Enhancing Enterprise Integration: Analyzing the Impacts of the Belt and Road Initiative on High-Quality Development in the People ’ s Republic of China

Amid the backdrop of globalization


Introduction
As the People's Republic of China (PRC) transitions from high-speed growth to high-quality development, achieving a greater level of openness to the global economy becomes increasingly critical and can serve as a fundamental aspect of the PRC's comprehensive reform, industrial transformation, and upgrading efforts.In line with this new development paradigm, the PRC introduced the "Belt and Road Initiative" (BRI) in 2013, signifying a high-level commitment to its construction and concept.The BRI has propelled the PRC's opening-up policy onto a new stage.
On one hand, the BRI facilitates improved transportation connectivity between the PRC and its trading partners, particularly emerging partners in Eurasia.This enhancement promotes economic integration across the Eurasian region, provides a high-quality platform for trade exchanges among countries along the route, and effectively utilizes the resource endowments of these countries to facilitate highquality import trade.On the other hand, the initiative presents abundant opportunities for domestic enterprises to deepen their cooperation with international trade partners.Given the spatial layout of the BRI, central cities along the route have emerged as crucial hubs and active participants in cross-regional economic cooperation.
In March 2015, the PRC government released its Vision and Actions to Promote the Joint Construction of the Silk Road Economic Belt and the 21st Century Maritime Silk Road, which identified 10 land-based cities along the silk road economic belt and 16 maritime towns along the 21st century maritime silk road (National Development and Reform Commission, Ministry of Foreign Affairs, and Ministry of Commerce of the People's Republic of China 2015). 1 Enterprises within these central cities along the BRI have invigorated logistics innovation, industrial development, and trade investment, and created avenues for high-quality import trade.The China Import Development Report 2021 emphasizes the increasingly prominent role of the import trade within the new development pattern (Wei 2021).Actively expanding imports has become a fundamental component of the PRC's campaign of opening-up to the outside world.
The report reveals that from 2014 to 2021 the PRC's imports from the 64 countries participating in the BRI increased from $483.4 billion to $776.5 billion on average annual growth of 8.7%.However, it is still necessary to determine whether the BRI contributed to the development of import trade quality beyond quantitative growth.To do so, it is essential to explore the corresponding mechanisms and potential variations across different scenarios to shed light on the impacts and challenges of the BRI and facilitate the PRC's double-cycle strategy and high-quality economic development. 2his study focuses on the core cities along the BRI and aims to examine the impact of the initiative on the growth pattern of the PRC's import trade.Specifically, it investigates whether the BRI has contributed to the enhanced quality of products imported by Chinese firms and seeks to elucidate the underlying mechanisms.Existing literature closely related to this study has shed light on various aspects of the BRI.With regard to foreign direct investment (FDI), Nugent and Lu (2021) demonstrated that the implementation of the BRI has significantly increased the level of FDI in the PRC's industries that are facing issues of excess production capacity or pollution.With regard to innovation among Chinese enterprises, through empirical analysis of the PRC's A-share listed companies, Li et al. (2022) found that the BRI has notably bolstered the sustainable innovation capabilities of domestic enterprises.
Concerning global value chains and carbon emissions, Ge, Dollar, and Yu (2020) discovered that most BRI countries exhibit weaker participation in global value chains compared to non-BRI countries.Building upon this, Shi et al. (2022) focused on the impact of global value chain participation on carbon emissions among BRI countries to highlight that BRI countries positioned further down on global value chains tended to experience increased carbon emissions.This perspective provides valuable insights for carbon emissions reduction efforts in BRI countries.
