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Although meteorological conditions play a significant role in air pollution, research on their effects on the relationship between air pollutants is limited. In this study, trends of six criteria air pollutants were investigated from 15 air quality monitoring stations (AQMSs) in Ulsan, a multi-industrial city in South Korea, during 2015-2019. Unlike CO and O 3 , SO 2 , NO 2 , PM 10 , and PM 2.5 showed statistically significant decreasing trends over the period. The companion relationship between PM 2.5 and gaseous pollutants was evaluated by their correlations [R (PM 2.5 -GPs)]. R (PM 2.5 -NO 2 ) was relatively high at almost all AQMSs, whereas high R (PM 2.5 -SO 2 ) was observed near the petrochemical industrial complex, suggesting a great influence of local emissions (vehicles and industries). R (PM 2.5 -CO) and the standardized regression coefficients of CO obtained from the multiple linear regression model were the highest, indicating that combustion processes may significantly contribute to PM 2.5 . The effect of temperature (T) was more apparent on R (PM 2.5 -GPs) than that of relative humidity, with significant values under T > 15 °C. Moreover, R (PM 2.5 -O 3 ) was positive at the T range of 12-18 °C, suggesting that reducing GPs emitted by industrial facilities during May-June may control PM 2.5 and O 3 in Ulsan. The methodology demonstrated in this study can be further used for a better understanding of the influences of environmental factors on the secondary PM 2.5 formation from gaseous precursors and the R (PM 2.5 -O 3 )., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Evaluation for the controlling policy's effectiveness to mitigate criteria air pollutants (CAPs) in South Korea during December 1, 2019-March 31, 2020 is difficult because of its coincidence with the COVID-19 social distancing. In this study, we differentiated the influence of three major driving factors (intensive controlling policy by the government, meteorological conditions, and social distancing) to the CAP variation in Ulsan, the largest industrial city in South Korea. In 2013-2019, the concentrations of PM 2.5 (2015-2019), PM 10 , SO 2 , and NO 2 decreased by 6.7, 1.6, 4.2, and 3.3%/year, respectively, whereas the O 3 concentration slightly increased by 0.7%/year. Trend analysis was used to predict the CAP concentrations before (January 1-February 21) and during (February 22-March 31) the social distancing in 2020. The difference between the measured and predicted concentrations was designated as the contribution of the three factors. The controlling policy was the most important driver of the CAP reductions. In particular, its contributions were 94.1% (January 1-February 21) and 87.4% (February 22-March 31) to the PM 2.5 decrease. The change in meteorological conditions considerably affected the CAP reductions, with the highest contributions of 35.2% (January 1-February 21) and 39.2% (February 22-March 31) to the O 3 decrease. On February 22-March 31, the effects of social distancing were 1.6, 0.6, 1.3, and 1.4% to the reduction of SO 2 , NO 2 , PM 10 , and PM 2.5 , respectively. Overall, a decrease in the CAP concentrations was apparent during January-March 2020 in Ulsan primarily due to the intensive controlling policies, not by the COVID-19 social distancing., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The outbreak of COVID-19 in Daegu, South Korea, early in 2020 has led this metropolitan city to become one of the major hotspots in the world. This study investigates the association of meteorology and the new daily COVID-19 confirmed cases and the effects of the city lockdown on the variation in criteria air pollutants (CAPs) in Daegu. Ambient temperature and relative humidity were negatively correlated to the new daily cases and played an important role in the spread of COVID-19. Wind speed could enhance the virus transmission through the inhalation of aerosols and/or droplets and contact with fomites. The lockdown has directly decreased the concentrations of CAPs. In particular, reductions of 3.75% (PM 10 ), 30.9% (PM 2.5 ), 36.7% (NO 2 ), 43.7% (CO), and 21.3% (SO 2 ) between the period before and during the outbreak were observed over the entire city. An increase in O 3 (71.1%) was affected by natural processes and photochemical formation other than the lockdown effects. The three central districts were the areas most affected by the virus and showed the highest reductions in CAPs (except for O 3 ) during the outbreak. Apart from the influence of the lockdown, the decreasing trend in CAPs may be a result of the actions taken by the government to mitigate air pollutants nationwide since 2019. The results of this study can be useful for government and medical organizations to understand the behavior of the virus in the atmosphere. Further studies are necessary to explore the detailed influences of the lockdown on the environment and public life.

The Vietnamese government has issued several directives of lockdown in Hanoi, the capital city, for a month (1–30 April 2020) to prevent the human-to-human transmission of COVID-19. This action has affected air pollution due to a decline in transportation. Therefore, this study investigates spatial and temporal change in the PM2.5 concentrations during the first 4 months of 2020 in Hanoi metropolitan area. Spatial distribution maps of the PM2.5 concentration in Hanoi were provided for the first time. The average PM2.5 concentrations at the 22 air monitoring stations were strongly correlated with the population. April had a significantly lower level of PM2.5 than the other 3 months. In particular, the concentrations of PM2.5 and NO2 decreased by 12 and 54%, respectively, between March and April, especially at areas for commercial activities. In April, a higher level of PM2.5 was recorded between Tuesday–Thursday, which is a reverse trend with that in March. Furthermore, Monday and Friday did not show rush hour peaks for the PM2.5 levels in April. A decrease in the PM2.5 concentrations was partly influenced by the long-range transport from the outside to Hanoi. This study implies that a reduction in traffic volumes and public activities may possibly improve the air quality. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) in 11 different sizes was collected at a semi-rural site in Ulsan, a multi-industrial city in South Korea, over one year from 2019 to 2020 to investigate the temporal patterns in size distribution and potential sources of polycyclic aromatic hydrocarbons (PAHs). The mean concentration of Σ 21 PAHs was higher in winter (0.29 and 0.45 ng/m3 for coarse and fine PM, respectively) than in summer (0.06 and 0.07 ng/m3). Although there was no statistically significant difference between day and night for the concentration of individual PAHs in both coarse and fine PM, the concentrations were generally higher during the day than at night. During the day, Σ 21 PAHs had two distinct peaks (0.056–0.10 μm and 3.20–5.60 μm) in winter, but they tended to partition to larger particles (1.00–1.80 μm and >18.0 μm) in summer. This result suggests that the volatilization of PAHs in smaller particles was enhanced by high-temperature conditions in summer, followed by their condensation onto larger particles. At night, Σ 21 PAH peaks were mainly around the size of 0.7 μm (droplet mode), suggesting the importance of heterogeneous-aqueous reactions. The results of the conditional bivariate probability function and concentration-weighted trajectory indicate that the high concentrations of PAHs in summer and winter were more affected by local pollution and long-range atmospheric transport, respectively. The results of the health risk assessment demonstrate that PAHs in fine PM contributed significantly to cancer risk compared to those in coarse PM. In conclusion, investigating the size distribution of PAHs in particles is necessary to understand their environmental behaviors and evaluate potential health risks. [Display omitted] • Polycyclic aromatic hydrocarbons (PAHs) were higher during the day than at night. • Day–night variation in the particle-size distribution of PAHs was apparent. • Long-range atmospheric transport became more significant in winter. • The concentration of PAHs in summer was more affected by local pollution. • Fine particles had a higher cancer risk of PAHs than coarse particles. [ABSTRACT FROM AUTHOR]