1 Introduction

The Fifth Plenary Session of the 18th Central Committee of the Communist Party of China identified “green” and “innovation” as part of the country's five major development strategies, signaling the beginning of exploring a more sustainable development model. Green mergers and acquisitions, as a rising green management approach in recent years, integrate green concepts, technologies, and management practices into strategic decision-making processes, serving as an important means to promote the green development of enterprises and facilitate the green transformation of heavily polluting companies (Pan et al., 2019; Qiu et al., 2018). Against the backdrop of ecological civilization construction, green mergers and acquisitions have gradually become a crucial method for adjusting the industrial structure of heavily polluting enterprises, optimizing resource allocation, reducing environmental pollution, and achieving sustainable development.

Green mergers and acquisitions refer to the implementation of mergers and acquisitions strategies that incorporate green concepts, aiming to protect the environment and achieve sustainable development (Pan et al., 2019; Qiu et al., 2018; Stavi et al., 2021). In recent years, the number of green M&A events has been steadily increasing. In 2018, the total scale of GMA in Malaysia, Indonesia, Spain, Canada, Brazil, and other countries reached 8.905 billion (Lu, 2022). Existing literature has primarily focused on factors influencing green mergers and acquisitions, such as environmental regulations, media pressure, changes in officials, organizational performance, and executive characteristics (Pan & Wu, 2020; Pan et al., 2019; Zhang et al., 2022). However, there is limited research on the outcomes of green mergers and acquisitions, and there are still some research gaps. Scholars have mainly explored the relationship between green mergers and acquisitions and firm performance (financial performance, innovation performance, export performance) (Gao & Hu, 2019; Liang et al., 2022b; Lu, 2022; Pan et al., 2021; Salvi et al., 2018), green mergers and acquisitions and corporate environmental management (environmental investment, sustainable development capability, environmental governance) (Li et al., 2020a; Lu, 2021; Pan et al., 2019; Zhao et al., 2021), and green mergers and acquisitions and managerial behavior (risk-taking behavior) (Li et al., 2020b).

However, firstly, in the research on green mergers and acquisitions and environmental management, scholars have not reached a consistent conclusion regarding their relationship. Some studies have found that green mergers and acquisitions are a sincere response by companies and can reduce environmental violations, promoting green innovation (Liang et al., 2022a, 2022b; Sun et al., 2023a; Zhao et al., 2021), significantly improving the level of corporate green management. After green mergers and acquisitions, companies experience enhanced financing capabilities, increased government subsidies, and heightened public monitoring awareness, leading to increased environmental investment, utilization of green environmental technologies, construction of a green corporate image, and maintenance of a green reputation (Bai et al., 2019; Chun & Davies, 2010; Salahodjaev, 2018; Sun et al., 2023b; Tian & Lin, 2019). However, other literature points out that green mergers and acquisitions can increase merger and management costs, inhibiting environmental investment (Lu, 2021) and exerting a negative impact on the level of environmental management. In the early stages of green mergers and acquisitions, buyer and seller companies may struggle to achieve economies of scale in a short period, resulting in increased management costs and a crowding-out effect on environmental investment (Spang et al., 2009). Furthermore, after the merger, innovation activities in the merged company and incentives for competitors' research and development may have a negative effect, leading to a decline in overall innovation capability (Haucap et al., 2019), thereby reducing the level of environmental management. Additionally, some studies have found a non-linear relationship between green mergers and acquisitions and the level of environmental management (such as environmental investment) at different stages of the corporate lifecycle. Green mergers and acquisitions can promote environmental investment in the growth and maturity stages of companies, while inhibiting environmental investment in the decline stage (Lu, 2021). Therefore, there is an urgent need to clarify the impact of green M&A on corporate environmental management.

Secondly, in previous research on green M&A and environmental management, scholars have mainly focused on the impact of green M&A on the level of environmental management. For example, Zhao and Jia (2022) suggest that green M&A integrates environmental concepts into traditional technology acquisitions, aiming to acquire innovative technologies and develop clean production to reduce corporate environmental governance costs and improve environmental image. Wu and Qu (2021) point out that heavily polluting companies, when making decisions on green M&A, often consider green development and transition to energy-efficient enterprises. However, scholars have rarely explored whether and how green M&A affects the quality of corporate environmental management. Pan et al. (2019) indicate that under media pressure, green M&A is merely a strategic tool for temporarily shifting media focus. After green M&A, corporate environmental investments do not significantly increase; it merely discloses more soft environmental information, with less disclosure of hard information that genuinely reflects the state of corporate environmental management. This may have a significant impact on the quality of environmental information disclosure. Therefore, there is an urgent need to further clarify the impact of green M&A on the quality of environmental management, such as the quality of environmental information disclosure.

The quality of environmental information disclosure refers to the quantitative evaluation of the extent to which a company discloses environmental information and measures its willingness to communicate environmental information with the external stakeholders (Wang & Zhang, 2019). Although China is making efforts to establish and improve mandatory disclosure systems for environmental information by listed companies, there are still issues regarding reliability and comparability. For example, there is a lack of uniformity and consistency in the recorded content, and the lack of clear regulations fails to meet the needs of investors. Therefore, it is necessary to strengthen regulatory supervision over the completeness and effectiveness of content disclosure. Previous studies have primarily explored the impact of internal factors such as firm characteristics, corporate governance structures, and the level of environmental management (Angela & Handoyo, 2021; Li & Wang, 2019; Zhu et al., 2019), as well as external factors such as pressures, market environments, and traditional cultures, on the quality of environmental information disclosure (Li et al., 2022c; Liang et al., 2022a; Liu et al., 2022).

Green mergers and acquisitions, as an important approach for heavily polluting companies to respond to the national ecological civilization strategy and implement green transformations (Pan et al., 2021), can influence the quality of environmental information disclosure in these companies. However, there are few studies that have examined the relationship between green mergers and acquisitions and environmental information disclosure. It is necessary to further clarify whether green mergers and acquisitions by heavily polluting companies can indeed enhance the quality of environmental information disclosure or if they are merely a means for these companies to gain legitimacy. In this process, what differences exist among companies with different property rights? How does the relationship between green mergers and acquisitions and the quality of environmental information disclosure change under different levels of government regulation?

