In order to identify the sources of indoor PM_2.5 and to check which factors influence the concentration of indoor PM_2.5 and chemical elements, indoor concentrations of PM_2.5 and its related elements in residential houses in Beijing were explored. Indoor and outdoor PM_2.5 samples that were monitored continuously for one week were collected. Indoor and outdoor concentrations of PM_2.5 and 15 elements (Al, As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Pb, Se, Tl, V, Zn) were calculated and compared. The median indoor concentration of PM_2.5 was 57.64 μg/m³. For elements in indoor PM_2.5, Cd and As may be sensitive to indoor smoking, Zn, Ca and Al may be related to indoor sources other than smoking, Pb, V and Se may mainly come from outdoor. Five factors were extracted for indoor PM_2.5 by factor analysis, explained 76.8% of total variance, outdoor sources contributed more than indoor sources. Multiple linear regression analysis for indoor PM_2.5, Cd and Pb was performed. Indoor PM_2.5 was influenced by factors including outdoor PM_2.5, smoking during sampling, outdoor temperature and time of air conditioner use. Indoor Cd was affected by factors including smoking during sampling, outdoor Cd and building age. Indoor Pb concentration was associated with factors including outdoor Pb and time of window open per day, building age and RH. In conclusion, indoor PM_2.5 mainly comes from outdoor sources, and the contributions of indoor sources also cannot be ignored. Factors associated indoor and outdoor air exchange can influence the concentrations of indoor PM_2.5 and its constituents.

In the context of the outbreak of coronavirus disease 2019 (COVID-19), strict lockdown policies were implemented to control nonessential human activities in Xi’an, northwest China, which greatly limited the spread of the pandemic and affected air quality. Compared with pre-lockdown, the air quality index and concentrations of PM_2.5, PM₁₀, SO₂, and CO during the lockdown reduced, but the reductions were not very significant. NO₂ levels exhibited the largest decrease (52%) during lockdown, owing to the remarkable decreased motor vehicle emissions. The highest K⁺ and lowest Ca²⁺ concentrations in PM_2.5 samples could be attributed to the increase in household biomass fuel consumption in suburbs and rural areas around Xi’an and the decrease in human physical activities in Xi’an (e.g., human travel, vehicle emissions, construction activities), respectively, during the lockdown period. Secondary chemical reactions in the atmosphere increased in the lockdown period, as evidenced by the increased O₃ level (increased by 160%) and OC/EC ratios in PM_2.5 (increased by 26%), compared with pre-lockdown levels. The results, based on a natural experiment in this study, can be used as a reference for studying the formation and source of air pollution in Xi’an and provide evidence for establishing future long-term air pollution control policies.

Cognitive fatigue in specific occupations may present a risk to personal safety. The study aimed to explore the characteristic volatile organic compounds (VOCs) in exhaled breath in response to cognitive fatigue, to provide a scientific basis for the non-invasive exhaled breath diagnostic techniques for cognitive fatigue assessing. Thirty healthy young adults were recruited and assigned to complete two 1.5-hour cognitive fatigue-inducing trials of the N-back task and one control trial of low emotion film watching of the same duration time. The Chalder Fatigue Scale was employed to assess the cognitive fatigue of the subjects before and after the induction and film watching. Exhaled VOCs were collected and detected using a Bio-VOC sampler and Thermal Desorption Gas Chromatography-Mass Spectroscopy method. The differences in exhaled VOCs between the pre- and post-induction and film watching was evaluated using either the paired t-test or the Wilcoxon signed-rank test. It was found that the scale scores of the task group (n = 50) significantly increased after the induction, whereas no such findings were observed in the control group (n = 10), indicating that the cognitive fatigue state of the task group was effectively induced through the performance of the N-back task. A total of 15 VOCs were identified in the exhaled breath samples of the task group. And only the level of isoprene changed significantly from 339.77 ± 162.21 μg/m³ to 604.18 ± 230.75 μg/m³ with the induction of cognitive fatigue. In contrast, the change of isoprene in the control group was not statistically significant. The study demonstrated that after inducing cognitive fatigue by N-back task in healthy young subjects, isoprene levels in exhaled breath increased significantly. It suggests that isoprene could be considered a characteristic volatile organic compound in exhaled breath associated with cognitive fatigue.

Exposure to PM_2.5 will accelerate the progression of cardiovascular diseases. Air purifier can reduce the PM_2.5 exposure and theoretically alleviate the influence of PM_2.5 on patients with stable coronary artery disease (SCAD). However, few studies of the protective effect showed significant results because the interferent effects of routine medication had not been taken into account. In order to explore the actual effect on patients with SCAD, we conducted a randomized crossover air purifier intervention trial. Levels of the subjects’ PM_2.5 exposure during intervention and cardiovascular indicators (inflammation, coagulation, plaque stability, and blood lipids) after intervention were detected, meanwhile the information of drug use was obtained by questionnaire. Then the kinds of drug used by more than 20% of the subjects were sorted out. And the influence of these drugs on cardiovascular indicators was summarized through literature review. Based on that, the drug use was included as a variable in linear mixed effects models that used to analyze the associations between PM_2.5 exposure reduction by air purifier and cardiovascular indicators. The result revealed that the interpretation contribution rate of drug use was more than that of PM_2.5 exposure. The level of C-reactive protein (CRP) significantly decreased on lag1, lag01 and lag02, while the level of high-density lipoprotein cholesterol (HDL-C) significantly increased on lag0, lag1 and lag01 associated with an interquartile range (IQR) decrease in PM_2.5 exposure. The study can provide reference for future relevant research in methodology.