Discussion
Various air pollutants such as PM10, NO2, and SO2 pose a great danger to public health, in particular to the respiratory system of individuals.12 It is known that, for every increase of PM10 by 10 μg/m3, mortality from all causes, cardiopulmonary diseases and lung cancer rises by 4%, 6% and 8%, respectively.13 Carbon monoxide (CO) and nitrogen dioxide (NO2) from diesel engines are known to raise the risk of lung cancer from 15% to 40%.14 These environmental pollutants are known to have a significant adverse effect on public health including mortality rates. As a result of increased residence times in the air and higher concentrations of pollutants, mortality rates are significantly affected and public health generally deteriorates.15 These air pollutants are closely affected by environmental factors such as wind speed and sunlight.
In our study, air pollutants such as PM10, NO2, and SO2 showed seasonal variations. In Korea, the use of coal or oil increases during cold weather, mainly in winter, and atmospheric pollution increases leading to high air pollution indicators (PM10, SO2, NO2) in winter (Figure 1C). In our study, the same sinusoidal pattern appeared in the frequency of COPD exacerbations (Figure 1B). During the entire 6-year observation period, 15110 individuals suffered COPD exacerbation, of which 17.9% were adults in their 20s, and 80% were elderly individuals older than 60 years of age (Figure 1A). When the distribution of the entire patient population was drawn in a time series, the number of individuals affected tended to be particularly high in winter, which is consistent with the pattern of major air pollution indicators (Figure 1B).
So which of the three air pollutants, at what concentrations and for how long, were individuals affected by COPD exacerbation? We utilized “DLNM packages” using R to analyze these factors. In conclusion, of the various air pollutants, only PM10 was significantly related to COPD exacerbation (Figure 2A), and it was found to affect lag-specific days 4 to 6. In particular, on lag-specific day 5, the risk of COPD exacerbation reached peak values (Figure 2A, Table 3). For a PM10 concentration of 30 µg/m3, which is the upper limit of “acceptable” fine dust levels, the risk of COPD exacerbation increased by 2.5%. At the median concentration of normal PM10 (46.98 µg/m3), it increased by 4.0%. When it was 80 µg/m3, which is the lower limit of “unacceptable” fine dust levels, the risk of COPD exacerbation increased by 7.0%. In the case of PM10 over 150 µg/m3, which is an extremely unacceptable level of PM10, CE risk increased by 13.7% (Table 3, Figure 3A, B). In addition, for the lag-cumulative effect of PM10, we calculated the risk of COPD exacerbation, and it was found that it continued to affect CE risk from lag day 6 to lag day 10 after exposure to PM10 (Figure 2B).
We analyzed the entire patient group in four age subgroups. (Table 4) For preschool age (less than 5 years old) and school age (less than 20 years old) individuals, the number of COPD exacerbations was small, so the confidence interval of the RR value was large and so did not produce meaningful results.
In the group of adults 20 years or older, PM10 level significantly increased the risk of COPD exacerbation on lag days 3 and 4. At lag day 0, NO2 and WS levels significantly increased the risk of COPD, and SS level significantly decreased the risk of COPD exacerbation.
Similar results were found in older people over the age of 60 with PM10 significantly increasing CE risk at lag days 3, 4, 5, and 6, and NO2 significantly increasing CE risk at lag day 6, WS increasing CE risk at lag day 0, and SS lowering CE risk at lag day 0.
Through this, it can be considered that CE risk was not high in adults over 20 years of age on a clear day without wind. On the other hand, on windy days when it was not sunny, CE risk increased in adults over 20 years of age. Unlike air pollutants, all these climate factors were found to affect CE risk only on the lag-specific day, not the lag days (after lag day 1).
The limitations of this paper are: 1) The study only covers data since 2007 when fine dust (PM10) measurement started in Korea. 2) Detailed indicators, such as PM2.5, were not tested at the time and were not included in the study.
Nevertheless, this paper has the following advantages. 1) This is a large-scale cohort study of patients in Korea. 2) Modeling considers each of the air pollutants and environmental factors in combination with linear, non-linear and lagged effect. 3) The study attempts to analyze each age group and the concentrations of pollution indicators.