In terms of production capacity cooperation and utilization, Feng et al. (2020) emphasized the significance of the various aspects of power cooperation, ranging from generation and transmission to technology development and capital-raising, considering that power is a crucial component of infrastructure.They propose that in designing and implementing the BRI, the PRC should prioritize strengthening its power cooperation with member countries of the Association of Southeast Asian Nations.Meanwhile, Zhao et al. (2022) argue that trade cooperation between the PRC and BRI countries should be evaluated based on the benefits derived.
As for economic development, Ma (2022) found that the BRI is playing a substantial role in improving local economic benefits, mainly by reducing transport costs for goods and people, and improving transport efficiency, thus promoting international trade and the flow of investment and increasing economic growth.Especially in low-income countries, this promotional effect is more pronounced.
This research broadens the scope of the aforementioned studies by examining the impact of the BRI on the growth pattern of the PRC's import trade, with a specific focus on import products' quality enhancement and the underlying mechanisms behind such enhancements.In addition, there is a small amount of literature on the impact of the BRI on core cities along the route.For example, Ma (2022) tested the promotion effect of the BRI on economic growth at the national level, while Kong et al. (2021) focused on testing the data of prefecture-level cities in the PRC and proved that the BRI is conducive to urban economic growth.Su et al. (2019) evaluated the health of the development ecosystem of 14 cities in the PRC along the BRI.In the literature on the relationship between the BRI and international trade, Wang, Qiu, and Choi (2019) proved that the initiative is beneficial to advancing the PRC's export performance through upgraded infrastructure and improved logistics, while Yu et al. (2020) focused on the export potential of the BRI for countries along the route.
Most studies have focused on the countries participating in the BRI and the relationship between the initiative and export performance, rather than import trade.Therefore, this study uses the BRI as a quasi-natural experiment and a difference-indifferences (DID) model with core cities along the route as the research objects.Using the PRC's customs import data from 2010 to 2015, we examine the impact and mechanism of the initiative on Chinese enterprises' import trade.This study also compares whether the BRI affects enterprises' import trade in terms of quantitative and/or qualitative growth.
Compared with the previous literature, the main innovations of this study are as follows.First, most of the existing studies assess the impact of the BRI on the import and export trade between the PRC and countries along the route at the national level.In contrast, this study takes core cities along the route as the research objects and pays attention to the impact of the BRI on Chinese enterprises' import trade.Second, this paper distinguishes the import structure of Chinese enterprises from two perspectives-"quantitative growth" and "qualitative growth"-and focuses on whether the impact comes from the quantitative or the qualitative growth model.This study provides novel explanations for further deepening the BRI effect, proactively expanding imports, and achieving the high-quality development of foreign trade.Third, this study examines the impact on and mechanism by which the BRI affects the quality of products imported by enterprises in core cities along the route by measuring the diversification of imported products and the urban innovation index.This will help deepen understanding of the intrinsic relationship between the BRI and import product quality.
The rest of the study is organized as follows.Section II provides the policy context and mechanism analysis.Section III describes the data and empirical method.Section IV presents the empirical results and commentary, section V discusses heterogeneity analysis, and section VI details the mechanism of action test.Section VII concludes and presents the policy implications.

