[Characteristic Analysis and Source Apportionment of VOCs in Urban Areas of Beijing in Summer].

Refined characterization of volatile organic compound (VOCs) components and source apportionment can provide scientific and effective support for ozone (O3) pollution prevention and control. Using hourly-resolution VOCs online data monitored at urban sites in Beijing from July to August in 2020, the chemical characteristics of VOCs and ozone formation potential (OFP) in environmental receptors during high and low ozone concentration periods were analyzed, and refined source apportionment was conducted with a positive matrix factorization (PMF) model. The results showed that the average φ[total volatile organic compounds (TVOCs)] at the monitoring sites during the observation period was 12.65×10-9, and the φ(TVOCs) during the high and low ozone concentration periods were 13.44×10-9 and 12.33×10-9, respectively, with an OFP of 107.6 µg·m-3and 99.2 µg·m-3, respectively. Ozone production was controlled by VOCs, with the highest reactivity of aromatic hydrocarbons and the top three species contributing to OFP being isoprene, toluene, and m/p-xylene. The main sources of VOCs in environmental receptors during low O3 periods included vehicular emissions (26.4%), background emissions (15.7%), solvent using (13.0%), auto repair (12.8%), secondary generation sources (9.7%), biomass combustion (6.1%), printing industry (5.7%), LNG-fueled vehicles (5.5%), and vegetation emissions (5.0%), of which background emissions, secondary generation, and printing industry sources have been little discussed in recent studies of VOCs source apportionment in Beijing. The contribution of auto repair sources and secondary generation sources increased by 3.4% and 2.6%, respectively, during the high O3 periods compared to those during the low O3 periods, and vehicular emissions remained the most significant source of VOCs contribution in the urban area of Beijing. Vegetation emissions rose from 07:00 pm and reach a maximum in the late afternoon. The contribution of background emission sources was less variable; vehicular emissions and LNG-fueled vehicle sources showed a morning and evening peak, with a relatively low contribution in the afternoon.

The Effect of Nanometer Oxide Additive on the Heat-Conducting Property of Barium Hydroxide Octahydrate.

Nanometer silicon dioxide additive can improve the thermal performance of barium hydroxide octahydrate as the phase change thermal energy storage material. Through measuring the changes of phase change temperature, degree of supercooling, thermal conductivity, the different effects of nanometer silicon dioxide additives of different mass fraction on barium hydroxide octahydrate thermal performance are compared. It can be seen that the precipitation of barium hydroxide octahydrate with nanometer silicon dioxide additive of 0.5% mass fraction improves greatly. The thermal conductivity of barium hydroxide octahydrate with nanometer silicon dioxide additive of 0.5% mass fraction increases to a very slight degree.