| Formaldehyde(FA)and dicarbonyl compounds(mainly meant glyoxal(GLY)and methylglyoxal(MGLY)in this study)are important oxygenated volatile organic compounds(OVOCs)in the current tropospheric atmosphere.Their chemical properties are very active and contribute to secondary pollution,but their quantity in the atmosphere may be underestimated,and one of the reasons is some emission sources of FA and dicarbonyls are neglected.Biomass burning(BB)may be one of the important primary emission sources,and precursors for FA and dicarbonyls can also be emitted from BB.To understand the contribution of BB to FA and dicarbonyl well,four typical biomasses in southern China were selected as the research object,that is rice straw,sugarcane residue,eucalyptus branch and leaf,and Phyllostachys pubescens branch and leaf.Through open burning tests in the laboratory,emission characteristics of FA and dicarbonyls were analyzed;factors influencing the emissions were discussed;VOC precursors to FA and dicarbonyls were identified,and primary emission factors of biomass open burning and potential secondary formation factor from VOC precursors were estimated.At last,the contribution of BB(including the primary emission and potential secondary formation)to FA and dicarbonyls in Guangdong Province was evaluated.The main results listed below:(1)FA,GLY,and MGLY in flue gas from the burning test in the laboratory were sampled and analyzed by DNPH derivation-HPLC-DAD / QQQ,and the influence of burning condition and biomass type on the emission characteristics were discussed.It’s found that FA has the highest concentration from the burning of rice straw and the lowest from Phyllostachys pubescens burning;Moisture content has a significant effect on the emissions of FA,GLY,and MGLY.Generally,the lower moisture content in the biomass,the less FA and dicarbonyls were emitted,but when the moisture content is less than 10%,the emission would increase;Burning load do not influence the emissions;The emissions are various during burning stages,and the FA concentration is higher during the smoldering than inflaming stage,while the GLY,MGLY and total aldehydes and ketones had opposite trend;the order of the FA,GLY and MGLY emission from different parts of biomass all were leaf and stem mixing> leaf + twigs> trunk >>> wet and dry mixing;had the same order.(2)By DNPH derivation-HPLC-DAD / QQQ and pre-concentrator-GC-FID / MS,46 kinds of volatile organic precursors of FA and dicarbonyls in the flue gas were collected and analyzed.Combined parameter method,the contribution of the secondary formation from the precursors to FA and dicarbonyls are estimated.The results showed that the secondary formation from the precursors contributed much more than the primary emission for FA and dicarbonyls.The dominant species of precursors mainly are ethylene,propylene,ethane,acetaldehyde,acetone,butane,and other low-carbon volatile organic compounds,of which ethylene accounted for about 30%.(3)The primary emission factor(PEF)and potential secondary formation factor(PSFF)were estimated.The range of PEF and PSFF of FA for the four biomasses were 0.08±0.09～0.82±0.41g/kg and 8.72±7.27～19.47±12.16g/kg,respectively.The range of PEF and PSFF of GLY were 0.01±0.01～0.04±0.02g/kg and 6.57±6.74～16.96±10.93g/kg,respectively.The range of PEF and PSFF for MGLY were 0.02±0.01～0.12±0.06 g/kg and 5.41±3.52～55.60±27.45g/kg,respectively.(4)Based on the PEF and PSFF for FA and dicarbonyls,the annual primary emission and potential secondary formation of FA,GLY,and MGLY from straw open burning and forest fires in 2013 to 2018 were estimated.The total amount of FA,GLY,MGLY from primary emissions,and potential secondary formation from straw open burning and forest fire are 20.22±13.33kt/a,16.74±11.36kt/a,and51.50±25.91kt/a in Guangdong Province in 2013～2018,respectively.The emission’s primary emissions and potential secondary formation emitted by BB contributed 3.20～15.61%,6.26～32.68%,and 19.84～60.02%to FA,GLY,and MGLY. |
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