PM_2.5 level has decreased significantly in Beijing in recent years due to the strict air quality control measures taken in Jingjinji Region and the surrounding areas. However, the variation characteristics of the concentrations of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) in Beijing in recent years are still not so clear. In order to understand the pollution status of PM_2.5-bound PAHs in Beijing, fifteen PAHs were measured in a typical urban area of Beijing from 1 March to 20 March 2018. The average mass concentration of the 15 PAHs was 21 ng/m³ and higher in the nighttime than that in the daytime. The proportion of 4-ring PAHs in 15 PAHs was highest (43%), while 6-ring PAHs was lowest (10%). The levels of PAHs were higher during heavy pollution episodes than those in non-heavy pollution episodes, and the proportions of 5- and 6-ring PAHs were increased during a heavy pollution episode. PAHs posed obvious carcinogenic risks to the exposed populations, and the risk was higher during heavy pollution episodes than the average value of the whole monitoring period. The main sources of PAHs were traffic emissions and coal/biomass burning. Air masses from the south-southeast had a great influence on the PM_2.5 levels during a heavy pollution episode. It is recommended that not only the PM_2.5 levels but also the PAHs levels bounded in PM_2.5 should be controlled to protect human health in Beijing.

In this paper, the yeast wastewater secondary treatment effluent using catalytic odor oxidation treatment, using an orthogonal reaction experiment to determine the best reaction conditions, and the online monitoring of the pH, oxidation-reduction potential (ORP), and liquid ozone concentration monitoring, to the catalytic odor oxidation reaction, chemical oxygen demand (COD), and color removal effect were analyzed. The results showed that the optimal reaction condition for the advanced treatment of yeast wastewater by catalytic ozonation was accomplished with manganese dioxide used as the catalyst and a catalyst dose of 6 g·L⁻¹, pH of 12, and catalytic ozonation reaction time of 20 min. The COD was effectively reduced from 880 mg·L⁻¹ to 387 mg·L⁻¹ under this condition, the chroma was reduced from 700 times to 40 times, and these two parameters of the effluent could meet the standard of GB25462-2010. The real-time monitoring system showed that the whole reaction can be divided into two processes. The first 14 min was the indirect reaction of ozone and then the direct oxidation reaction of ozone. This process was further verified by the change trend of COD and the amount of ozone depletion by COD removal. The average ozone consumption levels of the two stages were 1.97 and 4.91 mgO₃·mgCOD⁻¹. This system can effectively monitor the reaction of the catalytic odor oxidation in the complex system to guide the effective use of ozone in practical engineering applications.