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Ground‐based measurements of aerosol and trace gases were conducted at a rural site in Beijing in the summer of 2006 as a part of the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing 2006). The size‐resolved chemical composition of submicron aerosol was measured using an Aerodyne quadrupole aerosol mass spectrometer (AMS). The data obtained from 15 August to 10 September 2006 are presented. Meteorological analysis shows that the measurement period can be characterized as a cycle of low wind speed periods over the course of a few days (stagnant periods) followed by rapid advection of clean air from the north/northwest mostly due to passage of a midlatitude cyclone. Mass concentrations of total measured aerosol with diameters less than 1 μm (total PM1), which is defined as the sum of elemental carbon and nonrefractory components measured by the AMS, were highly variable, ranging from ∼2 to ∼100 μg m−3. Large variability of the PM1 composition and drastic changes in the sulfate (SO42−) size distribution were observed to be associated with the cycle of stagnant periods and advection of clean air, indicating that both chemical and physical properties of aerosols were significantly altered on a time scale of a few days. We have found the dominance of organic aerosol at lower total PM1 mass loadings and that of SO42− at higher mass loadings, which may have important implications for the PM control strategy in Beijing. Possible factors affecting the evolution of the mass concentration and size distribution of SO42− are discussed.

Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li 4 Ti 5 O 12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g À1 . This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries. NPG Asia Materials (2014) 6, e120; doi:10.1038/am.2014.61; published online 22 August 2014 INTRODUCTIONWith growing concern about the environment, climate change and a sustainable energy supply, studies have been focused on the development of green energy storage systems with high volumetric energy density, low price and improved safety. Compared to lithium battery systems, 1-6 rechargeable magnesium (Mg) batteries are considered to be a prospective candidate for reversible energy storage because of the great abundance of Mg resources, better chemical stability of metallic Mg in humid and oxygen-containing environments and higher volumetric capacity. [7][8][9] In particular, the increasing attention to rechargeable Mg batteries is due to the pioneering work of Aurbach's group. 10-14 Some progress has been achieved toward designing electrode materials 10,15-24 and electrolytes 25-29 for rechargeable Mg batteries. Nevertheless, rechargeable Mg batteries are still in their infancy. Therefore, alternative Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg-ion batteries. Recently, we have discovered the feasibility of utilizing spinel Li 4 Ti 5 O 12 , which is well known as a 'zero-strain' anode material for long-life stationary lithium-ion batteries, as an anode material for rechargeable Mg batteries. In this work, we further show that spinel Li 4 Ti 5 O 12 nanoparticles (LTO NPs) can exhibit excellent Mg storage performance under optimized conditions for rechargeable Mg batteries. This material shows a high reversible capacity of B175 mA h g À1 and superior cycling performance. By using an advanced atomic resolution scanning transmission electron

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. Laboratory experiments suggest that the large enhancement of K + could have been due to the presence of K-containing particles in ambient air. The interferences of alkali metals at m/z 41, 85, 87, and 133 were significant and need to be corrected for better quantification of organic aerosol. The AMS measurements are compared with other, collocated measurements: a particle-into-liquid sampler combined with an ion chromatograph (PILS-IC), a Sunset Laboratory semicontinuous carbonaceous aerosol analyzer, and a Berner impactor sampler followed by off-line ion chromatography analysis (for major inorganic ions). We have found good agreement between the AMS and the other instruments when we assume an AMS particle collection efficiency (CE) of 0.5 for the PRD data and CE = 1.0 for the CAREBEIJING data. These results suggest that the AMS CE could be significantly different in different locations. Possible factors affecting the variability in the CE values are discussed.

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