Impact of Environmental CSR, Service Quality, Emotional Attachment, and Price Perception on Word-of-Mouth for Full-Service Airlines

: This research aimed to develop a theoretical framework relating environmental corporate social responsibility (environmentally friendly business, compliance with environmental regulations, environmentally friendly products / services, environment-related mission, environmental preservation e ﬀ orts), service quality, emotional attachment, and word-of-mouth in the full-service airline industry. A quantitative approach with a survey methodology was used for attaining the research goals. Our empirical ﬁndings demonstrated that environmental corporate social responsibility plays a crucial role in eliciting airline customers’ word-of-mouth, and that service quality and emotional attached have a critical mediating e ﬀ ect. In addition, price perception moderated the degree of the relationship strength between environmental corporate social responsibility and word-of-mouth. The salient contribution of emotional attachment to the prediction power increase of the proposed model for word-of-mouth was also uncovered. Overall, this research presents apparent understanding of airline corporate social responsibility for the environment and its role in the process of generating word-of-mouth.


Introduction
An increasing number of customers have gradually awarded the significance of responsible consumption and of socially responsible companies pursuing social benefits rather than solely seeking excessive profits [1][2][3][4][5]. Recently, customers, especially those sensitive to a company's socially responsible activities for the society and the environment, often show a positive attitude toward the company and engage in repeat patronage behaviors [6][7][8][9][10]. A company's corporate social responsibility endeavors and its proactive promotions of such efforts play the significant role in affecting customers' purchase behaviors and improving the company's financial outcomes and market share [1,6,[11][12][13], which stimulate a company to achieve a corporate sustainability structure and create a propitious balance in terms of social, environmental, and economic benefits [14].
Corporate social responsibility, especially for the environment, nature, ecology, and its influence on customers' responses/behaviors is particularly fundamental in the airline industry [15][16][17] in that airline product consumption occurs in locations other than customers' residential areas and is not free from diverse environmental/ecological issues [12,16]. It is irrefutable that an airline firm's corporate sustainability actions with social and environmental responsibilities are fast becoming a critical facet of the company's successful operation and marketing tactics in the airline marketplace [16][17][18]. Recognizing the crucial value of corporate social responsibility in boosting customer positive responses for the company, airline operators are increasingly active in implementing corporate social responsibility initiatives for the environment and promoting corporate social responsibility practices as important tools for customer retention/attraction, word-of-mouth, and brand marketing strategies under the severely competitive market environment [12].
The current research literatures relative to hospitality management, tourism, and marketing have made endeavors to associate a firm's corporate social responsibility for the environment/society with various constructs that are essential in customer behavior formation [1,3,5,19]. Wang and Han [3] proposed that airline customers' perceptions of corporate social responsibility for the environment are related to cognitive evaluation factors (e.g., corporate image/reputation, quality) in generating behavioral intentions. Han et al. [7] explored customer perception of corporate ecological responsibility as it generates brand love, brand respect, and loyalty for the airline company and its services. Chen et al. [16] discussed the relationships between corporate social responsibility, positive emotion (e.g., trust), and customers' loyalty behaviors. Although the direct effect of corporate social responsibility on customer intentions/behaviors was verified in previous studies (e.g., [3,16]), the rare example of an empirical study of the airline industry that evaluates the association of the critical variables of corporate social responsibility, customer perception, emotional attachment, and behavioral intention exists [7]. Especially the perspective of exploring the interventional role of customer perceptions of airline service quality and their emotional attachment as mediation factors should be further emphasized, in that these two factors have always been regarded as the predominant elements affecting customer satisfaction with an airline and subsequent loyalty intentions [20][21][22][23][24][25], and Rashid et al. [8] indicated that corporate social responsibility actions could influence customer perceptions of service quality and their affective emotions/attitudes.
In addition, while some existing studies successfully unearthed the significance of environmental corporate social responsibility in customers' general loyalty generation processes and uncovered its particular role in explicating specific loyalties such as repurchase [6,9], engagement in positive corporate events [8], and revisiting [9], scholarly research on customer loyalty in the airline industry focused more on the re-flying behavior (e.g., [20]). Afifah and Asnan [6] pointed out that a loyal customer is not limited to being a consumer, but maintains the favorable attitudes and emotions for the same service provider. Han et al. [7] and Rajagurn [21] also expressed that customer loyalty to airlines is not only manifested in re-flying/repurchase but also in active word-of-mouth behaviors. It is worth mentioning that not all customers who have experienced airline services often consume airline services, but if they prefer a certain aircraft service, their positive verbal promotion will not stop and will continue to affect others' choices of airline services, that is, the committed customer will induce a positive world-of-mouth. Su et al. [9] also declared that a socially responsible corporation could foster customer commitment through strengthening customers' emotional attachments and their own perceived reputation. Thus, how environmental corporate social responsibility influences airline customers' perceptions of service quality and their emotional attachment, as well as their emotional attachment to positive word-of-mouth, deserves further discussion by researchers, since few relevant studies in the numerous literatures combine these vital constructs.
Furthermore, the significance of price perception has been stated in consumer behavior and tourism literature [22,[26][27][28]; for instance, the moderating role of price perception in the associations between experiential quality, satisfaction, and loyalty was examined in cruise tourism [22] and the restaurant industry [29], and hotel industry [30], whereas insufficient research has explored clearly the moderating effect of the price (airfare) perceived by full-service airline customers. Airfare is undoubtedly a significant factor affecting passenger behaviors in the airline industry [22][23][24], and further empirical research should be conducted to comprehend the moderating impact of price sensitivity on the relationship between airline customers' cognition, emotions, and loyalty [31]. Empirically investigating how perceived airfare influences (increases/decreases) the strength of the association between air customers' word-of-mouth and its predictors is undoubtedly a crucial process for clarifying air customers' post-purchase behaviors and would offer airline operators more insight in boosting the positive customer word-of-mouth through understanding how to develop an effective airline price strategy (or improving the existing pricing strategy).
To fill this void, this research was designed to build a conceptual framework linking environmental corporate social responsibility (environmentally friendly business, compliance with environmental regulations, environmentally friendly products/services, environment-related mission, environmental preservation efforts), service quality, emotional attachment, and word-of-mouth by contemplating the moderating impact of price perception in the full-service airline settings. In particular, we aimed (1) to identify the apparent role of environmental corporate social responsibility in airline customers' word-of-mouth generation processes, (2) to verify the mediating effect of service quality and emotional attachment, (3) to explore the moderating effect of price perception, and (4) to uncover the relative criticality of research constructs in inducing word-of-mouth.