To address these questions, this study conducts an empirical analysis using a sample of 908 observations from heavily polluting companies listed on the Shanghai and Shenzhen stock exchanges during the period of 2010–2019. The fixed effect model was used to empirically test the relationship between green mergers and acquisitions and the quality of environmental information disclosure and to explore the heterogeneous effects of government environmental regulation and property rights on the quality of green mergers and acquisitions and environmental information disclosure of heavily polluting enterprises. The research findings indicate that green M&A significantly and positively influences the environmental information disclosure quality of the main acquiring companies in heavily polluting industries. The level of government environmental regulation positively moderates the relationship between green M&A and environmental information disclosure quality, with a stronger positive relationship observed among state-owned enterprises.

This study contributes incrementally in several aspects.

First, it expands the research on outcome variables of green mergers and acquisitions. Previous literature mainly focused on the economic benefits of green mergers and acquisitions. However, due to scholars only considering the impact of green mergers and acquisitions on environmental management levels without considering environmental management quality, there have been inconsistent understandings regarding the relationship between green mergers and acquisitions and environmental management. In contrast, this study examines the impact of green mergers and acquisitions on the quality of environmental information disclosure, thereby clarifying the relationship between green mergers and acquisitions and environmental management quality and broadening the outcome variables of green mergers and acquisitions.

Second, this study extends the research on the antecedents of environmental information disclosure quality. Previous scholars primarily examined the influencing factors of environmental information disclosure quality from the perspective of internal factors such as firm characteristics, corporate governance structures, and environmental management levels, as well as external factors such as pressures, market environments, and cultural traditions. However, there has been limited research on the impact of green management events, such as green mergers and acquisitions, on environmental information disclosure quality. Therefore, this study investigates the significant role played by green mergers and acquisitions as an emerging green management approach in influencing environmental information disclosure quality, thus expanding the research on the influencing factors of environmental information disclosure quality.

Third, this study examines the contextual conditions of the relationship between green mergers and acquisitions and environmental information disclosure quality. Different ownership structures and varying levels of government environmental regulation pose distinct motivations for heavy polluting firms to engage in green mergers and acquisitions, resulting in varying levels of environmental information disclosure quality. This study clarifies the moderating effects of ownership structures and government environmental regulation levels, thereby enriching the boundary conditions of the relationship between green mergers and acquisitions and environmental information disclosure quality.

The rest of this paper is organized as follows. In the second section, three research hypotheses are proposed based on legitimacy theory and signaling theory. The third section covers data collection, variable measurement, and methodological introductions. Empirical analysis and hypothesis verification results are presented in the fourth section. The fifth section includes robustness checks. The sixth section concludes discusses of findings, implications and outlines limitations and future prospects. The seventh part is the research conclusion.

2 Theoretical analysis and research hypotheses

2.1 Theoretical analysis

According to the legitimacy theory, only when an organization's behavior meets the expectations of society and can be accepted by stakeholders can it obtain legitimacy, so as to help the enterprise enjoy a good reputation among the public and attract more investors to support the development of the enterprise (Yu, 2020). The main assumption of the legitimacy theory is that organizations achieve recognition of their goals by fulfilling social contracts, that is, enterprises accept the conditions put forward by the society, undertake social responsibilities to gain acceptance and better understanding, and realize the understanding between society and enterprises, essentially for the purposes of legitimacy, harmonious coexistence, and mutual benefit (Ogunode, 2022). The legitimacy theory can effectively explain the environmental practices of enterprises (Mousa & Hassan, 2015), organize the implementation of green mergers and acquisitions, help enterprises establish green culture, enhance sustainable development ability, improve the quality of environmental information disclosure, achieve harmony with the environment, and obtain legitimacy with the help of environmental protection awareness and technical support.

Signaling theory suggests that when companies communicate information to stakeholders, there is an information asymmetry phenomenon that needs to be addressed by transmitting unobservable information to individual stakeholders, thereby reducing information asymmetry between the company and stakeholders (Guo et al., 2021; Spence, 1974, 2002). Green M&A possesses unique speed and signaling advantages (Pan & Wu, 2020). By acquiring clean energy and energy-saving technologies, green M&A can promote environmental governance within the company (Zhao et al., 2021). Managers are motivated to signal a proactive commitment to environmental responsibility to stakeholders (Zhang et al., 2022) and enhance the company's green reputation and market position (Lu, 2021; Zhou et al., 2022). This motivates companies to choose to disclose high-quality environmental information (Lemma et al., 2019; Li et al., 2021).

2.2 Research hypotheses

As an emerging form of mergers and acquisitions, green mergers and acquisitions serve as an important means for heavy polluting firms to respond to the national ecological civilization strategy and implement green transformation (Pan et al., 2021). They provide these firms with a rapid pathway to establish a favorable ecological position and gain early advantages in strategic emerging sectors. Through green mergers and acquisitions, heavy polluting firms can acquire green technologies, develop clean production, improve energy efficiency, produce green products and services, and enhance their competitive edge in the green market (Salvi et al., 2018). This enables them to achieve the transformation and upgrading of polluting industries, ultimately leading to win–win outcomes for both the economy and society.

According to legitimacy theory, an organization can achieve legitimacy when its actions meet societal expectations and gain public support and recognition. Legitimacy not only aligns the organization's behavior with social norms but also enhances its reputation, earns the trust of various stakeholders, and provides more opportunities for development (Yu, 2020). Through green mergers and acquisitions, heavy polluting firms can obtain legitimate protection and development opportunities (Li et al., 2020b). Long-term organizational legitimacy requires proactive disclosure of high-quality corporate environmental information, which helps the public understand and perceive the organization, thereby improving the quality of environmental information disclosure.

Li et al. (2020a), based on legitimacy theory, empirically found that green mergers and acquisitions enhance a firm's core competitiveness in the product market and convey positive signals to stakeholders in the capital market, enabling them to obtain sustained and stable resource support and consolidate their sustainable development capabilities (Li et al., 2020a). Firms with excellent sustainable development capabilities choose to provide more detailed reports on green development, prompting them to disclose more detailed and high-quality environmental information (Hummel & Schlick, 2016). Zhao et al. (2021), based on legitimacy theory and using data from the Shanghai Stock Exchange and Shenzhen Stock Exchange for Chinese heavy polluting firms from 2009 to 2017, found that green mergers and acquisitions are substantial environmental management actions that can send sincere signals to the public and society, contributing to improved environmental governance and enhancing firm environmental performance (Zhao et al., 2021). As firms improve their environmental performance, the environmental information they disclose to the public also becomes more comprehensive, thereby enhancing the quality of their environmental information disclosure (Agyemang et al., 2021; Zhu et al., 2019).

