An article by zinfos974.com went viral on social networks as the title said « une ville de Maurice parmi les 500 villes les plus polluées du monde ». No wonder with words such as "most polluted cities" and "Beau-Bassin/Rose-Hill" Mauritians might stop scrolling their news feed or even have their jaws dropped.
I read the article and throughout it used the words "polluants" and "pollués". Even though the article cites the World Health Organization, it does not properly refer to the report as being "Ambient Air Pollution".
Ambient air quality refers to the quality of outdoor air in our surrounding environment. It is typically measured near ground level, away from direct sources of pollution.
The World Health Organization updated its Ambient Air Pollution Database (version 0.3, May 2016) which includes 3000 cities from 103 countries. The data presented in a spreadsheet can be downloaded here.
By sorting the PM10 column in the spreadsheet one may find that Beau-Bassin/Rose-Hill & Coromandel appears at row 111 with a PM10 reading 131 µg/m3.
The World Health Organization's recommended maximum PM10 mean level of air quality is 20 µg/m3 while that recorded by the Environment Statistics (Government of Mauritius) in 2011 was 131 µg/m3.
Other records from Mauritius that feature in the list are Bramsthan/Flacq (37 µg/m3, year 2010), Port-Louis (22 µg/m3, year 2010) and Midlands (20 µg/m3, year 2011).
The data published by the World Health Organization mainly aims to create awareness rather than ranking cities/countries with sensational titles.
Many cities in the world, including some expected to be among the most polluted, do not collect information or report on its outdoor air quality. WHO therefore cannot compare cities based on their levels of outdoor air pollution.
-- World Health Organization