Severe haze events with exceedingly high-levels of fine aerosols occur frequently over the past decades in the North China Plain (NCP), exerting profound impacts on human health, weather, and climate. The development of effective mitigation policies requires a comprehensive understanding of the haze formation mechanisms, including identification and quantification of the sources, formation, and transformation of the aerosol species. Haze evolution in this region exhibits distinct physical and chemical characteristics from clean to polluted periods, as evident from increasing stagnation and relative humidity, but decreasing solar radiation as well as explosive secondary aerosol formation. The latter is attributed to highly elevated concentrations of aerosol precursor gases and is reflected by rapid increases in the particle number and mass concentrations, both corresponding to nonequilibrium chemical processes. Considerable new knowledge has been acquired to understand the processes regulating haze formation, particularly in light of the progress in elucidating the aerosol formation mechanisms. This review synthesizes recent advances in understanding secondary aerosol formation, by highlighting several critical chemical/physical processes, that is, new particle formation and aerosol growth driven by photochemistry and aqueous chemistry as well as the interaction between aerosols and atmospheric stability. Current challenges and future research priorities are also discussed.

Cooking has been proven to be a significant source of primary organic aerosol, especially in megacities. However, the formation of secondary organic aerosol (SOA) derived from cooking emissions is still poorly understood. In this work, four prevalent Chinese domestic cooking types involving complicated cuisines and various cooking methods were chosen to conduct a lab simulation for SOA formation using a Gothenburg potential aerosol mass reactor (Go: PAM). After samples had been aged under OH exposures of 4.3–27.1 × 1010 molecules cm–3 s, the domestic cooking SOA was characterized by mass growth potentialities (1.81–3.16), elemental ratios (O/C = 0.29–0.41), and mass spectra. Compared with other organic aerosol (OA), domestic cooking SOA is a kind of less oxidized oxygenated OA (LO-OOA) with a unique oxidation pathway (alcohol/peroxide pathway) and mass spectra (characteristic peaks at m/z 28, 29, 41, 43, 44, 55, and 57). This study is expected to identify the cooking SOA under actual cooking conditions, which could contribute to the formulation of pollution source control as well as the health risk assessment of exposure to cooking fumes.

The variations in physicochemical properties of airborne particles collected during a typical transition from haze to dust were investigated using single particle analysis with transmission and scanning electron microscopes combined with online measurement of chemical compositions of airborne particles in Beijing in February 2013. The transition was divided into three phases based on the weather condition. During haze pollution (Phase 1), gaseous and particle pollutants enhanced gradually. Results from single particle analysis showed that more coatings and more anthropogenic elements (e.g., S) appeared on the surface of fine and coarse particles, which was probably caused by efficient aqueous-phase reactions under high humidity (70%) condition. Phase 2 was dust intrusion episode. PM10 reached over 1000 mu g m(-3). Larger fractions of mineral particles and bare-like soot particles were observed in fine particles, while the fraction of secondary particles with coatings decreased. The proportion of black carbon in submicron particles also increased. Photochemical oxidation in gas phase likely dominated in secondary formation under high O-3 concentration. After the dust episode (Phase 3), secondary formation enhanced obviously. Soot aged quickly and had a larger mode of 0.45 mu m than the other phases. The size modes of airborne fine particles during Phases 1 and 3 were 0.35 mu m, which were a bit larger than that during Phase 2 (0.24 mu m). These results indicate that dust plumes accompanied with strong wind brought mineral particles in both fine and coarse modes and freshly emitted particles with smaller sizes, and swept away pre-presence air pollutants. This study could provide detailed information on the physicochemical properties of airborne particles during typical severe pollution processes in a short time. Such short-term change should be taken into account in order to more accurately assess the environmental, climatic and health-related effects of airborne particles.

为探讨华北地区秋冬季重污染过程PM2.5（细颗粒物）中PAHs（多环芳烃）的污染水平、分布特征及来源,分别采集2018年11月17日—2019年1月19日德州市和北京市PM2.5样品利用气相色谱-质谱法测量两个站点6次重污染过程中26种PAHs浓度水平,分析PAHs污染特征、分子组成分布及其来源,并利用毒性当量因子估算了PAHs毒性.结果表明:①6次重污染过程中德州站点∑26PAHs浓度为62～191 ng/m3北京站点为61～129 ng/m3.②单位质量PM2.5中PAHs的浓度北京站点更高.③两个站点PAHs分子组成分布较为一致,萘、蒽、芴等低分子量的PAHs浓度较低,高分子量PAHs浓度较高,浓度最高的分别为苯并[b]荧蒽、苯并[a]芘、苯并[a]蒽和甲基荧蒽等.④特征比值结果显示,PAHs来源包括柴油车尾气、燃煤和生物质燃烧,德州站点受生物质燃烧影响更为显著.⑤毒性当量计算结果表明,德州站点毒性当量浓度（TEQ）高于北京站点,6次重污染过程中两个站点PAHs的TEQ平均值在6.5～17.2 ng/m3之间,低于国内其他一些地区,但苯并[a]芘的浓度在5.2～13.1 ng/m3之间,超过了GB 3095—2012《环境空气质量标准》日均值的标准限值（2.5 ng/m3）,对人体健康存在潜在危害.研究显示:秋冬季重污染过程中北京站点单位质量PM2.5中PAHs的浓度较高,两个点位PAHs分子组成分布特征及来源较为相似且均对人体健康存在潜在危害;应进一步加强对PAHs浓度水平的控制这不仅有利于持续改善PM2.5污染,也有助于减轻人体潜在的健康风险.

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.

 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.

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.