Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2021 Dec 5;33(1):134. doi: 10.1186/s12302-021-00575-y

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

© The Author(s) 2021

Open AccessThis 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/.

PMC Copyright notice

Fig. 2 — Air quality index and cut-off concentrations and health messages. Good air quality is considered satisfactory and air pollution poses little or no risk, moderate air quality is acceptable; however, for some pollutants there may be a moderate health concern, unhealthy for sensitive groups members of sensitive groups may experience health effects, unhealthy everyone may begin to experience health effects, very unhealthy health warnings of emergency conditions and hazardous health alert: everyone may experience more serious health effects