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. 2020 Aug 5;204:111035. doi: 10.1016/j.ecoenv.2020.111035

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© 2020 Elsevier Inc.

Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 3 — The trend between R₀ and air quality factors. A. R₀ and CO; B. R₀ and CO_24 h; C. R₀ and NO₂; D. R₀ and NO₂_24 h; Blue, high flow; red, medium flow; green, low flow. Solid line means significant association between observation variable and COVID-19, dotted line means no significant association between observation variable and COVID-19. . (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)