Real-Time Observation and Comparison of Atmospheric Formaldehyde Using PTR-ToF-MS and Mid-infrared Spectroscopy Based on Optical Absorption

This study investigated the real-time formaldehyde (HCHO) concentrations in an urban area of Ansan, South Korea, during the summer of 2024, using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) and Mid-Infrared Spectrometer (MIRA). Average concentrations of HCHO were 4.8±1.7 ppb for PTR-ToF-MS and 3.5±0.7 ppb for MIRA with PTR-ToF-MS, exhibiting higher sensitivity to HCHO variations. Findings with both instruments showed similar temporal trends (R2=0.82) with HCHO concentrations peaking during the daytime (PTR: 6.4 ppb, MIRA: 4.3 ppb) and declining at night (PTR: 2.1 ppb and MIRA: 1.7 ppb). The diurnal variations in HCHO concentration highlighted the active photochemical reaction that occur during the summer. This study provided fundamental insights into the characteristics of photochemical pollution in summer seasons through real-time observations of HCHO concentrations. The results from this study could contribute to urban air quality management through the development of long-term, continuous datasets and correlation analyses with other air pollutants in future research.