典型阔叶和针叶生物质燃烧萜烯类化合物排放特征

Emission of terpenoids from typical deciduous and coniferous biomass burning

萜烯类化合物是臭氧和二次有机气溶胶(SOA)的重要前体物.生物质燃烧是除生物源以外最重要的萜烯类化合物排放源.针对生物质燃烧萜烯类化合物的排放特征与排放机制,本研究以典型阔叶树种尾叶桉和针叶树种马尾松的燃烧为研究对象,开展燃烧模拟实验和热重分析实验.采用Tenax-TA吸附管采集烟气中的萜烯类化合物,并通过热脱附-气相色谱质谱联用仪(TD-GC-MS)进行分析.燃烧模拟实验结果表明,马尾松和尾叶桉燃烧排放萜烯的平均排放因子分别为(427.1±109.5)mg·kg^(-1)和(111.18±10.11)mg·kg^(-1),马尾松的平均排放因子是尾叶桉的4倍左右.萜烯类化合物中异戊二烯占比最高,其次是α-蒎烯.与其他研究相比,尾叶桉和马尾松燃烧的萜烯与CO、乙腈的排放比较低.空气气氛下的热重分析实验发现,尾叶桉和马尾松的燃烧过程均可划分为5个阶段,即脱水、蒸馏、吸热热解、放热热解、残碳生成.单萜烯的排放受燃烧阶段影响较大,随着燃烧的进行,排放浓度逐渐升高.总体而言,热解和残碳生成阶段的排放浓度比脱水和蒸馏阶段高,但单萜烯的单位失重排放量却是在蒸馏阶段最高.相比树枝和树皮,树叶的排放浓度和单位失重排放量最高,而且新鲜树叶的排放比枯叶高.本研究结果能够为排放清单的制定提供数据支持,并对未来研究森林火灾对萜烯类化合物的排放特征和环境影响具有参考意义.

Terpenoids are important precursors of ozone and secondary organic aerosol(SOA).Biomass burning is the most important emission source of terpenoids besides biogenic sources.This study investigated the emissions of terpenoids from the burning of typical deciduous and coniferous biomass,which were Eucalyptus urophylla and Pinus massoniana.Simulated burning experiments and thermo-gravimetric analysis were conducted,and terpenoids in the smoke were sampled in Tenax-TA adsorption tubes and analyzed by a Thermal-Desorption-Gas Chromatography-Mass Spectrometry(TD-GC-MS).The average emission factor of terpenoids from burning Pinus massoniana was 4 times higher than that from burning Eucalyptus urophylla,which were(111.18±10.11)mg·kg^(-1)and(427.1±109.5)mg·kg^(-1),respectively.Isoprene was the most emitted among terpenoids,followed byα-pinene.Emission ratios of terpenoids to CO and acetonitrile in this study were lower than in previous studies.From the results of thermo-gravimetric analysis under the air atmosphere,the burning process of the biomasses exhibited five stages,including dehydration,distillation,endothermic pyrolysis,exothermic pyrolysis,and charcoal formation.The emissions of monoterpenes largely varied with burning stages.The emission concentration increased as the burning progressed,with the highest concentrations in the pyrolysis and charcoal formation stages.However,the monoterpenes emissions per weight loss were the highest in the distillation stage.Leaves had higher emissions compared to branches and barks,and fresh leaves had higher emissions than leaf litter.These findings contribute to emission inventory data for terpenoids and can guide future research on the environmental impact of terpenoid emissions from forest fires.