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.