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Aerosol composition, oxidation properties, and sources in Beijing: results from the 2014 Asia-Pacific Economic Cooperation summit study

机译：北京的气溶胶成分，氧化性质和来源：2014年亚太经济合作组织峰会研究的结果

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The mitigation of air pollution in megacities remains a greatchallenge because of the complex sources and formation mechanisms of aerosolparticles. The 2014 Asia-Pacific Economic Cooperation (APEC) summit inBeijing serves as a unique experiment to study the impacts of emissioncontrols on aerosol composition, size distributions, and oxidationproperties. Herein, a high-resolution time-of-flight aerosol massspectrometer was deployed in urban Beijing for real-time measurements ofsize-resolved non-refractory submicron aerosol (NR-PM) species from 14 Octoberto 12 November 2014, along with a range of collocated measurements. Theaverage (±σ) PM was 41.6 (±38.9) μg mduring APEC, which was decreased by 53 % compared with that before APEC.The aerosol composition showed substantial changes owing to emissioncontrols during APEC. Secondary inorganic aerosol (SIA: sulfate + nitrate + ammonium)showed significant reductions of 62–69 %,whereas organics presented much smaller decreases (35 %). The results fromthe positive matrix factorization of organic aerosol (OA) indicated thathighly oxidized secondary organic aerosol (SOA) showed decreases similar to those of SIAduring APEC. However, primary organic aerosol (POA) from cooking, traffic, and biomass-burning sources were comparable to those before APEC, indicating thepresence of strong local source emissions. The oxidation properties showedcorresponding changes in response to OA composition. The averageoxygen-to-carbon level during APEC was 0.36 (±0.10), which is lowerthan the 0.43 (±0.13) measured before APEC, demonstrating a decreasein the OA oxidation degree. The changes in size distributions of primary andsecondary species varied during APEC. SIA and SOA showed significantreductions in large accumulation modes with peak diameters shifting from~ 650 to 400 nm during APEC, whereas those of POA remainedrelatively unchanged. The changes in aerosol composition, sizedistributions, and oxidation degrees during the aging processes were furtherillustrated in a case study of a severe haze episode. Our results elucidateda complex response of aerosol chemistry to emission controls, which hassignificant implications that emission controls over regional scales cansubstantially reduce secondary particulates. However, stricter emissioncontrols for local source emissions are needed for further mitigating airpollution in the megacity of Beijing.
机译：由于气溶胶颗粒的来源和形成机制复杂，因此减轻大城市的空气污染仍然是一个巨大的挑战。 2014年在北京举行的亚太经济合作组织（APEC）峰会是一项独特的实验，旨在研究排放控制对气溶胶成分，尺寸分布和氧化特性的影响。在此，2014年10月14日至11月12日，高分辨率的飞行时间气溶胶质谱仪在北京市区部署，用于实时测量尺寸分辨的非难溶性亚微米气溶胶（NR-PM）物种，以及一系列并列的测量。 APEC期间的平均（±σ）PM为41.6（±38.9）μg，与APEC之前相比降低了53％。由于APEC期间的排放控制，气溶胶成分显示出实质性变化。次生无机气溶胶（SIA：硫酸盐+硝酸盐+铵）显示出62-69％的显着减少，而有机物的显示则小得多（35％）。有机气溶胶（OA）的正矩阵分解结果表明，高氧化性次级有机气溶胶（SOA）的减少与SIAduring APEC相似。但是，来自烹饪，交通和生物质燃烧源的主要有机气溶胶（POA）与APEC之前的水平相当，这表明存在大量的本地源排放。氧化性能表现出对应于OA组成的相应变化。 APEC期间的平均氧气碳含量为0.36（±0.10），低于APEC之前的0.43（±0.13），表明OA氧化度降低了。 APEC期间主要和次要物种的大小分布变化。在APEC期间，SIA和SOA在大的累积模式下显示出明显的减少，峰值直径从650 nm变为400 nm，而POA的相对直径则保持相对不变。在严重雾霾事件的案例研究中，进一步说明了老化过程中气溶胶成分，尺寸分布和氧化度的变化。我们的结果阐明了气溶胶化学对排放控制的复杂反应，这具有重要意义，即区域范围内的排放控制可以显着减少次生颗粒。然而，为进一步缓解北京特大城市的空气污染，需要对本地源排放采取更严格的排放控制措施。

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