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. 2021 Sep 4;264:118713. doi: 10.1016/j.atmosenv.2021.118713

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© 2021 The Authors

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. 4 — Horizontal stacked bar chart for observed 2019 and 2020 monthly average median MDA8 O₃ mixing ratio (top-axis) and corresponding percent change ({[2020–2019]/2019}*100%) in AirNow observed (bottom axis; navy blue line/symbols) and simulated BASE (i.e., operational NAQFC with NEI2014v2 emissions) MDA8 O₃ (bottom axis; red line/symbols) at 25 specific AirNow observation sites (labeled in bar charts) based on highly ozone polluted cities in the American Lung Association “State of the Air® 2019” report for a) March, b) April, c) May, d) June, e) July, f) August, and g) September. If the % change is positive, the stacked bar chart's first/bottom line is 2019 and the second/top line is 2020. If the % change is negative, the first/bottom line is 2020 and second/top line is 2019. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)