Anthropogenic carbon dioxide origin tracing study in Anmyeon-do, South Korea: Based on STILT-footprint and emissions data.

Tracking the origin of greenhouse gases (GHGs) is critical for understanding regional GHG concentration variation and developing effective policies to reduce GHG emissions. This study provides quantitative information about the surface contribution to enhancement of carbon dioxide (CO2) concentration at Anmyeon-do (AMY), South Korea, using Stochastic Time-Inverted Lagrangian Transport (STILT) model and anthropogenic CO2 emission data. CO2 enhancement simulated by the STILT and emission data was positively correlated with measured CO2 anomalies at AMY with a correlation coefficient above 0.5. High and low CO2 days were selected using ground measurements of the CO2 mixing ratio at AMY during the winter season of 2018-2019. The surface contributions for the high and low CO2 days at AMY were compared quantitatively. When the high concentration was observed in AMY, the CO2 enhancements were dominated by domestic regions, especially from the metropolitan area in South Korea, due to the high footprint and large CO2 emissions. From the perspective of foreign regions, the surface contribution of eastern China regions (Shandong, Jiangsu-Shanghai) increased during high CO2 days compared to low CO2 days at AMY. During the high CO2 days, the ratio between CO2 and carbon monoxide, a co-emitted species, is large when the surface contribution of eastern China regions is relatively strong due to different regional combustion efficiency (i.e., high combustion efficiency in South Korea compared to that in China). The surface contribution based on STILT and emission data is useful for understanding the cause of high GHG concentration at the receptor (AMY in this study).

Estimation of Inactivation time for the SARS-CoV-2 virus from the UV biometer in South Korea.

The coronavirus disease 2019 (COVID-19) is a result of the infection by "severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and has caused various social and economic effects over the globe. As the SARS-CoV-2 is effectively inactivated by the exposure to the UV-B radiation (shorter than 315 nm), the exposure time for inactivation of the SARS-CoV-2 was estimated using the broadband UV observation instrument over 11 observation sites in South Korea. For the limitation of the UV biometer, which has limited spectral information, the coefficient for conversion from the erythemal UV (EUV) to the radiation for virus inactivation was adopted before estimating the inactivation time. The inactivation time of SARS-CoV-2 is significantly dependent on seasonal and diurnal variations due to the temporal variations of surface incident UV irradiance. The inactivation times in summer and winter were around 10 and 50 min, respectively. The inactivation time was unidentified during winter afternoons due to the weak spectral UV solar radiation in winter. As the estimation of inactivation time using broadband observation includes the uncertainty due to the conversion coefficient and the error due to the solar irradiance, the sensitivity analysis of the inactivation time estimation was also conducted by changing the UV irradiance.

Imaging particulate matter exposed pine trees by vehicle exhaust experiment and hyperspectral analysis.

This study analyzed spectral variations of the particulate matter (PM hereafter)-exposed pine trees using a spectrometer and a hyperspectral imager to derive the most effective spectral indices to detect the pine needle exposure to PM emission. We found that the spectral variation in the near-infrared (NIR hereafter) bands systemically coincided with the variations in PM concentration, showing larger variations for the diesel group whereas larger dust particles showed spectral variations in both visible and NIR bands. It is because the PM adsorption on needles is the main source of NIR band variation, and the combination of visible and NIR spectra can detect PM absorption. Fourteen bands were selected to classify PM-exposed pine trees with an accuracy of 82% and a kappa coefficient of 0.61. Given that this index employed both visible and NIR bands, it would be able to detect PM adsorption. The findings can be transferred to real-world applications for monitoring air pollution in an urban area.

The implication of the air quality pattern in South Korea after the COVID-19 outbreak.

By using multiple satellite measurements, the changes of the aerosol optical depth (AOD) and nitrogen dioxide (NO2) over South Korea were investigated from January to March 2020 to evaluate the COVID-19 effect on the regional air quality. The NO2 decrease in South Korea was found but not significant, which indicates the effects of spontaneous social distancing under the maintenance of ordinary life. The AODs in 2020 were normally high in January, but they became lower starting from February. Since the atmosphere over Eastern Asia was unusually stagnant in January and February 2020, the AOD decrease in February 2020 clearly reveals the positive effect of the COVID-19. Considering the insignificant NO2 decrease in South Korea and the relatively long lifetime of aerosols, the AOD decrease in South Korea may be more attributed to the improvement of the air quality in neighboring countries. In March, regional atmosphere became well mixed and ventilated over South Korea, contributing to large enhancement of air quality. While the social activity was reduced after the COVID-19 outbreak, the regional meteorology should be also examined significantly to avoid the biased evaluation of the social impact on the change of the regional air quality.