Corporate Social Responsibility for the Environment
Corporate social responsibility is a broad theoretical notion that encompasses a firm's social responsibility/responsiveness and its business activities for the social benefit/good [7,[32][33][34], which highly underpin the notion of corporate sustainability [14]. A company that actively implements and propels corporate social responsibility activities makes enduring efforts for social contributions serving the social needs of communities (e.g., donation programs, charity fundraising, disaster relief efforts, educational programs, employee volunteer activities, culture and art sponsorships, sports sponsorships) and environmental contributions (reduce, reuse, and respect programs, tree-planting projects, green management policy, environmental campaigns) [3,8,13]. Recently in the marketplace, developing a strong brand and strengthening the power of the existing brand are essential facets of business success and corporate sustainability [8,13,14], particularly in the airline industry [15][16][17]. Because of its effect on customer brand choice and brand power increase, corporate social responsibility, especially for the environment, has been a topic of significance among airline scholars and practitioners [3,12,17].
Environmental corporate social responsibility comprises (a) environmentally friendly business, (b) compliance with environmental regulations, (c) environmentally friendly products/services, (d) environment-related mission, and (e) environmental preservation efforts as its core factors [7]. These five dimensions are thus often used as measurement items for environmental corporate social responsibility in the extant literature [8,13]; the specific elaboration of these five dimensions is exhibited in Table 1. The major aspect of environmental corporate social responsibility is conserving the environment by minimizing the harmful impacts [8,35]. An airline company that is proactive for environmental corporate social responsibility is undoubtedly doing business in an ecologically responsible manner [3,[12][13][14][15][16][17][18]. The concept of environmental corporate social responsibility is hence alternatively used with the term "corporate ecological responsibility." Table 1. Dimensions of environmental corporate social responsibility.

