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In the United States, industrial compounds are routinely transported by rail in pressurized vessels, often near urban areas. A rupture of a vessel, for example due to a derailment, can result in the rapid release of a liquid-aerosol-gas mixture. The health consequences of such a release, especially close to population centers, are not well understood. To address this question, a series of controlled experimental releases of pressurized chlorine (Cl 2) was conducted at the Dugway Proving Ground (Dugway, Utah). Each trial consisted of the sudden breach of a tank containing at least 4,500 kg (kg) of pressurized liquid Cl 2. In this paper, we report on measured Cl 2 concentrations in three test structures downwind of the release. Based on these data, we estimate the indoor-outdoor exchange, transport through a multi-room structure, and the first-order loss rate due to reaction or sorption. This loss rate is particularly important for consequence assessment. For example, in a mobile office with a ventilation rate of about three air changes per hour, the reaction loss rate was approximately 2.5 h−1. This accounts for a nearly 20 percent reduction in toxic load to indoor occupants. Finally, the paper discusses the modeling and analysis of a typical urban hazard assessment. • In 2015 and 2016, a series of controlled release experiments of pressurized chlorine (Cl 2) was conducted. • An experiment consisted of the sudden breaching of a tank containing greater than 4,500 kg (kg) of pressurized liquid Cl 2. • The measurement of the Cl 2 plume's transport through an array of downwind structures. • This paper reports the results of an experiment that is unlikely to be conducted often. • The reaction between the gas and indoor surfaces is important for hazard and consequence assessment. • The current study found that total Cl 2 gas loss was faster than the trailer's air change rate. [ABSTRACT FROM AUTHOR]

In 2020, most countries around the world have observed varying degrees of public lockdown measures to mitigate the transmission of SARS-CoV-2. As an unintended consequence of reduced transportation and industrial activities, air quality has dramatically improved in many major cities around the world. In this paper, we analyze the environmental impact of the lockdown measures on P M 2.5 concentration levels in 48 core-based statistical areas (CBSA) of the United States, during the pre and post-lockdown period of January to June 2020. We model the effect of lockdown on the P M 2.5 concentration in different CBSAs while adjusting for various meteorological factors like temperature, wind-speed, precipitation and snow. Linear mixed effects models and functional regression methods with random intercepts are employed to capture the heterogeneity of the effect across different regions. Our analysis shows there is a statistically significant reduction in levels of P M 2.5 across most of the regions during the lock-down period, although interestingly, this effect is not uniform across all the CBSAs under consideration. • We examine the impact of the COVID-19 lockdown measures on the PM2.5 concentration level in USA. • We also investigate if there is any spatio-temporal heterogeneity in the effect of lockdown on air quality. • We use Linear mixed effects models and functional regression methods as primary tools of our analysis. • We adjust for local meteorological variables to remove their confounding effect on PM2.5 concentration. [ABSTRACT FROM AUTHOR]