In this study, we measured simultaneously particle matter (PM10 and PM2.5) mass and their heavy metal concentrations for three days at a Seoul subway station (outdoor, concourse, platform, and tunnel) to investigate airborne PM flows. The average PM10 concentration were 59 µg m-3 , 37 µg m-3 , 111 µg m-3 and 369 µg m-3 ; PM2.5 concentration were 43 µg m-3 , 28 µg m-3 , 58 µg m-3 and 132 µg m-3 in outdoor, concourse, platform and tunnel, respectively. Although PM temporal variations were highly correlated between adjacent sampling locations in subway station, PM2.5 temporal correlations were higher than PM10. The concentration of iron (Fe) was the highest among airborne trace metals in station sectors (concourse, platform, and tunnel). Using a simple mass balance model with Fe concentrations and ventilation rates, we calculated the origins of PMs in concourse and platform. 78% of PM10 and 62% of PM2.5 in platform were derived from the tunnel, whereas 84% of PM10 and 87% of PM2.5 in concourse from the filtered outdoor air. We further confirmed that the most effective way to reduce PM in platform to keep the highest peak under the national indoor air quality guideline is to reduce up to 80% PM input from tunnel source.
Legionella species are abundant in the built environment and are increasingly recognized as a cause of Legionnaires' disease (LD). As the number of cases of Legionnaires' disease acquired by local communities in the Seoul metropolitan area in Korea has been increased, there was concern that changes in environmental factors could affect disease outbreaks. We described the association between climatic variables and occurrence of legionellosis in Korea and Legionella detection rate in Seoul area. A total of 418 cases of legionellosis were reported between 2014 and 2017. There was a seasonal peak in summer. LD continuously occurred from early spring to winter every year and rapidly increased in summer. In the regression analysis, the primary variables of interest-PM2.5 (g/m 3 ), NO 2 (ppb), and a number of the date of issue O 3 warning were not significant except for average temperature (R 2 =0.8075). The Legionella detection rate in Seoul, Korea showed a trend similar to precipitation (P=0.708, ANOVA). A relatively high proportion of Legionella detection rate was shown, especially cooling tower (17.7%) and public bath (19.3%). This finding is in line with current understanding of the ecological profile of this pathogen and supports the assertion that legionellosis occurs through contamination of water sources.
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