Table 1:

Definition of variables included in the study

Variables		Definition
Dependent variables
Mental health		Total CES-D scores: 0–30
Psychological disorder		1 for psychological disorder; otherwise, 0.
Explanatory variables
Air quality	Air pollution	SO2 drainage of places where respondents are living in (2012) (unit: 10,000 tons)
	Square of air pollution	Square of SO2 drainage
Urban-rural variable		1 for urban areas and 0 for rural areas.
Personal features	Age	≧60 years old
	Gender	1 for male respondents and 0 for female.
	Marriage	1 for married respondents and 0 for single respondents.
	Primary school	Respondents having primary school education background are scored 1; otherwise, 0.
	Middle school	Respondents having middle school education background are scored 1; otherwise, 0.
	Vocational education, junior college and above	Respondents having education background of vocational education, junior college and above are scored 1; otherwise, 0.
	Physical disability	Disabled respondents are scored 1 and rest are scored 0.
	Assets	Amount of deposit in 2013 (unit: 1000 RMB)
	Chronic disease 1	Respondents with one or more chronic diseases are scored 1; otherwise, 0.
	Chronic disease 2	Respondents with three or more chronic diseases are scored 1; otherwise, 0.
Lifestyle	Smoking	Smoking respondents are scored 1 and rest scored 0.
	Drinking	Drinking respondents are scored 1 and rest scored 0.
	Social activity	Respondents having social activities in the past one month are scored 1; otherwise, 0.
	Employment	Respondents having jobs are scored 1; otherwise, 0.