COVID-19 restrictions index (C.R.I) - a new quantitative and comparative approach at the pandemic initiation in Italy and Israel

In January 2020, the new aggressive and lethal virus named SARS-CoV-2 was officially announced as spreading worldwide from China. This followed by initiation of restrictions on aviation and incoming traffic in many countries. During February-March of 2020, the majority of the world experienced an accelerating pandemic outbreak, driving the authorities to employ social distancing measures (lockdown) to slow the SARS-CoV-2 spreading. While the pandemic restrictions were implemented for health reasons, their environmental implications became evident as social distancing measures intensified. In this paper, we propose a novel index, which we named COVID-19 Restrictions Index (C.R.I), aimed at grading the strictness of the dynamic measures taken by national officials, in terms of their potential influence on air quality. The C.R.I. is an assigned ratio representing the severity of restriction measures on population mobility with respect to non-pandemic ‘business as usual’ behavior. The novel C.R.I. is used in this study to explore the pandemic-restriction patterns in the two greater cities of Milan (Italy) and Tel-Aviv (Israel). Our C.R.I. shows a good agreement with mobility data from these cities and was also found to closely follow the trend and intensity of the apparent transportation-related NOx changes. Although we focus here on the ‘first wave’ of the pandemic, a further evaluation based on data from a later period of the pandemic-measures (2020) and from a post-lockdown period (2021), confirmed the consistency of the C.R.I. as an indicator of air-pollution changes related to public mobility indicators.