of biomass burning smoke is found to be sporadic in nature. This sporadicity results in highly variable indicators of aerosol load and type (Angstrom exponent and fine mode fraction) with moderately significant increases in both. Regional dust and local pollution are the background aerosol in this highland region, whose elevation places it close to the free troposphere. Transported smoke particles were generally found to be more optical absorbing than in the lowlands: the hypothesis to explain this is the significantly higher amount of water vapor in Amazonia relative to the high mountain areas. The air-mass transport to La Paz was investigated using the HYSPLIT air-concentration five-days back trajectories. Two different patterns were clearly differentiated: westerly winds from the Pacific that clean the atmosphere and easterly winds favoring the transport of particles from Amazonia.Marie Skłodowska-Curie Individual Fellowships (IF) ACE_GFAT (grant agreement No 659398).European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 654109, ACTRIS-2

Characterizing the 2015 Indonesia fire event using modified MODIS aerosol retrievals

The Indonesian fire and smoke event of 2015 was an extreme episode that affected public health and caused severe economic and environmental damage. The MODIS Dark Target (DT) aerosol algorithm, developed for global applications, significantly underestimated regional aerosol optical depth (AOD) during this episode. The larger-than-global-averaged uncertainties in the DT product over this event were due to both an overly zealous set of masks that mistook heavy smoke plumes for clouds and/or inland water, and also an aerosol model developed for generic global aerosol conditions. Using Aerosol Robotic Network (AERONET) Version 3 sky inversions of local AERONET stations, we created a specific aerosol model for the extreme event. Thus, using this new less-absorbing aerosol model, cloud masking based on results of the MODIS cloud optical properties algorithm, and relaxed thresholds on both inland water tests and upper limits of the AOD retrieval, we created a research algorithm and applied it to 80 appropriate MODIS granules during the event. Collocating and comparing with AERONET AOD shows that the research algorithm doubles the number of MODIS retrievals greater than 1.0, while also significantly improving agreement with AERONET. The final results show that the operational DT algorithm had missed approximately 0.22 of the regional mean AOD, but as much as AOD&thinsp;=&thinsp;3.0 for individual 0.5∘ grid boxes. This amount of missing AOD can skew the perception of the severity of the event, affect estimates of regional aerosol forcing, and alter aerosol modeling and forecasting that assimilate MODIS aerosol data products. These results will influence the future development of the global DT aerosol algorithm.</p

Evolution of Biomass Burning Aerosol Properties During Transport in the Southeast Atlantic Region

Biomass burning (BB) is a major source of absorbing aerosols globally and accounts for about 40% of black carbon in the atmosphere. The Southern African region contributes approximately 35% of the planet’s BB aerosol emissions. During the austral winter and spring, smoke is transported westward towards the southeast Atlantic Ocean, where it overlies and interacts with a quasi-permanent stratocumulus (Sc) cloud deck. Aerosol-cloud-climate interactions contribute the largest uncertainty to model estimates of anthropogenic forcing. The SEA region thus exhibits a large model-to-model divergence of climate forcing due to aerosols. This makes studies in the region particularly valuable for understanding these interactions. Previous studies focusing on Southern Africa BB have explored the distribution of aerosol loading. However, changes in aerosol optical properties during transport are not well documented. This study aims to use remotely sensed observations to investigate the evolution of BB aerosol optical properties after emission within continental Africa, during transport over land, and over the Atlantic Ocean. Measurements taken from a collection of remote-sensing instruments during the ORACLES campaign are combined with results from two regional models, the WRF-AAM and WRF-CAM5, to explore the changes in the optical properties of smoke plumes as they age. The aerosol age is modeled using tracers from the WRF-AAM configured over the region’s spatial domain (14 ºN – 41 ºS, 34 ºW – 51 ºE). The study conducted an analysis of extinction, single scattering albedo (SSA), and extinction Angstrom exponent (EAE) in relation to aerosol age. Additionally, observations from airborne 4STAR, ground-based AERONET were compared with model results using WRF-CAM5. The analysis revealed that aerosol age varied distinctly with longitude and the physical and chemical processes associated with the transport drive changes in the optical properties. The aerosols sampled closest to the source exhibited lower SSA values relative to particles sampled along the coastline. Along the coastline, free tropospheric SSA peaked at about 5-6 days, before gradually decreasing over the ocean, with a minimum value observed after approximately 12 days. SSA was underestimated by WRF-CAM5, and the modeled values are constrained to a narrower range than observations highlighting the importance of improving the representation of mass absorption and extinction in regional climate models

Parameterization of single-scattering albedo (SSA) and absorption Ångström exponent (AAE) with EC/OC for aerosol emissions from biomass burning

Single-scattering albedo (SSA) and absorption Ångström exponent (AAE) are two critical parameters in determining the impact of absorbing aerosol on the Earth\u27s radiative balance. Aerosol emitted by biomass burning represent a significant fraction of absorbing aerosol globally, but it remains difficult to accurately predict SSA and AAE for biomass burning aerosol. Black carbon (BC), brown carbon (BrC), and non-absorbing coatings all make substantial contributions to the absorption coefficient of biomass burning aerosol. SSA and AAE cannot be directly predicted based on fuel type because they depend strongly on burn conditions. It has been suggested that SSA can be effectively parameterized via the modified combustion efficiency (MCE) of a biomass burning event and that this would be useful because emission factors for CO and CO2, from which MCE can be calculated, are available for a large number of fuels. Here we demonstrate, with data from the FLAME-4 experiment, that for a wide variety of globally relevant biomass fuels, over a range of combustion conditions, parameterizations of SSA and AAE based on the elemental carbon (EC) to organic carbon (OC) mass ratio are quantitatively superior to parameterizations based on MCE. We show that the EC/OC ratio and the ratio of EC/(EC + OC) both have significantly better correlations with SSA than MCE. Furthermore, the relationship of EC/(EC + OC) with SSA is linear. These improved parameterizations are significant because, similar to MCE, emission factors for EC (or black carbon) and OC are available for a wide range of biomass fuels. Fitting SSA with MCE yields correlation coefficients (Pearson\u27s r) of ∼0.65 at the visible wavelengths of 405, 532, and 660 nm while fitting SSA with EC/OC or EC/(EC + OC) yields a Pearson\u27s r of 0.94-0.97 at these same wavelengths. The strong correlation coefficient at 405 nm (r = 0.97) suggests that parameterizations based on EC/OC or EC/(EC + OC) have good predictive capabilities even for fuels in which brown carbon absorption is significant. Notably, these parameterizations are effective for emissions from Indonesian peat, which have very little black carbon but significant brown carbon (SSA = 0.990 ± 0.001 at 532 and 660 nm, SSA = 0.937 ± 0.011 at 405 nm). Finally, we demonstrate that our parameterization based on EC/(EC + OC) accurately predicts SSA during the first few hours of plume aging with data from Yokelson et al. (2009) gathered during a biomass burning event in the Yucatán Peninsula of Mexico