It can be seen that green mergers and acquisitions can enhance the improvement of environmental information disclosure quality through three aspects: environmental responsibility, green culture, and sustainable development capabilities. Firstly, based on legitimacy theory, through green mergers and acquisitions, companies can actively assume environmental responsibility, obtain long-term legitimacy, and align with their development goals and public demands (Liang et al., 2022b), thereby increasing public attention and satisfaction with environmental protection (Salahodjaev, 2018). In order to further enhance corporate legitimacy (Li et al., 2021) and convey the company's fulfillment of environmental responsibilities, improve corporate image and reputation (Axjonow et al., 2018), the acquiring companies will be motivated to enhance the quality of environmental information disclosure, allowing the public to have a clearer understanding of the efforts made by the company to achieve legitimacy. Secondly, the implementation of green mergers and acquisitions allows the acquiring companies to gradually form a green corporate culture that emphasizes resource conservation, environmental protection, and sustainable development (Lu, 2021). This culture is disseminated within the organization, making the acquiring companies more willing to proactively disclose their environmental information and improve the quality of environmental information disclosure, thereby conveying a green signal to society (Zhang et al., 2019a). Lastly, green mergers and acquisitions can help polluting companies gain legitimacy, obtain recognition from stakeholders, and promote their sustainable development capabilities (Li et al., 2020a). This enables the acquiring companies to genuinely respond to the legitimacy concerns regarding the environment by actively disclosing comprehensive, accurate, and improved corporate environmental information. This not only enhances the level of environmental protection but also earns broad recognition from the general public.

High-quality environmental information disclosure plays a crucial role in effective information transmission. Within the context of corporate green development, the quality of environmental information disclosure serves as a representative and significant measure, reflecting the level of corporate management and becoming an integral part of social and government supervision. Signal transmission theory suggests that to mitigate the risks associated with asymmetric information and adverse decision-making, heavily polluting companies place greater emphasis on enhancing the level of information disclosure to safeguard public interests. This enables them to transmit internal signals of their environmental performance to the market (Zhang et al., 2022a). Through green mergers and acquisitions, acquiring companies can enhance their green reputation and improve their environmental performance (Sun et al., 2023b), thereby encouraging environmentally responsible firms to disclose detailed and high-quality environmental information (Lemma et al., 2019; Li et al., 2021).

In summary, the implementation of green mergers and acquisitions by acquiring companies enables them to demonstrate their legitimacy, fulfill environmental responsibilities, cultivate a green culture, enhance sustainable development capabilities, and consequently improve the quality of environmental information disclosure. Green mergers and acquisitions communicate a signal to external stakeholders about the company's commitment to green development, leading to an enhanced green reputation, facilitating environmental governance, and encouraging proactive disclosure of more comprehensive and improved environmental information. This, in turn, earns social recognition and contributes to an overall improvement in the environmental information disclosure quality of acquiring companies. Based on the above analysis, the following hypotheses are proposed:

Hypothesis 1

Green mergers and acquisitions significantly and positively influence the environmental information disclosure quality of acquiring companies.

Enterprises, as key units in a market economy, operate within the framework of various political and economic institutions. Institutional arrangements beyond the market are essential for ensuring that companies respond to stakeholders beyond their immediate interests (Li et al., 2017). In emerging economies such as China, the government is one of the primary institutions influencing businesses, and its regulatory pressures have a significant impact on enterprises, especially those in energy-intensive and environmentally sensitive sectors (Li et al., 2016).

Government environmental regulation refers to the government's efforts to regulate market operations, achieve specific objectives, and supervise and regulate the environmental behaviors of enterprises through the formulation of laws, regulations, and policies (Chen & Feng, 2020; Li et al., 2017). It is an important means to encourage companies to take environmental protection actions (Shao et al., 2020). In order to meet legitimacy requirements, enterprises are motivated to accept government environmental regulations. Government environmental regulation enhances the proactive attitude and sense of responsibility of enterprises in disclosing environmental information, thereby maximizing their economic performance and ecological sustainability (Pan & Guo, 2018). Government environmental regulation is a situational factor that drives corporate environmental information disclosure. Specifically, firstly, stringent government environmental regulation can significantly drive the green investment behavior of heavily polluting enterprises, such as green acquisitions (Liao & Shi, 2018; Pan et al., 2019; **e, 2020). This leads to a reduction in pollution emissions and helps companies achieve better environmental performance (Cao & Ma, 2021; Zhao et al., 2021). Consequently, companies become more willing to disclose higher-quality environmental information (Agyemang et al., 2021), thereby gaining recognition from stakeholders and the government (Luo et al., 2017). Secondly, due to the difficulty of achieving true green transformation in the short term for heavily polluting enterprises, in the context of the concept that "Lucid waters and lush mountains are invaluable assets," higher levels of government environmental regulation compel companies to rapidly establish a green image through green acquisitions to demonstrate their commitment to environmental protection (Jankensgard, 2015). This encourages them to disclose higher-quality environmental information, garnering public goodwill and achieving legitimacy (Tzouvanas et al., 2020). Finally, in response to strict government environmental regulation, companies proactively participate in voluntary initiatives such as green acquisitions and clean production to optimize their environmental performance, improve the quality of environmental information disclosure, and benefit from government incentives or procurement opportunities (Chen & Chen, 2022).

On the contrary, when government environmental regulation is low, driven by short-term profitability and economic temptations, companies often prioritize activities that yield maximum economic benefits. The level of attention to environmental performance decreases, and companies are more inclined to invest in activities that bring rapid economic returns rather than difficult and low short-term profit activities, especially costly and high-risk green acquisitions (Lu, 2021; Pan et al., 2019). They may not disclose detailed environmental information to avoid scrutiny. Even if companies engage in green acquisitions, they may do so superficially, aiming to maximize profits rather than pollution control (Zhang et al., 2022), resulting in lower-quality environmental information disclosure.