Dimensions Descriptions
Environmentally friendly business [8,13,26] The company has a philanthropic reputation and is passionate about public welfare business, especially inputting financial funds/resources to organize activities to appeal for environmental awareness.
Compliance with environmental regulations [7,13,15] The company prefers to engage in environmental corporate social responsibility initiatives and operates its business under the premise of protecting the environment and complying with international regulations and local government policies.
Environmentally friendly products/services [7,8,13] The corporate social activities include creating and delivering safe, high-quality, and complete products/services that provide well-being for customers, meet ecological requirements, and will not cause environmental harm.
Environment-related mission [7,13,15] The company has an environment-related mission that is committed to environmental protection, eco-friendly service/product provision, and sustainable development.
Environmental preservation efforts [7,13,26] The company makes a series of efforts to engage in environmental preservation campaigns and attempts to reduce waste and use eco-friendly and energy-saving products.

Impact of Environmental Corporate Social Responsibility
A company's corporate social responsibility efforts as perceived by its customers are vital in explaining their intention formation and post-purchase behaviors [3,9,10,12,19]. As an example, Su et al. [9] reported that hospitality customers' perceptions of corporate social responsibility are a direct predictor of corporate/business reputation and customer satisfaction. Wang and Han [3] uncovered that a firm's corporate social responsibility activities are a vital factor affecting customers' cognitive estimations of the firm's performances and behavioral intentions. In addition, Tian et al. [10] identified that customers' perceptions of the corporate social responsibility of a firm help them have positive emotions and attitudes toward the firm. Seo et al. [36] also asserted that corporate social responsibility generally promotes firm performance for full-service airlines and affects customers' experiential service quality and emotions [8], which helps to generate a high level of trust and commitment/attachment to the company and its products [19]. More recently, Han et al. [12] uncovered that a company's corporate ecological responsibility is a significant contributor to enhancing customer affective evaluation of its products/services and increasing positive intention/behavior for the company. When a specific firm is active in corporate social responsibility praxes for the environment, consumers are likely to assess the firm's product performance in a favorable way [3] to have a positive affect for the firm [10] and to engage in positive behaviors towards the firm [12]. Therefore, we developed the following hypotheses: Hypothesis 1: Environmental corporate social responsibility has a significant influence on airline service quality.

Hypothesis 2:
Environmental corporate social responsibility has a significant influence on emotional attachment.

Hypothesis 3:
Environmental corporate social responsibility has a significant influence on word-of-mouth.

Airline Service Quality and Its Influence
It is generally known that when customer perception of the quality of the service is high, he/she builds positive behavioral intentions and becomes loyal to the company that generates the service [37,38]. The service quality is a salient factor in boosting a company's performance, evoking customers' positive emotional responses and sustaining an enduring valued relationship between the company and its customers [39,40]. Specifically, companies that offer similar kinds of service with a similar price levels can be easily compared by customers, and these customers may want a better service quality than the one from competitors [39,41]. Hence, service quality is regarded as an essential variable that explicates customer behaviors in many studies in a variety of consumer behavior and tourism contexts [40,42,43]. While the definition varies, the general consensus among researchers is that service quality refers to customers' subjective appraisals of general service excellence and its characteristics/attributes [28].
Existing evidence indicates that quality of service is an important driver of emotional attachment and customer post-purchase behavior [43][44][45][46]. Selnes [46] claimed that service/product quality affects customers' general evaluations of a particular brand. In the service sector of the airline industry, Shah et al. [47] evaluated the relationship between airline service quality and passenger satisfaction, and recent scholars have focused on both airline customers' perceptions and loyalty behavior generation. For instance, Seo et al. [36] pointed out that the comprehensive delivery of airline service can not only generate customers' emotional attachment to service quality, but also builds a favorable airline image, and passengers' positive experiences during their flight that are derived from quality in-flight product performance ultimately lead to their positive post-purchase behaviors [44,48,49]. Consistently, in the hospitality service context, Ryu et al. [45] identified that product quality is of importance in determining subsequent variables such as customer value perception, image, affect, and behavioral intentions. In their study, product quality comprises physical environment, food, and service performances. Their finding was consistent with the empirical researches of Hwang et al. [43] and Al-Ansi and Han [50], which identified that service/product quality is a vital indicator of customer attitude, emotional response, and behavioral intentions. The abovementioned studies indicated the utmost criticality of service quality in explicating customer decision-making processes and behaviors. Hence, we assumed the following hypotheses: Hypothesis H4: Airline service quality has a significant influence on emotional attachment.
Hypothesis H5: Airline service quality has a significant influence on positive word-of-mouth.

