A total of 61,058 COPD-related deaths of people aged 60 and older were obtained from January 1, 2015, to December 31, 2018. Among these, 33,731 deaths were males and 27,327 were females. 31,948 of the deceased were married, while 29,110 had some sort of alternative marital status (including divorced, widowed, and never married). Deaths in the 60–69, 70–79, 80–89, and ≥ 90 age groups were 6,527, 16,916, 27,781, and 9,834, respectively. The mean value and IQR for each type of air pollutant, weather condition, and COPD-related death are listed in Table 1.
Table 1
Data for ambient air pollutants, weather conditions, and COPD-related deaths in Chengdu from 2015 to 2018
| Mean | SD | Min. | 25% | 50% | 75% | Max. | IQR |
PM2.5 (µg/m3) | 58.7 | 38.9 | 8.0 | 31.0 | 47.0 | 74.0 | 254.0 | 43.0 |
SO2 (µg/m3) | 14.5 | 6.3 | 4.0 | 10.0 | 14.0 | 18.0 | 41.0 | 8.0 |
NO2 (µg/m3) | 40.5 | 13.1 | 13.0 | 31.0 | 38.0 | 49.0 | 92.0 | 18.0 |
CO (mg/m3) | 0.9 | 0.3 | 0.4 | 0.7 | 0.9 | 1.1 | 2.2 | 0.4 |
O3-8 h (µg/m3) | 98.8 | 51.8 | 11.0 | 59.0 | 88.0 | 137.0 | 279.0 | 78.0 |
Temperature (°C) | 16.7 | 7.3 | -1.9 | 9.9 | 17.3 | 23.0 | 29.8 | 13.1 |
RH (%) | 80.8 | 8.9 | 41.0 | 75.0 | 81.0 | 88.0 | 99.0 | 13.0 |
COPD-related deaths | 41.8 | 14.9 | 14.0 | 32.0 | 38.0 | 49.0 | 114.0 | 17.0 |
Age group (year) | | | | | | | | |
60–69 | 4.5 | 2.5 | 0 | 3.0 | 4.0 | 6.0 | 16.0 | 3.0 |
70–79 | 11.6 | 5.0 | 1.0 | 8.0 | 11.0 | 14.0 | 37.0 | 6.0 |
80–89 | 19.0 | 7.5 | 4.0 | 14.0 | 18.0 | 23.0 | 60.0 | 9.0 |
≥ 90 | 6.7 | 3.5 | 0 | 4.0 | 6.0 | 9.0 | 22.0 | 5.0 |
Gender | | | | | | | | |
Male | 23.1 | 8.8 | 7.0 | 17.0 | 21.0 | 27.0 | 62.0 | 10.0 |
Female | 18.7 | 7.5 | 4.0 | 13.0 | 17.0 | 23.0 | 61.0 | 10.0 |
Marital status | | | | | | | | |
Married | 21.9 | 8.4 | 5.0 | 16.0 | 20.0 | 26.0 | 62.0 | 10.0 |
Alternative statuses a | 19.9 | 7.9 | 4.0 | 14.0 | 19.0 | 24.0 | 55.0 | 10.0 |
a Alternative marital statuses include widowed, divorced, and never married. |
Abbreviations: PM2.5, particulate matter < 2.5 µm in aerodynamic diameter; SO2, sulfur dioxide; NO2, nitrogen dioxide; CO, carbon monoxide; O3-8 h, daily eight-hour mean concentration of ozone; RH, relative humidity; COPD, chronic obstructive pulmonary disease; SD, standard deviation; IQR, interquartile range. |
The concentrations of the PM2.5, SO2, NO2, CO, and O3 ambient air pollutants exhibited typical seasonal tendencies. The concentrations of PM2.5, NO2, and CO were considerably higher during winter, and lower during summer each year, while the seasonal variations of the O3 concentrations were the opposite. The concentrations of SO2 exhibited weaker seasonal tendencies than the other pollutants, although the pattern of higher in winter and lower in summer was also apparent (Figure S1).
