典型生物质燃烧排放酚类有机物的大气液相氧化动力学

生物质燃烧排放有机物是大气二次有机气溶胶(SOA)的重要前体物,但相关反应参数仍较为匮乏。选择其中4种代表性物质,间苯二酚(RES)、4-乙基苯酚(4-EP)、丁香酚(Eug)和2,4,6-三甲基苯酚(Trmp),利用相对速率法测定了其与·OH在液相(云雾条件)中的二级反应动力学参数,并估算了其在实际大气条件下的液相反应寿命。在pH=5.4,T=298 K条件下,测定以上4种前体物液相氧化的二级动力学常数(K)分别为(7.68±0.04)×109,(18.12±0.56)×109,(23.11±0.60)×109,(16.90±0.58)×109 L/(mol·s),所得到的K值不确定性为3.5%~12%。此外,还测定了体系在T=293,288 K时的K值,发现288 K时的K值比298 K时的低了22%~38%,说明温度对于酚类液相反应的双分子速率常数有一定影响。研究还发现,反应过程中前体物浓度为初始值1/2时,pH降低,说明反应过程中可能生成一定量的有机酸;这些化合物在不同情境下使用CAPRAM 3.0多相机制计算得到的大气寿命在数十秒到数十小时之间,进一步说明生物质燃烧排放酚类化合物对SOA的生成贡献值得重视。

KINETICS OF ATMOSPHERIC AQUEOUS-PHASE OXIDATION OF REPRESENTATIVE PHENOLIC COMPOUNDS EMITTED FROM BIOMASS BURNING

The organic compounds emitted from biomass burning are important precursors of atmospheric secondary organic aerosols, but relevant reaction parameters are still relatively lacking. This study selected four representative species, including resorcinol(RES), 4-ethylphenol(4-EP), eugenol(Eug) and 2,4,6-trimethylphenol(Trmp), and used the relative rate method to determine the second-order reaction rate constants of those species against oxidation by the hydroxyl radical in the atmospheric aqueous-phases(such as conditions of fog/cloud droplets), also estimated the liquid phase reaction life under actual atmospheric conditions. The kinetic constants(K) of the four precursors at 298 K, pH=5.4 were(7.68±0.04)×109 L/(mol·s),(18.12±0.56)×109 L/(mol·s),(23.11±0.60)×109 L/(mol·s) and(16.90±0.58)×109 L/(mol·s), respectively. The uncertainties of K values were 3.5%~12%. In addition, the K value at T=293 K and 288 K were also determined, and the values at 288 K were 22%~38% lower than those at 298 K, indicating that temperature had a significant influence on the bimolecular rate constants of those compounds. It was also found that when the precursor was consumed nearly half, the solution pH decreased, suggesting that a certain number of organic acids might be generated during oxidation. The atmospheric lifetimes calculated according to the CAPRAM 3.0 under different scenarios ranged from tens of seconds to tens of hours, indicating that the aqueous-phase oxidation of biomass burning emitted phenolic species had a considerable impact on the secondary organic aerosol formation.