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

To investigate personal exposures to nitrogen oxides (NO ) and nitrogen di-oxide (NO ) 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. 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 and NO and 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 and NO exposure levels. There were 349 follow-up visits with valid 24 h personal N