# An Assessment of Anthropogenic CO\({}_{2}\) Emissions by Satellite-Based Observations in China
## 1 Introduction  
Atmospheric carbon dioxide (CO\({}_{2}\)) is the most significant anthropogenic greenhouse gas (GHG) and its concentration in atmosphere has been increasing from 280 ppm since the preindustrial era to a level higher than 400 ppm at present at a global scale [1]. The enhancement of atmospheric CO\({}_{2}\) has been known as one of the factors inducing global warming and playing an important role in climate change. Anthropogenic CO\({}_{2}\) emissions, 70% of which come from fossil fuel combustion and industrial activities [2], are the main driver of the atmospheric CO\({}_{2}\) concentration increase. If atmospheric CO\({}_{2}\) concentration continues to increase at the current rate, 1.5 \({}^{\circ}\)C of global warming will be reached between 2030 and 2052, which will cause more climate extremes [3]. Atmospheric CO\({}_{2}\) concentration, moreover, will be continually increasing as the rapid development of industrialization requires enormous energy around the world. In order to slow down the increase of atmospheric COconcentration, many countries are making efforts for CO\({}_{2}\) emissions reduction. For that we need an efficient and reliable way to monitor CO\({}_{2}\) emissions in order to evaluate the effectiveness of CO\({}_{2}\) emissions reduction policy. Over the past 20 years, satellite-based measurements of greenhouse gases have been facilitating the way monitoring atmospheric constituents with the great advancement of satellite observing technology in the development of highly accurate sensors. It is also becoming the major data source to detect the change of atmospheric CO\({}_{2}\) concentration at regional and global scales [4; 5; 6; 7]. Compared with ground-based observation, CO\({}_{2}\) concentration retrieved by satellite has global coverage and consistent observation characteristics, which can better reveal the spatio-temporal variation of atmospheric CO\({}_{2}\) concentration. Currently, the GHG observing satellites in orbit include the Greenhouse gases Observing SATellite (GOSAT) from Japan, Orbiting Carbon Observatory 2 (OCO-2) from the USA and TanSat from China, which can provide us the column-averaged dry air mole fraction of CO\({}_{2}\) (XCO\({}_{2}\)) dataset since 2009 [8; 9; 10]. Many previous studies indicated that XCO\({}_{2}\) retrieved from satellite observations can detect changes of CO\({}_{2}\) concentration induced by anthropogenic emissions [11; 12; 13]. The anthropogenic emission is expected to induce an increase of about 4 ppm of XCO\({}_{2}\) around power plants [11]. With multi-year XCO\({}_{2}\) dataset available from GOSAT and OCO-2, anthropogenic CO\({}_{2}\) emissions have been quantified by excluding the background concentration. It was reported that megacities such as Los Angeles and Beijing, and high density urban regions such as eastern USA and the Beijing-Tianjin-Hebei area in northern China have about 2 ppm enhancements [14; 15; 16]. These studies mainly obtained regional CO\({}_{2}\) enhancements in contrast to the background using empirical conversion factors. It has been shown that the XCO\({}_{2}\) has a positive correlation with the anthropogenic CO\({}_{2}\) emissions through correlating OCO-2 observations with emission inventories [17]. The correlation implies that satellite-based observations are capable to quantitatively assess the anthropogenic CO\({}_{2}\) emissions through detection of XCO\({}_{2}\) enhancements. Estimation of anthropogenic emissions from satellite-based observation can support the investigation of carbon emissions as a data-driven method, which is different to the conventional method in calculating emission inventory. Satellite observations can detect the CO\({}_{2}\) changes in specific regions such as strong sources of anthropogenic emissions, e.g., megacities and high density urban area, so as to monitor CO\({}_{2}\) emissions effectively. These studies, however, mostly focus on investigating enhancement of CO\({}_{2}\) induced by anthropogenic emissions through regional contrast.