[A-AS05] 大気化学

[AAS05-12] Validation and correction of TROPOMI tropospheric NO₂ column density data using 4AZ-MAXDOAS at Chiba, Japan

*齊藤 輝¹、入江 仁士¹、Damiani Alessandro¹ (1.千葉大学)

キーワード：大気、衛星観測、二酸化窒素、大気科学、大気化学

To quantify and solve the reported negative bias in tropospheric nitrogen dioxide (tropNO₂) column data from the latest sensor TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite, we conducted ground-based four-different-azimuth-viewing multi-axis differential optical absorption spectroscopy (4AZ-MAXDOAS) observations at Chiba, Japan (35.63ºN, 140.10ºE, 21 m a.s.l.) in 2019. A comparison with simultaneous tropNO₂ observations by 4AZ-MAXDOAS enabled an evaluation of the spatial inhomogeneity of tropNO₂, which was considered responsible for a bias in results. Supported by inter-directional differences of up to 40% among 4AZ-MAXDOAS data, we found a significant horizontal spatial inhomogeneity in tropNO₂ around the observation site. We then compared 4AZ-MAXDOAS data with coincident TROPOMI data. TROPOMI data had a 53% smaller tropNO₂ column density as an annual average compared to 4AZ-MAXDOAS data, confirming the negative bias in TROPOMI data. However, the correlation between the magnitude of the bias and the coefficient of variance in four-azimuth directional data from 4AZ-MAXDOAS observations was not evident. This suggested that NO₂ horizontal inhomogeneity couldn't fully explain the observed bias. We also applied a correction using the tropNO₂ vertical profiles from 4AZ-MAXDOAS and the averaging kernels from TROPOMI. The correction reduced the bias to ~30% for annual average data, depending on the tropNO₂ profiles used, indicating that there was a significant contribution of tropNO₂ vertical profiles to the bias. These results not only quantified the reported negative bias but also emphasized the effectiveness of validation and correction using multi-directional ground-based data.