Presentation Information
[AAS08-P07]Temporal variations of some trace species observed with FTIR at Tsukuba
*Isao Murata1, Isamu Morino2 (1.Graduate School of Environmental Studies, Tohoku University, 2.National Institute for Environmental Studies)
Keywords:
FTIR,trace species,temporal variation
In collaboration with the National Institute for Environmental Studies, Tohoku University has been investigating the temporal and spatial variations of atmospheric trace species with solar infrared spectroscopy using FTIR at Tsukuba since 1998. We have contributed to the activity of the Detection of Atmospheric Composition Change/InfraRed Working Group (NDACC/IRWG) and collaborated on many species. 14 species are routinely analyzed with the retrieval strategies common in the IRWG. In this presentation, we report on the recent long-term variations of these species.
Bruker 125HR (120HR before March 2010) with a spectral resolution of 0.0035 cm-1 is used for the measurements. We can derive the column amounts of various atmospheric trace species from the infrared absorption spectra in the 2-15 µm range. Furthermore, the high spectral resolution allows us to measure the pressure broadening of individual absorption lines. Therefore, we can also retrieve vertical profiles for some species. For the analysis, we use SFIT4 v1.0.21, a spectral fitting program commonly used within the IRWG. The species routinely analyzed include O3, HNO3, HCl, HF, CO, N2O, CH4, HCN, C2H6, ClONO2, HCHO, OCS, NH3, C2H2, and NO2. Although the analysis period varies by species, the longest records date back to 2001 with almost no data gaps. For species such as O3 and HNO3 that utilize the 10 µm band, the analysis focuses on the period from 2014 due to observational constraints.
The following is an overview of the long-term trends, focusing on the column amounts:
O3: The total column amount showed a slight decrease of approximately -0.2%/yr between 2014 and 2025. While stratospheric ozone is increasing globally due to the effects of CFC regulations, satellite observations have also shown decreasing trends in some regions, and the factors driving these variations are currently being investigated. In Tsukuba, analysis of total ozone observed by Dobson spectrophotometer also shows a slight downward trend, which is consistent with our results. As for O3, we can derive vertical profiles because the degrees of freedom for signal (DOFS) is approximately 4 to 5. We analyzed partial columns for the troposphere, lower stratosphere, and middle stratosphere. This analysis revealed a significant decreasing trend in the lower stratosphere.
HCl and HF: These species also reflect the impact of CFC regulations. The amount of stratospheric chlorine started to decrease in the latter half of 1990s. HCl, a major chlorine reservoir, would be also expected to decrease. The column amounts of HCl from 2001 to 2025 show multi-year fluctuations. These are attributed to variations in stratospheric circulation. The linear trend for the entire period is nearly zero, with no clear decreasing trend yet observed. Regarding HF, which also originates from CFCs, the linear trend for 2001-2025 shows an increase of just under +1%/yr, likely because fluorine is also contained in HCFCs/HFCs. HF also exhibits multi-year fluctuations similar to those of HCl.
CH4 and N2O: Since 2010, CH4 has increased by approximately +0.6%/yr, and N2O by approximately +0.3%/yr. Both trends are consistent with the increase rates observed in surface concentrations.
CO: Despite large day-to-day variability, a decreasing trend exceeding -1%/yr has been observed since 2010, which also aligns with surface observation results.
We will also report on the long-term trends and driving factors for the other trace species.
Bruker 125HR (120HR before March 2010) with a spectral resolution of 0.0035 cm-1 is used for the measurements. We can derive the column amounts of various atmospheric trace species from the infrared absorption spectra in the 2-15 µm range. Furthermore, the high spectral resolution allows us to measure the pressure broadening of individual absorption lines. Therefore, we can also retrieve vertical profiles for some species. For the analysis, we use SFIT4 v1.0.21, a spectral fitting program commonly used within the IRWG. The species routinely analyzed include O3, HNO3, HCl, HF, CO, N2O, CH4, HCN, C2H6, ClONO2, HCHO, OCS, NH3, C2H2, and NO2. Although the analysis period varies by species, the longest records date back to 2001 with almost no data gaps. For species such as O3 and HNO3 that utilize the 10 µm band, the analysis focuses on the period from 2014 due to observational constraints.
The following is an overview of the long-term trends, focusing on the column amounts:
O3: The total column amount showed a slight decrease of approximately -0.2%/yr between 2014 and 2025. While stratospheric ozone is increasing globally due to the effects of CFC regulations, satellite observations have also shown decreasing trends in some regions, and the factors driving these variations are currently being investigated. In Tsukuba, analysis of total ozone observed by Dobson spectrophotometer also shows a slight downward trend, which is consistent with our results. As for O3, we can derive vertical profiles because the degrees of freedom for signal (DOFS) is approximately 4 to 5. We analyzed partial columns for the troposphere, lower stratosphere, and middle stratosphere. This analysis revealed a significant decreasing trend in the lower stratosphere.
HCl and HF: These species also reflect the impact of CFC regulations. The amount of stratospheric chlorine started to decrease in the latter half of 1990s. HCl, a major chlorine reservoir, would be also expected to decrease. The column amounts of HCl from 2001 to 2025 show multi-year fluctuations. These are attributed to variations in stratospheric circulation. The linear trend for the entire period is nearly zero, with no clear decreasing trend yet observed. Regarding HF, which also originates from CFCs, the linear trend for 2001-2025 shows an increase of just under +1%/yr, likely because fluorine is also contained in HCFCs/HFCs. HF also exhibits multi-year fluctuations similar to those of HCl.
CH4 and N2O: Since 2010, CH4 has increased by approximately +0.6%/yr, and N2O by approximately +0.3%/yr. Both trends are consistent with the increase rates observed in surface concentrations.
CO: Despite large day-to-day variability, a decreasing trend exceeding -1%/yr has been observed since 2010, which also aligns with surface observation results.
We will also report on the long-term trends and driving factors for the other trace species.