## 1 Introduction  
The fast urbanization with significant land cover change has influenced the urban microclimate, which may threaten the sustainability of atmospheric balance at regional scale [1,2]. Some of the regional atmospheric process such as CO\({}_{2}\) emission has become a critical issue in sustainable development [3]. In urban ecosystems, the process of absorbing CO\({}_{2}\) is correlated with oxygen emission, which forms a carbon and oxygen cycle in balance [4]. However, except the wide attention on the carbon cycle, few studies focus on the accompanying process of oxygen emission and consumption, which is also a link bridging the processes between nature and human beings. Oxygen is vital for the survival of life, and the maintenance of a certain concentration of atmospheric oxygen is the most fundamental aspect of human well-being. When the oxygen concentration is below 19.5% in a closed space, the human heart can be harmed by its increased workload, and people cannot survive when the oxygen concentration is less than 6%-7% [5]. On one side, oxygen is an important element of photosynthesis and respiration, and a certain concentration of atmospheric oxygen is needed to balance the ecosystem. On the other side, oxygen is an important raw material consumed in the chemical industry during the combustion of fossil fuels. Urbanization mainly involves deforestation and the large-scale use of fossil fuels. The rapidly rising CO\({}_{2}\) concentration in the atmosphere due to urbanization has caused global climate change, which in turn aroused widespread concern [6, 7, 8]. Meanwhile, the problem of an atmospheric oxygen imbalance has been gradually identified. [PERSON] [9] found that the oxygen concentration in the atmosphere fell by 0.0317% from 1990 to 2008. In densely populated city centers, the oxygen concentration is below 19%, and in some urban areas it is as low as 12%-17% [5]. Nevertheless, over half the world's population live in cities, and urbanization has become a significant trend in the development of human civilization. With the high population increasingly consuming resources and energy, urbanization results in dramatic changes in land cover and environment [9, 10, 11]. As large amounts of green vegetation are converted to artificial impervious surfaces, the exchange of materials between the atmosphere and ground surface will be significantly affected [12,13]. Thus, urbanized areas, especially regions strongly affected by human disturbance causing significant surface changes [14,15], have become important in global environmental change studies. Compared with studies of the carbon balance that focus on global warming, there have been few studies of the global oxygen balance. The quantitative methods used in oxygen balance studies have been improved to increase the accuracy of estimation. Some researchers have used the area of green vegetation cover to indicate carbon sequestration and oxygen emission [16]. Some researchers have used plant photosynthesis products of net primary productivity (NPP) to make estimations [17,18], while others found that remote sensing technology made the calculation more effective [19, 20, 21, 22, 23]. [PERSON] [24] conducted an urban oxygen balance study in Nanjing, China. However, the study was relatively subjective and lacked a scientific basis in its assessment, because the estimation was based on empirical oxygen emission coefficients of several land use types without chemical formulas and ecological mechanisms. In more recent studies, the analysis and application of the oxygen balance has been strengthened. [PERSON] _et al._[25] applied an oxygen balance index to quantitatively evaluate the urban oxygen balance. [PERSON] _et al._[26] and [PERSON] [27] analyzed the role of green vegetation in the oxygen balance, and [PERSON] _et al._[28] and [PERSON] [29] calculated the need for ecological land in cities based on the oxygen balance. The city and the region have a close connection in terms of landscape function [30].