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Monthly mean ± SD concentrations of air pollutants in Korea, between December and April of the most recent four years.
All values present mean ± SD of all daily concentrations per each month.
Paired t-test was used for comparison of (A) PM2.5, (B) PM10, (C) NO2, and (D) CO levels on the same day in the current year versus each prior year.
⁎p < 0.05 vs. 1 prior year; †p < 0.05 vs. 2 prior year; §p < 0.05 vs. 3 prior year.
