At present, digital finance in China has shown vigorous development and has played a crucial role in promoting urban haze governance. This section firstly analyses the direct impact of digital finance on urban haze governance and examines the heterogeneous effects of different degrees of government emphasis and different levels of cities. Secondly, the indirect transmission mechanisms of green innovation, collaborative innovation, advanced industrial structures, and productive services agglomeration respectively are examined. Finally, the spatial effects of digital finance on haze governance were explored and corresponding research hypotheses are put forward.
2.1 Direct impact of digital finance on haze governance
With the rapid development of the Internet, digital finance has increasingly integrated with traditional finance by relying on new digital technologies such as artificial intelligence and big data. Digital finance has significantly reduced the costs and pollution that may arise in the development of finance and related industries by taking traditional business online, improving the efficiency of financial services and promoting green consumption (Lu, 2018; Du et al, 2022). With more inclusive and efficient service capabilities, it effectively promoted the country's green development and haze governance. Specifically, digital finance relies on online business models such as the Internet and online banking to help users handle online loans, financial management and payment and other financial businesses. This new financial model improves the efficiency of traditional financial services and breaks time and space constraints, while also reducing the consumption of resources such as labor, transportation, and paper, and greatly reducing the emission of pollutants such as haze. In addition, many new service platforms derived from digital finance, such as "Ant Forest" and second-hand trading platforms, will implicitly cultivate the concept of green consumption and environmental awareness among residents, reduce resource waste and pollutant emissions by encouraging green consumption patterns and reuse of resources, thereby promoting haze governance.
Herein, we propose hypothesis 1a: digital finance development can promote urban haze governance.
The Chinese government attaches great importance to the control of haze pollution, which is crucial to public safety and sustainable development, and regards it as a top priority of the current environmental management work. Due to the obvious negative externalities of haze pollution and other problems, the central government has set a clear target for the annual average concentration of PM2.5, and has taken the annual assessment results of haze control as an important basis for evaluating local government officials (Liu et al, 2021; Zhu, 2014; Zhu and Zhang, 2019). In this context, local officials will pay more attention to the prevention and governance of haze at source, actively improve the design and planning of related policies and gradually improve the green standard system. Furthermore, the advantages of digital finance in data analysis, information matching and other fields will be exerted, and the flow of funds will be guided into environmental protection and green industries, which ultimately have a positive impact on the governance of haze.
Herein, we propose hypothesis 1b: in cities with a high level of government emphasis, digital financial development can better promote haze governance.
In addition, digital finance has a path dependence on the traditional financial market, and its development is closely related to the level of urban economic. Considering that the city level is another dimension to measure the economic development of cities, large and medium-sized cities generally have a higher level of economic development and obvious advantages in many fields such as politics, economy, and culture. Such cities are often given priority in development, and their accompanying policy effects may influence the impact of digital finance on haze control.
Herein, we propose hypothesis 1c: digital finance development can better promote haze governance in cities with higher level.
2.2 Indirect impact of digital finance on haze control
2.2.1 Technological innovation
Generally, green innovation is a research and development(R&D) process accompanied by a long cycle, high investment, and high risk. The scientific research budget of enterprises is often difficult to meet the huge funds needed for green innovation in the initial R&D, achievement transformation and later market promotion. Although governments have introduced corresponding policies to support and subsidize green innovation activities, which have improved the enthusiasm of enterprises to participate in green innovation to a certain extent, but the key challenge of financing is still unresolved. As one of the typical representatives of the digital economy era, digital finance is a new financial model in which new digital technology is deeply integrated with the traditional financial industry. Firstly, digital finance can break the time and space limitations of traditional finance, and provide reliable financial support for relevant subjects participating in green innovation activities by integrating idle funds and widening financing channels. At the same time, this process also saves a lot of economic and time costs for lenders, indirectly reducing the cost of green innovation and improving the profitability (Khin and Ho, 2018). Secondly, digital finance can alleviate information asymmetry. Relying on the advantages of new digital technologies in data analysis, information matching and other fields, digital finance can analyze a large amount of behavioral data of related subjects (mainly enterprises) with green innovation over a period of time, leading to more accurate identification and evaluation of their credit and qualifications (Beck et al, 2018), and avoidance of potential risks, which to a certain extent increases the likelihood of success of green innovation activities. Finally, the unique inclusiveness of digital finance can effectively compensate for the disadvantages of traditional financial institutions in neglecting the "tail" of micro and small enterprises and disadvantaged groups, providing micro and small enterprises and relatively less developed regions with the possibility to participate in green innovation activities by lowering the service threshold, etc.
Green innovation is an important way to alleviate the environmental pollution. As relevant innovations are widely used in production and life, they will effectively improve the cleanliness and energy efficiency of enterprises, and promote the generation of solar energy, photovoltaic and other renewable energies, reduce pollutant emissions in the process of production, R&D, and residential consumption, aiming at achieving regional haze governance at source. In addition, green innovation can also reduce the level of urban pollution at the end of environmental governance and promote work of haze governance by reducing haze management costs and improving haze management efficiency.
Herein, we propose hypothesis 2a: digital finance can indirectly promote urban haze governance by enhancing green innovation capability.
