Assessment of atmospheric CO<sub>2</sub> concentration enhancement from anthropogenic emissions based on satellite observations

Abstract

Anthropogenic CO2 emissions are the dominant factor driving atmospheric CO2 concentration enhancement. However, the magnitude of the increase of CO2 concentration due to regional anthropogenic emissions remains unclear. Satellite-derived observations of atmospheric CO2 concentration provide a promising and effective means by which to monitor and evaluate regional anthropogenic CO2 emissions. This study used the column-averaged dry air mole fraction of CO2 (XCO2) derived from the observations of the greenhouse gases observation satellite (GOSAT) to assess quantitatively the effect of anthropogenic emissions on CO2 enhancement in two study areas located within the same latitudinal zone (35°–50°N): one in northern China and the other in the eastern USA. The study collected original XCO2 data (v02.xx) from a five-year period (2010–2014), released by the GOSAT project of the National Institute for Environmental Studies in Japan. Two high-density urban areas were selected as anthropogenic emission regions (emission-regions). These areas comprised the Beijing-Tianjin-Hebei area centered on Beijing (43 million square kilometers) in northern China and the urban agglomeration that includes New York City (55 million square kilometers) in the eastern USA, for which the magnitudes of anthropogenic CO2 emissions were about 950 and 1312 Tg CO2/a, respectively, according to the CO2 emission inventory in 2010 released by the Carbon Dioxide Information Analysis Center (CDIAC). Two regions with lower emissions, considered as background-regions for comparison with the emission-regions, were prepared according to the distribution of potential temperature and CO2 emission data from CDIAC, where anthropogenic CO2 emissions in 2010 were about 127 and 123 Tg CO2/a, respectively. The yearly averaged XCO2 data were calculated based on the seasonally averaged XCO2 data using the original GOSAT XCO2 retrievals from the four regions. In comparison with the background-regions, the results showed the enhancements of CO2 concentration in the emission-regions were, on average, 1.8 and 2.0 ppm in the Beijing-Tianjin-Hebei area and urban agglomeration in the USA, respectively. The maximum and minimum enhancements in China were 2.4 ppm in 2010 and 1.3 ppm in 2014, respectively. The maximum and minimum enhancements in the USA were 2.6 ppm in 2012 and 1.6 ppm in 2010, respectively. Moreover, the enhancements were highest in winter (2.4±0.6 and 2.8±0.8 ppm in China and the USA, respectively). Intriguingly, analysis of the monthly variations revealed that CO2 concentration in the Beijing-Tianjin-Hebei area decreased anomalously by 3.2 ppm during the Asia-Pacific Economic Cooperation (APEC) summit in November 2014 compared with the period before the summit. This anomalous drop probably reflects the effects of the artificial control of CO2 emissions implemented by the government during the APEC summit in order to improve air quality. The above enhancements of CO2 concentration prefer to be slightly less than the actual enhancements of CO2 concentration induced by anthropogenic emissions due to bio-ecological flux in the emission-regions. Based on an investigation of bio-ecological flux in the Beijing-Tianjin-Hebei area in earlier researches, the actual CO2 enhancement induced by anthropogenic emissions should be added an increment of less than 0.6 ppm absorbed by the bio-ecological system to the above-mentioned 1.8 ppm enhancement. The study results demonstrate the efficacy of using satellite-derived observations for evaluating the impact of anthropogenic emissions on the enhancement of atmospheric CO2 by analyzing changes in regional CO2 concentration. This provides a promising method with which to verify regional anthropogenic emissions and to support governmental oversight, control, and decision making regarding CO2 emission reduction.