黑碳颗粒物是人类活动排放到大气中的重要温室物种, 但对其气候效应的认知仍然存在很大的不确定性.老化过程对黑碳颗粒物性质的改变, 是造成这种不确定性的重要来源. 针对黑碳老化这一研究热点, 本文综述了国内外基于实验室和外场研究的进展, 从影响黑碳微观性质的角度出发, 总结梳理了老化过程对黑碳混合态, 包括形貌和化学组分的影响, 并在此基础上, 探讨了与气候效应相关的黑碳颗粒物的吸光性、吸湿性、云凝结核与冰核活性在老化过程中的变化. 伴随着老化过程的进行, 黑碳颗粒物由初始的外混态向内混态转变, 形貌由枝杈状结构经填充-塌缩-持续被包裹的过程逐渐演变成近似球形的核壳结构. 黑碳颗粒物中的化学组分在排放初期会受到共同排放组分的影响, 并在老化过程中表现出二次组分增加的趋势. 由于包裹物在黑碳外层的累积, 老化过程会导致黑碳颗粒物吸光性的增强, 但增强倍数受到包裹物厚度、形貌和化学组分的共同影响. 并且, 在讨论颗粒物群体的吸光增强倍数时, 黑碳颗粒物之间混合态的非均一性也需要纳入考虑. 老化过程会增强黑碳颗粒物的吸湿性与云凝结核活性, 这与包裹物本身的性质密切相关, 但相关的外场研究还十分缺乏. 针对黑碳颗粒物是否具有冰核活性以及老化过程是否会改变其活性的问题, 现有研究仍然没有定论. 在此基础上, 本文提出了黑碳老化未来的研究方向: 探究真实燃烧条件下不同来源黑碳颗粒物的理化特性与老化特征; 在不同大气环境中开展综合观测, 识别出复杂大气条件下影响黑碳老化的关键因素; 推动黑碳老化促进区域大气污染的机制研究; 加强黑碳颗粒物与间接气候效应相关的性质研究.

 大气二次有机气溶胶是PM2.5 的主要组分,  具有重要的环境和气候效应.  在其主要生成途径中,  气溶胶液态水中的液相生成是当前大气化学研究领域的前沿科学问题之一.  液相二次有机气溶胶(aqueous secondary organic aerosol, aqSOA) 前体物通过摄取进入湿气溶胶后,  参与气溶胶内部的液相反应,  生成有机硫、 有机氮等aqSOA.  本文对aqSOA 前体物的摄取过程、 生成的化学机制以及当前主要的研究手段进行详细总结,  并对该领域未来研究进行展望. aqSOA 前体物的摄取受到相对湿度、 气溶胶水溶性等因素的影响,  从而影响其进入气溶胶的后续反应.aqSOA 生成的化学机制可分为自由基反应和非自由基反应,  其中,  自由基反应以OH 自由基液相化学为主;  非自由基反应则多为羰基化合物的液相反应.  近年来,  先进的离线和在线质谱技术的发展推动了对实际环境大气中aq-SOA 生成机制的认识,  并从分子层面识别出aqSOA 产物,  但aqSOA 生成的大气化学过程仍未明晰.  未来研究中,  开发新的分析技术,  扩充aqSOA 反应动力学数据库,  进一步完善模型模拟,  为aqSOA 生成研究提供新思路.

Biomass burning is one of the major sources of carbonaceous aerosols, which affects air quality, the radiation budget and human health. Field straw residue burning is a widespread type of biomass burning in Asia, while its emissions are poorly understood compared with wood burning emissions. In this study, lab-controlled straw (wheat and corn) burning experiments were designed to investigate the emission factors and light absorption properties of different biomass burning organic aerosol (BBOA) fractions, including water-soluble organic carbon (WSOC), humic-like substances (HULIS) and water-insoluble organic carbon (WISOC). The influences of biofuel moisture content and combustion efficiency on emissions are comprehensively discussed. The emission factors of PM2.5, organic carbon (OC) and elemental carbon (EC) were 9.3±3.4, 4.6±1.9 and 0.21±0.07 g kg−1 for corn burning and 8.7±5.0, 3.9±2.8 and 0.22±0.05 g kg−1 for wheat burning, generally lower than wood or forest burning emissions. Though the mass contribution of WISOC to OC (32 %–43 %) was lower than WSOC, the light absorption contribution of WISOC (57 %–84 % at 300–400 nm) surpassed WSOC due to the higher mass absorption efficiency (MAE) of WISOC. The results suggested that BBOA light absorption would be largely underestimated if only the water-soluble fractions were considered. However, the light absorption of WSOC in the near-UV range, occupying 39 %–43 % of the total extracted OC absorption at 300 nm, cannot be negligible due to the sharper increase of absorption towards shorter wavelengths compared with WISOC. HULIS were the major light absorption contributors to WSOC, due to the higher MAE of HULIS than other high-polarity WSOC components. The emission levels and light absorption of BBOA were largely influenced by the burning conditions, indicated by modified combustion efficiency (MCE) calculated by measured CO and CO2 in this study. The emission factors of PM2.5, OC, WSOC, HULIS and organic acids were enhanced under lower MCE conditions or during higher moisture straw burning experiments. Light absorption coefficients of BBOA at 365 nm were also higher under lower MCE conditions, which was mainly due to the elevated mass emission factors. Our results suggested that the influence of varied combustion efficiency on particle emissions could surpass the differences caused by different types of biofuels. Thus, the burning efficiency or conditions should be taken into consideration when estimating the influence of biomass burning. In addition, we observed that the ratios of K+/OC">K+/OC and Cl-/OC">Cl−/OC increased under higher MCE conditions due to the enhancement of potassium and chlorine released under higher fire temperatures during flaming combustion. This indicates that the potassium ion, as a commonly used biomass burning tracer, may lead to estimation uncertainty if the burning conditions are not considered.