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. 2021 Dec 7;11:23517. doi: 10.1038/s41598-021-02776-0

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Ratio of the estimated $Δ_{j}$ for NO₂ divided by the estimated $Δ_{j}$ for PM_2.5 (ρ). A negative ratio implies that the change in NO₂ following the declaration of the state of emergency was in the opposite direction of the corresponding changes for PM_2.5 (i.e., one pollutant increased while the other decreased). For example, in KY, we found a decline in NO₂ but an increase in PM_2.5 following the state-level emergency declaration.