As shown in Table 2, correlations were observed among ambient air pollutants and weather conditions, except between SO2 and temperature, and between temperature and relative humidity.
Table 2
Spearman’s correlation coefficients of air pollutants and weather conditions
| PM2.5 | SO2 | NO2 | CO | O3-8 h | Temperature | RH |
PM2.5 | 1 | | | | | | |
SO2 | 0.540 a | 1 | | | | | |
NO2 | 0.799 a | 0.435 a | 1 | | | | |
CO | 0.820 a | 0.450 a | 0.712 a | 1 | | | |
O3-8 h | -0.215 a | 0.092 a | -0.227 a | -0.368 a | 1 | | |
Temperature | -0.511 a | -0.028 | -0.478 a | -0.551 a | 0.712 a | 1 | |
RH | -0.109 a | -0.254 a | -0.118 a | 0.064 a | -0.510 a | -0.037 | 1 |
aP < 0.05. |
Abbreviations: PM2.5, particulate matter < 2.5 µm in aerodynamic diameter; SO2, sulfur dioxide; NO2, nitrogen dioxide; CO, carbon monoxide; O3-8 h, daily eight-hour mean concentration of ozone; RH, relative humidity. |
Associations were apparent between COPD-related mortality and IQR increases in the concentrations of PM2.5 (43 µg/m3), SO2 (8 µg/m3), NO2 (18 µg/m3), CO (0.4 mg/m3), and O3 (78 µg/m3) after the influences of weather conditions (i.e., daily mean temperature and relative humidity) were controlled. The days corresponding to the greatest effects of PM2.5 (RR = 1.019, 95% CI: 1.006–1.033), SO2 (RR = 1.034, 95% CI: 1.016–1.053), NO2 (RR = 1.027, 95% CI: 1.011–1.043), CO (RR = 1.025, 95% CI: 1.006–1.044), and O3 (RR = 1.038, 95% CI: 1.015–1.061) were one-day, one-day, one-day, zero-day, and two-day lags in the single-day lag models, respectively. The estimate results calculated from the multi-day lag models were similar, although a small amount higher than the results from the single-day lag models for each pollutant. The days corresponding to the greatest estimate results for PM2.5, SO2, NO2, CO, and O3 were lag03, lag01, lag03, lag01, and lag03 in the multi-day lag models, respectively (Fig. 2). The exposure-response curves exhibited linear relationships between each pollutant and the log-relative risk of COPD-related mortality (Fig. 3).
Statistically significant associations between COPD-related mortality and pollutants in the 60–69 age group were not observed but were observed in the ≥ 90 age group, with the exception of CO. Statistically significant associations between COPD-related mortality and PM2.5 were only observed in the ≥ 90 age group. The greatest effects of SO2, NO2, and O3 in the 70–79 age group were at lag1 (RR = 1.051, 95% CI: 1.018–1.085), lag0 (RR = 1.029, 95% CI: 1.002–1.057), and lag1 (RR = 1.054, 95% CI: 1.009–1.101), respectively, while the greatest effects of NO2, and O3 in the 80–89 age group were both at lag0 (RR for NO2 = 1.029, 95% CI: 1.007–1.051, RR for O3 = 1.029, 95% CI: 1.003–1.056), and the greatest effects of PM2.5, SO2, NO2, and O3 in the ≥ 90 age group were at lag1 (RR = 1.036, 95% CI: 1.004–1.069), lag1 (RR = 1.055, 95% CI: 1.011–1.102), lag1 (RR = 1.048, 95% CI: 1.010–1.088), and lag2 (RR = 1.071, 95% CI: 1.016–1.129), respectively (Figure 4).