II. Mechanism Analysis
The proactive expansion of the import trade is crucial for the PRC to achieve the high-quality development of its foreign trade.As the PRC has become the secondlargest economy in the world and more foreign high-quality products, services, and enterprises are entering the country, it will force the transformation and upgrading of the domestic industrial structure, increase the degree of competition in the domestic market, and improve the business environment in the PRC (Zhang et al. 2020).Therefore, the PRC has been holding the China International Import Expo since 2018 and is giving increasing attention to the role of the import trade in promoting economic development. 3On the one hand, the expansion of imported goods and services due to the BRI is conducive to further reducing tariff levels and eliminating various nontariff barriers, thereby reducing the institutional and input costs brought by the import links of enterprises, effectively reducing the risk of interruption to the import trade of enterprises and increasing the type and scale of products imported by enterprises, which will lead enterprises to import products of higher quality (Amiti and Khandelwal 2013) and bring new development opportunities for the industrial transformation and upgrading of importing countries (Halpern et al. 2015, Kong et al. 2021).Zhou et al. (2022) found that by improving this import trade environment, the BRI can significantly improve the quality of food imports from BRI countries.On the other hand, the BRI promotes facility connectivity, which is the basis for cooperation and development between countries.By strengthening trade exchange platforms through the PRC-led infrastructure construction in BRI countries, the PRC's markets can be fully developed by utilizing more high-quality resource endowments (e.g., energy) provided by BRI countries.At the same time, existing studies show that transportation infrastructure development and improved connectivity reduce trade costs and promote trade facilitation and liberalization (De Soyres et al. 2019;De Soyres, Mulabdic, and Ruta 2020;Yang et al. 2020), which can enable the PRC to expand its economic opening to the outside world.
Faced with the rise of anti-globalization and trade protectionism, it is becoming increasingly difficult for the World Trade Organization to effectively resolve trade issues (Jia and Liu 2020).In response, the PRC has put forward new and higher requirements for an enhanced process of opening up.On the basis of actively expanding imports, it is necessary to bring in, or import, high-quality products.The PRC will continue to gradually optimize the technical efficiency and complexity of importing industries to improve the quality of imported products.Therefore, this study proposes two hypotheses.Hypothesis 1 is that the BRI will be conducive to improving the quality of products imported by enterprises in core cities along the BRI's route.
The BRI provides enterprises with a wide range of trade platforms, advocates trade liberalization, and enables enterprises to sell and profit in larger markets.Expanded market size and demand promote enterprise innovation (Aw, Roberts, and Yi Xu 2011).At the same time, trade liberalization has also intensified market competition.The huge market provided by the BRI comprises many countries, and the market preferences of different countries vary, forcing companies that seek a larger market share to improve product quality to adapt to different international markets.The requirement of differentiation becomes an external incentive to promote the innovation capability of enterprises (Bloom, Draca, and Van Reenen 2016;Geng and Kali 2021;Li, Chen, and Wohlfarth 2022).According to the resource-based theory (Wernerfelt 1984), the BRI brings more available production factors to associated firms, and firms have more available resources that can be allocated for innovation, reducing the crowding-out effect of innovation activities (Wu and Si 2022).The existing literature argues that increased openness to the outside world leads domestic firms to absorb the intermediate technology of high-quality imports, enhancing their own (Halpern, Koren, and Szeidl 2015).As the PRC's gross domestic product (GDP) per capita rises, efficiency and labor productivity become particularly important.Economic growth is driven by capital, labor, and high-quality development through scientific and technological innovation.It shows that local innovation capability plays a vital role in enterprises' product quality.
At the same time, the BRI promotes cooperation in significant infrastructure projects, constructs industrial parks, develops international strategies with more flexible cooperation models, and fully integrates domestic enterprises into global value chains.Thus, it broadens the idea of international cooperation, provides more resources and opportunities for import diversification, and makes it possible to create diversified products.Product diversification expands the variety of intermediate inputs available for final products, significantly increasing technological content.As the intermediate inputs complement products, they also improve the total factor productivity of domestic enterprises and increase demand for quality import products.In addition, countries import a greater variety of products, which generates a more substantial technological spillover effect through acquired knowledge and technology and leads to more product competition (Hsieh and Klenow 2009).Thus, enterprises are prompted to accelerate research and development efforts and improve productivity.Enterprises that import also seek to improve the quality of their imported products as a product of the fierce competition (Feenstra and Sasahara 2018;Feenstra, Ma, and Xu 2019).Therefore, this study proposes hypothesis 2, which is that the BRI improves the innovation index of core cities and the diversification of imported products, which ultimately enhances the quality of products imported by enterprises.