Emotional Attachment and Its Influence
It is vital for a firm to provide positive emotional experiences to their customers and to increase customers' emotional attachment to the firm [51][52][53]. Indisputably, increasing and strengthening the function of emotional attachment have been shown to boost customers' behavioral outcomes (e.g., positive word-of-mouth, favorable behavioral intention, loyalty, retention) [52][53][54][55]. The key aspect of emotional attachment comprises the emotional tie between a customer and a company [55,56]. Researchers stressed the effect of emotional attachment on the company's positive outcomes [52,53]. For instance, under the festival context, Hudson et al. [52] asserted that emotional attachment triggers attendees' behavioral outcomes. Specifically, in their evidential study of music festival attendees' behavior, they identified that word-of-mouth becomes greater for attendees with greater emotional attachment. In their study, emotional attachment is a key driver of post-purchase behaviors. Their finding maintains the consistency of the empirical research of Lee et al. [53] that uncovered the significant relationship between emotional attachment and brand loyalty behaviors in the family restaurant context. The major aspect of brand loyalty in their research included word-of-mouth along with repeat patronage. According to this evidence, the following hypothesis was proposed: Hypothesis H6: Emotional attachment has a significant influence on positive word-of-mouth.

Price Perception and Its Influence
A growing number of customers/clients are becoming highly price-conscious [57] because it is easy for individuals to know the cost of things/products/services through the Internet or mobile phones. While low price (actual) largely attracts budget-minded customers [22], perceived price attracts a large number of price-conscious customer groups who are eager to find the best deal [28,58]. The actual price of a firm's product becomes meaningful to customers only through customers' subjective interpretation [23,28]. This subjective interpretation process forms price. In other words, the real price is encoded by the customers in a manner that is meaningful to them as a pattern of perceived price through such personal interpretation processes [28,56]. The terms "price perception" and "perceived price reasonableness" are interchangeably used. In the airline industry, it is undeniable that passengers are increasingly seeking the best price (better deal) [22], as it is not difficult for most passengers to make a price comparison [23]. Considering this phenomenon regarding airline customers' price sensitivity, offering fair/reasonable airfare to airline customers therefore is of utmost significance in deriving their positive post-purchase behaviors for the airline [23,24].
Numerous studies in the present literature showed experimental evidence regarding the impact of perceived price on the formation of customers' behavioral intentions [23,29,59,60]. Varki and Colgate [60] claimed that price reasonableness that customers perceive while consuming a service product influences customer loyalty intention formation. In the context of airline industry, airline passengers' perceived service quality and their loyalty is related to the price/cost structure of service [31,36], and a better airline operation should deliver the service tailored to segmented passenger demands [36]. Moreover, Chua et al. [22] identified that traveler appraisal of price is a vital factor influencing their loyalty formation. In their research, measures for passenger loyalty mostly comprised intentions and preference rather than actual behaviors. Han and Hwang [23] examined air travelers' decision formation and found that travelers' perceived level of airfare significantly influences their intention to re-patronize the airline. Anuwichanont [31] also verified that price perception has a moderating effect on the relationships between airline customers' cognition (i.e., brand affection and trust) and attitudinal and behavioral loyalty. Likewise, Jeaheng et al. [30] illustrated the important role of perceived price as a moderator in the hotel industry. When travelers perceive that the price of a product is reasonable and its value is high, the product and its attribute performance are likely to result in positive cognitive and affective evaluations of overall product experiences and in behavioral intentions [29,59]. Similarly, in the service context, Ryu and Han [29] proved that customer price perception/reasonableness considerably increases the impact of restaurant product performance and affects their intention generation process for revisiting the restaurant and recommending it to others. The studies' arguments mentioned above revealed that the addition of interaction between price perception and antecedents of customer post-purchase decisions/behaviors contribute to better explanation of customer behavioral intention formation. Consequently, we established the following hypotheses: Hypothesis H7a: Price perception has a significant influence on the relationship between environmental corporate social responsibility and word-of-mouth.
Hypothesis H7b: Price perception has a significant influence on the relationship between airline service quality and word-of-mouth.
Hypothesis H7c: Price perception has a significant influence on the relationship between emotional attachment and word-of-mouth.

