珠江三角洲热带亚热带植物排放氯甲烷观测研究

As an ozone depleting substance, methyl chloride (CH3Cl) is the most abundant chlorine-containing compound in the atmosphere, and contributes 16% to the total chlorine from long-lived gases in the troposphere. Accurate estimation of global CH3Cl emission is vital to evaluate the amount of reactive chlorine and its capacity in destroying stratospheric ozone. Previous studies revealed that CH3Cl was largely from tropical and subtropical plants, but large uncertainties still exist in the CH3Cl emission from tropical and subtropical sources. At present, relatively high levels of ambient CH3Cl were observed in the Pearl River Delta region. The present study is targeted on CH3Cl in this tropical/subtropical region, and plans to measure CH3Cl emission factors from living plants by dynamic enclosure method and emission fluxes of CH3Cl from forest litters by static chamber method. High resolution selective reagent ionization proton transfer reaction time of flight mass spectrometry (HR-SRI-PTR-TOF-MS) will be employed to on-line monitoring of CH3Cl variations when measuring the emission. To determine factors influencing emission fluxes, parameters such as temperature, relative humidity, pressure, photosynthetically active radiation (PAR) were also determined during field experiments. The study would benefit better understanding of CH3Cl emission in tropical/subtropical regions and narrowing the uncertainties of its regional and global emission estimates.

氯甲烷（CH3Cl）是一种破坏臭氧层物质，是大气中浓度最高的含氯有机物，贡献了大气中长寿命气体总氯量的16%，正确估算氯甲烷排放量对评价大气中反应性氯原子的含量及对臭氧层破坏能力有重要意义。研究表明热带亚热带植物是氯甲烷最大的排放源，然而全球对于氯甲烷这一排放源的估算有很大不确定性。当前珠江三角洲地区是氯甲烷的高值区。本项目拟在珠江三角洲热带亚热带森林地区选取典型植物，运用高分辨多离子源质子转移反应飞行时间质谱（HR-SRI-PTR -TOF-MS）等先进在线测量技术，用动态包裹法测定活体植物氯甲烷排放因子，用静态箱法测定森林凋落物氯甲烷排放通量，并通过实验过程中同步测量温度、湿度、气压、光等参数条件，探讨氯甲烷排放的影响因素及其规律性。研究工作对深入认识氯甲烷排放源特征、减小区域和全球氯甲烷排放估算量的不确定性有较重要的意义。

氯甲烷是一种破坏臭氧层物质，是大气中浓度最高的含氯有机化合物，贡献了大气中长寿命气体总含氯量的16%，正确估算大气中氯甲烷排放量对评价大气中反应性氯的含量及对臭氧层破坏能力有重要意义。前期研究表明热带亚热带地区植物排放是氯甲烷最大的排放源，然而全球对于氯甲烷这一排放源的估算有很大不确定性。对于处在热带亚热带地区的珠江三角洲，前期一些研究都发现这一地区大气氯甲烷浓度远高于全球本底水平，本项目在珠三角地区通过定点长期观测获得热带亚热带地区大气中氯甲烷年际变化趋；通过网格化多点同步观测揭示了珠三角地区氯甲烷浓度的时空分布特征及排放热点区域；并进一步通过在全国14个站点的长达两年的同步观测，揭示了氯甲烷在整个中国的时空分布特征和季节变化特征；并通过氯甲烷与植物排放源标志物BVOCs、燃烧源标志物一氧化碳等其他典型排放源标志物的相关性初步对其来源进行判识；发现在北方一些站点冬季浓度水平较高且与一氧化碳有较强相关性，因而通过对比采样站点供暖燃煤时段与非燃煤阶段大气中氯甲烷浓度水平，发现燃煤阶段大气中氯甲烷浓度水平均高于非燃煤阶段；为了排除气象条件的影响，更进一步通过测定不同种类原煤燃烧证实在燃煤燃烧过程中对大气中氯甲烷有重要贡献，并且通过对比原煤在明火燃烧阶段和闷烧阶段排放到大气中的氯甲烷浓度，发现闷烧阶段原煤燃烧排放到大气中氯甲烷高于明火燃烧阶段的排放。通过此次定点长期观测、区域网格化观测和多点长时间同步观测研究获得了一系列有重要科学意义的野外实地观测数据和源谱排放数据，为进一步估算区域及全国氯甲烷排放量及其在全球排放量中所占地位提供坚实的基础数据。