Abstract
Carbon dioxide (CO2) is a significant atmospheric greenhouse gas and its concentrations can be observed by in situ surface stations, aircraft flights and satellite sensors. This paper investigated the ability of the CO2 satellite observations to monitor, analyze and predict the horizontal and vertical distribution of atmospheric CO2 concentration at global scales. CO2 observations retrieved by an Atmospheric Infrared Sounder (AIRS) were inter-compared with the Global Atmosphere Watch Program (GAW) and HIAPER Pole-to-Pole Observations (HIPPOs), with reference to the measurements obtained using high-resolution ground-based Fourier Transform Spectrometers (FTS) in the Total Carbon Column Observing Network (TCCON) from near-surface level to the mid-to-high troposphere. After vertically integrating the AIRS-retrieved values with the column averaging kernels of TCCON measurements, the AIRS observations are spatio-temporally compared with HIPPO-integrated profiles in the mid-to-high troposphere. Five selected GAW stations are used for comparisons with TCCON sites near the surface of the Earth. The results of AIRS, TCCON (5–6 km), GAW and TCCON (1 km) CO2 measurements from 2007 to 2013 are compared, analyzed and discussed at their respective altitudes. The outcomes indicate that the difference of about 3.0 ppmv between AIRS and GAW or other highly accurate in situ surface measurements is mainly due to the different vertical altitudes, rather than the errors in the AIRS. The study reported here also explores the potential of AIRS satellite observations for analyzing the spatial distribution and seasonal variation of CO2 concentration at global scales.
Highlights
Carbon dioxide (CO2) is considered as one of the primary greenhouse gases (GHGs) in the Earth’s atmosphere [1]
This paper presents the results of a study on spatio-temporal validation of Atmospheric Infrared Sounder (AIRS) CO2 observations using the Global Atmosphere Watch Program (GAW), HIAPER Pole-to-Pole Observations (HIPPOs) and Total Carbon Column Observing Network (TCCON)
The specific objective of this paper are (1) to study the potential of the combination of high-resolution in situ surface and aircraft measurements for validating AIRS observations by using GAW observations, HIPPO aircraft measurements, TCCON column data and AIRS-retrieved observations; (2) to develop the method and the parameters for validating AIRS using in situ surface and aircraft measurements by vertically integrating the high-resolution HIPPO in situ aircraft and AIRS profiles with column averaging kernels of Fourier Transform Spectrometers (FTS) measurements; (3) to inter-compare the AIRS observations with GAW, TCCON (1 km, 5–6 km) and HIPPO-integrated profiles for understanding the differences of CO2 at their respective altitudes; (4) to analyze the spatial distribution, rising trend and seasonal variation using monthly averaged AIRS observations
Summary
Carbon dioxide (CO2) is considered as one of the primary greenhouse gases (GHGs) in the Earth’s atmosphere [1]. Once CO2 is added to the atmosphere, it exists for a long time: between 300 and 100 years [2]. Understanding and managing the global carbon cycle requires analysis of the spatial distribution and temporal changes of highly accurate CO2 observations. CO2 concentrations are often measured by in situ surface stations, aircraft flights or satellite instruments. The horizontally sparse surface stations can continuously observe the near-surface CO2 concentration at fixed sites with high accuracy. Due to the uneven distribution of ground-based stations, it is not possible to provide the macroscopic monitoring information of CO2 concentrations, especially for the monitoring of CO2 over the ocean, polar region, desert, and other underpopulated areas. Aircraft observations have similar problems and cannot provide sufficient, stable and continuous monitoring information of atmospheric CO2 concentrations.
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