In conclusion, when government environmental regulation is high, companies are motivated and willing to engage in green acquisitions to enhance their environmental performance (Zhao et al., 2021), establish a green image, improve environmental efficiency, and disclose more high-quality environmental information to meet legitimacy requirements. Conversely, when government environmental regulation is low, influenced by short-term profitability motives, companies are more inclined to pursue activities that yield quick economic returns and are reluctant to engage in costly and high-risk investments such as green acquisitions (Lu, 2021). Even if green acquisitions take place, they may be superficially implemented, prioritizing profit maximization over pollution control, resulting in the disclosure of low-quality and detailed environmental information. Therefore, this study proposes the following hypothesis:

Hypothesis 2

Government environmental regulation positively moderates the relationship between corporate green acquisitions and environmental information disclosure quality. Specifically, a higher level of government environmental regulation strengthens the positive relationship between corporate green acquisitions and environmental information disclosure quality, while a lower level of government environmental regulation weakens this relationship.

Different types of ownership structure impose different responsibilities on companies and have varying impacts on their environmental behavior (**ong & Luo, 2021). Scholars primarily categorize ownership structure into state-owned enterprises and non-state-owned enterprises. Compared to non-state-owned enterprises, state-owned enterprises possess inherent political connections that relieve them from the need to strive for legitimacy. They also face minimal legitimacy penalties. As a result, state-owned enterprises lack the motivation to engage in green acquisitions and are unlikely to disclose extensive environmental information. Therefore, this study argues that ownership structure can moderate the relationship between green acquisitions and environmental information disclosure quality.

Firstly, the natural political connections of state-owned enterprises mean that implementing sincere green acquisitions does not yield additional legitimacy benefits (Zhao & Jia, 2022). This lack of motivation for green acquisitions in state-owned enterprises also means that they do not need to enhance the quality of environmental information disclosure to gain legitimacy. Specifically, on the one hand, state-owned enterprises have a clear advantage in competition due to their possession of more critical resources and higher political legitimacy compared to non-state-owned enterprises (Zhang et al., 2019b). They do not rely on issuing social responsibility reports or engaging in green actions to attract government attention, and the positive impact of disclosing environmental information is relatively limited for them (Marquis & Qian, 2014). In contrast, non-state-owned enterprises face inherent disadvantages and consider legitimacy as a strategic requirement. They urgently need to meet government and public demands through green acquisitions and other green actions, actively disclose environmental information to showcase their environmental efforts, and gain legitimacy (Tang et al., 2021).On the other hand, compared to managers of non-state-owned enterprises, managers of state-owned enterprises have higher social status and political backgrounds, which result in a lack of strong motivation to engage in social practices and green actions such as green acquisitions (Chen et al., 2018). They do not need to enhance the quality of environmental information disclosure to gain recognition from the government and the public. In contrast, managers of non-state-owned enterprises are eager to establish good relationships with the government (Dong, 2021) and have the motivation to proactively assume environmental responsibilities. They engage in green acquisitions, introduce environmental technologies, actively reduce pollution, disclose comprehensive environmental information, and send positive signals to gain government support (Guo & Shi, 2022). Therefore, compared to non-state-owned enterprises, state-owned enterprises participating in green acquisitions and environmental actions do not experience better legitimacy benefits. This lack of additional motivation for state-owned enterprises to implement green acquisitions means that they do not need to rely on disclosing high-quality environmental information to gain legitimacy.

Secondly, the political relationships of state-owned enterprises reduce the likelihood of severe penalties for environmental pollution (Chen et al., 2021). These enterprises can seek protection through political connections, leading to relaxed government regulations and reduced penalties for environmental violations (Luo & Liu, 2019). Moreover, compared to non-state-owned enterprises, state-owned enterprises benefit from a higher level of "shelter effect" provided by their political relationships, allowing them to engage in environmentally polluting activities and evade environmental responsibilities (Van Rooij et al., 2017). Therefore, state-owned enterprises lack the motivation to adopt green management practices such as green acquisitions, and they do not need to enhance the quality of environmental information disclosure to evade environmental penalties. Conversely, non-state-owned enterprises face greater risks of legal penalties, which incentivize them to actively engage in activities like green acquisitions to improve the environment. As a result, they are more likely to disclose higher-quality environmental information to demonstrate goodwill to the government and avoid legal penalties.

Based on the above analysis, we find that state-owned enterprises possess inherent political connections, which means they do not need to actively engage in green acquisitions. Even if they do participate in such activities, they do not rely on enhancing the quality of environmental information disclosure to gain legitimacy. Conversely, non-state-owned enterprises, in order to obtain legitimacy and a good reputation, actively pursue green acquisitions and improve the quality of environmental information disclosure. Therefore, we propose the following hypothesis:

Hypothesis 3

The positive relationship between green acquisitions and the quality of environmental information disclosure is weaker in state-owned enterprises compared to non-state-owned enterprises (state-owned enterprises weaken the positive relationship between green acquisitions and the quality of environmental information disclosure).

3 Data collection and research design

3.1 Sample selection and data source

The study focuses on publicly listed companies in the heavily polluting industries in the Shanghai and Shenzhen stock markets. The analysis is based on M&A data from the years 2010 to 2019. The process of data selection and processing follows the approach of Pan et al. (2019) and includes the following steps:

Initially, a list of publicly listed companies involved in M&A activities during the ten-year period is collected. The sample is then subjected to a secondary screening process: ① Only acquisitions involving publicly listed companies as buyers are included. ② Samples with acquisition amounts below 1 million RMB and equity acquisition ratios below 30% are excluded. ③ Multiple acquisitions by the same company within the same year are merged. ④ M&A samples involving asset divestitures, asset swaps, debt restructuring, and share repurchases are removed. ⑤ Only equity acquisitions are retained, and transactions involving land and asset purchases are excluded. ⑥ According to the “Management Directory for Environmental Verification Industry Classification of Listed Companies” (Circular of the Environmental Protection Department [2008] No. 373) and the “Industry Classification Guidelines for Listed Companies” published by the China Securities Regulatory Commission in 2012, this study divides the heavily polluting enterprises into 25 industries. The industry codes for heavily polluting industries are as follows: B06, B07, B08, B09, B10, B11, B12, C13, C14, C15, C17, C18, C19, C22, C25, C26, C27, C28, C29, C30, C31, C32, C33, D44, and D45. After screening, this study uses unbalanced panel data and ultimately collects 908 M&A samples. To eliminate the interference of extreme values, a 1% Winsorization is applied to the main continuous variables.

