key: cord-0820130-n8ldrwq1
authors: Ju, Min Jae; Oh, Jaehyun; Choi, Yoon-Hyeong
title: Changes in air pollution levels after COVID-19 outbreak in Korea
date: 2020-08-04
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2020.141521
sha: 36909b2b97f6216ea610f1e3faca1630fbfa350b
doc_id: 820130
cord_uid: n8ldrwq1

Abstract In order to control the spread of COVID-19, social distancing measures were implemented in many countries. This study investigated changes in air pollution during the social distancing after the COVID-19 outbreak in Korea. Ambient PM2.5, PM10, NO2, and CO that are particularly related to industrial activities and traffic were reduced during the social distancing in response to the COVID-19 outbreak. In March 2020, immediately after social distancing, mean levels of PM2.5, PM10, NO2, and CO decreased nationwide from last year's mean levels by 16.98 μg/m3, 21.61 μg/m3, 4.16 ppb, and 0.09 ppm, respectively (p-value for the year-to-year difference < 0.001, =0.001, =0.008, <0.001), a decrease by 45.45%, 35.56%, 20.41%, and 17.33%, respectively. Changes in ambient O3 or SO2 were not observed to be attributable to social distancing. Our findings, that such effort for a short period of time resulted in a significant reduction in air pollution, may point toward reducing air pollution as a public health problem in a more sustainable post-COVID-19 world.

J o u r n a l P r e -p r o o f Data of ambient air pollution between December 1 st and April 30 th of the most recent four years were collected from 446 nationwide atmospheric monitoring stations to be able to capture urban background air pollution in Korea, provided by the Korea Ministry of Environment (http://www.airkorea.or.kr/web). The location of monitoring stations is presented in Supplemental Figure 1 . At each monitoring station, ambient air pollution of PM 2.5 , PM 10 , NO 2 , CO, SO 2 , and O 3 concentrations were detected hourly, then nationwide daily average and regional average per 17 administrative division were computed from those values. Also, monthly mean air pollution was computed for the average per each month; monthly mean was not computed when the available number of daily measures was less than 75% (National Institute of Environmental Research, 2019b).

Statistical data analysis was performed using SAS software (version 9.4; SAS Institute Inc.).

Values of p < 0.05 were considered as statistically significant. Concentrations of all PM 2.5 , PM 10 , NO 2 , and CO were normally distributed, and mean and standard deviation (SD) were used to describe the concentration of air pollutants. Paired t-test was used for comparing the differences of PM 2.5 , PM 10 , NO 2 , and CO levels on the same day in the current year versus each prior year.

Further, in order to show regional variation of air pollution levels, a graphical model was developed with a geographic information system using QGIS software (version 3.8.2). In Korea, the COVID-19 date of onset was January 20, 2020 when the first case was confirmed in an imported person from Wuhan, China. On the same day, the Korean government raised the COVID-alert level to "yellow". The number of confirmed cases in Korea increased gradually until mid-February, but the number sharply increased after February 18, 2020 with a regional outbreak from the religious cluster in Daegu metropolitan city-11 cases by January 31; 3,150 cases by February 29; 9,786 cases by March 31; and 10,765 cases by April 30, 2020. On February 23 rd , the Korean government raised the COVID-alert to the highest level of "red", and "social distancing" spontaneously began from citizens. Finally, on February 29 th , to prevent wide-scale public COVID-19 infection, the Korean government officially suggested "social distancing" through March 21 st , and subsequently declared "stronger social distancing" for a total of four weeks through April 19 th . Social distancing levels, their government action, and guideline for the public are described in Table 1 . In particular, "stronger social distancing" J o u r n a l P r e -p r o o f J o u r n a l P r e -p r o o f 

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