Proposed Theoretical Framework
The proposed model is shown in Figure 1. The model encompassed environmental corporate social responsibility, airline service quality, and emotional attachment for the explication of the formation of airline customers' word-of-mouth. In addition, it comprised price perception as a moderator. Our theoretical framework included a total of seven hypotheses. Specifically, H1-H6 were related to the direct relationships among the research constructs, and H7a-H7c were associated with the moderating impact of price perception.

Measures and Survey Development
The measures of the study variables originated with the existing tourism and marketing studies [7,28,[61][62][63][64]. A seven-point scale (1 = "strongly disagree"; 7 = "strongly agree") was utilized to measure all constructs with multiple items. A total of five measurement items were used (e.g., "This Hypothesis 7a Hypothesis 7b Hypothesis 7c Figure 1. The proposed theoretical model.

Measures and Survey Development
The measures of the study variables originated with the existing tourism and marketing studies [7,28,[61][62][63][64]. A seven-point scale (1 = "strongly disagree"; 7 = "strongly agree") was utilized to measure all constructs with multiple items. A total of five measurement items were used (e.g., "This airline does business in a manner that is consistent with protecting the environment") to evaluate environment corporate social responsibility. To measure airline service quality, a total of three items were utilized (e.g., "Staff at this airline provided genuine service"). Additionally, we used three items for the measurement of emotional attachment (e.g., "I love this airline"). Price perception was assessed with two items (e.g., "This airline is reasonably priced"). Lastly, word-of-mouth was measured with two items (e.g., "I will encourage other people to use this airline"). The survey questionnaire contained these measurement items along with research description. The pre-test of the initial questionnaire version was completed with tourism academics and airline practitioners. The modification of the survey questionnaire was made on the basis of their feedback. Next, the survey questionnaire was finalized with the thorough review of academic experts.

Data Collection and Samples
Data collection was conducted through an online survey structure. The online market research company's system and database were used. The samples were randomly selected from the company's database. Undoubtedly, passengers commonly conduct their travel activities using online service platforms, particularly in Korea (i.e., bookings, price search, flight details). Thus, the survey invitation email was sent to potential respondents via the system. Only those people who had traveled with a full-service airline within the last year were requested to start the survey by accessing it through the URL included in the invitation email. Finally, 300 usable responses were obtained through this procedure, which is sufficient sample to perform in the SEM analysis structure. Among these participants, about 48.7% were male airline customers, whereas 51.3% were female airline customers. The respondents' average age was 33.38 years old. About 45.7% of the participants reported that they were married. Regarding the education level, about 69.7% reported that they had a four-year bachelor's degree, followed by two-year college graduates (12.7%), graduate degree holders (12.3%), and high school graduates or less (5.3%). With regard to the frequency of air travel, about 46.7% answered that they traveled with their airline 2-3 times within the last year, followed by one time (40.3%), 4-5 times (8.0%), and 6 times or more (5.0%). All respondents indicated that they had an air travel experience within the last year.

Data Analysis
Both SPSS 20 and AMOS 20 were essential tools used for the data analysis. We first generated a measurement model by employing a confirmatory factor analysis for the examination of measurement quality. Next, we generated a structural model by conducting a structural equation modeling for the evaluation of the proposed conceptual framework. In addition, the thresholds suggested by Hair et al. [65] were used to determine a goodness of fit model. The influence of indirect impacts was examined to verify the mediating role of study variables. Moreover, a test for metric invariance was employed to assess the proposed moderating effect.

Measurement Model Evaluation
A confirmatory factor analysis was performed. Its outcomes for the measurement model evaluation are shown in Table 2. This table also includes correlations and squared correlations between study variables, along with mean and standard deviation values. Overall, the model contained satisfactory goodness-of-fit statistics (χ 2 = 147.757, df = 79, p < 0.001, χ 2 /df = 1.870, RMSEA = 0.054, CFI = 0.986, IFI = 0.986, TLI = 0.981). All factor loadings were significant (p < 0.01). Composite reliability of the measures was evaluated. Our results showed that all composite reliability values exceeded the minimum threshold of 0.70 (environmental corporate social responsibility = 0.965; airline service quality = 0.931; emotional attachment = 0.930; price perception = 0.921; word-of-mouth = 0.892), guaranteeing the internal consistency of the construct measures [65]. In addition, all the average variance extracted (AVE) values (environmental corporate social responsibility = 0.845; airline service quality = 0.817; emotional attachment = 0.815; price perception = 0.854; word-of-mouth = 0.805) exceeded the ideal criterion of 0.50 [65]. These scores were also greater than the squared correlations among constructs. Thus, both convergent validity and discriminant validity of the construct measures were confirmed.