The data for this study were collected from multiple sources. M&A events were exported from the Guotai An database. Data for the selected samples were manually collected from the M&A announcements, annual reports, social responsibility reports, and sustainable development reports of the listed companies. Manual judgments were made to determine whether the M&A activities qualified as green acquisitions for heavily polluting enterprises. Data related to environmental management, certification, information disclosure, liabilities, performance, and governance of listed companies were obtained from the CSMAR database. These data were aggregated to derive the environmental information disclosure quality of the companies. Some missing data were manually collected. Government environmental regulatory data were obtained from the Public Information Transparency Index (PITI) reports for 120 cities. Data regarding ownership nature and control variables were sourced from the Wind and CSMAR databases. Stata 17 was used as the statistical analysis software.

3.2 Key variables definition and explanation

3.2.1 Dependent variable: environmental information disclosure quality

Following the methodology of Wang et al. (2021) and Li et al. (2022b), the environmental information disclosure quality (referred to as EID) of listed companies was measured using the scoring data from relevant items in the CSMAR database, including environmental management, certification, information disclosure, liabilities, performance, and governance. The total score for EID is 37, with a higher score indicating a higher level of completeness and standardization in information disclosure. Due to the presence of missing data in some dimensions of indicators, the total score was calculated as the sum of indicator scores when there were no missing values in any dimension to ensure comprehensive measurement. Table 1 provides the specific scoring criteria for environmental information disclosure quality.

Table 1 Scoring criteria for environmental information disclosure quality
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3.2.2 Explanatory variable: green M&A

Green M&A (GMA) refers to the implementation of mergers and acquisitions strategies that incorporate green principles, technologies, and management practices, with the aim of environmental protection and achieving sustainable development (Pan et al., 2019; Qiu et al., 2018). Accordingly, we conducted a text search analysis to identify and assess green M&A. Firstly, we manually collected and downloaded announcements, annual reports, and other relevant information related to M&A activities involving heavily polluting listed companies from the Shanghai Stock Exchange and Shenzhen Stock Exchange. Secondly, we carefully searched these reports, paying special attention to key information sections such as the M&A background, purpose, impact, company's development strategy, core business of the acquiring and target companies, etc. We extracted valuable information using keywords or word roots such as “green,” “clean technology,” “bioenergy,” “renewable,” “environmentally friendly,” “environment,” “solar energy,” or “air quality.” Finally, if the M&A information contained our keywords, we conducted a comprehensive analysis to determine whether the transaction could help the heavily polluting company achieve green production. If it was a green M&A, the value of this variable was set to 1; otherwise, it was considered a non-green M&A with a value of 0.

3.2.3 Moderator variables

Government Environmental Regulation (GR): Based on the research by Shen and Feng (2012), this study utilizes the Pollution Information Transparency Index (PITI Index) jointly released by the Institute of Public and Environmental Affairs (IPE) and the Natural Resources Defense Council (NRDC) since 2008. The PITI Index comprehensively and objectively reflects and evaluates the current implementation of national environmental information disclosure policies by local governments in China. It aims to assess the environmental information disclosure status of 113 key cities in China and measure the level of government environmental regulation management to better protect the environment and promote social sustainable development. The PITI Index not only reflects the environmental transparency of local governments but also indicates the regulatory intensity of government environmental responsibilities (Li et al., 2016). A higher PITI Index value indicates stronger government environmental regulation in the city where the company is located, while a lower value indicates weaker regulation. Therefore, the PITI Index is adopted as a measure of government environmental regulation, and missing values for certain cities are replaced with the average values of the respective provinces or regions (He et al., 2013).

Property Rights Nature (SOE): State-owned enterprises (SOEs) refer to enterprises in which state-owned capital holds a relatively high proportion of total capital and are regulated by the government. Unlike private enterprises, SOEs represent the will and interests of the government and are owned or controlled by the state. Based on this definition, we construct a dummy variable where a value of 1 indicates that the controlling shareholder of the enterprise is state-owned, and a value of 0 indicates otherwise.

3.2.4 Control variables

Drawing from the studies of Liu et al. (2022) and Zheng et al. (2017), this study controls for firm-specific variables and corporate governance variables. Specifically, firm-specific variables include: firm size (Size), profitability (Roa), financial leverage (Lev), listing age (ListAge), employee size (Esize), book-to-market ratio (Bm), and cash ratio (Cashflow). Corporate governance variables include board size (Board), ownership concentration of the largest shareholder (Top1), CEO duality (Dual), and proportion of independent directors (Indep). Additionally, following the approach of Kong et al. (2021), this study also controls for the following fixed effects: time fixed effects, industry fixed effects, and province fixed effects to ensure the accuracy and reliability of the results.

There are 908 observed values of heavily polluting A-share listed enterprises in Shanghai and Shenzhen from 2010 to 2019, and the relationship between green M&A and environmental information disclosure is analyzed, and the moderator role of the government's environmental supervision level and the nature of property rights is clarified. Table 2 provides the definitions and measurement methods of all variables in this study.

Table 2 Definitions and explanations of variables
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3.3 Model design

After conducting the Hausman test and rejecting the null hypothesis, we employed the fixed effects model to analyze the relationship between green M&A and the environmental information disclosure quality. We constructed Model (1) to test Hypothesis 1. Additionally, we included the interaction term between government regulatory level and green M&A in Model (2) to test Hypothesis 2. Furthermore, we introduced the interaction term between property rights nature and green M&A in Model (3) to test Hypothesis 3. The details are as follows:

$$ {\text{EID}}_{i,\,t} = \beta_{0} + \beta_{1} {\text{GMA}}_{i,\,t} + \delta {\text{controls}} + \varepsilon_{{{\text{i}},{\text{t}}}} $$
(1)
$$ {\text{EID}}_{i,t} = \beta_{0} + \beta_{1} {\text{PITI}}_{i,t} + \beta_{2} {\text{GMA}}_{i,t} + \beta_{3} {\text{PITI}}_{i,t} *{\text{GMA}}_{i,t} + \delta {\text{controls}} + \varepsilon_{i,t} $$
(2)
$$ {\text{EID}}_{i,t} = \beta_{0} + \beta_{1} {\text{SOE}}_{i,t} + \beta_{2} {\text{GMA}}_{i,t} + \beta_{3} {\text{SOE}}_{i,t} *{\text{GMA}}_{i,t} + \delta {\text{controls}} + \varepsilon_{i,t} $$
(3)

In the equation, β0 represents the intercept term, while β1–3 and δ are regression coefficients. ε denotes the error term. Controls represents all control variables. EID stands for the environmental information disclosure quality, GMA represents green M&A, PITI represents the government regulatory level, and SOE represents the Property rights nature.

