[A-AS11] Atmospheric Chemistry

[AAS11-P29] Analysis of diurnal variation of isoprene and air pollutant column amounts observed with FTIR at Rikubetsu

*Tomoo Nagahama¹, Isamu Morino² (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute for Environmental Studies)

Keywords:Isoprene, Air pollutants, Diurnal variation, Troposphere

Most of the hydrocarbons in the atmosphere that contribute to forming air pollutants, such as tropospheric ozone, are emitted as volatile organic compounds (VOCs). About 1/3 of the VOCs in the atmosphere are isoprene, one of the major biogenic VOCs. Therefore, understanding the spatiotemporal variability of both isoprene and air pollutants in the atmosphere is essential to understanding air pollution. In order to understand the details of the diurnal variation of these atmospheric column amounts, we conducted high-frequency observations of solar absorption spectra using a high-resolution Fourier Transform InfraRed spectrometer (FTIR), which is used for stratospheric and tropospheric trace gases monitoring observations to determine the diurnal variation of isoprene and tropospheric ozone, methanol, and formic acid column amounts. Observations were conducted during the daytime on June 18 and 19, 2024, using a ground-based high-resolution FTIR (Bruker IFS120/5HR) operated with the National Institute for Environmental Studies in Rikubetsu, Hokkaido. The observations were made every 4 minutes with a resolution of 0.007 cm^-1 over the range of 8 to 14 μm in the solar absorption spectrum. The tropospheric column amount of each trace gas was determined for the 260 solar absorption spectra obtained using the SFIT4 (version 1.0.21) software. The observed tropospheric column amount of isoprene increased with sunrise. This indicates that the chemical lifetime of isoprene is short and that the tropospheric column amount depends on the amount emitted from the surface. On the other hand, tropospheric ozone and methanol tropospheric column amounts increased for about 2 hours after sunrise but then remained almost constant or decreased. The tropospheric column amount of formic acid decreased from sunrise until about 2 hours after sunrise and then increased for about 2 hours before reducing. The chemical lifetime of these air pollutants is several days, well longer than that of isoprene (about 1 hour). The tropospheric column amounts of air pollutants show more complex temporal variations than isoprene, suggesting that these substances are likely to be influenced by atmospheric transport and other factors rather than the oxidation of isoprene generated near the observation site. In the presentation, we will report the temporal variation of tropospheric column amounts of isoprene and air pollutants, the correlation between isoprene and air pollutants, and the results of backward trajectory analysis.