Trace gas emissions from combustion of peat, crop residue, domestic biofuels, grasses, and other fuels: configuration and Fourier transform infrared (FTIR) component of the fourth Fire Lab at Missoula Experiment (FLAME-4)

摘要

During the fourth Fire Lab at Missoula Experiment (FLAME-4, October–November2012) a large variety of regionally and globally significant biomass fuelswas burned at the US Forest Service Fire Sciences Laboratory in Missoula,Montana. The particle emissions were characterized by an extensive suite ofinstrumentation that measured aerosol chemistry, size distribution, opticalproperties, and cloud-nucleating properties. The trace gas measurementsincluded high-resolution mass spectrometry, one- and two-dimensional gaschromatography, and open-path Fourier transform infrared (OP-FTIR)spectroscopy. This paper summarizes the overall experimental design forFLAME-4 – including the fuel properties, the nature of the burn simulations,and the instrumentation employed – and then focuses on the OP-FTIR results. TheOP-FTIR was used to measure the initial emissions of 20 trace gases:CO, CO, CH, CH, CH, CH,HCHO, HCOOH, CHOH, CHCOOH, glycolaldehyde, furan, HO, NO,NO, HONO, NH, HCN, HCl, and SO. These species include mostof the major trace gases emitted by biomass burning, and for several of thesecompounds, this is the first time their emissions are reported for importantfuel types. The main fire types included African grasses, Asian rice straw,cooking fires (open (three-stone), rocket, and gasifier stoves), Indonesian andextratropical peat, temperate and boreal coniferous canopy fuels, US cropresidue, shredded tires, and trash. Comparisons of the OP-FTIR emissionfactors (EFs) and emission ratios (ERs) to field measurements of biomassburning verify that the large body of FLAME-4 results can be used to enhancethe understanding of global biomass burning and its representation inatmospheric chemistry models.Crop residue fires are widespread globally and account for the most burnedarea in the US, but their emissions were previously poorly characterized.Extensive results are presented for burning rice and wheat straw: two majorglobal crop residues. Burning alfalfa produced the highest average NHEF observed in the study (6.63 ± 2.47 g kg), while sugar canefires produced the highest EF for glycolaldehyde (6.92 g kg) andother reactive oxygenated organic gases such as HCHO, HCOOH, andCHCOOH. Due to the high sulfur and nitrogen content of tires, theyproduced the highest average SO emissions (26.2 ± 2.2 g kg)and high NO and HONO emissions. High variability wasobserved for peat fire emissions, but they were consistently characterizedby large EFs for NH (1.82 ± 0.60 g kg) and CH(10.8 ± 5.6 g kg). The variability observed in peat fire emissions,the fact that only one peat fire had previously been subject to detailedemissions characterization, and the abundant emissions from tropicalpeatlands all impart high value to our detailed measurements of theemissions from burning three Indonesian peat samples. This study alsoprovides the first EFs for HONO and NO for Indonesian peat fires. Opencooking fire emissions of HONO and HCN are reported for the first time, andthe first emissions data for HCN, NO, NO, HONO, glycolaldehyde, furan,and SO are reported for "rocket" stoves: a common type of improvedcookstove. The HCN / CO emission ratios for cooking fires (1.72 × 10 ± 4.08 × 10)and peat fires (1.45 × 10 ± 5.47 × 10)are well below and above thetypical values for other types of biomass burning, respectively. This wouldaffect the use of HCN / CO observations for source apportionment in someregions. Biomass burning EFs for HCl are rare and are reported for the firsttime for burning African savanna grasses. High emissions of HCl were alsoproduced by burning many crop residues and two grasses from coastalecosystems. HCl could be the main chlorine-containing gas in very freshsmoke, but rapid partitioning to aerosol followed by slower outgassingprobably occurs.