Elevated Levels of the Pollutant PM2.5 in Crowded Subways of Cities with High COVID-19 Related Mortality-Has COVID-19 Gone Underground?

Abstract

A nationwide study by [1] in the United States indicated a connection between long-term exposure to particulate matter PM2.5 and COVID-19 related mortality [1]. COVID-19 had been found to be adherent to particulate matter and it has been suggested that PM2.5 is an airborne co-factor in COVID-19 infection [2]. PM2.5 minimum and maximum levels in subways have been found several times higher than surface level. An elevated mean PM2.5 concentration of 381 μg/m³ was reported on the Victoria Underground, approximately 16 times higher than surface PM2.5 results [3]. The World Health Organization guideline recommends that PM2.5 levels should not exceed an average level of 25 μg/m³ 24-hour. The guideline stipulates that a PM2.5 concentration of 10 μg/m³/24 hr is the lowest level at which combined cardiopulmonary and lung cancer mortality have been shown to rise in response to chronic exposure to PM2.5 [4]. Commuter use of underground rail is significant. On a global scale the use of transport via subways represents around 11% of worldwide public transport. In New York, the daily ridership is 5 million and decreased by 90% after the institution of the New York lockdown [5]. More than 200 million passengers commute daily in the 156 underground networks around the world. With the movement of rural populations to urban areas as in China, the ridership is increasing exponentially as in subways of Beijing and Shanghai.