Table 1 shows the medians and interquartile ranges of the mortality rates of the four diseases, concentrations of the five air pollutants, and confounding factors averaged from 2001 to 2018. The population of South Korea, as of 2010 (in the middle of the study period) was 50,515,666 persons. Throughout the study period, a total of 4,558,640 all-cause mortalities were recorded. Among them, 242,711 deaths were attributed to IHD, 509,740 deaths to CVD, 160,174 deaths to PN, and 138,271 deaths to CLRD.
Table 1. Characteristics of the study area
Characteristics
|
Median (first–third quartile range)
|
Number of districts analyzed
|
249
|
IHDa: Age-adjusted mortality rate (per 100,000)
|
21.6 (19.4–25.3)
|
CVDb: Age-adjusted mortality rate (per 100,000)
|
50.7 (46.5–54.5)
|
PNc: Age-adjusted mortality rate (per 100,000)
|
12.2 (10.9–13.5)
|
CLRDd: Age-adjusted mortality rate (per 100,000)
|
13.8 (11.7–16.0)
|
Carbon monoxide (ppb) e
|
554 (476–624)
|
Nitrogen dioxide (ppb)
|
20.1 (14.6–26.8)
|
Sulfate dioxide (ppb)
|
4.89 (4.15–5.56)
|
Ozone (ppb)
|
24.3 (21.6–27.6)
|
PM10 (µg/m3)
|
50.2 (46.1–55.5)
|
Altitude (m)
|
124 (59.9–220)
|
Population density (per km2)
|
361 (109–6042)
|
Higher-education rate f (%)
|
34.4 (22.9–43.0)
|
Smoking rate g (%)
|
25.1 (23.5–26.8)
|
Obesity rate h (%)
|
22.4 (20.9–24.4)
|
GRDP j (million won)
|
22.9 (16.7–29.0)
|
From 2001 to 2018, the population of all 249 South Korean administrative districts, Si-Gun-Gus, were studied. The South Korean population, as of 2010 (in the middle of the study period) was 50,515,666 persons. Throughout the study period, a total of 4,558,640 all-cause deaths were recorded. Among them, 242,711 deaths were attributed to IHD, 509,740 deaths to CVD, 160,174 deaths to PN, and 138,271 deaths to CLRD.
a Ischemic Heart Disease (IHD): Total number of deaths by IHD in 2001–2018 was 242,711. The annual raw mortality rates throughout the study period were adjusted for each district’s age distribution to the standard South Korean population in 2010.
b Cerebrovascular Disease (CVD): Total number of deaths by CVD in 2001–2018 was 509,740.
c Pneumonia (PN): Total number of deaths by PN in 2001–2018 was 160,174.
d Chronic Lower Respiratory Disease (CLRD): Total number of deaths by CLRD in 2001–2018 was 138,271.
e Air pollution data from 2001 to 2018, in daily mean concentrations according to the positions of monitoring stations were accessed using the AirKorea database. An interpolation model based on a geographical information system was applied to yield the average air pollutant concentration throughout the study period of the corresponding districts.
f Rate of >15-year-old persons with college education or more in 2010
g Rate of current smokers adjusted for the age of the national standard population in 2010
h Rate of population with body mass index > 25 kg/m2 adjusted for the age of the national standard population in 2010
i Gross Regional Domestic Product per capita (GRDP) in 2011
For IHD, an increased SO2 concentrations were significantly associated with a higher mortality rate (odds ratio per interquartile range [OR] 1.09; 95% CI, 1.05–1.12), whereas other air pollutants had null associations. For CVD, SO2 (OR 1.03; 95% CI 1.01–1.05) and PM10 (OR 1.04; 95% CI 1.02–1.07) concentrations had significant associations with a higher mortality rate. For PN, O3 (OR 1.06; 95% CI 1.02–1.09) concentrations had significant positive associations with a higher mortality rate, while SO2 (OR 0.968; 95% CI 0.943–0.994), NO2 (OR 0.893; 95% CI 0.861–0.923), and PM10 (OR 0.947; 95% CI 0.919–0.980) concentrations had significant negative associations. For CLRD, O3 concentrations were associated with an increased mortality rate (OR 1.08; 95% CI 1.01–1.13), while CO (OR 0.891; 95% CI 0.856–0.935), NO2 (OR 0.822; 95% CI 0.780–0.865), and PM10 (OR 0.934; 95% CI 0.902–0.977) concentrations had negative associations. Figure 1 shows the ORs and 95% CIs of the estimated associations.
In the subgroup analysis that divided the 249 districts into capital or non-capital areas (77:172 districts) and into urban or rural areas (168:81 districts), positive associations between SO2 concentrations and IHD mortality were consistently observed in all subgroups, while other pollutant-disease pairs showed null or mixed associations(Figures 2 and 3). Table 2 summarizes the qualitative associations between disease mortality and air pollutant concentrations in the corresponding subgroup schema. A ‘+’ denote a significant positive association, a ‘–’ to negative, or blank to insignificant. For example, associations between CVD mortality and NO2 concentrations exhibited a paradoxical pattern in the subgroup analysis because a significant negative association was found in capital districts but positively associated in non-capital areas. However, null associations were found nationwide and in urban and rural areas. In contrast, significant negative associations were found between NO2 concentrations and CLRD mortality nationwide and in capital, non-capital, and urban areas; however, positive associations were found in rural areas.
Table 2. Significant associations between mortality rates and air pollutant concentrations nationwide and in capital, non-capital, urban, and rural areas.
Ischemic heart disease mortality rate
|
Air pollutant
|
Nationwide
|
Capital
|
Non-capital
|
Urban
|
Rural
|
CO
|
|
|
|
–
|
|
SO2
|
+
|
+
|
+
|
+
|
+
|
NO2
|
|
|
+
|
|
|
O3
|
|
|
|
+
|
|
PM10
|
|
|
|
|
|
Cerebrovascular disease mortality rate
|
Air pollutant
|
Nationwide
|
Capital
|
Non-capital
|
Urban
|
Rural
|
CO
|
|
|
|
|
+
|
SO2
|
+
|
+
|
+
|
+
|
|
NO2
|
|
–
|
+
|
|
|
O3
|
|
|
–
|
|
|
PM10
|
+
|
|
+
|
|
+
|
Pneumonia mortality rate
|
Air pollutant
|
Nationwide
|
Capital
|
Non-capital
|
Urban
|
Rural
|
CO
|
|
|
|
|
|
SO2
|
–
|
|
|
|
|
NO2
|
–
|
–
|
|
–
|
|
O3
|
+
|
|
|
+
|
|
PM10
|
–
|
|
|
–
|
|
Chronic Lower Respiratory Disease mortality rate
|
Air pollutant
|
Nationwide
|
Capital
|
Non-capital
|
Urban
|
Rural
|
CO
|
–
|
|
–
|
–
|
|
SO2
|
|
|
|
|
+
|
NO2
|
–
|
–
|
–
|
–
|
+
|
O3
|
+
|
+
|
|
+
|
|
PM10
|
–
|
|
|
|
|
“+” denotes a positive association, which means increased air pollutant concentrations are associated with higher mortality rates in the study districts.
“–” denotes a negative association, which that means the opposite of “+”.
Blank denotes null associations.
The significance of the associations was determined using 95% confidence intervals.