BACKGROUND: Ambient carbon monoxide (CO) exposure has been identified as an emerging environmental risk factor contributing to the progression of pulmonary tuberculosis (PTB). However, the epidemiological evidence remains inconsistent. This study aims to investigate the short-term association between low-level CO exposure and PTB outpatient visits in a developing region. METHODS: We conducted a time-series study utilizing a distributed lag non-linear model (DLNM) combined with mediating effect analysis, based on daily CO and PTB cases from 2011 to 2020 in Ningbo, China. RESULTS: Among all patients with PTB, a 0.1 mg/m CONCLUSION: Our findings indicate that ambient CO exposure, even at low levels, has a short-term impact on PTB in developing regions. Temperature plays a partial mediating role in this relationship. Consequently, it is critical to enhance environmental monitoring and early warning systems to effectively address the prevalence of PTB and the delays in health-seeking behavior.