4 Empirical results and analysis

4.1 Descriptive statistics analysis

According to Table 3, the mean of GMA is 0.525, indicating that green M&A companies account for a high proportion of 52.5% in the sample. This suggests that green M&A is given significant attention by heavily polluting enterprises and serves as an important pathway for their green transformation. The mean of EID is 7.38, with a maximum value of 33, a minimum value of 0, and a standard deviation of 6.775. This indicates that the overall environmental information disclosure quality is relatively low in the sample companies, with significant fluctuations in the data and large differences in the environmental information disclosure quality among companies. Therefore, it is necessary to take effective measures to enhance the quality of environmental information disclosure in companies, in order to better communicate relevant environmental information to the public, stakeholders, and government, and promote the consideration of environmental impact while pursuing economic development.

Table 3 Descriptive statistics
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4.2 Group difference analysis

The sample was divided into two groups based on whether the merger and acquisition behavior of heavily polluting enterprises complied with green standards: the Green M&A group (GMA = 1) and the Non-Green M&A group (GMA = 0). T-tests were conducted to assess the impact of these two groups on environmental information disclosure quality, aiming to obtain more accurate results.

The results of the group mean difference test are presented in Table 4. The mean of the Green M&A subgroup is 8.761, while the mean of the Non-Green M&A subgroup is 5.852. The former is significantly higher than the latter at the 1% level, indicating that Green M&A has significantly improved the environmental information disclosure quality of the firms. The results of the difference test provide evidence, to some extent, in support of Hypothesis 1 in this study.

Table 4 Group difference analysis
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4.3 Correlation analysis

Table 5 presents the Pearson correlation coefficients between variables. According to the data results, there is a significant positive correlation between GMA and EID, with a correlation coefficient of 0.215, significant at the 5% level. This result provides preliminary support for Hypothesis 1 in this study.

Table 5 Pearson correlation coefficients of each variable
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4.4 Analysis of multiple regression results

Given that the data used in this study are unbalanced panel data, we conducted a Hausman test to determine whether to use a fixed effects model or a random effects model. The results rejected the null hypothesis, indicating that the fixed effects model should be employed. The regression results are presented in Table 6. Model 1 represents the baseline regression with only control variables. Model 2 includes the variable of green M&A, which shows a significant positive correlation with environmental information disclosure quality (β = 1.7594, p < 0.01), confirming Hypothesis 1. In model 4, the interaction term is found to be significant and positive, suggesting that stringent government environmental regulation enhances the positive impact of green M&A on environmental information disclosure quality (β = 0.0670, p < 0.01), supporting Hypothesis 2. In model 6, the interaction effect is negative (β = − 0.4363, non-significant), but the regression results are not statistically significant, indicating that Hypothesis 3 is not supported. This could be due to the high costs and risks associated with green M&A (Lu, 2021). After engaging in green M&A, companies are more willing to voluntarily enhance their environmental information disclosure quality to obtain compensation effects and demonstrate their achievements to stakeholders. Therefore, even state-owned enterprises are more inclined to improve their image through green M&A to achieve long-term development goals.

Table 6 Regression results
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To further explore the influence of state-owned enterprises and non-state-owned enterprises on the relationship between green mergers and acquisitions (GMA) and environmental information disclosure quality (EID), we conducted subgroup regression analysis as shown in Table 7. It can be observed that compared to non-state-owned enterprises (β = 1.7861, p < 0.01), the relationship between GMA and EID is stronger in state-owned enterprises (β = 2.0283, p < 0.1). The reason for this could be that state-owned enterprises, to a certain extent, represent the government's position and are responsible for responding to national policies. In the context of the government's strong advocacy for environmental protection, state-owned enterprises need to swiftly implement the national guidelines for green development, respond promptly, and take a leading role (Qiu et al., 2018). Therefore, after engaging in green mergers and acquisitions, executives in state-owned enterprises are more willing to proactively disclose high-quality environmental information to demonstrate their timely response to national policies and fulfill their social responsibilities.

Table 7 Regression results by property rights nature type
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5 Robustness tests

5.1 Lagged dependent variable

After green mergers and acquisitions, a certain period of integration is required for the acquiring company to fully utilize and absorb the target company's advantages in green technology, talent, and capital resources. The resulting effects may exhibit some degree of lag (Zhang et al., 2023). Therefore, this study considers the long-term effects of green M&A on the environmental information disclosure quality of heavily polluting companies. We lagged the environmental information disclosure quality by one period (referred to as EID1) and removed samples of companies that underwent green M&A continuously for two years to reduce errors. We controlled for year, industry, and province in the analysis. The specific regression results are shown in Table 8.

Table 8 Regression results with dependent variable lagged by one period
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In Model 2, the regression coefficient of green M&A on the lagged environmental information disclosure quality remains significantly positive (β = 1.6904, p < 0.01). In Model 4, the interaction term between green M&A and government environmental regulation remains significantly positive (β = 0.0556, p < 0.05). In Model 6, the interaction term between green M&A and property rights nature is negative but not significant (β = − 0.6788, ns). The lagged dependent variable test results are consistent with the original findings, indicating the robustness of the research results.

Based on further subgroup analysis, we explored the moderating effect of corporate property rights nature. Table 9 shows that in the non-state-owned enterprise group, there is still a significant positive correlation between green M&A and environmental information disclosure quality (β = 1.8244, p < 0.01). In the state-owned enterprise group, the coefficient of green M&A is 1.8056, but not significant. This indicates that in the heavily polluting industry, compared to state-owned enterprises, non-state-owned enterprises continue to have a significant positive impact on environmental information disclosure quality one year after the occurrence of green M&A. It may be because state-owned enterprises tend to disclose high-quality environmental information in the period of green M&A to timely respond to the national green development policy. However, due to their inherent political connections, state-owned enterprises do not need to make efforts to gain legitimacy, and they face fewer environmental penalties (Zhao & Jia, 2022). Therefore, one year after the occurrence of green M&A, they do not need to improve the environmental information disclosure quality to gain legitimacy. On the other hand, non-state-owned enterprises lack inherent advantages and have less close connections with stakeholders. This drives non-state-owned enterprises to seize the opportunity of green M&A, improve environmental information disclosure quality, and convey a positive image of long-term social responsibility to the outside world, thus gaining legitimacy. Consequently, compared to state-owned enterprises, the positive impact of green M&A on environmental information disclosure quality is more enduring for non-state-owned enterprises.