A. Data Description
Confined to the data available, this study determines the sample period as 2010-2015 and matches the PRC's customs import database with the China City Statistical Yearbook (National Bureau of Statistics of China 2015).Then, we obtain import trade data at the enterprise level and economic indicators at the city level. 4fter deleting the missing data in the PRC's customs import data and data that cannot be matched between customs import data and the China City Statistical Yearbook, this study observes 874,671 enterprises and 287 prefecture-level cities that are included in the Vision and Actions to Promote the Joint Construction of the Silk Road Economic Belt and the 21st Century Maritime Silk Road, issued by the National Development and Reform Commission, the Ministry of Foreign Affairs, and the Ministry of Commerce in March 2015.Meanwhile, this study adds Lianyungang, Suzhou, Hohhot, and other critical land-based and port cities along the route.Due to the lack of data, Hong Kong, China and Macau, China are not considered in this study.This study also identifies 37 core cities along the BRI. 5 In addition, some significant data are logarithmically treated in this study, such as per capita GDP, year-end household population, and the number of college students per 10,000 people.Table 1 reports the specific variables and descriptive statistics.

Difference-in-Differences Model
In terms of the benchmark model, this study uses the DID model to estimate the implementation effect of the BRI on Chinese enterprises.Following Lyu et al. (2019) and Chen et al. (2021), we select 37 core cities along the BRI as the policy implementation group and noncore cities as the control group, and construct the following model: The explained variable, y it , is used to measure the quantitative growth of enterprises' import trade, including total import value, total quantity, and average price.y it is also used to measure the qualitative growth of enterprises' import trade, including import products' quality.ydyl i is a dummy variable, indicating whether the enterprises are located in a BRI city.t t is the dummy variable, indicating whether the policy is implemented.We refer to the practice of Kong et al. (2021) and set 2013 as the year of implementation for the BRI.And the core explanatory variable ydylt it is the interactive item of firm i and year t.This study focuses on the sign and significance of coefficient α, while β i , t , and " it denote the fixed effects of firm, year, and random error terms, respectively; X it denotes a set of city-level control variables.

Variable Measures a. Explained Variables
Following Gervais (2015) and Roberts et al. (2012), this study estimates import product quality at the firm-product-country-year level.For a specific product with a Harmonized System (HS) code in the PRC's customs import data, the import volume of firm i from country m in year t is simplified as in equation ( 3): That is, equation (4): where ln E mt À ln P mt is a dummy variable set from country and year dimensions, ln p imt denotes the price the firm pays for imported products from country m, and ( À 1) ln γ imt measures the residual value of imported products' quality.However, this measure does not consider price endogeneity and product diversification.We learn from Khandelwal (2010) and Khandelwal, Schott, and Wei (2013) that, conditional on price, imports with higher market shares are assigned higher quality; therefore, we add the scale of market demand in equation ( 4) to control product variety and use the average price as the instrumental variable of the imported products' price, p imt .The average price is that of imported products from countries other than country m.Equation ( 5) is as follows: Equation ( 5) can be used to obtain the quality of a specific HS product imported by company i from country m in year t.To unify the dimensional unit of equation ( 5) to obtain standardized quality data of import products, equation ( 6) shows: where min quality imt and max quality imt denote the minimum and maximum values of a specific HS product at the firm-country-year level, respectively.The overall quality indicator is shown in equation ( 7) as follows: where v imt denotes the value quantity (value) in the PRC's customs import data.
In addition, this study will measure the import characteristics of enterprises in terms of the quantity of growth-which includes the total import value (value), the total quantity (quantity), and the average price (price)-and compares them with the quality of imported products.This helps to understand further the significance of the BRI for the high-quality development of enterprises.

b. Core Explanatory Variables
The core explanatory variable in this study is the dummy variable (ydylt it ), which is constructed using enterprise i and year t.Specifically, t t denotes the year dummy variable.According to when the PRC proposed the BRI, we set 2013 as the starting year of the initiative.The year before 2013 is set to 0, and the year after 2013 is set to 1. ydyl i denotes the dummy variable of the policy implementation group, which is set to 1 if the enterprise is located in the city covered by the policy, and 0 otherwise.

c. Control Variables
In line with Lu, Dong, and Ye (2021), we set control variables according to whether the city is a provincial capital city or a municipality directly under the central government and whether it is a crucial city in the Yangtze River Economic Belt. 6hese cities belong to the provinces' development centers, and they are likely to be included among the core cities along with the BRI.Combined with the research of Kong et al. (2021), Ma (2022), Mohsin et al. (2022), and Wu and Si (2022), we also select the following control variables in this study: (i) regional economic development: per capita GDP of each city; (ii) city size: year-end household population; (iii) support of government policies: proportion of fiscal expenditure to local GDP; (iv) level of urban infrastructure: urban road area per capita; (v) level of opening up of cities to the outside world: proportion of actual foreign capital use to local GDP; (vi) level of regional informatization: postal and telecommunication business income; (vii) industrial structure: proportion of secondary industry to local GDP (since industry plays a crucial role in urban development, especially manufacturing); and (viii) level of human capital: average years of schooling (as with most of the existing studies).However, since it is difficult to obtain data from prefecture-level cities, we use the number of college students per 10,000 people.