Under the influence of digital finance, innovation activities will show more obvious characteristics of openness and diversity. With its unique advantages of breaking through time and space constraints, digital finance will provide real possibilities for joint research and development and collaborative innovation between different regions (cities). Thanks to the instant interaction in the digital economy era, to effectively fill the gaps in regional innovation, regions with a relatively weak innovation base can more conveniently and timely absorb the latest research achievements of developed regions in basic research and other aspects in the process of participating in cooperative innovation (Gomber et al, 2018);while regions with relatively strong innovation capacity can accelerate the marketisation of R&D results through the spillover effect of knowledge. On the whole, beyond accelerating the diffusion of new knowledge and strengthening exchanges and cooperation between regions, digital finance has also significantly reduced the cost of repeated R&D, stimulated the enthusiasm of different regions to participate in joint R&D and collaborative innovation, and ultimately improved the overall innovation capacity of the country (Teece, 2018). In addition, when choosing partners in different regions, it is inevitable to examine the professional capabilities of the target party and its self-adaptability. The rapid development of digital finance can reduce the cost of information collection, speed up the transmission of information, and identify potential risks in the process of cooperative research and development, providing an important technological guarantee for more extensive and in-depth collaborative innovation activities between different cities (Nambisan et al, 2017).
The effectiveness of technological innovation in alleviating environmental pollution has been well documented in existing studies. Compared to the "fighting alone" innovation situation in various regions, trans-regional joint R&D and collaborative innovation will avoid duplication of R&D, save innovation costs, and reduce the risk of failure. Meanwhile, it will also improve the joint control mechanism of trans-regional haze governance by taking advantages of the regional complementarity of economic development, and develop joint R&D in the cutting-edge energy-saving and pollution governance technologies. The joint research and development of related core technologies will ultimately promote the regional haze governance.
Herein, we propose hypothesis 2b: digital financial development can indirectly promote urban haze governance by increasing the intensity of cooperation and innovation between cities.
2.2.2 Industrial structure
From the perspective of industrial structure upgrading, firstly, digital finance can provide many opportunities for enterprises to carry out innovative and entrepreneurial activities by virtue of reducing financing costs and widening financing channels (Shane and Venkataraman, 2000),which in turn will give rise to a number of high-quality new enterprises and increase the added value of related products; Secondly, relying on digital technologies such as artificial intelligence and big data, digital finance will accelerate the creation of new products and new markets, replace traditional industries and backward enterprises, and gradually form industrial clusters with high-tech as the core. In general, most of the above processes will take place in advanced manufacturing and service industries, and will continue to penetrate into other traditional industries. With the increasing use of digital finance in various industries, it will greatly promote the upgrading of the industrial structure from low level to high level (Levine, 2002), that is, the proportion of the tertiary industry will continue to increase, and eventually the Chinese industrial structure will upgrade. With the continuous advancement of China's industrial structure upgrading process, it will significantly reduce the reliance on highly polluting traditional energy sources, and promote urban haze governance by increasing the use of low-carbon energy and green energy, while improving quality and efficiency and optimizing the energy structure.
Herein, we propose hypothesis 3a: digital finance development can indirectly contribute to urban haze control by promoting the industrial structure upgrading.
From the perspective of producer services agglomeration, the vigorous development of high-tech industries and new industries is one of the most important directions to improve the quality of China's economic development. As an important part of the service industry, producer services need the support of various production factors (technology, talent, and capital, etc.). The rapid development of digital finance speeds up the transregional flow of above factors, while strengthening the horizontal and vertical linkages among related industries. Finally, it will promote the agglomeration of productive service industries (Bruhn and Love, 2014). With the improvement of the agglomeration of producer services, relevant enterprises concentrated in a certain space may cooperate to build complete waste treatment equipment in order to save production costs, avoiding duplication of investment while also achieving energy saving and emission reduction. In addition, industrial agglomeration can better attract related talents to work, and gradually form a high-level and professional research team, which is conducive to promoting integration and complementary advantages among various sectors of the productive services industry (Xu and Lin, 2018), providing a constant impetus to promote the transformation and upgrading of the manufacturing industry, achieving efficient production, energy saving and haze governance.
Herein, we propose hypothesis 3b: digital finance development can indirectly achieve urban haze governance by increasing the agglomeration of productive services.
2.2 The spatial spillover effect of digital finance on haze governance
With the help of digital technology, the greatest advantage of digital finance is that it can break the time and space limitations of traditional economic activities. While speeding up information collection and transmission, it also strengthens the intensity and depth of the spatial connection of financial and economic activities between regions. In the context of China's vigorous development of a green economy and the increased emphasis on pollution governance, we should fully Seize the opportunities brought by digital finance to deal with the new challenges that may be faced in the future national competition. Existing studies have found that digital finance not only has a significant spatial correlation, but can also influence carbon emissions, green development, economic growth, and economic quality in neighboring regions through spillover effects (Wu et al, 2022; Li et al, 2022; Liu et al, 2022). As an important part of the regional economic quality, environmental protection and haze governance will inevitably show stronger spatial correlation under the influence of digital finance.
Herein, we propose hypothesis 4a: while digital finance promotes the urban haze governance, it will also affect the haze governance of neighboring cities through spatial spillover effects.
In addition, although digital finance can promote haze governance of surrounding cities through spatial spillover effects, there are certain spatial boundaries for the spillover effects, and with the increase of spatial distance, the spillover effects brought by digital finance will gradually decline (Helsley and Strange, 1990). Firstly, although digital finance can largely break time and space constraints, financial institutions are still more likely to engage in high-frequency exchanges with local financial service demanders, but the impact on surrounding areas (especially remote areas) may be relatively limited. Secondly, local government protectionism will be another important reason for limiting spatial spillover borders in reality. Although China's market-oriented reforms have achieved significant results, market segmentation and trade barriers between different administrative regions still objectively exist, and local protectionism will lead to a significant attenuation of the cross-regional (especially beyond provincial borders) effects of digital finance.
Herein, we propose hypothesis 4b: with the increase of spatial distance, the spillover effect of digital finance on haze control in neighboring regions will show a gradual decay, and there is a certain spatial boundary.