Table 9 Regression results of lagged one-period group analysis
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5.2 Alternative indicator method

In this study, the robustness of the analysis was further examined using an alternative indicator for environmental information disclosure. Following the approach of Wang Feng, Yang Siyue, and Liu Na (2020), the environmental information disclosure quality was replaced with a ratio method, where the sum of various items was divided by the total score (referred to as newEID). The results are presented in Table 10, and the significance of the key variables remained unchanged. The regression coefficient of green M&A on environmental information disclosure quality remained significantly positive (β = 0.0476, p < 0.01). The interaction term between green M&A and government environmental regulation also remained significantly positive (β = 0.0018, p < 0.01), indicating the robustness of the model. The interaction term between green M&A and property rights nature negatively moderated the relationship with environmental information disclosure quality, but it remained insignificant.

Table 10 Regression results with replaced indicator for dependent variable
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5.3 Reverse causality test

In order to mitigate endogeneity issues arising from reverse causality, this study employs instrumental variable (IV) approach to examine the results. Following the study by Zhang (2021), we select the time point of the conclusion of the 18th National Congress of the Communist Party as the instrumental variable for green M&A. This variable is based on the fact that the nation has elevated ecological civilization to a strategic level and implemented a series of new measures to promote green management, which are conducive to facilitating green M&A of heavily polluting enterprises but have little impact on the environmental information disclosure quality. The essence of the instrumental variable is the occurrence of the 18th National Congress. The value is 1 after the 18th National Congress and 0 otherwise, with 2013 as the cutoff point. Table 11 presents the first-stage results of the 2SLS instrumental variable regression. The IV is statistically significant, indicating the fulfillment of the relevance requirement of the instrumental variable. The second-stage results shows that even when considering endogeneity issues, specifically reverse causality, green M&A still significantly improve the environmental information disclosure quality. This confirms the robustness of the results in this study.

Table 11 Reverse causality test
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5.4 Placebo test

Although this study controls for observable factors as much as possible in variable selection, there may still be some unobservable random factors that influence the regression results. To test whether the above results are affected by unobserved factors, we conducted a placebo test following the approach of Song et al. (2019). We repeated the above procedure 500 and 1000 times, respectively, to enhance the identification power of the placebo test. We also plotted the distributions of the estimated coefficients and their p-values to observe their significance. The logic behind this test is that if the improvement in corporate environmental information disclosure quality is driven by the implementation of green M&A, then the estimated coefficients should tend to zero. Figures 1 and 2 present the results of the placebo test, with the average estimated coefficient being approximately 0.000. Therefore, the placebo test passes, indicating the robustness of the results.

Fig. 1
figure 1

Placebo test—500 random samples

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Fig. 2
figure 2

Placebo test—1000 random samples

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6 Discussion

6.1 Discussion of findings

This study utilizes the data of mergers and acquisitions in heavily polluting industries from 2010 to 2019 as the research sample and constructs an empirical model to examine the relationship between green M&A and environmental information disclosure quality by companies. The study also explores the moderating effects of government environmental regulatory level and property rights nature on the relationship between green M&A and environmental information disclosure quality.

Firstly, the study found that green mergers and acquisitions of heavy polluting enterprises can significantly improve the quality of their environmental information disclosure. Green M&A, as a sustainable strategy suitable for the transformation of heavily polluting enterprises and consistent with the national conditions of China, can enhance environmental information disclosure quality. It informs the government and the public of the positive environmental protection actions taken by the enterprise, hel** the enterprise gain legitimacy. Consistent with previous research findings that green M&A can significantly promote enterprises' investment in environmental protection (Lu, 2021) and enhance enterprises' environmental image (Zhao & Jia, 2022), it can realize the green development of heavily polluting enterprises and transform them into energy-saving and environmental protection enterprises (Wu & Qu, 2021).

Secondly, the study found that government environmental regulation strengthens the positive impact of green M&A on environmental information disclosure quality. A higher level of government environmental regulation makes the environmental actions of enterprises engaging in green M&A more transparent, and they are more willing to disclose high-quality environmental information to demonstrate their commitment to environmental protection (Jankensgard, 2015). This finding is consistent with previous studies that found positive regulatory effects of government environmental regulation on environmental performance (Zhang & Luo, 2022) and on the positive relationship between green innovation and corporate social responsibility fulfillment in the manufacturing industry (Yu et al., 2022).

Thirdly, through grou** regression, it is found that in the year of green M&A, there is a significant positive relationship between green M&A and environmental information disclosure quality in both state-owned enterprise group and non-state-owned enterprise group, but the relationship between green M&A and environmental information disclosure quality in state-owned enterprise group is stronger. Consistent with the research of Fu et al. (2022), Zhong and Peng (2022), Sun et al. (2023a), they believe that green innovation has a stronger positive impact on state-owned enterprises and they are more willing to take environmental responsibility. However, Zhao et al. (2021) believe that due to the natural political connection of state-owned enterprises, they can destroy legitimate interests and avoid illegal punishment, which leads to the weakening of the positive correlation between green M&A and corporate environmental governance. Li (2022) argues that state-owned enterprises are less likely to take the initiative to implement green innovation.

Another interesting finding is that one year after the occurrence of green M&A, the relationship between green M&A and the quality of environmental information disclosure in non-state-owned enterprises is still significantly positive, while the relationship is no longer significant in state-owned enterprises. It may be that state-owned enterprises represent the position of the government to a certain extent and shoulder the responsibility of responding to national policies. In the context of the strong advocacy of environmental protection by the state, state-owned enterprises need to quickly implement the national green development policies, make timely responses, and play a pioneering role (Qiu et al., 2018). Therefore, in the period of green mergers and acquisitions, executives of state-owned enterprises are more willing to proactively disclose high-quality environmental information to show their attitude of timely response to national policies and assume corresponding social responsibilities. However, due to the natural political relationship of state-owned enterprises, they do not need to make efforts to obtain legitimacy and face less environmental punishment (Zhao & Jia, 2022). Therefore, one year after green M&A, they do not need to improve the quality of environmental information disclosure to obtain legitimacy. Non-state-owned enterprises lack inherent advantages and are not closely connected with stakeholders, so that non-state-owned enterprises will seize the opportunity of green mergers and acquisitions, improve the quality of environmental information disclosure, and convey to the outside world a good image of enterprises to fulfill their long-term social responsibilities, so as to obtain legitimacy. Therefore, compared with state-owned enterprises, green mergers and acquisitions have a more sustained positive impact on the quality of environmental information disclosure of non-state-owned enterprises.