Mechanism Test Model
The empirical test of this study shows that the BRI improves the quality of products imported by Chinese enterprises.Whether or not the two channels of hypothesis 2 are realized needs to be verified by constructing a mediating effect model based on the Baron and Kenny (1986) method.The mediating effect model is as follows: In this study, the mediating variables are product diversity (div) and an urban innovation index (inv).According to the steps of the mediating effect model, the first step is the same as the basic regression.If the results are significant, the second step is to test the effect of the BRI on product diversity and the urban innovation index.If it is still significant, the next step is to test the BRI's combined effect on intermediary variables and the quality of imported products.
For the mediating variable of product diversity, referring to Boschma, Minondo, and Navarro (2012), we match the customs database HS 96 codes with the International Standard Industrial Classification RV3 and obtain the four-digit product data.Then, we measure the revealed comparative advantage (RCA) index in the firmcity-product level: where W f , h, t is the amount of imported product h in city f and year t; W f , t is the total amount of imported products in city f in year t; W h, t is the total amount of imported product h in the country in year t.W t is the amount of all imported products in the country in year t.Referring to Hausmann and Hidalgo (2010), we take RCA = 1 and RCA = 0.5 as the critical values and sum up RCA above the critical values to determine the degree of product diversity.A larger value indicates that the type of imported product is more diverse.Then, we get the import product diversification indicators div1 and div0.Referring to Yu and Cai (2021), we measure the innovation power index of each city from the China City and Industry Innovation Power Report 2017 (Kou and Yang 2017).

IV. Results of the Difference-in-Differences Model
A. Balance Test Drawing on Gentzkow (2006) and Li, Lu, and Wang (2016), this land study compares the differences in control variables between BRI core and noncore cities, as shown in Table 2. First, observing the statistical characteristics of the variables in columns ( 1) and ( 2), there are 64.9%core cities and 2.8% noncore cities among the provincial capitals and municipalities.There are 29.7% core cities among the key cities belonging to the Yangtze River Economic Belt, while only 13.2% are noncore cities.The values of indicators for core cities are higher than those for noncore cities for indicators such as per capita regional GDP, year-end household population, road area per capita, post and telecommunications business income (regional GDP), actual foreign investment, and the number of college students per 10,000 people.This suggests that the economic development level, city scale, infrastructure construction capacity, information level, openness to the outside world, and human capital status of core cities are better than those of noncore cities.Meanwhile, government support for and the industrial structure of noncore cities are both slightly higher than those of core cities, though the former finding is not significant.So if there are no control variables, column (3) shows that there are indeed significant differences between the two groups of cities for various indicators.In contrast, after adding control variables, as shown in column (4), the differences in the characteristics all become smaller, and most of the indicators are no longer significant.Therefore, if we choose appropriate control ENHANCING ENTERPRISE INTEGRATION 347 variables to balance the economic aspects of core and noncore cities, this study's empirical analysis is more convincing.

B. Benchmark Regression
This section constructs a DID model to study the impact of participating in the BRI on Chinese enterprises' imports.The results are shown in Table 3, with columns (1) and ( 2) presenting the impact of the BRI on import products' quality, which is logarithmically treated.In column (2), we add the control variables at the level of core cities along the route.The results show that the regression coefficient of the interaction term ydylt is significantly positive at the 1% level, suggesting that the BRI significantly improves the quality of products imported by Chinese enterprises.
Further, columns (3)-( 5) use total import value, import quantity, and average price of imported products, respectively, as dependent variables.The results show that the BRI also significantly increases total import value and the average price of products, but the coefficients are significantly lower.At the same time, the impact on the total quantity of imports is negative, and the coefficient is small.Thus, the BRI mainly strengthens Chinese enterprises' imports through improved product quality.Now that the PRC's economy has entered a new normal stage and enterprises are constantly exploring new development models, the BRI offers significant potential for enterprises to upgrade their imports from crude and quantity oriented to intensive and quality oriented.

C. Validity Analysis of Difference-in-Differences Estimation: Parallel Trend Test
To test the validity of the DID model, this study conducted a parallel trend test for the policy implementation group and the control group to determine whether the BRI meets the prerequisites for DID estimation.pre3, pre2, and pre1 denote 3 years before (2010), 2 years before ( 2011) and 1 year before (2012) BRI implementation, respectively, while post1 (2014) and post2 (2015) refer to 1 year and 2 years after the implementation, respectively.They all represent the intersection of the time dummy variables and the ydyl treatment variable.We use them to take regression tests using import products' quality.The results are shown in Table 4 and Figure 1.The coefficients before 2013 are not significant at the 1% level, which means that before implementing the BRI, there was no significant difference in the quality of imported products between the treatment group and the control group.And the significance of coefficients increased significantly after 2013, which means that after the BRI, there was a significant difference between the import product quality of the treatment group versus the control group.Therefore, this study passes the parallel trend test and can use the DID model to measure the impact of the BRI.

