[Personal nitrogen oxides exposure levels and related influencing factors in adults over 35 years old in Tianjin and Shanghai].

Objective: To investigate personal exposures to nitrogen oxides (NO_X) and nitrogen di-oxide (NO₂) and the influence of baseline personal characteristics, living environment and daily activity patterns of the participants on the exposures among adults over 35 in Tianjin and Shanghai.

Methods: In this panel study, 91 healthy nonsmoking adults aged over 35 from Tianjin and Shanghai participated in our study. The study was conducted in summer and winter. The participants were followed for three times with an interval of at least two weeks. Only participants in Shanghai were followed once in winter because of the COVID-19 pandemic. Twenty-seven participants completed follow-up visits in both seasons. We measured their 24 h personal exposures to NO_X and NO₂and collected their baseline and time-activity information through questionnaire/diary. The linear mixed model was used to analyze the associations between potential influencing factors and personal NO_X and NO₂ exposure levels.

Results: There were 349 follow-up visits with valid 24 h personal NO₂ and NO_X exposure measurements in the two cities. The ave-rage 24 h personal exposures to NO₂ and NO_X (volume fraction) in Tianjin participants were 18.0×10^-9 and 26.2×10^-9 in summer, and 31.0×10^-9 and 54.9×10^-9 in winter, respectively; and the average 24 h personal exposures to NO₂ and NO_X in Shanghai participants were 38.7×10^-9 and 100.0×10^-9 in summer, and 45.5×10^-9 and 139.2×10^-9 in winter, respectively. The results of univariate regression analysis showed that their personal NO_X exposure levels were significantly associated with city, season, gender, average daily cooking times, and ambient NO₂ concentrations measured at fixed-site monitoring stations. In addition to the above factors, the personal NO_X exposure levels were also significantly associated with educational level and the personal NO₂ exposure levels were also significantly associated with passive smoking, average daily home time, cooking energy type, residential distance from main traffic road, and use of kitchen ventilators. Multivariate regression analysis showed that the personal exposure levels of NO₂ and NO_X were significantly lower in Tianjin than that in Shanghai, were significantly lower in summer than that in winter, and were significantly and positively associated with ambient NO₂ concentrations measured at fixed-site monitoring stations. In addition, personal NO_X exposure levels were significantly lower in females than in males, and personal NO₂ exposure levels were significantly positively associated with average daily cooking times and significantly inversely associated with average daily home time. For every interquartile range (IQR) increase (12.7×10^-9) in ambient NO₂, the personal NO₂ exposure levels increased by 27.5% (95%CI: 17.0%-38.9%), and personal NO_X exposure levels increased by 16.1% (95%CI: 7.1%-25.8%).

Conclusion: Season, city and ambient NO₂ concentrations are significant influencing factors of personal exposure levels of NO₂and NO_X. At the same time, the personal exposures levels of NO₂are also affected by lifestyle factors. Our study provides scientific evidence for making precise air pollution control decisions and reducing the exposure levels of NO_X in the population.