6.2 Theoretical implications

Firstly, this study extends the study of green M&A on the quality of corporate environmental information disclosure. Previous studies focused more on the impact of green mergers and acquisitions on environmental protection investment, and there were inconsistent research conclusions (Lu, 2021; Sun et al., 2023b; Zhao et al., 2021), the reason is that the quality of environmental information disclosure is not considered. Exploring how green mergers and acquisitions affect the quality of environmental information disclosure can provide new evidence for the above debate. However, few people pay attention to this. Through the discovery of hypothesis 1, this paper can answer the above debate and provide new evidence on how green M&A affects the quality of environmental information disclosure.

Secondly, the level of government environmental supervision positively moderates the relationship between corporate green M&A and the quality of environmental information disclosure. With many scholars, we explored the level of government supervision to actively regulate corporate environmental management, green innovation and sustainable development (Li & Wang, 2019; Wang et al., 2021; Yu et al., 2022). Existing studies have explored the role of government environmental supervision level in the relationship between green M&A and environmental information disclosure quality. Through hypothesis 2, this paper answers the above relationship from a new perspective and adds new evidence.

Thirdly, previous studies have not reached a consensus on the moderating effect of property rights on the relationship between green M&A and environmental governance, green innovation (Sun et al., 2023a; Zhao et al., 2021). This study finds (hypothesis 3) that in the year of green M&A, the environmental disclosure quality of both state-owned and non-state-owned enterprises significantly improves. However, the positive impact of green M&A on the environmental disclosure quality of non-state-owned enterprises is more sustainable compared to state-owned enterprises. Thus, this study provides new evidence for the relationship from the perspective of green M&A, further enriching research on the moderating effects of property rights.

6.3 Practical implications

This study explores the impact of green M&A on the environmental disclosure quality of heavily polluting enterprises, clarifying the ways and means by which these enterprises can enhance their environmental disclosure quality. It provides new insights for heavily polluting enterprises to achieve green transformation and offers reference suggestions for both the government and the enterprises themselves.

6.3.1 Government level

Firstly, the government should strengthen the enforcement of environmental protection laws and regulations, encouraging enterprises in the heavily polluting industries to adopt green mergers and acquisitions as a means to improve the environmental conditions. Secondly, the government should enhance communication and dialogue with businesses, gaining timely understanding of the challenges faced by heavily polluting companies, and implementing targeted measures with increased investment to improve the effectiveness of government support and achieve better outcomes. Lastly, to ensure the effectiveness of business transformation, the government must establish a comprehensive and impartial evaluation mechanism. As an external participant in the business operations, the government lacks understanding of the organizational production processes; thus, it should place special emphasis on information feedback. With the rapid development of cutting-edge technologies such as big data, blockchain, and cloud computing, the government can utilize various media channels such as the internet and news media to collect feedback information related to corporate reforms, enabling more people to understand the reform needs of heavily polluting companies and thereby promoting the implementation of green mergers and acquisitions and improving the environmental information disclosure quality.

6.3.2 Enterprise level

Firstly, heavily polluting companies should actively adopt green merger and acquisition measures to change their development models, achieve green transformation, and strive to build a sustainable and environmentally friendly enterprise. Companies should establish the concept of sustainable and high-quality development, adapt to the new requirements of environmental protection and social responsibility, enhance green environmental awareness, and fundamentally align with policy requirements. Secondly, state-owned enterprises should take on the role of policy pioneers in implementing green transformation in the future. They should strengthen their own management and improve environmental information disclosure quality to achieve better policy response outcomes. This can be done through implementing appropriate incentive mechanisms that align individual interests with the overall interests of the company, inspiring the initiative of managers and other employees, and enhancing the cohesion of the enterprise to achieve the goal of green transformation. Thirdly, it is advisable to establish a dedicated legal department that actively responds to government environmental regulations. Companies should actively learn and master the latest environmental laws and regulations in order to adjust their production methods in a timely manner, comply with environmental policies, and avoid environmentally detrimental actions. Additionally, companies need to establish a sound internal system, including rules and regulations and process standards, and strictly enforce relevant provisions to ensure that all work is well-founded and effectively promote the implementation of green merger and acquisition projects.

6.4 Limitations and future research

This study has made valuable contributions to the understanding of the relationship between green M&A and environmental information disclosure quality. However, there are still certain limitations that need to be addressed. Firstly, in terms of control variable selection, although this study has incorporated previous research findings and examined a wide range of relevant data, it has not fully considered the characteristics of the acquisition events themselves, which could have significant implications for the study of green M&A performance. Therefore, it is necessary for future research to further explore these factors in depth. Secondly, due to the diverse content and features involved in green M&A, there is currently no unified and reliable definition or measurement standard established in the academic community to evaluate green M&A. In this study, a content analysis method was employed, and the identification of green M&A was manually collected, which may be subject to subjective biases.

7 Conclusion

This study utilized data on M&A in heavily polluting industries from 2010 to 2019 to construct an empirical model investigating the relationship between green M&A and the quality of corporate environmental disclosure. The study introduced the moderating effects of government environmental regulation and property rights on the relationship between green M&A and environmental disclosure quality. The specific research conclusions are as follows:

Firstly, employing fixed-effects regression, this study tested the impact of green M&A on environmental disclosure quality. The results revealed a significant improvement in environmental disclosure quality for heavily polluting enterprises following green M&A. This provides new evidence for enhancing corporate environmental disclosure quality.

Secondly, utilizing moderation effects, the study examined the regulatory role of government environmental regulation. The results indicated that higher levels of government environmental regulation strengthen the positive impact of green M&A on environmental disclosure quality. This finding offers insights for policymakers on adjusting regulatory policies to promote sustainable development in enterprises.

Thirdly, through subgroup analysis, it was found that one year after green M&A, the positive correlation between green M&A and environmental disclosure quality remained significant for non-state-owned enterprises but not for state-owned enterprises. This suggests that in heavily polluting industries, the positive impact of green M&A on environmental disclosure quality lasts longer in non-state-owned enterprises compared to state-owned enterprises.

This study employed fixed-effects regression and utilized various methods such as lagged dependent variables, alternative indicator approaches, reverse causality tests, and placebo tests to examine the robustness of the research conclusions. The results of robustness tests confirmed the validity of the above conclusions.