D. Robustness Tests 1. Placebo Test
To test whether the city-time variables are missing, we draw on Li, Lu, and Wang (2016) and La Ferrara, Chong, and Duryea (2012) to randomly select cities along the BRI from the sample.We then conduct a placebo test on the base regression results in column (2) of Table 3 to obtain the spurious estimated coefficients.This procedure is repeated 500 times, obtaining the distribution of the estimated coefficients for the random control group shown in Figure 2. According to the principle of the placebo test, if the interaction term obtained from the spurious treatment group does not significantly affect the explained variable-that is, the coefficient estimates of ydylt are around 0-it indicates that the DID model is identified without error.From Figure 2, the mean values of the spuriously estimated coefficients fluctuate around 0; therefore, the regression results do not lead to serious bias from the omission of both city-time level variables.

Score Propensity Matching Test
To avoid possible nonrandom bias in the selection of core cities along the BRI, this study uses the combination of propensity score matching and the DID model for robustness testing.Based on the control variables such as provincial capital cities or municipalities, per capita GDP, year-end household population, fiscal expenditure, and the ratio of secondary industry to regional GDP, this study establishes a logit model for cities along the BRI, and performs 1-1 nearest neighbor.Then, we obtain the kernel density distribution before and after the matching sample shown in Figures 3 and 4   ENHANCING ENTERPRISE INTEGRATION 351 revealing that the distribution patterns of the treatment group and control group overlap after matching, which weakens the sample selection bias.Further, we take the regressions of import products' quality, total amount of imports, and average product price.The results in Table 5 show that the BRI still significantly increases import  products' quality, total imports, and the average price of products.While the coefficient size is significantly lower, it remains consistent with the baseline regression results.It indicates that the BRI has promoted enterprises' quality-based import trade patterns.

A. Nature of Enterprises
This study classifies firms into state-owned enterprises (SOEs), private, and foreign firms-using the classification method of Yu (2015)-and examines sensitivity to the BRI among the three different types of firms. 7Table 6 reports the results of this regression, which show that the BRI significantly improves the quality of imported products among foreign firms, while the impact on SOEs and private firms is not significant.The possible reasons are that the market dynamics of SOEs are low and their institutional systems are chronically inefficient, thereby failing to provide 7 According to the enterprise registration form code in the PRC's customs trade database, we classify 110, 141,143,and 151 as SOEs;310,320,330,340,210,220,230,and 240 as foreign-funded enterprises; and the rest are classified as private enterprises.In simple terms, SOEs include collective enterprises and state-owned enterprises; foreign-funded enterprises include wholly foreign-owned enterprises, Chineseforeign joint ventures, and Chinese-foreign cooperative enterprises; and private enterprises include private enterprises and individual industrial and commercial households.
sufficient benefits to stimulate them to import high-quality products (Hale and Long 2006).However, foreign-owned enterprises have a more flexible institutional system and can effectively absorb the technological spillovers of imported products and improve their innovation capabilities.Therefore, foreign enterprises have more demand for high-quality imported products, while the BRI has prompted foreign enterprises to introduce more high-quality products, thus improving import products' quality.

B. Type of Imports
Following the process used on the United Nations trade statistics website, we match the HS code and the Broad Economic Categories generalized classification to obtain the data of imported intermediate goods and capital goods, and then regress the imports of the two groups of products with the BRI. 8The results are shown in columns (1) and ( 2) of Table 7.The regression results show that the BRI significantly impacts import product quality for capital goods, but not for intermediate goods.A possible reason is that there are processing issues in the PRC's import trade.For example, processing trade enterprises may only have the capacity to undertake simple assembly or assembly procedures in the production division system and therefore do not obtain foreign core technologies.As a result, processing trade enterprises import many intermediate goods, which may replace the innovation activities of enterprises and lead to enterprises lacking highly skilled personnel.Thus, enterprises are left unable to absorb the technological spillover effects of imported intermediate goods and achieve enterprise transformation and upgrading, thereby failing to improve import products' quality (Liu and Qiu 2016).
In contrast, the PRC's industrial structure matches its capital goods imports.Thus, it increases demand for complete sets of foreign equipment and advanced capital goods (Herrerias and Orts 2013).The BRI has created conditions for imported capital goods in terms of reduced costs and transportation distances, and enterprises can import more advanced machinery and equipment from abroad to produce products that cannot be produced due to technical constraints.Thus, it improves the quality of imported products (Goldberg et al. 2009).