Structural Model Evaluation
A structural equation modeling was conducted in order to inspect the proposed conceptual framework. Table 3 and Figure 2 include the details of the structural model evaluation results. Our finding showed that the proposed model had a satisfactory fit to the data (χ 2 = 99.122, df = 58, p < 0.001, χ 2 /df = 1.709, RMSEA = 0.049, CFI = 0.990, IFI = 0.990, TLI = 0.987). Overall, the proposed model contained an adequate level of explanatory power for word-of-mouth. Specifically, about 85.7% of the total variance in word-of-mouth was accounted for by environmental corporate social responsibility, airline service quality, and emotional attachment.  finding showed that the proposed model had a satisfactory fit to the data (χ 2 = 99.122, df = 58, p < 0.001, χ 2 /df = 1.709, RMSEA = 0.049, CFI = 0.990, IFI = 0.990, TLI = 0.987). Overall, the proposed model contained an adequate level of explanatory power for word-of-mouth. Specifically, about 85.7% of the total variance in word-of-mouth was accounted for by environmental corporate social responsibility, airline service quality, and emotional attachment.   The hypothesized impact of environmental corporate social responsibility on its outcome variables was tested. The results indicated that environmental corporate social responsibility exerted a significant influence on airline service quality (β = 0.215, p < 0.01), emotional attachment (β = 0.429, p < 0.01), and word-of-mouth (β = 0.088, p < 0.05), which supported the establishment of Hypotheses 1, 2, and 3. The proposed effect of airline service quality on emotional attachment and word-of-mouth was evaluated. Our result revealed that airline service quality had a significant impact on emotional attachment (β = 0.476, p < 0.01) and word-of-mouth (β = 0.247, p < 0.01). Hence, Hypotheses 4 and 5 were supported. The proposed impact of emotional attachment on word-of-mouth was analyzed. As expected, the influence of emotional attachment on word-of-mouth (β = 0.715, p < 0.01) was significant. Hence, Hypothesis 6 was supported.
Subsequently, the indirect effect of research constructs was examined. Our results indicated that environmental corporate social responsibility contained a significant impact on word-of-mouth (β = 0.433, p < 0.01) indirectly through airline service quality and emotional attachment. Our result also revealed that airline service quality had a significant effect on word-of-mouth indirectly through emotional attachment (β = 0.340, p < 0.01). Given this result, the significant mediating role of airline service quality and emotional attachment was evident within the proposed theoretical framework. Next, the total effect of research variables on word-of-mouth was examined. As displayed in Table 3, our result revealed that emotional attachment contained the greatest total influence on word-of-mouth (β = 0.715, p < 0.01), followed by airline service quality (β = 0.588, p < 0.01), and environmental corporate social responsibility (β = 0.521, p < 0.01).

Invariance Model Evaluation
An invariance model was operated to evaluate the hypothesized moderating effect of price perception. All responses were divided into (high) and (low) price perception groups by using a K-means cluster analysis. A total of 198 cases were clustered into the high group, and 102 cases were clustered into the low group. A baseline model using these two groups of price perception was generated. As reported in Table 4, the baseline model was found to adequately fit to the data (χ 2 = 181.466, df = 125, p < 0.001, χ 2 /df = 1.452, RMSEA = 0.039, CFI = 0.986, IFI = 0.986, TLI = 0.982). Employing a chi-square examination, the baseline model was compared to the nested models where a particular path of interest was restricted to be equal between two groups of price perception. Findings of the chi-square examination indicated that the path from environmental corporate social responsibility to word-of-mouth was not significantly different between price perception groups (∆χ 2 (1) = 0.079, p > 0.05). However, while the link for the high group of price perception was significant (p < 0.05), the path for the low group was not significant (p > 0.05). That is, although the chi-square difference across two groups was not significant, the group difference on the environmental corporate social responsibility-word-of-mouth link exists. Thus, Hypothesis 7a was supported. Moreover, our results showed that the relationships between airline service quality and word-of-mouth (∆χ 2 (1) = 0.213, p > 0.05) and between emotional attachment and word-of-mouth (∆χ 2 (1) = 0.897, p > 0.05) were not significantly different between two groups. Therefore, Hypotheses 7b and 7c were not supported. The detailed findings of the invariance test are displayed in Table 4 and Figure 2. Note. ECSR = environmental corporate social responsibility, ASQ = airline service quality, EA = emotional attachment, WOM = word-of-mouth. † While the link for the high group of price perception was significant, the path for the low group was not significant. That is, although the chi-square difference across two groups was not significant, the group difference on the ECSR-WOM link exists. Thus, Hypothesis 7a was supported. * p < 0.05, ** p < 0.01.