The RRs for PM2.5, SO2, NO2, and O3 in males were 1.018 (95% CI: 1.001–1.035), 1.037 (95% CI: 1.013–1.062), 1.026 (95% CI: 1.006–1.047), 1.040 (95% CI: 1.008–1.074), respectively, corresponding to zero-day, one-day, zero-day, and one-day lags. The RRs for PM2.5, SO2, NO2, and O3 in females were 1.023 (95% CI: 1.003–1.042), 1.030 (95% CI: 1.004–1.057), 1.034 (95% CI: 1.011–1.058), and 1.051 (95% CI: 1.018–1.086), respectively, corresponding to one-day, one-day, one-day, and two-day lags. The RRs for CO were not observed in either males or females. The RRs for PM2.5, SO2, NO2, CO, and O3 in married individuals were 1.022 (95% CI: 1.004–1.040), 1.041 (95% CI: 1.016–1.066), 1.036 (95% CI: 1.016–1.058), 1.032 (95% CI: 1.007–1.058), and 1.040 (95% CI: 1.007–1.075), respectively, corresponding to two-day, one-day, zero-day, zero-day, and one-day lags. The RRs for PM2.5, SO2, and O3 in alternative marital status individuals (including divorced, widowed, and never married) were 1.019 (95% CI: 1.001–1.038), 1.026 (95% CI: 1.001–1.053), and 1.050 (95% CI: 1.008–1.095), respectively, corresponding to zero-day, one-day, and zero-day lags. Statistically significant differences for the effects of airborne pollutants on COPD-related mortality were not observed between males and females, nor were they found between married individuals and alternative marital status individuals (Figure 5).
By adding the remaining pollutants each time as covariates into the models, two-pollutant model simulations were conducted for each pollutant corresponding to their greatest effective days. The effects of O3 remained steady after adjusting for PM2.5, SO2, NO2, and CO each time in the models. The effects of PM2.5, SO2, and NO2 remained after adjusting for CO and O3, respectively, while attenuating to zero after adjusting for each other. The effects of CO remained after adjusting for O3, while attenuating to zero after adjusting for PM2.5, SO2, and NO2 (Table 3).
Table 3
RRs for two-pollutant models including PM2.5, SO2, NO2, CO, and O3 b
Airborne pollutant | | RR | RR 95% CI |
| Lower | Upper |
PM2.5 | | 1.019 a | | 1.006 | 1.033 |
| +SO2 | 1.006 | | 0.989 | 1.023 |
| +NO2 | 1.006 | | 0.987 | 1.025 |
| +CO | 1.023 a | | 1.003 | 1.043 |
| +O3 | 1.016 a | | 1.003 | 1.030 |
SO2 | | 1.034 a | | 1.016 | 1.053 |
| +PM2.5 | 1.001 | | 0.9978 | 1.004 |
| +NO2 | 1.024 | | 0.998 | 1.051 |
| +CO | 1.036 a | | 1.014 | 1.058 |
| +O3 | 1.030 a | | 1.011 | 1.049 |
NO2 | | 1.027 a | | 1.011 | 1.043 |
| +PM2.5 | 1.022 | | 0.9997 | 1.045 |
| +SO2 | 1.012 | | 0.989 | 1.035 |
| +CO | 1.033 a | | 1.011 | 1.055 |
| +O3 | 1.024 a | | 1.007 | 1.040 |
CO | | 1.025 a | | 1.006 | 1.044 |
| +PM2.5 | 1.012 | | 0.983 | 1.041 |
| +SO2 | 1.011 | | 0.987 | 1.035 |
| +NO2 | 1.002 | | 0.975 | 1.029 |
| +O3 | 1.020 a | | 1.001 | 1.040 |
O3 | | 1.038 a | | 1.015 | 1.061 |
| +PM2.5 | 1.034 a | | 1.011 | 1.057 |
| +SO2 | 1.035 a | | 1.011 | 1.059 |
| +NO2 | 1.035 a | | 1.012 | 1.058 |
| +CO | 1.038 a | | 1.015 | 1.061 |
Abbreviations: PM2.5, particulate matter < 2.5 µm in aerodynamic diameter; SO2, sulfur dioxide; NO2, nitrogen dioxide; CO, carbon monoxide; O3, ozone; RR, relative risk; CI, confidence interval. |
a P < 0.05. |
b RRs for PM2.5, SO2, NO2, CO, and O3 were from one-day, one-day, one-day, zero-day, and two-day lags, respectively. |