Elevated levels of PM2.5 in crowded Subways of Cities with High COVID-19 related Mortality

Muscat Baron, Y.

BACKGROUND: Recent literature indicates that the pollutant, particulate matter PM2.5, may have an impact on COVID-19 related mortality. COVID-19 has been found adherent to PM2.5 and may be involved in the transmission and the exacerbation of COVID-19 infection, possibly due to PM2.5 adverse influence on respiratory immunity. The PM2.5 levels in underground subways have been found up to 90 times higher than the surface levels. Moreover, the commuter congestion in the presence of such high levels of PM2.5 further encouraged COVID-19 human to human transmission. METHOD: The levels of PM2.5 were retrieved from literature assessing particulate matter PM2.5 measured on subway platforms in two groups of cities. These cities were differentiated by the COVID-19 population percentage mortality rate (0.007% vs 0.09% (p<0.0004) the city population, more than a 10-fold difference. Data regarding the number of stations, length of the networks (km) and the annual ridership were also obtained from literature related to underground commuting. RESULTS: The population percentage mortality related to COVID-19 infection correlated significantly for both minimum (p<0.01) and maximum (p<0.00001) levels of PM2.5. The city subways with low COVID-19 mortality had minimum platform PM2.5 levels of 27.4 (SD+/-17.2g/m3) compared to 63.4g/m3 (SD+/-10.8g/m3) in cities with high COVID-19 associated mortality (p<0.01). Subway maximum levels of PM2.5 in cities with low COVID-19 mortality was 53.4g/m3 (SD+/-21.8g/m3) while that of underground networks with high COVID-19 mortality had maximum platform PM2.5 levels of 172.1g/m3 (SD+/-98g/m3) (p<0.001). The cities with higher COVID-19 mortality had longer networks 230km (SD+/-111km) versus 119km (SD+/-99km) ( p<0.03) and more stations 191 (SD+/-109) versus 102 (SD+/-94) (p<0.047). Although the annual ridership in the cities with the high COVID-19 mortality was higher (1034x106 vs 751x106) this did not achieve statistical significance. The maximum PM2.5 correlated with the number of stations (p<0.045) and the length of the networks (p< 0.044). The minimum PM2.5 did not achieve similar significant correlations to subway variables. Ridership significantly correlated with number of stations (p<0.01) and the length of the network (p<0.02). CONCLUSION: Underground networks may have inherent characteristics accelerating spread of COVID-19 infection and consequent mortality. The highly elevated levels of PM2.5 in overcrowded subways with extensive reach may have acted as a co-factor to disseminate the pandemic. Keywords: COVID-19, mortality, PM2.5, Subway/Underground