C. Cities' Locations
Although the sampled cities are all participants in the BRI, there are large differences in the cities' geographic locations and levels of economic development.Therefore, it is necessary to distinguish the impact of the BRI on the imports of enterprises in different cities along the land and maritime silk roads. 9The results are presented in Table 7: The coefficients of the ydt and ylt interaction items are insignificant and significantly positive in columns (3) and (4), respectively.This indicates that the impact of the BRI on the quality of imported products by enterprises is mainly reflected in the cities along the maritime silk road.In contrast, the impact on cities along the land silk road is not significant.It is not difficult to understand why there is a geographic discrepancy since cities along the maritime silk road are located mainly in the eastern region.They have geographic advantages, faster economic development, a stronger awareness of enterprise research and innovation, greater government support, and stronger demand for foreign high-end technology products.Therefore, the sensitivity of imported products' quality in cities along the maritime silk road is significantly different from that of the land silk road.

A. Product Diversity
Column (1) of Table 8 is the regression result of equation ( 8), which shows that the BRI significantly improves imported products' quality.Columns ( 2) and ( 4) are the regression results of equation ( 9), which shows that whether the threshold value of the RCA index is 1.0 or 0.5, the BRI significantly increases the level of imported product diversity.Columns (3) and ( 5) are the regression results of equation ( 10).The results report the impact of the core explanatory variable (BRI) and the intermediary variable (product diversity) on the quality of imported products.We can find that the estimated coefficient of the intermediary variable (product diversity) is positive, indicating that product diversity and import products' quality are positively correlated, and that the BRI improves the quality of enterprises' imports through the path of increased diversity.Therefore, hypothesis 2 is verified.

B. City Innovation Index
Table 9 shows the test results of the city innovation index.Column (1) examines the effect of the BRI on the quality of imported products.The results show that the BRI significantly contributes to import products' quality; column (2) examines the effect of the BRI on import products' quality and shows that the BRI is conducive to increased urban innovation.Finally, we examine the effect of urban innovation on import products' quality and find that an improvement in urban innovation can significantly promote import products' quality.Therefore, the BRI can enhance the quality of imported products by improving the city innovation index.This finding verifies hypothesis 2.

A. Main Conclusions
While the PRC's imports continue to expand, there is a dearth of literature examining the impact of the BRI on imports.In this study, we utilize the PRC's customs import data from 2010 to 2015 and employ a DID model to investigate the influence of the BRI on Chinese enterprises' import trade and the underlying mechanisms of this influence.Specifically, we focus on differentiating between quantity growth and quality growth by considering total import value, import quantity, average import price, and the quality of imported products.Our objective is to determine whether the observed effect stems from a quantity growth or a quality growth model.The main findings are as follows: Firstly, in contrast to the quantity growth model, the BRI significantly promotes the import product quality of Chinese enterprises, and this effect withstands robustness testing.Secondly, a heterogeneity test reveals that the BRI impacts the import products' quality of different enterprises in varying ways.Foreign enterprises, capital goods, and enterprises located in cities along the maritime silk road are more likely to experience a positive influence on their import products' quality due to the BRI.Finally, in terms of the underlying impact mechanism, the BRI affects the import products' quality of the PRC's firms through two main channels: (i) an increase in product diversity, and (ii) the enhancement of cities' innovation capacity.
By shedding light on the impact of the BRI on the PRC's imports and elucidating the mechanisms involved, this study contributes to the existing literature and provides valuable insights for policymakers and businesses.