Synopsis of the Research
Practicing/promoting environmental corporate social responsibility and inducing customers' positive behaviors are undeniably the key challenges for every airline. This study was a research endeavor to unearth the role of environmental corporate social responsibility in increasing airline service quality, eliciting emotional attachment, and enhancing word-of-mouth behavior in the full-service airline industry. This study provided experimental evidence regarding the criticality of the airline firm's environmental corporate social responsibility efforts in explicating the word-of-mouth generation process. The mediating effects of airline service quality and emotional attachment were also demonstrated. In addition, our findings unearthed the relative criticality of emotional attachment in determining word-of-mouth. Our results further uncovered the vital role of price perception as a moderator that affects the link between environmental corporate social responsibility and word-of-mouth. In general, the research objectives were satisfactorily obtained.

Discussion
Lately, corporate social responsibility of airline industry is highly acknowledged as a credible social and economic tool in tourism industry. However, this booming established debate on how to balance corporate social responsibility and environmental preservation is an essential topic for academics and practitioners [7,14,26,36]. This study identified that the airline's environmental corporate social responsibility encompasses environmentally friendly business, compliance with environmental regulations, environmentally friendly products/services, environment-related mission, and environmental preservation endeavors, which are all strong influencing factors on customer word-of-mouth formation. That is, environmental corporate social responsibility is a key constituent of explicating airline customers' cognitive/affective evaluations of their airline experiences and post-purchase behaviors. Our finding also implies that environmentally responsible airline business is the critical representative of the airline's corporate social responsibility practices. Practitioners should therefore be active in meeting the environmental expectations of the customers, as well as of the entire society, when doing their airline business in the marketplace. Accordingly, airline practitioners should make more endeavors towards protecting the environment, complying with the international/governmental/local regulations, developing environmentally friendly products and technologies, having an environment-related mission, and minimizing the hazardous environmental impact.
Although corporate social responsibility for the environment is the vital current issue of the airline marketplace, existing knowledge of it and its role in customer decision formation/behavior, which is an imperative facet of an airline's success, was rather limited. The present research successfully filled this void by enriching the airline literature. Airline researchers need to understand the criticality of environmental corporate social responsibility to customer word-of-mouth study, particularly when developing a theoretical framework pertinent to airline service quality and customer post-purchase behaviors. Based on our result, airline operators should also make diverse efforts to help their customers build positive perceptions/beliefs about their airline's corporate social responsibility efforts for the environment. Despite the huge changes in airline industry service quality, this study attempted to look deeper into the serious implications of airline consumption on the environment and nature. Policy makers are committed to being consistent with customer knowledge and awareness in preserving nature and a healthy environment.
In light of our results, emotional attachment indicated a salient role in inducing airline customers' word-of-mouth behaviors. This finding is consistent with extant studies that emphasize the substantial impact of affect/emotion on customer behavior [51,52,55]. Being aware of the importance of emotional attachment, airline operators should deal with this concept in an active way. According to recent studies [66,67], dealing with core and service encounter quality (e.g., comfortable in-flight atmospherics, employee friendliness, employee attitude, employee courteousness, reliable services, nutritious and healthy in-flight meals) will induce customers' positive affective evaluations of an airline and their attachment to the airline brand. Our empirical evidence also supported the criticality of airline service quality in boosting customer emotional attachment to the airline. As this evidence shows, such endeavors towards emotional attachment improvement would lead to increased word-of-mouth behavior for the airline. It is also essential for airline practitioners to consider the significant impact of environmental corporate social and service quality to establish customers' emotions and feelings. They might enhance collaboration with active nature issues related to environmental pollution in order to underpin a healthy environmental development (i.e., Electric Airplane).
On the other hand, airline passenger price perception was an important moderator, particularly in the relationship between environmental corporate social responsibility and word-of-mouth. The degree of the influence of environmental corporate social responsibility on word-of-mouth was greater in the high price perception group (high group: β = 0.120, p < 0.05) than in the low group (low group: β = 0.063, p > 0.05). This finding is consistent with previous studies that emphasized the moderating nature of price perception/reasonableness in the extant literature [22,23,59]. Our finding implies that at similar levels of customer awareness/perception of a specific airline's environmental corporate social responsibility efforts, customers who perceive that an airline is reasonably/adequately priced are more inclined to engage in positive word-of-mouth behavior for the airline than those with a low level of price perception.
Furthermore, outcomes of the indirect influence assessment uncovered the important mediating nature of airline service quality and emotional attachment. In other words, in our proposed conceptual framework, both airline service quality and emotional attachment obviously mediated the effect of environmental corporate social responsibility on word-of-mouth. This result is consistent with the prior studies asserting the significance of cognition and emotional factors as mediators [64,68]. Especially of interest, from the results of this research, is the fact that the indirect effect of environmental corporate social responsibility (β = 0.433, p < 0.01) on word-of-mouth is larger than its direct effect (β = 0.088, p < 0.05). Thus, while it is clear that environmental corporate social responsibility has a positive effect on word-of-mouth, customer word-of-mouth can increase even further if airline service quality and emotional attachment are involved and activated. That is, if airline service quality and emotional attachment are present, the effect of environmental corporate social responsibility on word-of-mouth generation can be maximized.

