New Tropical Peatland Gas and Particulate Emissions Factors Indicate 2015 Indonesian Fires Released Far More Particulate Matter (but Less Methane) than Current Inventories Imply

Abstract

Deforestation and draining of the peatlands in equatorial SE Asia has greatly increased their flammability, and in September-October 2015 a strong El Niño-related drought led to further drying and to widespread burning across parts of Indonesia, primarily on Kalimantan and Sumatra. These fires resulted in some of the worst sustained outdoor air pollution ever recorded, with atmospheric particulate matter (PM) concentrations exceeding those considered "extremely hazardous to health" by up to an order of magnitude. Here we report unique in situ air quality data and tropical peatland fire emissions factors (EFs) for key carbonaceous trace gases (CO 2 , CH 4 and CO) and PM 2.5 and black carbon (BC) particulates, based on measurements conducted on Kalimantan at the height of the 2015 fires, both at locations of "pure" sub-surface peat burning and spreading vegetation fires atop burning peat. PM 2.5 are the most significant smoke constituent in terms of human health impacts, and we find in situ PM 2.5 emissions factors for pure peat burning to be 17.8 to 22.3 g·kg −1 , and for spreading vegetation fires atop burning peat 44 to 61 g·kg −1 , both far higher than past laboratory burning of tropical peat has suggested. The latter are some of the highest PM 2.5 emissions factors measured worldwide. Using our peatland CO 2 , CH 4 and CO emissions factors (1779 ± 55 g·kg −1 , 238 ± 36 g·kg −1 , and 7.8 ± 2.3 g·kg −1 respectively) alongside in situ measured peat carbon content (610 ± 47 g-C·kg −1 ) we provide a new 358 Tg (± 30%) fuel consumption estimate for the 2015 Indonesian fires, which is less than that provided by the GFEDv4.1s and GFASv1.2 global fire emissions inventories by 23% and 34% respectively, and which due to our lower EF CH4 produces far less (~3×) methane. However, our mean in situ derived EF PM2.5 for these extreme tropical peatland fires (28 ± 6 g·kg −1 ) is far higher than current emissions inventories assume, resulting in our total Remote Sens. 2018, 10, 495; doi:10.3390/rs10040495 www.mdpi.com/journal/remotesensing Remote Sens. 2018, 10, 495 2 of 31 PM 2.5 emissions estimate (9.1 ± 3.5 Tg) being many times higher than GFEDv4.1s, GFASv1.2 and FINNv2, despite our lower fuel consumption. We find that two thirds of the emitted PM 2.5 come from Kalimantan, one third from Sumatra, and 95% from burning peatlands. Using new geostationary fire radiative power (FRP) data we map the fire emissions' spatio-temporal variations in far greater detail than ever before (hourly, 0.05 • ), identifying a tropical peatland fire diurnal cycle twice as wide as in neighboring non-peat areas and peaking much later in the day. Our data show that a combination of greatly elevated PM 2.5 emissions factors, large areas of simultaneous, long-duration burning, and very high peat fuel consumption per unit area made these Sept to Oct tropical peatland fires the greatest wildfire source of particulate matter globally in 2015, furthering evidence for a regional atmospheric pollution impact whose particulate matter component in...

Constraining the Emission of Particulate Matter From Indonesian Peatland Burning Using Continuous Observation Data

“…Journal of Geophysical Research: Atmospheres concentrations of these two categories of particulate matter could range from 6 to 35%, as estimated by comparing the PM 2.5 and PM 10 data observed in Singapore during a wildfire event ( Figure S6). The observed PM and CO ratios at Pekanbaru in 2013 and 2014 were comparable to those observed as a result of peat/peatland fires in Kalimantan in 2015 (Jayarathne et al, 2018;Stockwell et al, 2016;Wooster et al, 2018) as well as the data obtained in Selangor in Malaysia (Roulston et al, 2018). The range of PM and CO ratios also overlaps with an experimental study of Malaysian peat fires (Othman & Latif, 2013).…”

“…Emission factors of the CO observed in peatland and peat burning in the tropical Asian region have been investigated by previous field studies. The emission factors of the CO from peatland and peat burning ranged from 148 to 291 g kg À1 (Christian et al, 2003;Hamada et al, 2013;Huijnen et al, 2016;Matsueda & Inoue, 1999;Nara et al, 2017;Smith et al, 2018;Stockwell et al, 2016;Wooster et al, 2018). These values and the reported enhancement ratios of CO and CO 2 can be translated to modified combustion efficiency (MCE), which is defined as MCE = 1/(1 + CO/CO 2 ) (Yokelson et al, 1996).…”

“…The peatland fire is one of the largest sources of greenhouse gases from wildfires (van der Werf et al, 2017). For instance, Wooster et al (2018) estimated that 692 ± 213 Tg of CO 2 was emitted to the atmosphere from equatorial Asia during a peatland fire event in 2015.…”

“…In addition to greenhouse gases, the peatland burning also emits particulate matter as well as its precursors (Black et al, 2016;Engling et al, 2014;Fujii et al, 2014;Gaveau et al, 2014;Huijnen et al, 2016;Iinuma et al, 2007;Jayarathne et al, 2018;Parker et al, 2016;Roulston et al, 2018;Whitburn et al, 2016;Wooster et al, than 1 K. Aerosol particles emitted by tropical peatland burning influence the cloud formation process over the region (Rosenfeld, 1999). These aerosol particles also influence the health and lives of the people living in the region (Crippa et al, 2016;Koplitz et al, 2016;Kunii et al, 2002).…”

Fires, Smoke Exposure, and Public Health: An Integrative Framework to Maximize Health Benefits From Peatland Restoration

“…Third, emissions factors of OC and BC from tropical peatland burning are uncertain. Information from new field campaigns suggests that our results may be conservative (Roulston et al, 2018;Wooster et al, 2018). Fourth, there is uncertainty in the health impacts, with our estimates based on studies in the U.S. and Europe.…”