B. Policy Implications
In line with the findings of this study and to further deepen the BRI effect, actively expand imports, and achieve the high-quality development of foreign trade, the following policy recommendations can be suggested.
The findings of this study show that the BRI improves the quality of products imported by enterprises.Therefore, Chinese enterprises can achieve high-quality development by actively integrating into international trade patterns.Policymakers should seek to improve interactions between the BRI and import expositions.At such import expositions, the countries and regions along the BRI can showcase their development achievements and discuss investment opportunities to better connect with the huge dividends of the PRC's domestic market.The PRC's regions should adhere to the "bringing-in" strategy, implement a series of trade policies to expand imports, optimize the import structure, and expand the import of technology-based, high-end products.In particular, the PRC should focus on introducing industries such as integrated circuits and biomedicine to improve its core competitiveness and accelerate the development of related domestic industries.Further, the PRC should establish and improve the high-quality bringing-in service system of enterprises, improve the production and supply chains of the PRC's manufacturing sector, better meet the needs of Chinese companies for foreign industries and services, and provide a high-quality import trade exchange platform for domestic and foreign companies.
The results of the subsample regression in this study show that the BRI also significantly improves the import products' quality of foreign-funded enterprises, capital goods, and enterprises in cities along the maritime road.Therefore, given the different nature of enterprises, SOEs and private enterprises should be encouraged to take tailored measures to participate in the BRI and strengthen foreign trade through various means, especially to promote the development of tertiary and high-end manufacturing industries.For different imports, more targeted BRI policies can encourage enterprises to import high-quality intermediate goods, especially advanced technology equipment and key components to truly achieve technological progress in the PRC's manufacturing industry.Mutual coordination is needed among different cities along the BRI's core routes, especially cities along the maritime road, which can act as guides or "leading sheep," by capitalizing on their development position and driving Chinese enterprises to bring in high-quality products.
Finally, the influence mechanism test in this study shows that product diversification and urban innovation capabilities are important paths for the BRI to influence the quality of enterprises' imported products.Therefore, the PRC should enhance the diversification of imported products, optimize and upgrade the structure of imports, and introduce and absorb advanced foreign technology and management experience.At the same time, the government needs to provide sound policy support, establish incentive systems for enterprises, and fully protect and stimulate their independent innovation, especially through increased investment in independent research and the development of technology-intensive industries.Enterprises should also make full use of import product diversification and innovation capabilities to drive high-quality foreign openings through the BRI, thereby improving the quality of enterprises' imported products.

C. Limitations
From the perspective that core BRI coastal cities are driving high-quality foreign openings, this study discusses the effects of the BRI on the quality of enterprises' imported products.However, due to the availability of data and the dimension of the study, there are still four points to be improved in future studies.First, this study is based on the import trade data of Chinese enterprises from 2010 to 2015, which reflects only the short-term effect of the BRI on Chinese enterprises' imports.We look forward to obtaining longer-term-horizon data for long-term effect assessment in the future.Second, most of the existing literature has measured export products' quality, so there may be limitations and shortcomings in measuring import products' quality based on the measurement method used for exports.We hope to obtain more accurate and rigorous measurements in future studies.Third, the high-quality opening to the outside world should include improved import products' quality, efficiency, technical complexity, and structure.Therefore, we should take a more comprehensive and systematic view to understand how the PRC achieves high-quality trade transactions under the BRI, which is another important direction to be explored in future research.Finally, this study reveals that product diversity and innovation capacity of cities are important mechanisms influencing import products' quality, but are there also other mechanisms that influence import products' quality?Taken together, these are important considerations for future research.

Figure 1 .
Figure 1.Parallel Trend Test of the Difference-in-Differences Model ,

Figure 3 .
Figure 3. Kernel Density Distribution before Sample Matching

Figure 4 .
Figure 4. Kernel Density Distribution after Sample Matching

Table 2 .
Balance Test

Table 3 .
Base Regression Results FE ¼ fixed effect, N ¼ number of observations.Note: Values in parentheses are standard errors.*** and ** denote variables at 1% and 5% significance levels, respectively.Source: Authors' calculations.

Table 5 .
Estimation of the Difference-in-Differences Model FE ¼ fixed effect, N ¼ number of observations.Note: Values in parentheses are standard errors.*** denotes variables at 1% significance level.Source: Authors' calculations.

Table 6 .
Distinguished Examination of the Nature of the Enterprise

Table 7 .
Types of Imports and Distinctions between Cities along the Land and Maritime Silk Roads

Table 8 .
Impact of Product Diversity on Enterprises' Imports FE ¼ fixed effect, N ¼ number of observations, RCA ¼ revealed comparative advantage.Note: Values in parentheses are standard errors.*** denotes variables at 1% significance level.Source: Authors' calculations.

Table 9 .
Impact of City Innovation Index on Firm Imports