Theoretical Implications
The final result included an important theoretical meaning in that, by considering only the influence of price perception, the corporate social responsibility, airline service quality, emotional attachment, and word-of-mouth relationships were scarcely explored. The present study is one of very few studies to provide evidence that airline customers' perceptions of the airfare determine the magnitude of the impact of environmental corporate social responsibility on their word-of-mouth. Although previous researchers identified the significant moderating effect of price perception in the service industry, the novelty of this study is in underpinning its active role in the airline and corporate sustainability framework. Moreover, this study makes a significant contribution to the sustainable development of the airline industry in particular, which increases the likelihood of future practices and integrations between customers and corporate responsibility to preserve nature and the physical environment [20,24,36]. Additionally, as an indirect effect it provides researchers and practitioners with the important information that integrating the mediators of airline service quality and emotional attachment into the theoretical framework is important to better comprehend the role of environmental corporate social responsibility in airline customer word-of-mouth formation.

Managerial Implications
From the managerial perspective, full-service airline operators need to develop efficient methods that help customers feel the reasonableness of the airfare. According to Han and Hyun [68] and O'Cass and McEwen [69] stressing product exclusivity is an adequate strategy to improve customers' cognition that the product/service is reasonably priced. Full-service airline management should therefore emphasize the exclusivity of their airplane product (accomplishment, monetary wealth, privileges) when advancing the marketing contents (e.g., phrases/words) and advertisements. For instance, including a dynamic structure of action words within the marketing campaigns/advertisements of a full-service airline, which will possibly strengthen the product exclusivity (e.g., upscale class, success, prosperity, flourishes), would be a critically persuasive tool encouraging customers to choose the airline and spread positive word-of-mouth for the airline.
Overall, the study model makes a theoretical and practical contribution to the airline industry's future development that emphasizes substantive solutions to global environmental issues and the social commitments of firms to preserve nature by optimizing sustainability, which highly impacts customer service quality expectations and intentions.

Limitations and Directions for Future Research
This study has several limitations that offer some opportunities for future research. First, the research sample is limited to the travelers who experienced full-service airline services within the past one year prior to this study, thus the results of study could not reflect travelers' dynamic and real-time reactions. In this situation, respondents had to recall their previous airline experiences and then answer a questionnaire online. Therefore, in order to evaluate travelers' genuine on-site full-service airline experiences, a face-to-face interview survey in the aircraft or more real-time approaches could be administered to reflect more accuracy in future research. Second, this research solely focuses on the airline sector for the empirical evaluation of the proposed conceptual framework. Hence, one should be careful when interpreting our results in other luxury tourism sectors (e.g., luxury cruise, luxury hotel, luxury restaurant, luxury resort). Scholars in the future should examine the applicability and effectiveness of the proposed theoretical framework in such contexts.